Get 20M+ Full-Text Papers For Less Than $1.50/day. Start a 14-Day Trial for You or Your Team.

Learn More →

11H-Indeno[1,2-b]quinoxalin-11-one 2-(4-ethylbenzylidene)hydrazone

11H-Indeno[1,2-b]quinoxalin-11-one 2-(4-ethylbenzylidene)hydrazone molbank Short Note 1 1 1 , 2 , Anastasia R. Kovrizhina , Elizaveta I. Samorodova and Andrei I. Khlebnikov * Kizhner Research Center, Tomsk Polytechnic University, 634050 Tomsk, Russia; anaskowry@gmail.com (A.R.K.); betani47@gmail.com (E.I.S.) Scientific Research Institute of Biological Medicine, Altai State University, 656049 Barnaul, Russia * Correspondence: aikhl@chem.org.ru; Tel.: +7-3822-706349 Abstract: 11H-Indeno[1,2-b]quinoxaline derivatives present an important type of nitrogen-containing heterocyclic compound that are useful intermediate products in organic synthesis and have potential pharmaceutical applications. A new 11H-indeno[1,2-b]quinoxalin-11-one-2-(4-ethylbenzylidene)hydrazone (compound 3) was synthesized. Compound 3 is the first example of an azine derivative based on the 11H-indeno[1,2-b]quinoxaline system. The Z,E-isomerism of compound 3 was investigated by DFT calculations. Bioavailability was evaluated in silico using ADME predictions. According to the ADME results, compound 3 is potentially highly bioavailable and has potential to be used for the treatment of neuroinflammation and ischemia–reperfusion injury. Keywords: azine; aldazine; 11H-indeno[1,2-b]quinoxalin-11-one; DFT; ADME 1. Introduction Compounds containing a C=N bond attached to a heterocyclic moiety exhibit various chemical reactivities and often possess pharmacological activities. Prominent representa- Citation: Kovrizhina, A.R.; tives of these compounds are azines, which can be regarded as hydrazine derivatives of Samorodova, E.I.; Khlebnikov, A.I. 0 00 000 the general formula RR C=N-N=CR R . Azines have recently attracted attention owing 11H-Indeno[1,2-b]quinoxalin-11-one to their diverse therapeutic activities [1,2]. The synthesis of azines can be performed by the 2-(4-ethylbenzylidene)hydrazone. condensation of hydrazine with two moles of aldehyde/ketone under reflux conditions [1]. Molbank 2021, 2021, M1299. https:// doi.org/10.3390/M1299 Azines are often the major products obtained by the thermal decomposition of diazo compounds [2]. The process is bimolecular and involves the nucleophilic attack of the Academic Editor: Ian R. Baxendale carbon atom of the first diazo compound (which gives carbene by the removal of N ) on the terminal nitrogen of the second compound. Zhao et al. reported the formation of Received: 9 October 2021 symmetrical azines produced by the copper catalyzed homocoupling of oximes [3]. Nan- Accepted: 19 November 2021 jundaswamy and co-workers reported on the iodine catalyzed synthesis of symmetrical Published: 23 November 2021 azines by treating NH NH H O with carbonyl compounds at 0–10 C [4]. 2 2 2 A prominent drug belonging to the class of azines is Guanabenz (Figure 1) [5], which Publisher’s Note: MDPI stays neutral has always been considered a guanylhydrazone derivative. Figure 1 shows two tautomeric with regard to jurisdictional claims in forms of Guanabenz (A and B), with the azine form (B) being more stable [6,7]. Addition- published maps and institutional affil- ally, important examples are the antihypertensive agent bearing 2,6-dichlorophenyl and iations. a 1,1-diamino moieties [5], the trypanocidal agent containing the azine unit attached to imidazopyridine [8], the antibacterial compound [9], and the anticancer agent [10] (Figure 1) 4-((E)-((E)-((4-bromophenyl)(phenyl)methylene)hydrazono)methyl)2,6-dimethoxyphenol (BRH) that was active against MCF-7 cancerous cell lines [11]. Copyright: © 2021 by the authors. At present, the variation in conjugation via the azine substructure and its modulation Licensee MDPI, Basel, Switzerland. depending on the substituents has not been fully investigated. It is important to study This article is an open access article redox properties and the associated characteristics of electron exchange and their influence distributed under the terms and on chemical bonds in these systems, especially in azines containing heterocyclic fragments conditions of the Creative Commons of pharmacological importance. In this work, we have synthesized the first representative Attribution (CC BY) license (https:// of an azine with a 11H-indeno[1,2-b]quinoxaline moiety that is contained in numerous creativecommons.org/licenses/by/ biologically active compounds possessing anti-inflammatory [12], antimicrobial [13], anti- 4.0/). Molbank 2021, 2021, M1299. https://doi.org/10.3390/M1299 https://www.mdpi.com/journal/molbank Molbank 2021, 2021, x FOR PEER REVIEW 5 of 5 Molbank 2021, 2021, M1299 2 of 7 Molbank 2021, 2021, x FOR PEER REVIEW 5 of 5 cancer [14], and JNK inhibitory [12] properties. The bioavailability and electronic structure of the synthesized compound were evaluated with the use of computational methods. Figure 1. Examples of biologically active azines. At present, the variation in conjugation via the azine substructure and its modulation depending on the substituents has not been fully investigated. It is important to study redox properties and the associated characteristics of electron exchange and their influ- ence on chemical bonds in these systems, especially in azines containing heterocyclic frag- ments of pharmacological importance. In this work, we have synthesized the first repre- sentative of an azine with a 11H-indeno[1,2-b]quinoxaline moiety that is contained in nu- merous biologically active compounds possessing anti-inflammatory [12], antimicrobial [13], anticancer [14], and JNK inhibitory [12] properties. The bioavailability and electronic structure of the synthesized compound were evaluated with the use of computational methods. Figure 1. Examples of biologically active azines. Figure 1. Examples of biologically active azines. 2. Results and Discussion 2. Results and Discussion At present, the variation in conjugation via the azine substructure and its modulation 2.1. Synthesis 2.1. Synthesis depending on the substituents has not been fully investigated. It is important to study We preliminary obtained 11H-indeno[1,2-b]quinoxaline-11-one (1) and its hydrazone We preliminary obtained 11H-indeno[1,2-b]quinoxaline-11-one (1) and its hydra- redox properties and the associated characteristics of electron exchange and their influ- (2). The simplest way to synthesize compound 1 consists in the condensation of ninhydrin zone (2). The simplest way to synthesize compound 1 consists in the condensation of ence on chemical bonds in these systems, especially in azines containing heterocyclic frag- with o-phenylenediamine [15] (Scheme 1). The 11H-indeno[1,2-b]quinoxalin-11-one hy- ninhydrin with o-phenylenediamine [15] (Scheme 1). The 11H-indeno[1,2-b]quinoxalin- ments of pharmacological importance. In this work, we have synthesized the first repre- drazone (2) was obtained by the nucleophilic addition of hydrazine hydrate to ketone 1 11-one hydrazone (2) was obtained by the nucleophilic addition of hydrazine hydrate to sentative of an azine with a 11H-indeno[1,2-b]quinoxaline moiety that is contained in nu- [16] (Scheme 1). ketone 1 [16] (Scheme 1). merous biologically active compounds possessing anti-inflammatory [12], antimicrobial [13], anticancer [14], and JNK inhibitory [12] properties. The bioavailability and electronic structure of the synthesized compound were evaluated with the use of computational methods. 2. Results and Discussion 2.1. Synthesis Scheme Scheme 1 1.. Synthesis Synthesis of of compounds compounds 1 1 and and 2 2. . We preliminary obtained 11H-indeno[1,2-b]quinoxaline-11-one (1) and its hydrazone For the first time, we have obtained a new functional compound, 11H-indeno[1,2-b] (2). The simplest way to synthesize compound 1 consists in the condensation of ninhydrin For the first time, we have obtained a new functional compound, 11H-indeno[1,2- quinoxalin-11-one 2-(4-ethylbenzylidene)hydrazone (3, Scheme 2), which contains an azine with o-phenylenediamine [15] (Scheme 1). The 11H-indeno[1,2-b]quinoxalin-11-one hy- b]quinoxalin-11-one 2-(4-ethylbenzylidene)hydrazone (3, Scheme 2), which contains an group and an indenoquinoxaline system. This compound is of interest as a potential Molbank 2021, 2021, x FOR PEER REVIEW drazone (2) was obtained by the nucleophilic addition of hydrazine hydrate to ketone 5 of 1 5 azine group and an indenoquinoxaline system. This compound is of interest as a potential biologically active compound that could find application in medicinal, organic, and mate- [16] (Scheme 1). biologically active compound that could find application in medicinal, organic, and ma- rial chemistry. terial chemistry. Further modification of compound 2 to the target product 3 was performed by the action of p-ethylbenzaldehyde (Scheme 2). The reaction proceeds for 2 h under reflux in ethanol in the absence of alkalis or acids. At the end of the process, complete conversion was observed (control by TLC, eluent hexane: ethyl acetate (2:1, v/v)). The expected crude azine was isolated by filtration with 89% yield. The compound was purified by recrystal- Scheme 1. Synthesis of compounds 1 and 2. lization from ethanol. For the first time, we have obtained a new functional compound, 11H-indeno[1,2- b]quinoxalin-11-one 2-(4-ethylbenzylidene)hydrazone (3, Scheme 2), which contains an Scheme 2. Synthesis of title compound 3. Scheme 2. Synthesis of title compound 3. azine group and an indenoquinoxaline system. This compound is of interest as a potential Further modification of compound 2 to the target product 3 was performed by the biologically active compo According to the NM u R nd th dataat co (CDC uld l3), find the recrysta applicatll ion in med ized compou icinal nd , org 3 wa anic s ob , ta and m ined as a- action of p-ethylbenzaldehyde 1 (Scheme 2). The reaction proceeds for 2 h under reflux in terial chem a Z,E-isomer mixt istry. ure. The H NMR spectrum (Figure S1) contains two distinct low-field ethanol in the absence of alkalis or acids. At the end of the process, complete conversion signals of the imine proton N=CH at 8.91 and 8.85 ppm with relative integral intensities Further modification of compound 2 to the target product 3 was performed by the was observed (control by TLC, eluent hexane: ethyl acetate (2:1, v/v)). The expected action of 0.35/0.65,p as -ethylbenzaldeh well as typicay l s de (Scheme ignals of th2). The re e ethyl grou action proceeds p at 1.30 (two for 2 h overlaunder id triplet reflux in s from crude azine was isolated by filtration with 89% yield. The compound was purified by ethano differen l in t iso thm e absence o ers) and 2.75 f alkalis or ppm (multiplet). acids. At Si the gn end als of of t h the e i process, ndenoqui complete noxaline he con te v rersion ocycle recrystallization from ethanol. was observed were observed bet (control by TLC, el ween 7.5 and 8 u.e 5 ppm. S nt hexan ee p: e ara thy tion of l acet at the (2 e is:1 omers , v/v))wa . The e s imx poss pectied ble c prob- rude According to the NMR data (CDCl ), the recrystallized compound 3 was obtained as az ably ine w duae s to iso al rel ated by ative fly ilt lo raw energ tion with y 8 b9a% rr yi ier e lfor d. The co the isomeriz mpound was ation of the carbon purified by re –ni crystal- trogen a Z,E-isomer mixture. The H NMR spectrum (Figure S1) contains two distinct low-field lization double bond from ethano (see, e.g., [17] and l. our DFT results described below). The main characteristics of the title compound 3: yellow crystals, M.p. 195–196 °С, soluble in acetone and chloroform. The NMR data are presented in Section 3.1, Figure S1, and Figure S2. 2.2. DFT Study of Aldazine Isomerism Azines can exhibit Z,E-isomerism due to the presence of two C=N bonds. We studied the relative stability of four possible geometric isomers of compound 3 in chloroform us- ing the DFT method. The lowest-energy conformations of the isomers were found with B3LYP/G functional implemented in ORCA 5.0 software. The ma-def2-SVP basis set [18] was used for final geometry optimizations. This basis set includes diffuse functions perti- nent for an adequate treatment of azine lone pair interactions. The optimized structures of the geometric isomers are presented in Figure S3. The E,E-isomer was found to be the most thermodynamically stable (here and below, the first symbol in isomer notation de- scribes the configuration of the azine C=N bond attached to the indenoquinoxaline moiety while the second symbol refers to the C=N bond near the p-ethylphenyl fragment). The Z,E-, E,Z- and Z,Z-isomers have the calculated Gibbs free energies 3.16, 4.91 and 7.13 kJ/mol, respectively, higher than the E,E-isomer. Based on these results, we propose that the synthesized compound 3 consists of relatively more stable E,E- and Z,E-isomers, as the other two isomers with Z-orientation of the p-ethylphenyl substituent are character- ized by higher Gibbs free energies. It should be noted that only the E,E-isomer has the optimized structure with a fully coplanar arrangement of molecular moieties. To evaluate the energy barriers for Z,E isomerization of both azine C=N bonds, we applied the climbing image nudged elastic band (CI-NEB) methodology, which is efficient at finding minimum energy paths and saddle points [19]. The climbing images (CIs) ob- tained for E,E Z,E and E,E E,Z isomerization of compound 3 can be considered good approximations of the corresponding transition states. The CIs and other intermedi- ate images on the minimum energy paths are shown in Figure S4, where the interpolated energy diagrams are presented. Based on the calculated DFT energies of CIs, we have estimated the barriers as 89 and 84 kJ/mol for E,E Z,E and E,E E,Z isomerization, respectively. The obtained results suggest that the interconversion in both pairs of isomers occurs via in-plane inversion of the nitrogen atom like in other similar compounds [17,20], i.e., without rotation around C=N double bonds. Thus, the values of N-N=C valence an- gles in CIs are close to 160° (Figure S4). The calculated isomerization barriers are high enough to explain the distinct signals of isomers in the NMR spectra of compound 3. However, they are close in magnitude, for Molbank 2021, 2021, x F M Oo R lb P an EE k 2 R0 R 21 EV , 2I 0EW 21, x FOR PEER REVIEW 5 of 5 5 of 5 Molbank 2021, 2021, x F M Oo R lb P an EE k 2 R0 R 21 EV , 2I0EW 21, x FOR PEER REVIEW 5 of 5 5 of 5 Molbank 2021, 2021, M1299 3 of 7 Scheme 2. Synthesis Sche of tit m le e c2 omp . Syn otund hesis 3 .o f title compound 3. According to the NM AccR o rd da in ta g (to CDCl the 3NM ), thR e re da cr ta ys (CDCl tallized 3), th coe m re po cr un ysd ta 3 ll iw zed as o co bm tai po ned un a ds 3 was obtained as signals of the imine proton N=CH at 8.91 and 8.85 ppm with relative integral intensities 1 1 a Z,E-isomer mixture a Z,.E The -iso m H erNM mix R ture spec . The trum H (Fi NM gure R spec S1) co tru nm tai n (Fi s gure two d Si1 st ) ico nct nta loiw ns -ftw ield o distinct low-field 0.35/0.65, as well as typical signals of the ethyl group at 1.30 (two overlaid triplets from signals of the imin si e gn pr ao ls too n f N= the CH imia nt e 8pr .91 o to an nd N= 8.8 CH 5 ppm at 8.wi 91th an re d l8 a.ti 8v 5e ppm integr wi ath l i n re tens latiiv tie es in tegral intensities Scheme 2. Synthesis Sche of tit m le e c2 omp . Syn otund hesis 3 .o f title compound 3. different isomers) and 2.75 ppm (multiplet). Signals of the indenoquinoxaline heterocycle 0.35/0.65, as well a 0s .3typi 5/0.6 ca 5,l a si s gn well als a os f typi the ethy cal si l gn gro alup s of a t th 1e .3ethy 0 (tw l o gro ov up erla ai t d 1 .tr 30 ip ( ltw ets of ro ov m er laid triplets from were observed between 7.5 and 8.5 ppm. Separation of the isomers was impossible probably different isomers) d ain ff d er 2ent .75 ippm some(rs m)ul ati nd pl 2 et .7 ).5 S ppm ignal(s m oul f th tipl e iet nd ).eno Sign qui als no oxa f th lie ne inh dete eno ro qcycl uino exa line heterocycle According to the NM AccR o rd da in ta g (to CDCl the 3NM ), thR e re da cr ta ys (CDCl tallized 3), c th oe mre po cr un ysd ta 3 ll iw zed as o co bm tai po ned un a d s 3 was obtained as due to a relatively low energy barrier for the isomerization of the carbon–nitrogen double were observed betwere ween o 7 b.ser 5 av ned d 8 b .5 et ppm. weenS 7 ep .5 a ara nd ti o 8n .5 o ppm. f the iS so ep m aer ras tio wa n s ofi m thpo e iss soim bler e pr s wa obs - impossible prob- 1 1 a Z,E-isomer mixture a Z,.E The -iso m H erNM mix R ture spec . The trum H (Fi NM gure R spec S1) co tru nm tai n (Fi s gure two d Si1 st ) ico nct nta loiw ns -ftw ield o distinct low-field ably due to a bond relaa tib v (see, lel y y due lo e.g., w toener a [ 17 re gy l ]aand ti ba vel rry our ier lo f w o DFT r ener the rgy esults iso ba mer rrdescribed i iz er a ti fo or n th ofe th ibelow). se om caer rb io za nti –o nn itro ofgen the carbon–nitrogen signals of the imin si e gn pr ao ls too n f N= the CH imia nt e 8pr .91 o to an nd N= 8.8 CH 5 ppm at 8.wi 91th an re d l8 a.ti 8v 5e ppm integr wi ath l i n re tens latiiv tie es in tegral intensities double bond (see, d e. og. ub , [ le 17 b ]o an nd d (o see ur , DF e.g. T , re [1s 7ul ] ats n d d escr our iDF bed T b re el so ul w ts ). described below). The main characteristics of the title compound 3: yellow crystals, M.p. 195–196 C, solu- 0.35/0.65, as well a 0s .3typi 5/0.6 ca 5,l a si s gn well als a os f th typi e ethy cal si l gn gro alup s oa f t th 1e .3ethy 0 (tw l o gro ov up erla ai t d1 .tr 30 ip ( ltw ets of ro ov m er laid triplets from The main characte The ristim cs ao in f th che ar ti atl cte e ri co st m ics poo un f th d e 3:ti yel tle lo co w mcr po ys un tad ls, 3M : yel .p.lo 1w 95– cr 196 yst a °lС, s, M.p. 195–196 °С, ble in acetone and chloroform. The NMR data are presented in Section 3.1, Figures S1 and S2. different isomers) d ain ff d er 2ent .75 ippm some (rs m)ul ati nd pl 2 et .7 ).5 S ppm ignal(s m oul f th tipl e iet nd ).eno Sign qui als no oxa f th lie ne inh dete eno ro qcycl uino exa line heterocycle soluble in acetone so an lub d chl le io nro af ce orm. tone The andNM chlR oro df ao ta rm. are The prese NM nted R d ia n ta S a ec re tio pr nese 3.1n , ted Fig ure in S S ec 1tio , n 3.1, Figure S1, were observed betwere ween o 7 b.ser 5 av ned d 8 b .5 et ppm. weenS 7 ep .5 a ara nd ti o 8n .5 o ppm. f the iS so ep m aer ras tiwa on s ofi m thpo e iss soim bler e pr s wa ob- s impossible prob- and Figure S2. and Figure S2. 2.2. DFT Study of Aldazine Isomerism ably due to a relaa tib vlel y y due low to ener a re gy la ti ba vel rry ier lo f w or ener the gy iso ba mer rriiz er a ti fo or n th ofe th ise om caer rb io za nti –o nn itro ofgen the carbon–nitrogen double bond (see, d e. og. ub , [ l1 e 7 b ]o an nd d (o see ur , DF e.g. T , re [1s 7ul ] a ts n d d escr our iDF bed T b re el so ul w ts ). described below). Azines can exhibit Z,E-isomerism due to the presence of two C=N bonds. We studied 2.2. DFT Study of Ald 2.2.az D ine FT Is Stud omey ris of mAld azine Isomerism The main characte The ristim cs ao in f th che ar ti atl cte e ri co st m ics poo un f th d e 3:ti yel tle lo co w mcr po ys un tad ls, 3M : yel .p.lo 1w 95– cr 196 yst a °l С, s, M.p. 195–196 °С, the relative stability of four possible geometric isomers of compound 3 in chloroform Azines can exhibit A Z z,iE n-es iso ca mn er eix sm hib d iue t Z,to E- th iso e m pr er ese ism nce d ue of to tw th o C= e pr N ese bon n ce ds. of We two studi C=N ed b onds. We studied soluble in acetone so an lub d chl le io nro af ce orm. tone The andNM chlR oro df ao ta rm. are The prese NM nted R d ia n ta S a ec re tio pr nese 3.1n , ted Fig ure in S S ec 1,tio n 3.1, Figure S1, using the DFT method. The lowest-energy conformations of the isomers were found the relative stabilith ty e ore f flo aur tiv po e st ss ai b b il le ity geo ofm fo etr uri c po iso ssm iber le s geo of m coetr mpo ic iun sod m 3 er is no chl f co or m opo form und us- 3 in chloroform us- and Figure S2. and Figure S2. with B3LYP/G functional implemented in ORCA 5.0 software. The ma-def2-SVP basis ing the DFT methio nd g . th The e D lo FT west me -th ener odgy . The con lo fo west rma- ti ener ons gy of co the n fio so rm ma er tis on were s of th foe u n iso d m wi er th s were found with set [18] was used for final geometry optimizations. This basis set includes diffuse functions B3LYP/G functionB a3 l L im YP/ plG em fu ented nctio in n a l O iR m CA ple m 5.ented 0 softw in a re O.R The CA m 5.0 a -so def2 ftw -a Sre VP . The basim s set a-def2 [18]- SVP basis set [18] 2.2. DFT Study of Ald 2.2az . D ine FT Is Stud omey ris of mAld azine Isomerism pertinent for an adequate treatment of azine lone pair interactions. The optimized structures was used for finalwa geo s m used etry fo or pti fim nailz geo atiom ns. etr Thi y o s pti bam sis set izatio in ncl s. ude This s ba difsi fuse s set fun incl ctio ude ns s pe dirti ffuse - functions perti- Azines can exhibit A Z z,i E n-es iso ca mn er eix sm hi b d iue t Z,to E- th iso e m pr er ese ism nce d ue of to tw th o C= e pr N ese bon nce ds. of We two studi C=N ed b onds. We studied of the geometric isomers are presented in Figure S3. The E,E-isomer was found to be nent for an adequa nent te tre foa r tm an ent ado eq f ua azte ine tre loa n te mpa ent ir o if n t aer zia nce tilo on ns. e pa The ir o in pti ter m ai cz ti ed on st s. ruc The ture opti s mized structures the relative stabilith ty e ore f flo aur tiv po e st ss aib b ille ity geo ofm fo etr uri c po iso ssm iber le s geo of m coetr mpo ic i un sod m 3 er is no chl f co or m opo form und us- 3 in chloroform us- the most thermodynamically stable (here and below, the first symbol in isomer notation of the geometric iso of m th er e s geo are m pr etr ese ic n iso ted m er ins Fi agure re pr ese S3. n T ted he E in ,E Fi -igure somer S 3wa . Ts h e foE un ,Ed -i so tom be ert h wa e s found to be the ing the DFT methio nd g . th The e D lo FT west me -th ener odgy . The con lo fo west rma- ti ener ons gy of co the n fio so rm ma er tis on were s of th foe u n iso d m wi er th s were found with most thermod describes ynam mo ica stl th ly the er stm ab configuration o ld e yn (her am e ia ca nld ly bst elof a ob w, le the th (he er azine fe irst and sy C=N b m el bo ow, l bond in th iso e fm iattached rst er sy no m tab ti oo lto n in d the i e- som indenoquinoxaline er notation de- B3LYP/G functionB a3 l L im YP/ plG em fented unctio in na l O iR m CA ple m 5.0 ented softw in a re O.R The CA m 5.0 a -so def2 ftw -S are VP . The basim s set a-def2 [18]- SVP basis set [18] scribes the configura scri ti b o es n o th f e th co e n az fiigura ne C= tiN onb o ofn th d e att az aic n h e ed C= to N th bo e n in dd aeno ttacq hui ed n o to x a th lie ne inm deno oiety quinoxaline moiety moiety while the second symbol refers to the C=N bond near the p-ethylphenyl fragment). was used for final wa geo s m used etry fo opti r fim nailz geo atiom ns. etr Thi y o s pti bam sis set izatio in ncl s. ude This s d ba ifsi fuse s set fun incl ctio ude ns s pe dirti ffuse - functions perti- while the second wh sym ilb e oth l r e ef seco ers n to d th sy e m C= bo N l rb ef oer nd s to nea th r e th C= e p N -ethy bonld phen neayl r th fra e gm p-ethy ent)l.phen The yl fragment). The The Z,E-, E,Z- and Z,Z-isomers have the calculated Gibbs free energies 3.16, 4.91 and nent for an adequa nent te tre foa r tm an ent ado eq f ua azi te ne tre loa n te mpa ent ir o in f taer zia nce tilo on ns. e The pair o in pti ter m aicz ti ed on st s. ruc The ture opti s mized structures Z,E-, E,Z- and Z,Z Z-,i E so -, m Eer ,Zs - h an av de Z th ,Z e -ic so alm cul era sted ha v G e ibb the s c fre ale cul ener ated gi es Gibb 3.1 s6 f , re 4.e 91 ener and gi es 7.13 3 .16, 4.91 and 7.13 7.13 kJ/mol, respectively, higher than the E,E-isomer. Based on these results, we propose of the geometric iso ofm th er e s geo are m pr etr ese ic n iso ted m i er n s Fi agure re pr ese S3. n T ted he E in ,E Fi -igure somer S 3 wa . Ts h e foE un ,Ed -i so tom be ert h wa e s found to be the kJ/mol, respectivel kJ/ y, m hio gh l, re erspec than ti t v h el e y, E,h Ei-gh iso er m th era . n B a tsed he E o ,E n- th iso ese mer re . sul Based ts, we on pr tho ese po se resul tha ts t , we propose that most thermodynam mo ica stl l th y er stm ab o ld e yn (her am e ia ca nld ly bst ela ob w, le th (he erfe irst ansy d b m el bo ow, l in th iso e fm irst er sy no m tab ti o o ln i n d i e- somer notation de- that the synthesized compound 3 consists of relatively more stable E,E- and Z,E-isomers, as the synthesized co th m e po syun nth desi 3 z ced on si cst om s po of un reld ati 3v el coy nsi mst os reo st f r ael bla e tiE v,el Ey - a m no dre Z ,st E- aib so le m E er ,E s, - a an s d Z,E-isomers, as scribes the configura scri tib oes n o th f e th co e n az fiigura ne C= tiN onb o ofn th d e att az aicn h e ed C= to N th bo e n in dd aeno ttacq h ui ed n o to x a th lie ne inm deno oiety quinoxaline moiety the other two isomers with Z-orientation of the p-ethylphenyl substituent are characterized the other two isom th er e s owi ther th tw Z-o o ri iso enta mer tio s n wi oth f th Z e -o pri -ethy entalti phen on oyl f th subs e p-ti ethy tuent lphen are yl ch subs aracte tituent r- are character- while the second wh sym ilb e oth l r e ef seco ers n to d th sy e m C= bo N l rb ef oer nd s n to ea th r e th C= e p N -ethy bonld phen neayl r th fra e gm p-ethy ent)l.phen The yl fragment). The by higher Gibbs free energies. It should be noted that only the E,E-isomer has the optimized ized by higher Giibb zed s fb re y e h ener igher gi es. Gi bb It s sh fre oul e d ener be gi nes. ote d It th sh ao t ul on dl y be th n e ote E,d E -th iso am t o er n lh y ath s t e hE e ,E-isomer has the Z,E-, E,Z- and Z,Z Z-,i E so -, m Eer ,Zs - h an av de Z th ,Z e -ic so alm cul era sted ha v G e ibb the s f cre ale cul ener ated gi es Gibb 3.1 s6 f , re 4.e 91 ener and gi es 7.13 3 .16, 4.91 and 7.13 structure with a fully coplanar arrangement of molecular moieties. optimized structure opti wi m th iz ed a f ul stlruc y cture opla n wi ar th a rr a a ful nge ly c mo ent pla o n fa m r a orr lec an ul ge ar m m ent oieti ofes. m olecular moieties. kJ/mol, respectivel kJ/ y, m hio gh l, er re spec than ti t v h el e y, E,h Ei-gh iso er m th er.a n B a tsed he E o ,E n- th iso ese mer re . sul Based ts, we on pr tho ese po se resul tha ts t , we propose that To evaluate the energy barriers for Z,E isomerization of both azine C=N bonds, we To evaluate the ener To g ev y a ba lua rri te erth s e foener r Z,E g y iso ba m rri erer izs ati fo or nZ of ,E b io so th m a er zi in za e ti C= onN ofb o bn oth ds, awe zine C=N bonds, we the synthesized co th m e po syun nth desi 3 z co ed n si cst om s po of un reld ati 3 v el coy nsi mst os reo st f a rel bla e tiE v,el Ey - a m nd ore Z ,st E- aib so le m E er ,E s, - a an s d Z,E-isomers, as applied the climbing image nudged elastic band (CI-NEB) methodology, which is efficient applied the climbia nppl g im ied age thn e udge climb di n elg ast im ic ab ge an nd udge (CI-d NE elB ast ) m ic etho band d o (CI logy -NE , wh B) im ch etho is ef dfo ic lo ient gy , which is efficient the other two isom th er e s owi ther th tw Z-o o ri iso enta mer tio s n wi oth f th Z e -o pri -ethy entalti phen on oyl f th subs e p- ti ethy tuent lphen are yl ch subs aracte tituent r- are character- at finding minimum energy paths and saddle points [19]. The climbing images (CIs) at finding minimu at m f i ener ndin gg y m pa in th im s a un m d ener sadd gly e pa poi th ns tsa [n 1d 9 ]s . a The ddle cli poi mb nits ng [1 im 9]a . ges The (cli CIs m )b o in b- g images (CIs) ob- ized by higher Giibb zed s fb re y e h ener igher gi es. Gi bb It s sh fre oul e d ener be gi no es. te d It th sh ao t ul on dl y be th n e ote E,d E -th iso am t o er n lh y ath s t e hE e ,E-isomer has the obtained for E,E Z,E and E,E E,Z isomerization of compound 3 can be considered tained for E,E ta Z in ,E ed a n fo dr E E,,E E E Z,,Z E ia so nd m E er ,E iz ation E o,f Z c io so mm po er un iza dti 3 o n ca o nf b ce om copo nsi un der d ed 3 ca n be considered optimized structure opti wi m th iz a ed ful stlruc y co ture pla n wi ar th a rr a a fn ul ge ly c mo ent pla o n fa m r a orr lec an ul ge ar m m ent oieti ofes. m olecular moieties. good approximatigo ono s d of a th ppr e co oxrr im espo ation nd s iof ng th tra e co nsi rr tiespo on stn ad tes. ing The tran CI siti s o an nd st o ath tes. er The inter CI ms ed an i-d other intermedi- good approximations of the corresponding transition states. The CIs and other intermediate To evaluate the ener To g ev y a ba lua rri te erth s e foener r Z,E g y iso ba m rer rier izs ati fo or n Z of ,E b io so th m a er ziin za e ti C= onN of b o bn od th s, awe zine C=N bonds, we ate images on the a m te in ii m m au ge ms o ener n th gy e m pa in th im s a u re m s ener hown gy i n p a Fi th gure s are S s 4h , o wh wn er ie n th Fie gure inter Spo 4, wh lated er e the interpolated images on the minimum energy paths are shown in Figure S4, where the interpolated applied the climbia nppl g im ied age thn e udge climb di n elg ast im ic ab ge an nd udge (CI-d NE elB ast ) m ic etho band d o (CI logy -NE , wh B) im ch etho is ef d fo ic lo ient gy , which is efficient energy diagrams ener are pr gyese din ated gra.m B s ased are pr onese thn e ted cal.cul Baa sed ted o DF n th T e ener calcul gies ato ed f CIs, DFT w ener e ha gi ves e of CIs, we have energy diagrams are presented. Based on the calculated DFT energies of CIs, we have at finding minimu at m f i ener ndin gg y m pa in th im s a un m d ener sadd gly e pa poi th ns tsa [n 1d 9 ]s . a The ddle cli poi mb nits ng [1 im 9]a . ges The (cli CIs m ) b o ib n- g images (CIs) ob- estimated the barresti iers m as ated 89 a tn hd e 8 ba 4 rr kJ/ ier m s oa ls fo 8r 9 E a,n E d 84 kJ/ Zm ,Eo a ln fo dr E E ,E ,E E Z ,Z ,E i so anm d er E,iE z ation ,E ,Z isomerization, estimated the barriersta as ined 89 fand or E,84 E kJ/mol ta Z in ,E ed afor n fo dr EE E,,,EE E Z E Z ,,E Z ,E iand a so nm d er EE,,i EE z ation E E o,,fZ Z c iisomerization, o so mm po er un izd ati 3 o ca n o nf b ce om copo nsi un der d ed 3 ca n be considered respectively. The o re bspec tained tiv re elsul y. The ts sug obgest tained tha re t th sul e ts in sug terco gest nver thsi at oth n ie ni n bter oth co pa ni v rs ero si fo is no im n er bo s th pairs of isomers respectively. The obtained goodr a esults pproxisuggest matigo ono s d that of a th ppr e the co oxrr iinter m espo atio conversion n nd s iof ng th tra e co nsi rr in tiespo oboth n stn ad tes. pairs ing The tra of n CI si isomers ti s o an nd st o ath tes. er The inter CI ms ed an i-d other intermedi- occurs via in-plane o cc inurs versi vio an i n o- fpl th a e nn ei itro nvgen ersio an to o m f th like e nin itro oth gen er a si to m m ila lr ike coin m po oth un erd si s m [1i7 la ,2 r 0co ], mpounds [17,20], ate images on the a m te in ii m m au ge ms o ener n th gy e m pa it nh im s a u re m s ener hown gy i n p a Fi th gure s are S s 4h , o wh wn er ie n th Fie gure inter Spo 4, l wh ated er e the interpolated occurs via in-plane inversion of the nitrogen atom like in other similar compounds [17,20], i.e., without rotatiio .e. n , a wi rou thnd out C= roN tati do on ub alr e ou bo nd nd C= s. Thus N do,ub thle e va boln ues ds. o Thus f N-N= , thC e v va al lence ues o a f n N - -N=C valence an- energy diagrams ener are pr gyese din ated gra.m B s ased are pr onese thn e ted cal.cul Baa sed ted o DF n th T e ener calgi cul es ato ed f CIs, DFT w ener e ha gi ves e of CIs, we have i.e., without rotation around C=N double bonds. Thus, the values of N-N=C valence angles gles in CIs are close gles to i1 n6 CIs a 0° (Fire gure clo se S4)t.o 160° (Figure S4). estimated the barresti iers m as ated 89 a tn hd e 8 ba 4 rr kJ/ ier m s oa l s fo 8r 9 E a,n E d 84 kJ/ Zm ,Eo a ln fo dr E E ,E ,E E Z ,Z ,E i so anm d er E,iE z ation ,E ,Z isomerization, in CIs are close to 160 (Figure S4). The calculated isoThe merica za lti cul on a ted barr ii so erm s er are iz h ati ig o h n eno barr ug ier hs to are ex h pl ig ah in eno the ug dih st to in ct exsi pl gn ain a ls th e distinct signals respectively. The o re bta spec ined tiv re elsul y. The ts sug obgest tained tha re t th sul e ts in sug terco gest nver thsi at oth n ie ni n bo ter thco pa ni v rs ero si fo is no im n er bo s th pairs of isomers The calculated isomerization barriers are high enough to explain the distinct signals of isomers in the NM of iso R spec mers tra in o th f e co NM mpo Run spec d 3 tra . H o ofweve compo r, th un ey d a 3re . H cl oo weve se inr, m th agn ey ia tude re cl,o fse or in magnitude, for occurs via in-plane o cc inurs versi vi o an i n o- fpl tha e nn ei i tro nvgen ersio an to o m f th like e nin itro oth gen er a sito mm ila lr ike com in po oth un erd si s m [1i7 la ,2 r 0co ], mpounds [17,20], of isomers in the NMR spectra of compound 3. However, they are close in magnitude, for i.e., without rotatiio .e. n , awi rou th nd out C= ro N tati do on ub alr e ou bo nd nd C= s. Thus N do,ub thle e va boln ues ds. o Thus f N-N= , th C e v va allence ues o a f n N - -N=C valence an- example, to the rotational barrier about the C–N bond in acetamide [21]. These data agree gles in CIs are close gles to i1 n6 CIs a 0° (Fire gure clo se S4)t.o 160° (Figure S4). with the observed difficulties in the isolation of individual isomers of the title compound. The calculated isoThe merica zalti cul on a ted barr ii so erm s a er re iz h ati ig o h n eno barr ug ier hs to are ex h pl ig ah in eno the ug dih st to in ct exsi pl gn ain als th e distinct signals of isomers in the NM of iso R spec mers tra in o th f e co NM mpo Run spec d 3 tra . H o ofweve compo r, th un ey d a 3re . H cl oo weve se inr, m th agn ey ia tude re cl, o fse or in magnitude, for 2.3. In Silico ADME Predictions We evaluated the ADME characteristics of the most potent JNK and cell-based sys- tems of compound 3 using the SwissADME online tool [22]. We obtained bioavailability radar plots that display an assessment of the drug-likeness of azine 3. Six important physicochemical properties, including lipophilicity, size, polarity, solubility, flexibility, and insaturation, were considered. It was found that the investigated heterocyclic azine in general has satisfactory ADME properties as can be seen from a radar representation of bioavailability shown in Figure S5. The only unfavorable property is a high insaturation score of compound 3, which is true of most 11H-indeno[1,2-b]quinoxalin-11-one deriva- tives. Noticeably, the known JNK inhibitor SP600125 of the anthrapyrazolone series [23] also has enhanced insaturation. Compared to SP600125, compound 3 has a higher pre- Molbank 2021, 2021, M1299 4 of 7 dicted lipophilicity, which usually correlates with decreased water solubility, increased metabolism, and slower excretion. Additionally, higher lipophilicity makes it more likely to penetrate the skin. According to the calculated ADME parameters (Table 1) and bioavail- ability radars for compound 3 and SP600125 (Figure S5), the synthesized azine 3 is expected to be bioavailable. Table 1. Physicochemical ADME properties of compound 3. Property Compound 3 Formula C H N 24 18 4 Molecular Weight (g/mol) 362.43 Heavy Atoms 28 0.08 Fraction Csp Rotatable Bonds 3 H-bond Acceptors 4 H-bond Donors 0 Molar Refractivity 114.42 Topological Polar Surface Area (tPSA), Å 50.50 Lipophilicity (Consensus Log P ) 4.84 o/w BBB Permeation Yes 3. Materials and Methods 3.1. General Information and Compound 3 Synthesis LC/MS analysis was performed on an Agilent Infinity chromatograph (Santa Clara, CA, USA) with an AccurateMass QTOF 6530 mass detector (Santa Clara, CA, USA). Chro- matographic conditions: column Zorbax EclipsePlusC18 1.8 m, 2.1  50 mm; eluent H O: ACN (85%); flow 0.2 mL/min. Ionization source: ESI in positive mode. The H and C NMR spectra were recorded on a Bruker AVANCE III HD instrument (Billerica, 1 13 MA, USA) (operating frequency H—400 MHz; C—100 MHz). The melting point of the obtained compound was measured using a Melting Point Apparatus SMP30 (Cole-Parmer Instrument Company, Vernon Hills, IL, USA), heating rate 3.0 C/min. IR spectra were recorded on an FT-IR spectrometer Nicolet 5700 (Thermo Fisher Scientific Inc., Waltham, MA, USA) with KBr pellets. The reaction was monitored by thin layer chromatography (TLC) on Silufol UV-254 and Merck plates, silica gel 60, F254. Known compounds 11H-indeno[1,2-b]quinoxaline-11-one (1) and its hydrazone (2) were prepared according to methods described in the literature [15,16]. 11H-indeno[1,2-b]quinoxalin-11-one 2-(4-ethylbenzylidene)hydrazone (3). p-Ethylbenzaldehyde (0.3 mmol, 0.04 mL) was added to a solution of compound 2 (0.3 mmol, 0.074 g) in 25 mL EtOH under permanent stirring. Then, the reaction mixture was refluxed under stirring for 2 h. The reaction was monitored by TLC (eluent: chloroform). After cooling, the precipitate was filtered out and washed with EtOH. The title compound 3 was obtained as yellow crystals (yield 89%); M.p. 195–196 C (from ethanol). H NMR (400 MHz, CDCl ), , ppm: 1.23–1.34 (m, 3H, CH CH ), 2.69–2.80 (m, 2H, 3 2 3 CH CH ), 7.49–7.68 (m, 2H, H-2, H-3), 7.73–7.86 (m, 2H, H-7, H-8), 8.09 (d, 1H, J 4 Hz, 2 3 H-9), 8.18 (d, 1H, J 6 Hz, H-6), 8.25–8.34 (m, C H ), 8.32 (d, 1H, J 4 Hz, H-4), 8.74 (d, 1H, 6 4 J 4 Hz, H-1), 8.85 (s, 0.15 H, H-12), 8.91 (s, 0.85 H, H-12) (atom numbering is shown in Scheme 3). C NMR (100 MHz, CDCl ), , ppm: 15.34, 15.50, 29.16, 29.29, 122.59, 126.93, 128.14, 128.67, 128.79, 129.30, 129.49, 129.74, 129.77, 130.11, 130.46, 130.85, 130.93, 131.70, 132.18, 132.80, 134.47, 134.65, 138.32, 142.50, 142.70, 149.20, 150.83, 151.85, 151.96, 154.41, 155.77. IR (KBr), cm : n(C=N) 1546, 1587. LC/MS (ESI+); m/z: 363.1605 experimental + + ([C H N + H] = 363.1604 theor.); m/z: 385.1425 exp. ([C H N + Na] = 385.1424 theor.); 24 18 4 24 18 4 exit time 140–170 s. The ratio of isotopic peaks corresponds to the theoretical m/z: 363.16 (100%), 364.16 (27%), 365.16 (4%). Molbank 2021, 2021, x FOR PEER REVIEW 5 of 5 stirring for 2 h. The reaction was monitored by TLC (eluent: chloroform). After cooling, the precipitate was filtered out and washed with EtOH. The title compound 3 was ob- tained as yellow crystals (yield 89%); M.p. 195–196 °C (from ethanol). H NMR (400 MHz, CDCl3), δ, ppm: 1.23–1.34 (m, 3H, CH2CH3), 2.69–2.80 (m, 2H, CH2CH3), 7.49–7.68 (m, 2H, H-2, H-3), 7.73–7.86 (m, 2H, H-7, H-8), 8.09 (d, 1H, J  4 Hz, H- 9), 8.18 (d, 1H, J  6 Hz, H-6), 8.25–8.34 (m, C6H4), 8.32 (d, 1H, J  4 Hz, H-4), 8.74 (d, 1H, J   4 Hz, H-1), 8.85 (s, 0.15 H, H-12), 8.91 (s, 0.85 H, H-12) (atom numbering is shown in Scheme 3). C NMR (100 MHz, CDCl3), δ, ppm: 15.34, 15.50, 29.16, 29.29, 122.59, 126.93, 128.14, 128.67, 128.79, 129.30, 129.49, 129.74, 129.77, 130.11, 130.46, 130.85, 130.93, 131.70, 132.18, 132.80, 134.47, 134.65, 138.32, 142.50, 142.70, 149.20, 150.83, 151.85, 151.96, 154.41, −1 155.77. IR (KBr), cm : ν(C=N) 1546, 1587. LC/MS (ESI+); m/z: 363.1605 experimental + + ([C24H18N4 + H] = 363.1604 theor.); m/z: 385.1425 exp. ([C24H18N4 + Na] = 385.1424 theor.); Molbank 2021, 2021, M1299 5 of 7 exit time 140–170 s. The ratio of isotopic peaks corresponds to the theoretical m/z: 363.16 (100%), 364.16 (27%), 365.16 (4%). Scheme Scheme 3 3.. Atom numberi Atom numbering ng for N for NMR MR as assignments signments i in n mol molecule ecule 3 3. . Molbank 2021, 2021, xM FO olb Ra n Pk EE 20 R 2 1 R, EV 202 IEW 1, x FOR PEER REVIEW 5 of 5 5 of 5 1 13 1 13 The H NMR and C NMR spectrum are shown in Figures S1 and S2. The H NMR and C NMR spectrum are shown in Figures S1 and S2. 3.2. DFT Calculations 3.2. DFT Calculations The ORCA 5.0 computational chemistry software [24] was used for DFT calculations The ORCA 5.0 computational chemistry software [24] was used for DFT calculations of E,E-, E,Z-, Z,E- and Z,Z-isomers of compound 3. Before the calculations, conforma- of E,E-, E,Z-, Z,E- and Z,Z-isomers of compound 3. Before the calculations, conformation tion searches were performed for geometric isomers using the VConf 2.0 program of searches were performed for geometric isomers using the VConf 2.0 program of the Ver- the VeraChem suite software (VeraChem LLC, Germantown, MD, USA). For the best ten aChem suite software (VeraChem LLC, Germantown, MD, USA). For the best ten confor- conformations found for each isomer, singlet state geometry optimizations were carried mations found for each isomer, singlet state geometry optimizations were carried out with out with ORCA 5.0 employing the BLYP functional and def2-SVP basis set. Afterwards, ORCA 5.0 employing the BLYP functional and def2-SVP basis set. Afterwards, the lowest- Scheme 2. SynthesSche is of t m ite le 2 c . omp Synto hund esis 3 o.f title compound 3. the lowest-energy conformation of each isomer was re-optimized with the use of the energy conformation of each isomer was re-optimized with the use of the B3LYP/G func- B3LYP/G functional, ma-def2-SVP basis set, and D3BJ dispersion correction. Solvation According to the A NM ccoR rd d in at g a to (CDCl the NM 3), th Re dre atcr a ys (CDCl talliz 3ed ), th ce om repo crys un ta dl l3 iz w ed as co ob m ta po inun edd a s 3 was obtained as tional, ma-def2-SVP basis set, and D3BJ dispersion correction. Solvation effects were taken effects were taken into account using the CPCM model with chloroform as a solvent. Fre- 1 1 a Z,E-isomer mix ature Z,E. -The isom er H m NM ixture R spec . The tru m H (NM Figure R spec S1) tru con m ta (iFi ns gure two S d 1i)st co inn ct talio n w s -tw fieo ld d istinct low-field into account using the CPCM model with chloroform as a solvent. Frequency calculations quency calculations were performed for the optimized geometries in order to establish the signals of the imsi ingn e pr als oto ofn th N= e iCH mina e t pr 8.9 o1 to a n n N= d 8CH .85 ppm at 8.9wi 1 a th n d re 8 l.a 8ti 5v ppm e integr with al i re ntens lativie ties in tegral intensities were performed for the optimized geometries in order to establish the nature of the sta- nature of the stationary points. For CI-NEB calculations of the isomerization paths and 0.35/0.65, as well0 a .3 s 5typi /0.65 ca , l as siwell gnal s as oftypi the ca ethy l sign l gro als up of a th t e 1.ethy 30 (tw l gro o oup vera la t i1 d. 3tr 0i p (tw lets o o fro ver ml aid triplets from tionary points. For CI-NEB calculations of the isomerization paths and barriers, the DFT barriers, the DFT approximation indicated different iso above mersd )with ia fn fer d ent 2 B3L .75 iso ppm YP/G mers (m ) functional a ul nti dpl 2.et 75 ). ppm Sign was a (l m s applied ul ofti th pl e et in ).d S eno ignq aui ls n oo f xa the lin in e d h eno etero qui cycl noxa e line heterocycle approximation indicated above with B3LYP/G functional was applied using 10 interme- were observed bet were wee o nb 7 ser .5 v an ed d b 8et .5 wee ppm. n 7 S.ep 5 aa n ra dti 8o .5 n ppm. of the Siep soa m ra er tis owa n os f th im e po iso ss m iber le s pr wa ob s -impossible prob- using 10 intermediate images for each isomerization. Analysis and visualization of the diate images for each isomerization. Analysis and visualization of the DFT results were ably due to a rela ab tilv y eld y ue low to ener a relgy ati v ba elrr y iler ow foener r the gy is o ba m rr er ier iz afti oo r n th of e ith soe mca errb izo ati n– on ni tro of gen the carbon–nitrogen DFT results were made with Chemcraft 1.8 program. The ORCA 5.0 output files for the made with Chemcraft 1.8 program. The ORCA 5.0 output files for the lowest-energy con- double bond (seed , o e. ub g.,l e [1b 7o ] n ad n d (see our , e. DF g.,T [1 re 7s ] ul an ts d d oescr ur DF ibed T re bs el ul ots w )d . escribed below). lowest-energy conformations, CIs, and minimum energy path trajectories are available in formations, CIs, and minimum energy path trajectories are available in the Supplemen- The main characte The rist m ics ain o fch th ae ra ti cte tle ric st oim cs po of un th d e 3 ti : tl yel e c lo om w po crys untd al s, 3: M yel .p. lo w 195 cr –ys 196 ta l° s, С,M .p. 195–196 °С, the Supplementary Materials. soluble in acetonso e a ln ub dl chl e in o ro ace fo to rm. ne a The nd chl NM oR ro d fo arm. ta a re The prNM esen R ted da ita n a Sre ec tio prn ese 3.n 1ted , Fig in ure Sec S1 tio , n 3.1, Figure S1, tary Materials. and Figure S2. and Figure S2. 3.3. ADME Predictions 3.3. ADME Predictions The physicochemical properties of selected compounds were computed using Swis- 2.2. DFT Study of 2 Ald .2. az DFT ine Stud Isomy e rof ism Ald azine Isomerism The physicochemical properties of selected compounds were computed using sADME (http://www.swissadme.ch) (accessed on 20 September 2021). Azines can exhibA it z Z i,n E es -iso cam n er exih sm ib id t ue Z,E to -i so thm e pr eri ese smn d ce ue of to tw th oe C= prN ese bn oce nd o s. f We twos C= tudi N ed bo nds. We studied SwissADME (http://www.swissadme.ch) (accessed on 20 September 2021). the relative stabilth ity e re ofl f ao tiur ve po sta ss biib lilty e geo of fm our etr po ic i ss so ib m le er geo s of m cetr om ic po iso un m der 3s in o fchl coo m ro po foun rm dus- 3 in chloroform us- 4. Conclusions ing the DFT meth in o g dth . The e DFT lowest meth -ener od. gy The coln of west orm- aener tiongy s o fco th ne fo irm som ati er os ns were of th fe o u iso nd m wi ers thwere found with 4. Conclusions In this work, we presented the synthesis of the previously unknown compound 3 B3LYP/G functioB n3 aL l Y im P/ pl G e m fuented nction ia nl O im Rpl CA em 5ented .0 sof tw in a O re R . CA The 5m .0 a so -def2 ftwa -S re VP . The basi m sa set -def2 [18 -S ] VP basis set [18] (11H-indeno[1,2-b]quinoxalin-11-one 2-(4-ethylbenzylidene)hydrazone). The compound In this work, we presented the wa syn s used the fo si r sf of ina wa lthe geo s p used mretr ev f y ious oo r pti fin ly m al i unkno geo zatim on etr s. w Thi y n com opti s ba m si ip z s set oun ation d in s. cl 3 Thi ude s s ba dsi iff s set use fiun nclctio ude n s s d pe iffrti use - functions perti- nent for an adequa nent te tre for aa tm n ent adeq of ua az te in tre e la otn m e ent paio r fi n atzer ina e cti lo o n n e s. pa The ir in ot pti era m citi zo ed ns. stThe ructure opti s mized structures structure was confirmed by NMR, IR, and LC/MS methods. According to the DFT results, (11H-indeno[1,2-b]quinoxalin-11-one 2-(4-ethylbenzylidene)hydrazone). The compound of the geometric o iso f th me er geo s ar m e etr prese ic iso nted mer in s a Fi re gure prese S3n . ted The in E ,Fi E- gure isom S er 3 .wa Ths e fE o,un E-d iso to m b er e wa the s found to be the compound 3 has a thermodynamically favorable E,E-configuration. The calculated isomer- structure was confirmed by NMR, IR, and LC/MS methods. According to the DFT results, most thermodynm am oi st ca th lly erst m ao bd le yn (h aer me ica an lld y st bel ab olw, e (h th er e e fia rst ndsy bel mo bw, ol ith n e iso first mer sy nm ota bo tilo in n d iso e-mer notation de- ization paths suggest that the E,Z-isomerization occurs via in-plane inversion of the azine scribes the configura scrib ties onth oe f th coe na fiz gura ine C= tioN n o bfo th nd e a att zia n ce hC= ed N to b th oe nd in a d tt eno ach qed ui n to o x th al e in in e d m eno oiety quinoxaline moiety nitrogen atoms. An in silico estimation of ADME characteristics indicates that compound 3 while the secondwh syim le bth ole ref seco ers nto d sy thm e b C= olN ref ber on s dto n ea thr e th C= e N p-b ethy ond l phen nearyl th f e ra pgm -ethy enltphen ). The yl fragment). The can cross the blood–brain barrier and thus has perspectives to be used for the treatment Z,E-, E,Z- and ZZ ,Z ,E -i-so , E m ,Z er - sa h na dv e Z,th Z-e iso ca m lcul ersa ted hav e Gth ibb e sc a fre lcul e ener atedgi G es ibb 3s .1 f 6re , 4 e .9 ener 1 an gi des 7.1 33 .1 6, 4.91 and 7.13 of neuroinflammation and ischemia–reperfusion injury like other indenoquinoxaline ana- kJ/mol, respectivkJ/ ely, mh oilgh , re er spec thati nv tel hy, e E h ,E igh -iso erm th er a.n B ta hsed e E ,o En -i so thm ese er re . B sul ased ts, o we n th pr ese opo re se sul th ts a,t we propose that logues [12]. Despite using classic methods to obtain azine derivatives, we have discovered a the synthesized c th oe msy pon un thd esi 3z ed con c si ost ms po ofun rel da 3 ti v co eln y sim sto s re of st rel ab alti e vE el ,E y - m an od re Z st ,E a- b ilso e m E,er E-s, an as d Z,E-isomers, as new class of azines based on the heterocyclic system of 11H-indeno[1,2-b]quinoxalin-11-one, the other two isoth me er o s th wi erth tw Zo - o iri so enta merti s owi n th of th Z-e ori p- enta ethy ti lo phen n ofyl th subs e p-ethy tituent lphen are yl c h subs aracte tituent r- are character- which is of great interest for further study of possible biologically active compounds. ized by higher G ii zbb eds b fre y e hiener ghergi G es. ibb It s sh fre o e ul ener d be gin es. ote It d sh tho aul t o dn b ly e th no e te E d ,E th -iso at m on er ly hth as e th Ee ,E -isomer has the optimized structure opti wi mith zed a fst ul ruc ly c ture opl a wi na th r a a rr fa ul nlge y c m oent pla n oa fr m arr ola ec nul gea m r ent mo io eti f m es. o lecular moieties. Supplementary Materials: The following are available online. Figure S1: The H NMR spectrum of To evaluate the ener To ev gy alba uarte rier ths e fener or Zg ,E y iba sor m rier eris za fo tir on Z ,of E ib so oth mer az iz in ati e o C= n N of b bo on th d s, azwe ine C=N bonds, we recrystallized compound 3; Figure S2: The C NMR spectrum of compound 3; Figure S3: The struc- applied the climba ippl ng iim ed a ge the nc udge limbd in e g la im sta ic ge ba n n udge d (CId -NE elaB st)i c mb etho andd (CI olo -NE gy, B wh ) m ich etho is d efo flo icigy ent , wh ich is efficient tures of E,E-, Z,E-, E,Z-, and Z,Z-isomers of compound 3 optimized by the DFT method; Figure S4: at finding minimat um fi n ener ding gy mpa int im hs ua m n d ener sadg d y le pa poi thn s ts an [d 19 s]a . d The dle cli poi m n b ts in [g 19 im ]. a The ges cli (CIs mb ) io nb g -images (CIs) ob- The energy diagrams and the climbing image conformations for E,E Z,E and E,E E,Z iso- tained for E,E ta in Zed ,E a fo nr dE E ,E ,E Z E,,E Z a in so dm Eer ,Ei zatio n E ,o Zf icso om mpo eriun zad ti o 3n ca of n cb oe m co po nun sid d er 3ed ca n be considered merization of compound 3; Figure S5: goBioavailability od approximati go radar on od s of appr plots the oco xiof m rra espo compound tionn s d of in th g tra e 3co n and rr siespo tio SP600125. n st nd ates. ing tra The nsi CI tis oa nn st da o tes. ther The inter CIm s a ed nd i- other intermedi- Files: ORCA 5.0 output files for fourageometric te images o isomers n the ate miof in m im a the ge um s o title ener n th compound, gy e m p ia ntih m s a um re XYZ ener shown files gy p in a for tFi hs a gure CIre s Sh 4o , wn wh er ine Fi th gure e inter S4po , wh lated ere the interpolated energy diagrams ener are gy pr ese dian gra ted m . s Ba ased re pr oese n th nted e ca . lB cul ased ated o n DF th T e ener calcul gies ated of DF CIs, T ener we h gi av es e of CIs, we have conformations and isomerization trajectories. estimated the barr esti ierm s a as ted 89 ta h n e dba 84 rr kJ/ ierm s a os l 8 fo 9r aE n,d E 84 kJ/ Z m ,E ol a fn od r E E,,E E Z E,,E Z a iso nd m Eer ,Ei zatio n E,, Z isomerization, respectively. The re ob spec tainti ed vel re y. sul The ts sug obta gest ined th re at sul the tsi n sug tergest conv ter hasi t o th ne ii n n b ter oth co pa nvier rs si oo f n is io nm ber oth s pairs of isomers occurs via in-plan oe cc in urs ver vsi ia o in n o -pl f th an e en iin tro ver gen sion ato of m th le ike niin tro o gen ther a to sim mi lla ike r co in m opo thun er si ds m[i1 la 7r ,2co 0]m , pounds [17,20], i.e., without rotai ti .e. on , wi arou tho nd ut C= rota N tid oo nub arlou e b nd on d C= s. N Thus doub , th le e bva on ld ues s. Thus of N,- N= the C va va lues lence of aN n- -N=C valence an- gles in CIs are clo gl se es to in 1 CIs a 60° (Fi regure close S4 to ). 160° (Figure S4). The calculated iso The mer ca izla cul tio an ted ba rr iso ier ms er aire za h tiio gn h b eno arrug ierh s a to re ex hipl gh a ieno n thug e d hi st to i n ex ct pl sia gn ina th ls e distinct signals of isomers in the o NM f iso Rm spec ers tra in th of e c NM ompo R spec undtra 3. H of o c weve ompo r,un they d 3a . re H o cl weve ose ir, n m tha ey gn aire tude clo , se for in magnitude, for Molbank 2021, 2021, M1299 6 of 7 Author Contributions: Conceptualization was conducted by A.R.K. and A.I.K.; methodology and experimental work were conducted by A.R.K. and E.I.S.; data analysis, writing and editing of the paper were conducted by A.R.K. and A.I.K.; project administration and supervision was conducted by A.I.K. All authors have read and agreed to the published version of the manuscript. Funding: This research was supported by the Ministry of Science and Higher Education of the Russian Federation (project no. Nauka FSWW-2020-0011) and by the Tomsk Polytechnic University development program. The synthesis and DFT study of compound 3 were funded by the Russian Science Foundation (grant No. 17-15-01111). Institutional Review Board Statement: Not applicable. Informed Consent Statement: Not applicable. Data Availability Statement: The data presented in this study are available in this article. Acknowledgments: The authors wish to thank Alexander A. Bondarev for the MS analysis of compound 3. Conflicts of Interest: The authors declare no conflict of interest. References 1. Outirite, M.; Lebrini, M.; Lagrenée, M.; Bentiss, F. New one step synthesis of 3,5-disubstituted pyrazoles under microwave irradiation and classical heating. J. Heterocycl. Chem. 2008, 4, 503–505. [CrossRef] 2. Regitz, M.; Weise, G.; Lenz, B.; Förster, U.; Urgast, K.; Maas, G. Diazo Compounds. Part 67. Electrophilic Diazoalkane Substitution with Donor-substituted Cations. Bull. Soc. Chim. Belg. 1985, 94, 499–520. [CrossRef] 3. Zhao, M.-N.; Liang, H.; Ren, Z.-H.; Guan, Z.-H. Copper-Catalyzed N–N Bond Formation by Homocoupling of Ketoximes via N–O Bond Cleavage: Facile, Mild, and Efficient Synthesis of Azines. Synthesis 2012, 1501–1506. [CrossRef] 4. Nanjundaswamy, H.; Pasha, M. Rapid, Chemoselective and Facile Synthesis of Azines by Hydrazine/I . Synth. Commun. 2007, 37, 3417–3420. [CrossRef] 5. Diamant, S.; Agranat, I.; Goldblum, A.; Cohen, S.; Atlas, D. -adrenergic activity and conformation of the antihypertensive specific 2-agonist drug, guanabenz. Biochem. Pharmacol. 1985, 34, 491–498. [CrossRef] 6. Ramakrishnan, A.; Chourasiya, S.S.; Bharatam, P.V. Azine or hydrazone? The dilemma in amidinohydrazones. RSC Adv. 2015, 5, 55938–55947. [CrossRef] 7. Chourasiya, S.S.; Kathuria, D.; Nikam, S.S.; Ramakrishnan, A.; Khullar, S.; Mandal, S.K.; Chakraborti, A.K.; Bharatam, P.V. Azine-Hydrazone Tautomerism of Guanylhydrazones: Evidence for the Preference Toward the Azine Tautomer. J. Org. Chem. 2016, 81, 7574–7583. [CrossRef] 8. Sundberg, R.J.; Dahlhausen, D.J.; Manikumar, G.; Mavunkel, B.; Biswas, A.; Srinivasan, V.; Musallam, H.; Reid, W.A., Jr.; Ager, A.L. Cationic antiprotozoal drugs. Trypanocidal activity of 2-(4 -formylphenyl)imidazo[1,2-a]pyridinium guanylhydrazones and related derivatives of quaternary heteroaromatic compounds. J. Med. Chem. 1990, 33, 298–307. [CrossRef] 9. Davydov, V.; Sokol, V.; Polyanskaya, N.; Linko, R.; Ryabov, M.; Sergienko, V. Synthesis, crystal structure, and spectral studies of 10-(2-Benzothiazolylazo)-9-phenanthrol. Crystallogr. Rep. 2012, 57, 227–234. [CrossRef] 10. Giorgi, G.; Ponticelli, F.; Savini, L.; Chiasserini, L.; Pellerano, C. On the isomerism/tautomerism of hydrazones. Crystal structures, study in solution and theoretical calculations of new series of -N-heterocyclic hydrazones. J. Chem. Soc. Perkin Trans. 2 2000, 11, 2259–2264. [CrossRef] 11. Ganga, M.; Sankaran, K.R. Synthesis, spectral characterization, DFT, molecular docking and biological evaluation of some newly synthesized asymmetrical azines of 3,5-dimethoxy-4–hydroxy benzaldehyde. Chem. Data Collect. 2020, 28, 100475–100489. [CrossRef] 12. Schepetkin, I.A.; Khlebnikov, A.I.; Potapov, A.S.; Kovrizhina, A.R.; Matveevskaya, V.V.; Belyanin, M.L.; Quinn, M.T. Synthesis, biological evaluation, and molecular modeling of 11H-indeno[1,2-b]quinoxalin-11-one derivatives and tryptanthrin-6-oxime as c-Jun N-terminal kinase inhibitors. Eur. J. Med. Chem. 2019, 161, 179–191. [CrossRef] [PubMed] 13. Kotharkar, S.A.; Shinde, D.B. Synthesis of antimicrobial 2,9,10-trisubstituted-6-oxo-7,12-dihydrochromeno[3,4-b]quinoxalines. Bioinorg. Med. Chem. Let. 2006, 16, 6181–6184. [CrossRef] 14. Tseng, C.-H.; Chen, Y.-R.; Tzeng, C.-C.; Liu, W.; Chou, C.-K.; Chiu, C.-C.; Chen, Y.-L. Discovery of indeno[1,2-b]quinoxaline derivatives as potential anticancer agents. Eur. J. Med. Chem. 2016, 108, 258–273. [CrossRef] 15. Pearson, B.D. Indenoquinolines. III. Derivatives of 11H-Indeno-[1,2-b]quinoxaline and related indenoquinolines. J. Org. Chem. 1962, 27, 1674–1678. [CrossRef] 16. Balamurugan, G.; Velmathi, S. Quinoxaline based redox relay receptor for iodide ions and its application towards real sample analysis and logic gate function. Sens. Actuators B 2018, 256, 126–134. 17. Warren, C.H.; Wettermark, G.; Weiss, K. Cis-trans isomerization about the carbon-nitrogen double bond. Structures of the isomers of N-benzylideneaniline. J. Am. Chem. Soc. 1971, 93, 4658–4663. 18. Zheng, J.; Xu, X.; Truhlar, D.G. Minimally augmented Karlsruhe basis sets. Theor. Chem. Acc. 2011, 128, 295–305. [CrossRef] Molbank 2021, 2021, M1299 7 of 7 19. Ásgeirsson, V.; Birgisson, B.O.; Bjornsson, R.; Becker, U.; Neese, F.; Riplinger, C.; Jónsson, H. Nudged Elastic Band Method for Molecular Reactions Using Energy-Weighted Springs Combined with Eigenvector Following. J. Chem. Theory Comput. 2021, 17, 4929–4945. [CrossRef] 20. Blanco, F.; Alkorta, I.; Elguero, J. Barriers about Double Carbon-Nitrogen Bond in Imine Derivatives (Aldimines, Oximes, Hydrazones, Azines). Croat. Chem. Acta 2009, 82, 173–183. 21. Gasparro, F.P.; Kolodny, N.H. NMR Determination of the Rotational Barrier in N,N-dimethylacetamide. J. Chem. Educ. 1977, 54, 258–261. [CrossRef] 22. Daina, A.; Michielin, O.; Zoete, V. SwissADME: A free web tool to evaluate pharmacokinetics, drug-likeness and medicinal chemistry friendliness of small molecules. Sci. Rep. 2017, 7, 42717. [CrossRef] [PubMed] 23. Bennett, B.L.; Sasaki, D.T.; Murray, B.W.; O’Leary, E.C.; Sakata, S.T.; Xu, W.; Leisten, J.C.; Motiwala, A.; Pierce, S.; Satoh, Y.; et al. SP600125, an anthrapyrazolone inhibitor of Jun N-terminal kinase. Proc. Natl. Acad. Sci. USA 2001, 98, 13681–13686. [CrossRef] [PubMed] 24. Neese, F.; Wennmohs, F.; Becker, U.; Riplinger, C. The ORCA quantum chemistry program package. J. Chem. Phys. 2020, 152, 224108. [CrossRef] [PubMed] http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Molbank Multidisciplinary Digital Publishing Institute

11H-Indeno[1,2-b]quinoxalin-11-one 2-(4-ethylbenzylidene)hydrazone

Download PDF
7 pages

Loading next page...
 
/lp/multidisciplinary-digital-publishing-institute/11h-indeno-1-2-b-quinoxalin-11-one-2-4-ethylbenzylidene-hydrazone-txCUdwswTU

References (22)

Publisher
Multidisciplinary Digital Publishing Institute
Copyright
© 1996-2021 MDPI (Basel, Switzerland) unless otherwise stated Disclaimer The statements, opinions and data contained in the journals are solely those of the individual authors and contributors and not of the publisher and the editor(s). MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Terms and Conditions Privacy Policy
ISSN
1422-8599
DOI
10.3390/M1299
Publisher site
See Article on Publisher Site

Abstract

molbank Short Note 1 1 1 , 2 , Anastasia R. Kovrizhina , Elizaveta I. Samorodova and Andrei I. Khlebnikov * Kizhner Research Center, Tomsk Polytechnic University, 634050 Tomsk, Russia; anaskowry@gmail.com (A.R.K.); betani47@gmail.com (E.I.S.) Scientific Research Institute of Biological Medicine, Altai State University, 656049 Barnaul, Russia * Correspondence: aikhl@chem.org.ru; Tel.: +7-3822-706349 Abstract: 11H-Indeno[1,2-b]quinoxaline derivatives present an important type of nitrogen-containing heterocyclic compound that are useful intermediate products in organic synthesis and have potential pharmaceutical applications. A new 11H-indeno[1,2-b]quinoxalin-11-one-2-(4-ethylbenzylidene)hydrazone (compound 3) was synthesized. Compound 3 is the first example of an azine derivative based on the 11H-indeno[1,2-b]quinoxaline system. The Z,E-isomerism of compound 3 was investigated by DFT calculations. Bioavailability was evaluated in silico using ADME predictions. According to the ADME results, compound 3 is potentially highly bioavailable and has potential to be used for the treatment of neuroinflammation and ischemia–reperfusion injury. Keywords: azine; aldazine; 11H-indeno[1,2-b]quinoxalin-11-one; DFT; ADME 1. Introduction Compounds containing a C=N bond attached to a heterocyclic moiety exhibit various chemical reactivities and often possess pharmacological activities. Prominent representa- Citation: Kovrizhina, A.R.; tives of these compounds are azines, which can be regarded as hydrazine derivatives of Samorodova, E.I.; Khlebnikov, A.I. 0 00 000 the general formula RR C=N-N=CR R . Azines have recently attracted attention owing 11H-Indeno[1,2-b]quinoxalin-11-one to their diverse therapeutic activities [1,2]. The synthesis of azines can be performed by the 2-(4-ethylbenzylidene)hydrazone. condensation of hydrazine with two moles of aldehyde/ketone under reflux conditions [1]. Molbank 2021, 2021, M1299. https:// doi.org/10.3390/M1299 Azines are often the major products obtained by the thermal decomposition of diazo compounds [2]. The process is bimolecular and involves the nucleophilic attack of the Academic Editor: Ian R. Baxendale carbon atom of the first diazo compound (which gives carbene by the removal of N ) on the terminal nitrogen of the second compound. Zhao et al. reported the formation of Received: 9 October 2021 symmetrical azines produced by the copper catalyzed homocoupling of oximes [3]. Nan- Accepted: 19 November 2021 jundaswamy and co-workers reported on the iodine catalyzed synthesis of symmetrical Published: 23 November 2021 azines by treating NH NH H O with carbonyl compounds at 0–10 C [4]. 2 2 2 A prominent drug belonging to the class of azines is Guanabenz (Figure 1) [5], which Publisher’s Note: MDPI stays neutral has always been considered a guanylhydrazone derivative. Figure 1 shows two tautomeric with regard to jurisdictional claims in forms of Guanabenz (A and B), with the azine form (B) being more stable [6,7]. Addition- published maps and institutional affil- ally, important examples are the antihypertensive agent bearing 2,6-dichlorophenyl and iations. a 1,1-diamino moieties [5], the trypanocidal agent containing the azine unit attached to imidazopyridine [8], the antibacterial compound [9], and the anticancer agent [10] (Figure 1) 4-((E)-((E)-((4-bromophenyl)(phenyl)methylene)hydrazono)methyl)2,6-dimethoxyphenol (BRH) that was active against MCF-7 cancerous cell lines [11]. Copyright: © 2021 by the authors. At present, the variation in conjugation via the azine substructure and its modulation Licensee MDPI, Basel, Switzerland. depending on the substituents has not been fully investigated. It is important to study This article is an open access article redox properties and the associated characteristics of electron exchange and their influence distributed under the terms and on chemical bonds in these systems, especially in azines containing heterocyclic fragments conditions of the Creative Commons of pharmacological importance. In this work, we have synthesized the first representative Attribution (CC BY) license (https:// of an azine with a 11H-indeno[1,2-b]quinoxaline moiety that is contained in numerous creativecommons.org/licenses/by/ biologically active compounds possessing anti-inflammatory [12], antimicrobial [13], anti- 4.0/). Molbank 2021, 2021, M1299. https://doi.org/10.3390/M1299 https://www.mdpi.com/journal/molbank Molbank 2021, 2021, x FOR PEER REVIEW 5 of 5 Molbank 2021, 2021, M1299 2 of 7 Molbank 2021, 2021, x FOR PEER REVIEW 5 of 5 cancer [14], and JNK inhibitory [12] properties. The bioavailability and electronic structure of the synthesized compound were evaluated with the use of computational methods. Figure 1. Examples of biologically active azines. At present, the variation in conjugation via the azine substructure and its modulation depending on the substituents has not been fully investigated. It is important to study redox properties and the associated characteristics of electron exchange and their influ- ence on chemical bonds in these systems, especially in azines containing heterocyclic frag- ments of pharmacological importance. In this work, we have synthesized the first repre- sentative of an azine with a 11H-indeno[1,2-b]quinoxaline moiety that is contained in nu- merous biologically active compounds possessing anti-inflammatory [12], antimicrobial [13], anticancer [14], and JNK inhibitory [12] properties. The bioavailability and electronic structure of the synthesized compound were evaluated with the use of computational methods. Figure 1. Examples of biologically active azines. Figure 1. Examples of biologically active azines. 2. Results and Discussion 2. Results and Discussion At present, the variation in conjugation via the azine substructure and its modulation 2.1. Synthesis 2.1. Synthesis depending on the substituents has not been fully investigated. It is important to study We preliminary obtained 11H-indeno[1,2-b]quinoxaline-11-one (1) and its hydrazone We preliminary obtained 11H-indeno[1,2-b]quinoxaline-11-one (1) and its hydra- redox properties and the associated characteristics of electron exchange and their influ- (2). The simplest way to synthesize compound 1 consists in the condensation of ninhydrin zone (2). The simplest way to synthesize compound 1 consists in the condensation of ence on chemical bonds in these systems, especially in azines containing heterocyclic frag- with o-phenylenediamine [15] (Scheme 1). The 11H-indeno[1,2-b]quinoxalin-11-one hy- ninhydrin with o-phenylenediamine [15] (Scheme 1). The 11H-indeno[1,2-b]quinoxalin- ments of pharmacological importance. In this work, we have synthesized the first repre- drazone (2) was obtained by the nucleophilic addition of hydrazine hydrate to ketone 1 11-one hydrazone (2) was obtained by the nucleophilic addition of hydrazine hydrate to sentative of an azine with a 11H-indeno[1,2-b]quinoxaline moiety that is contained in nu- [16] (Scheme 1). ketone 1 [16] (Scheme 1). merous biologically active compounds possessing anti-inflammatory [12], antimicrobial [13], anticancer [14], and JNK inhibitory [12] properties. The bioavailability and electronic structure of the synthesized compound were evaluated with the use of computational methods. 2. Results and Discussion 2.1. Synthesis Scheme Scheme 1 1.. Synthesis Synthesis of of compounds compounds 1 1 and and 2 2. . We preliminary obtained 11H-indeno[1,2-b]quinoxaline-11-one (1) and its hydrazone For the first time, we have obtained a new functional compound, 11H-indeno[1,2-b] (2). The simplest way to synthesize compound 1 consists in the condensation of ninhydrin For the first time, we have obtained a new functional compound, 11H-indeno[1,2- quinoxalin-11-one 2-(4-ethylbenzylidene)hydrazone (3, Scheme 2), which contains an azine with o-phenylenediamine [15] (Scheme 1). The 11H-indeno[1,2-b]quinoxalin-11-one hy- b]quinoxalin-11-one 2-(4-ethylbenzylidene)hydrazone (3, Scheme 2), which contains an group and an indenoquinoxaline system. This compound is of interest as a potential Molbank 2021, 2021, x FOR PEER REVIEW drazone (2) was obtained by the nucleophilic addition of hydrazine hydrate to ketone 5 of 1 5 azine group and an indenoquinoxaline system. This compound is of interest as a potential biologically active compound that could find application in medicinal, organic, and mate- [16] (Scheme 1). biologically active compound that could find application in medicinal, organic, and ma- rial chemistry. terial chemistry. Further modification of compound 2 to the target product 3 was performed by the action of p-ethylbenzaldehyde (Scheme 2). The reaction proceeds for 2 h under reflux in ethanol in the absence of alkalis or acids. At the end of the process, complete conversion was observed (control by TLC, eluent hexane: ethyl acetate (2:1, v/v)). The expected crude azine was isolated by filtration with 89% yield. The compound was purified by recrystal- Scheme 1. Synthesis of compounds 1 and 2. lization from ethanol. For the first time, we have obtained a new functional compound, 11H-indeno[1,2- b]quinoxalin-11-one 2-(4-ethylbenzylidene)hydrazone (3, Scheme 2), which contains an Scheme 2. Synthesis of title compound 3. Scheme 2. Synthesis of title compound 3. azine group and an indenoquinoxaline system. This compound is of interest as a potential Further modification of compound 2 to the target product 3 was performed by the biologically active compo According to the NM u R nd th dataat co (CDC uld l3), find the recrysta applicatll ion in med ized compou icinal nd , org 3 wa anic s ob , ta and m ined as a- action of p-ethylbenzaldehyde 1 (Scheme 2). The reaction proceeds for 2 h under reflux in terial chem a Z,E-isomer mixt istry. ure. The H NMR spectrum (Figure S1) contains two distinct low-field ethanol in the absence of alkalis or acids. At the end of the process, complete conversion signals of the imine proton N=CH at 8.91 and 8.85 ppm with relative integral intensities Further modification of compound 2 to the target product 3 was performed by the was observed (control by TLC, eluent hexane: ethyl acetate (2:1, v/v)). The expected action of 0.35/0.65,p as -ethylbenzaldeh well as typicay l s de (Scheme ignals of th2). The re e ethyl grou action proceeds p at 1.30 (two for 2 h overlaunder id triplet reflux in s from crude azine was isolated by filtration with 89% yield. The compound was purified by ethano differen l in t iso thm e absence o ers) and 2.75 f alkalis or ppm (multiplet). acids. At Si the gn end als of of t h the e i process, ndenoqui complete noxaline he con te v rersion ocycle recrystallization from ethanol. was observed were observed bet (control by TLC, el ween 7.5 and 8 u.e 5 ppm. S nt hexan ee p: e ara thy tion of l acet at the (2 e is:1 omers , v/v))wa . The e s imx poss pectied ble c prob- rude According to the NMR data (CDCl ), the recrystallized compound 3 was obtained as az ably ine w duae s to iso al rel ated by ative fly ilt lo raw energ tion with y 8 b9a% rr yi ier e lfor d. The co the isomeriz mpound was ation of the carbon purified by re –ni crystal- trogen a Z,E-isomer mixture. The H NMR spectrum (Figure S1) contains two distinct low-field lization double bond from ethano (see, e.g., [17] and l. our DFT results described below). The main characteristics of the title compound 3: yellow crystals, M.p. 195–196 °С, soluble in acetone and chloroform. The NMR data are presented in Section 3.1, Figure S1, and Figure S2. 2.2. DFT Study of Aldazine Isomerism Azines can exhibit Z,E-isomerism due to the presence of two C=N bonds. We studied the relative stability of four possible geometric isomers of compound 3 in chloroform us- ing the DFT method. The lowest-energy conformations of the isomers were found with B3LYP/G functional implemented in ORCA 5.0 software. The ma-def2-SVP basis set [18] was used for final geometry optimizations. This basis set includes diffuse functions perti- nent for an adequate treatment of azine lone pair interactions. The optimized structures of the geometric isomers are presented in Figure S3. The E,E-isomer was found to be the most thermodynamically stable (here and below, the first symbol in isomer notation de- scribes the configuration of the azine C=N bond attached to the indenoquinoxaline moiety while the second symbol refers to the C=N bond near the p-ethylphenyl fragment). The Z,E-, E,Z- and Z,Z-isomers have the calculated Gibbs free energies 3.16, 4.91 and 7.13 kJ/mol, respectively, higher than the E,E-isomer. Based on these results, we propose that the synthesized compound 3 consists of relatively more stable E,E- and Z,E-isomers, as the other two isomers with Z-orientation of the p-ethylphenyl substituent are character- ized by higher Gibbs free energies. It should be noted that only the E,E-isomer has the optimized structure with a fully coplanar arrangement of molecular moieties. To evaluate the energy barriers for Z,E isomerization of both azine C=N bonds, we applied the climbing image nudged elastic band (CI-NEB) methodology, which is efficient at finding minimum energy paths and saddle points [19]. The climbing images (CIs) ob- tained for E,E Z,E and E,E E,Z isomerization of compound 3 can be considered good approximations of the corresponding transition states. The CIs and other intermedi- ate images on the minimum energy paths are shown in Figure S4, where the interpolated energy diagrams are presented. Based on the calculated DFT energies of CIs, we have estimated the barriers as 89 and 84 kJ/mol for E,E Z,E and E,E E,Z isomerization, respectively. The obtained results suggest that the interconversion in both pairs of isomers occurs via in-plane inversion of the nitrogen atom like in other similar compounds [17,20], i.e., without rotation around C=N double bonds. Thus, the values of N-N=C valence an- gles in CIs are close to 160° (Figure S4). The calculated isomerization barriers are high enough to explain the distinct signals of isomers in the NMR spectra of compound 3. However, they are close in magnitude, for Molbank 2021, 2021, x F M Oo R lb P an EE k 2 R0 R 21 EV , 2I 0EW 21, x FOR PEER REVIEW 5 of 5 5 of 5 Molbank 2021, 2021, x F M Oo R lb P an EE k 2 R0 R 21 EV , 2I0EW 21, x FOR PEER REVIEW 5 of 5 5 of 5 Molbank 2021, 2021, M1299 3 of 7 Scheme 2. Synthesis Sche of tit m le e c2 omp . Syn otund hesis 3 .o f title compound 3. According to the NM AccR o rd da in ta g (to CDCl the 3NM ), thR e re da cr ta ys (CDCl tallized 3), th coe m re po cr un ysd ta 3 ll iw zed as o co bm tai po ned un a ds 3 was obtained as signals of the imine proton N=CH at 8.91 and 8.85 ppm with relative integral intensities 1 1 a Z,E-isomer mixture a Z,.E The -iso m H erNM mix R ture spec . The trum H (Fi NM gure R spec S1) co tru nm tai n (Fi s gure two d Si1 st ) ico nct nta loiw ns -ftw ield o distinct low-field 0.35/0.65, as well as typical signals of the ethyl group at 1.30 (two overlaid triplets from signals of the imin si e gn pr ao ls too n f N= the CH imia nt e 8pr .91 o to an nd N= 8.8 CH 5 ppm at 8.wi 91th an re d l8 a.ti 8v 5e ppm integr wi ath l i n re tens latiiv tie es in tegral intensities Scheme 2. Synthesis Sche of tit m le e c2 omp . Syn otund hesis 3 .o f title compound 3. different isomers) and 2.75 ppm (multiplet). Signals of the indenoquinoxaline heterocycle 0.35/0.65, as well a 0s .3typi 5/0.6 ca 5,l a si s gn well als a os f typi the ethy cal si l gn gro alup s of a t th 1e .3ethy 0 (tw l o gro ov up erla ai t d 1 .tr 30 ip ( ltw ets of ro ov m er laid triplets from were observed between 7.5 and 8.5 ppm. Separation of the isomers was impossible probably different isomers) d ain ff d er 2ent .75 ippm some(rs m)ul ati nd pl 2 et .7 ).5 S ppm ignal(s m oul f th tipl e iet nd ).eno Sign qui als no oxa f th lie ne inh dete eno ro qcycl uino exa line heterocycle According to the NM AccR o rd da in ta g (to CDCl the 3NM ), thR e re da cr ta ys (CDCl tallized 3), c th oe mre po cr un ysd ta 3 ll iw zed as o co bm tai po ned un a d s 3 was obtained as due to a relatively low energy barrier for the isomerization of the carbon–nitrogen double were observed betwere ween o 7 b.ser 5 av ned d 8 b .5 et ppm. weenS 7 ep .5 a ara nd ti o 8n .5 o ppm. f the iS so ep m aer ras tio wa n s ofi m thpo e iss soim bler e pr s wa obs - impossible prob- 1 1 a Z,E-isomer mixture a Z,.E The -iso m H erNM mix R ture spec . The trum H (Fi NM gure R spec S1) co tru nm tai n (Fi s gure two d Si1 st ) ico nct nta loiw ns -ftw ield o distinct low-field ably due to a bond relaa tib v (see, lel y y due lo e.g., w toener a [ 17 re gy l ]aand ti ba vel rry our ier lo f w o DFT r ener the rgy esults iso ba mer rrdescribed i iz er a ti fo or n th ofe th ibelow). se om caer rb io za nti –o nn itro ofgen the carbon–nitrogen signals of the imin si e gn pr ao ls too n f N= the CH imia nt e 8pr .91 o to an nd N= 8.8 CH 5 ppm at 8.wi 91th an re d l8 a.ti 8v 5e ppm integr wi ath l i n re tens latiiv tie es in tegral intensities double bond (see, d e. og. ub , [ le 17 b ]o an nd d (o see ur , DF e.g. T , re [1s 7ul ] ats n d d escr our iDF bed T b re el so ul w ts ). described below). The main characteristics of the title compound 3: yellow crystals, M.p. 195–196 C, solu- 0.35/0.65, as well a 0s .3typi 5/0.6 ca 5,l a si s gn well als a os f th typi e ethy cal si l gn gro alup s oa f t th 1e .3ethy 0 (tw l o gro ov up erla ai t d1 .tr 30 ip ( ltw ets of ro ov m er laid triplets from The main characte The ristim cs ao in f th che ar ti atl cte e ri co st m ics poo un f th d e 3:ti yel tle lo co w mcr po ys un tad ls, 3M : yel .p.lo 1w 95– cr 196 yst a °lС, s, M.p. 195–196 °С, ble in acetone and chloroform. The NMR data are presented in Section 3.1, Figures S1 and S2. different isomers) d ain ff d er 2ent .75 ippm some (rs m)ul ati nd pl 2 et .7 ).5 S ppm ignal(s m oul f th tipl e iet nd ).eno Sign qui als no oxa f th lie ne inh dete eno ro qcycl uino exa line heterocycle soluble in acetone so an lub d chl le io nro af ce orm. tone The andNM chlR oro df ao ta rm. are The prese NM nted R d ia n ta S a ec re tio pr nese 3.1n , ted Fig ure in S S ec 1tio , n 3.1, Figure S1, were observed betwere ween o 7 b.ser 5 av ned d 8 b .5 et ppm. weenS 7 ep .5 a ara nd ti o 8n .5 o ppm. f the iS so ep m aer ras tiwa on s ofi m thpo e iss soim bler e pr s wa ob- s impossible prob- and Figure S2. and Figure S2. 2.2. DFT Study of Aldazine Isomerism ably due to a relaa tib vlel y y due low to ener a re gy la ti ba vel rry ier lo f w or ener the gy iso ba mer rriiz er a ti fo or n th ofe th ise om caer rb io za nti –o nn itro ofgen the carbon–nitrogen double bond (see, d e. og. ub , [ l1 e 7 b ]o an nd d (o see ur , DF e.g. T , re [1s 7ul ] a ts n d d escr our iDF bed T b re el so ul w ts ). described below). Azines can exhibit Z,E-isomerism due to the presence of two C=N bonds. We studied 2.2. DFT Study of Ald 2.2.az D ine FT Is Stud omey ris of mAld azine Isomerism The main characte The ristim cs ao in f th che ar ti atl cte e ri co st m ics poo un f th d e 3:ti yel tle lo co w mcr po ys un tad ls, 3M : yel .p.lo 1w 95– cr 196 yst a °l С, s, M.p. 195–196 °С, the relative stability of four possible geometric isomers of compound 3 in chloroform Azines can exhibit A Z z,iE n-es iso ca mn er eix sm hib d iue t Z,to E- th iso e m pr er ese ism nce d ue of to tw th o C= e pr N ese bon n ce ds. of We two studi C=N ed b onds. We studied soluble in acetone so an lub d chl le io nro af ce orm. tone The andNM chlR oro df ao ta rm. are The prese NM nted R d ia n ta S a ec re tio pr nese 3.1n , ted Fig ure in S S ec 1,tio n 3.1, Figure S1, using the DFT method. The lowest-energy conformations of the isomers were found the relative stabilith ty e ore f flo aur tiv po e st ss ai b b il le ity geo ofm fo etr uri c po iso ssm iber le s geo of m coetr mpo ic iun sod m 3 er is no chl f co or m opo form und us- 3 in chloroform us- and Figure S2. and Figure S2. with B3LYP/G functional implemented in ORCA 5.0 software. The ma-def2-SVP basis ing the DFT methio nd g . th The e D lo FT west me -th ener odgy . The con lo fo west rma- ti ener ons gy of co the n fio so rm ma er tis on were s of th foe u n iso d m wi er th s were found with set [18] was used for final geometry optimizations. This basis set includes diffuse functions B3LYP/G functionB a3 l L im YP/ plG em fu ented nctio in n a l O iR m CA ple m 5.ented 0 softw in a re O.R The CA m 5.0 a -so def2 ftw -a Sre VP . The basim s set a-def2 [18]- SVP basis set [18] 2.2. DFT Study of Ald 2.2az . D ine FT Is Stud omey ris of mAld azine Isomerism pertinent for an adequate treatment of azine lone pair interactions. The optimized structures was used for finalwa geo s m used etry fo or pti fim nailz geo atiom ns. etr Thi y o s pti bam sis set izatio in ncl s. ude This s ba difsi fuse s set fun incl ctio ude ns s pe dirti ffuse - functions perti- Azines can exhibit A Z z,i E n-es iso ca mn er eix sm hi b d iue t Z,to E- th iso e m pr er ese ism nce d ue of to tw th o C= e pr N ese bon nce ds. of We two studi C=N ed b onds. We studied of the geometric isomers are presented in Figure S3. The E,E-isomer was found to be nent for an adequa nent te tre foa r tm an ent ado eq f ua azte ine tre loa n te mpa ent ir o if n t aer zia nce tilo on ns. e pa The ir o in pti ter m ai cz ti ed on st s. ruc The ture opti s mized structures the relative stabilith ty e ore f flo aur tiv po e st ss aib b ille ity geo ofm fo etr uri c po iso ssm iber le s geo of m coetr mpo ic i un sod m 3 er is no chl f co or m opo form und us- 3 in chloroform us- the most thermodynamically stable (here and below, the first symbol in isomer notation of the geometric iso of m th er e s geo are m pr etr ese ic n iso ted m er ins Fi agure re pr ese S3. n T ted he E in ,E Fi -igure somer S 3wa . Ts h e foE un ,Ed -i so tom be ert h wa e s found to be the ing the DFT methio nd g . th The e D lo FT west me -th ener odgy . The con lo fo west rma- ti ener ons gy of co the n fio so rm ma er tis on were s of th foe u n iso d m wi er th s were found with most thermod describes ynam mo ica stl th ly the er stm ab configuration o ld e yn (her am e ia ca nld ly bst elof a ob w, le the th (he er azine fe irst and sy C=N b m el bo ow, l bond in th iso e fm iattached rst er sy no m tab ti oo lto n in d the i e- som indenoquinoxaline er notation de- B3LYP/G functionB a3 l L im YP/ plG em fented unctio in na l O iR m CA ple m 5.0 ented softw in a re O.R The CA m 5.0 a -so def2 ftw -S are VP . The basim s set a-def2 [18]- SVP basis set [18] scribes the configura scri ti b o es n o th f e th co e n az fiigura ne C= tiN onb o ofn th d e att az aic n h e ed C= to N th bo e n in dd aeno ttacq hui ed n o to x a th lie ne inm deno oiety quinoxaline moiety moiety while the second symbol refers to the C=N bond near the p-ethylphenyl fragment). was used for final wa geo s m used etry fo opti r fim nailz geo atiom ns. etr Thi y o s pti bam sis set izatio in ncl s. ude This s d ba ifsi fuse s set fun incl ctio ude ns s pe dirti ffuse - functions perti- while the second wh sym ilb e oth l r e ef seco ers n to d th sy e m C= bo N l rb ef oer nd s to nea th r e th C= e p N -ethy bonld phen neayl r th fra e gm p-ethy ent)l.phen The yl fragment). The The Z,E-, E,Z- and Z,Z-isomers have the calculated Gibbs free energies 3.16, 4.91 and nent for an adequa nent te tre foa r tm an ent ado eq f ua azi te ne tre loa n te mpa ent ir o in f taer zia nce tilo on ns. e The pair o in pti ter m aicz ti ed on st s. ruc The ture opti s mized structures Z,E-, E,Z- and Z,Z Z-,i E so -, m Eer ,Zs - h an av de Z th ,Z e -ic so alm cul era sted ha v G e ibb the s c fre ale cul ener ated gi es Gibb 3.1 s6 f , re 4.e 91 ener and gi es 7.13 3 .16, 4.91 and 7.13 7.13 kJ/mol, respectively, higher than the E,E-isomer. Based on these results, we propose of the geometric iso ofm th er e s geo are m pr etr ese ic n iso ted m i er n s Fi agure re pr ese S3. n T ted he E in ,E Fi -igure somer S 3 wa . Ts h e foE un ,Ed -i so tom be ert h wa e s found to be the kJ/mol, respectivel kJ/ y, m hio gh l, re erspec than ti t v h el e y, E,h Ei-gh iso er m th era . n B a tsed he E o ,E n- th iso ese mer re . sul Based ts, we on pr tho ese po se resul tha ts t , we propose that most thermodynam mo ica stl l th y er stm ab o ld e yn (her am e ia ca nld ly bst ela ob w, le th (he erfe irst ansy d b m el bo ow, l in th iso e fm irst er sy no m tab ti o o ln i n d i e- somer notation de- that the synthesized compound 3 consists of relatively more stable E,E- and Z,E-isomers, as the synthesized co th m e po syun nth desi 3 z ced on si cst om s po of un reld ati 3v el coy nsi mst os reo st f r ael bla e tiE v,el Ey - a m no dre Z ,st E- aib so le m E er ,E s, - a an s d Z,E-isomers, as scribes the configura scri tib oes n o th f e th co e n az fiigura ne C= tiN onb o ofn th d e att az aicn h e ed C= to N th bo e n in dd aeno ttacq h ui ed n o to x a th lie ne inm deno oiety quinoxaline moiety the other two isomers with Z-orientation of the p-ethylphenyl substituent are characterized the other two isom th er e s owi ther th tw Z-o o ri iso enta mer tio s n wi oth f th Z e -o pri -ethy entalti phen on oyl f th subs e p-ti ethy tuent lphen are yl ch subs aracte tituent r- are character- while the second wh sym ilb e oth l r e ef seco ers n to d th sy e m C= bo N l rb ef oer nd s n to ea th r e th C= e p N -ethy bonld phen neayl r th fra e gm p-ethy ent)l.phen The yl fragment). The by higher Gibbs free energies. It should be noted that only the E,E-isomer has the optimized ized by higher Giibb zed s fb re y e h ener igher gi es. Gi bb It s sh fre oul e d ener be gi nes. ote d It th sh ao t ul on dl y be th n e ote E,d E -th iso am t o er n lh y ath s t e hE e ,E-isomer has the Z,E-, E,Z- and Z,Z Z-,i E so -, m Eer ,Zs - h an av de Z th ,Z e -ic so alm cul era sted ha v G e ibb the s f cre ale cul ener ated gi es Gibb 3.1 s6 f , re 4.e 91 ener and gi es 7.13 3 .16, 4.91 and 7.13 structure with a fully coplanar arrangement of molecular moieties. optimized structure opti wi m th iz ed a f ul stlruc y cture opla n wi ar th a rr a a ful nge ly c mo ent pla o n fa m r a orr lec an ul ge ar m m ent oieti ofes. m olecular moieties. kJ/mol, respectivel kJ/ y, m hio gh l, er re spec than ti t v h el e y, E,h Ei-gh iso er m th er.a n B a tsed he E o ,E n- th iso ese mer re . sul Based ts, we on pr tho ese po se resul tha ts t , we propose that To evaluate the energy barriers for Z,E isomerization of both azine C=N bonds, we To evaluate the ener To g ev y a ba lua rri te erth s e foener r Z,E g y iso ba m rri erer izs ati fo or nZ of ,E b io so th m a er zi in za e ti C= onN ofb o bn oth ds, awe zine C=N bonds, we the synthesized co th m e po syun nth desi 3 z co ed n si cst om s po of un reld ati 3 v el coy nsi mst os reo st f a rel bla e tiE v,el Ey - a m nd ore Z ,st E- aib so le m E er ,E s, - a an s d Z,E-isomers, as applied the climbing image nudged elastic band (CI-NEB) methodology, which is efficient applied the climbia nppl g im ied age thn e udge climb di n elg ast im ic ab ge an nd udge (CI-d NE elB ast ) m ic etho band d o (CI logy -NE , wh B) im ch etho is ef dfo ic lo ient gy , which is efficient the other two isom th er e s owi ther th tw Z-o o ri iso enta mer tio s n wi oth f th Z e -o pri -ethy entalti phen on oyl f th subs e p- ti ethy tuent lphen are yl ch subs aracte tituent r- are character- at finding minimum energy paths and saddle points [19]. The climbing images (CIs) at finding minimu at m f i ener ndin gg y m pa in th im s a un m d ener sadd gly e pa poi th ns tsa [n 1d 9 ]s . a The ddle cli poi mb nits ng [1 im 9]a . ges The (cli CIs m )b o in b- g images (CIs) ob- ized by higher Giibb zed s fb re y e h ener igher gi es. Gi bb It s sh fre oul e d ener be gi no es. te d It th sh ao t ul on dl y be th n e ote E,d E -th iso am t o er n lh y ath s t e hE e ,E-isomer has the obtained for E,E Z,E and E,E E,Z isomerization of compound 3 can be considered tained for E,E ta Z in ,E ed a n fo dr E E,,E E E Z,,Z E ia so nd m E er ,E iz ation E o,f Z c io so mm po er un iza dti 3 o n ca o nf b ce om copo nsi un der d ed 3 ca n be considered optimized structure opti wi m th iz a ed ful stlruc y co ture pla n wi ar th a rr a a fn ul ge ly c mo ent pla o n fa m r a orr lec an ul ge ar m m ent oieti ofes. m olecular moieties. good approximatigo ono s d of a th ppr e co oxrr im espo ation nd s iof ng th tra e co nsi rr tiespo on stn ad tes. ing The tran CI siti s o an nd st o ath tes. er The inter CI ms ed an i-d other intermedi- good approximations of the corresponding transition states. The CIs and other intermediate To evaluate the ener To g ev y a ba lua rri te erth s e foener r Z,E g y iso ba m rer rier izs ati fo or n Z of ,E b io so th m a er ziin za e ti C= onN of b o bn od th s, awe zine C=N bonds, we ate images on the a m te in ii m m au ge ms o ener n th gy e m pa in th im s a u re m s ener hown gy i n p a Fi th gure s are S s 4h , o wh wn er ie n th Fie gure inter Spo 4, wh lated er e the interpolated images on the minimum energy paths are shown in Figure S4, where the interpolated applied the climbia nppl g im ied age thn e udge climb di n elg ast im ic ab ge an nd udge (CI-d NE elB ast ) m ic etho band d o (CI logy -NE , wh B) im ch etho is ef d fo ic lo ient gy , which is efficient energy diagrams ener are pr gyese din ated gra.m B s ased are pr onese thn e ted cal.cul Baa sed ted o DF n th T e ener calcul gies ato ed f CIs, DFT w ener e ha gi ves e of CIs, we have energy diagrams are presented. Based on the calculated DFT energies of CIs, we have at finding minimu at m f i ener ndin gg y m pa in th im s a un m d ener sadd gly e pa poi th ns tsa [n 1d 9 ]s . a The ddle cli poi mb nits ng [1 im 9]a . ges The (cli CIs m ) b o ib n- g images (CIs) ob- estimated the barresti iers m as ated 89 a tn hd e 8 ba 4 rr kJ/ ier m s oa ls fo 8r 9 E a,n E d 84 kJ/ Zm ,Eo a ln fo dr E E ,E ,E E Z ,Z ,E i so anm d er E,iE z ation ,E ,Z isomerization, estimated the barriersta as ined 89 fand or E,84 E kJ/mol ta Z in ,E ed afor n fo dr EE E,,,EE E Z E Z ,,E Z ,E iand a so nm d er EE,,i EE z ation E E o,,fZ Z c iisomerization, o so mm po er un izd ati 3 o ca n o nf b ce om copo nsi un der d ed 3 ca n be considered respectively. The o re bspec tained tiv re elsul y. The ts sug obgest tained tha re t th sul e ts in sug terco gest nver thsi at oth n ie ni n bter oth co pa ni v rs ero si fo is no im n er bo s th pairs of isomers respectively. The obtained goodr a esults pproxisuggest matigo ono s d that of a th ppr e the co oxrr iinter m espo atio conversion n nd s iof ng th tra e co nsi rr in tiespo oboth n stn ad tes. pairs ing The tra of n CI si isomers ti s o an nd st o ath tes. er The inter CI ms ed an i-d other intermedi- occurs via in-plane o cc inurs versi vio an i n o- fpl th a e nn ei itro nvgen ersio an to o m f th like e nin itro oth gen er a si to m m ila lr ike coin m po oth un erd si s m [1i7 la ,2 r 0co ], mpounds [17,20], ate images on the a m te in ii m m au ge ms o ener n th gy e m pa it nh im s a u re m s ener hown gy i n p a Fi th gure s are S s 4h , o wh wn er ie n th Fie gure inter Spo 4, l wh ated er e the interpolated occurs via in-plane inversion of the nitrogen atom like in other similar compounds [17,20], i.e., without rotatiio .e. n , a wi rou thnd out C= roN tati do on ub alr e ou bo nd nd C= s. Thus N do,ub thle e va boln ues ds. o Thus f N-N= , thC e v va al lence ues o a f n N - -N=C valence an- energy diagrams ener are pr gyese din ated gra.m B s ased are pr onese thn e ted cal.cul Baa sed ted o DF n th T e ener calgi cul es ato ed f CIs, DFT w ener e ha gi ves e of CIs, we have i.e., without rotation around C=N double bonds. Thus, the values of N-N=C valence angles gles in CIs are close gles to i1 n6 CIs a 0° (Fire gure clo se S4)t.o 160° (Figure S4). estimated the barresti iers m as ated 89 a tn hd e 8 ba 4 rr kJ/ ier m s oa l s fo 8r 9 E a,n E d 84 kJ/ Zm ,Eo a ln fo dr E E ,E ,E E Z ,Z ,E i so anm d er E,iE z ation ,E ,Z isomerization, in CIs are close to 160 (Figure S4). The calculated isoThe merica za lti cul on a ted barr ii so erm s er are iz h ati ig o h n eno barr ug ier hs to are ex h pl ig ah in eno the ug dih st to in ct exsi pl gn ain a ls th e distinct signals respectively. The o re bta spec ined tiv re elsul y. The ts sug obgest tained tha re t th sul e ts in sug terco gest nver thsi at oth n ie ni n bo ter thco pa ni v rs ero si fo is no im n er bo s th pairs of isomers The calculated isomerization barriers are high enough to explain the distinct signals of isomers in the NM of iso R spec mers tra in o th f e co NM mpo Run spec d 3 tra . H o ofweve compo r, th un ey d a 3re . H cl oo weve se inr, m th agn ey ia tude re cl,o fse or in magnitude, for occurs via in-plane o cc inurs versi vi o an i n o- fpl tha e nn ei i tro nvgen ersio an to o m f th like e nin itro oth gen er a sito mm ila lr ike com in po oth un erd si s m [1i7 la ,2 r 0co ], mpounds [17,20], of isomers in the NMR spectra of compound 3. However, they are close in magnitude, for i.e., without rotatiio .e. n , awi rou th nd out C= ro N tati do on ub alr e ou bo nd nd C= s. Thus N do,ub thle e va boln ues ds. o Thus f N-N= , th C e v va allence ues o a f n N - -N=C valence an- example, to the rotational barrier about the C–N bond in acetamide [21]. These data agree gles in CIs are close gles to i1 n6 CIs a 0° (Fire gure clo se S4)t.o 160° (Figure S4). with the observed difficulties in the isolation of individual isomers of the title compound. The calculated isoThe merica zalti cul on a ted barr ii so erm s a er re iz h ati ig o h n eno barr ug ier hs to are ex h pl ig ah in eno the ug dih st to in ct exsi pl gn ain als th e distinct signals of isomers in the NM of iso R spec mers tra in o th f e co NM mpo Run spec d 3 tra . H o ofweve compo r, th un ey d a 3re . H cl oo weve se inr, m th agn ey ia tude re cl, o fse or in magnitude, for 2.3. In Silico ADME Predictions We evaluated the ADME characteristics of the most potent JNK and cell-based sys- tems of compound 3 using the SwissADME online tool [22]. We obtained bioavailability radar plots that display an assessment of the drug-likeness of azine 3. Six important physicochemical properties, including lipophilicity, size, polarity, solubility, flexibility, and insaturation, were considered. It was found that the investigated heterocyclic azine in general has satisfactory ADME properties as can be seen from a radar representation of bioavailability shown in Figure S5. The only unfavorable property is a high insaturation score of compound 3, which is true of most 11H-indeno[1,2-b]quinoxalin-11-one deriva- tives. Noticeably, the known JNK inhibitor SP600125 of the anthrapyrazolone series [23] also has enhanced insaturation. Compared to SP600125, compound 3 has a higher pre- Molbank 2021, 2021, M1299 4 of 7 dicted lipophilicity, which usually correlates with decreased water solubility, increased metabolism, and slower excretion. Additionally, higher lipophilicity makes it more likely to penetrate the skin. According to the calculated ADME parameters (Table 1) and bioavail- ability radars for compound 3 and SP600125 (Figure S5), the synthesized azine 3 is expected to be bioavailable. Table 1. Physicochemical ADME properties of compound 3. Property Compound 3 Formula C H N 24 18 4 Molecular Weight (g/mol) 362.43 Heavy Atoms 28 0.08 Fraction Csp Rotatable Bonds 3 H-bond Acceptors 4 H-bond Donors 0 Molar Refractivity 114.42 Topological Polar Surface Area (tPSA), Å 50.50 Lipophilicity (Consensus Log P ) 4.84 o/w BBB Permeation Yes 3. Materials and Methods 3.1. General Information and Compound 3 Synthesis LC/MS analysis was performed on an Agilent Infinity chromatograph (Santa Clara, CA, USA) with an AccurateMass QTOF 6530 mass detector (Santa Clara, CA, USA). Chro- matographic conditions: column Zorbax EclipsePlusC18 1.8 m, 2.1  50 mm; eluent H O: ACN (85%); flow 0.2 mL/min. Ionization source: ESI in positive mode. The H and C NMR spectra were recorded on a Bruker AVANCE III HD instrument (Billerica, 1 13 MA, USA) (operating frequency H—400 MHz; C—100 MHz). The melting point of the obtained compound was measured using a Melting Point Apparatus SMP30 (Cole-Parmer Instrument Company, Vernon Hills, IL, USA), heating rate 3.0 C/min. IR spectra were recorded on an FT-IR spectrometer Nicolet 5700 (Thermo Fisher Scientific Inc., Waltham, MA, USA) with KBr pellets. The reaction was monitored by thin layer chromatography (TLC) on Silufol UV-254 and Merck plates, silica gel 60, F254. Known compounds 11H-indeno[1,2-b]quinoxaline-11-one (1) and its hydrazone (2) were prepared according to methods described in the literature [15,16]. 11H-indeno[1,2-b]quinoxalin-11-one 2-(4-ethylbenzylidene)hydrazone (3). p-Ethylbenzaldehyde (0.3 mmol, 0.04 mL) was added to a solution of compound 2 (0.3 mmol, 0.074 g) in 25 mL EtOH under permanent stirring. Then, the reaction mixture was refluxed under stirring for 2 h. The reaction was monitored by TLC (eluent: chloroform). After cooling, the precipitate was filtered out and washed with EtOH. The title compound 3 was obtained as yellow crystals (yield 89%); M.p. 195–196 C (from ethanol). H NMR (400 MHz, CDCl ), , ppm: 1.23–1.34 (m, 3H, CH CH ), 2.69–2.80 (m, 2H, 3 2 3 CH CH ), 7.49–7.68 (m, 2H, H-2, H-3), 7.73–7.86 (m, 2H, H-7, H-8), 8.09 (d, 1H, J 4 Hz, 2 3 H-9), 8.18 (d, 1H, J 6 Hz, H-6), 8.25–8.34 (m, C H ), 8.32 (d, 1H, J 4 Hz, H-4), 8.74 (d, 1H, 6 4 J 4 Hz, H-1), 8.85 (s, 0.15 H, H-12), 8.91 (s, 0.85 H, H-12) (atom numbering is shown in Scheme 3). C NMR (100 MHz, CDCl ), , ppm: 15.34, 15.50, 29.16, 29.29, 122.59, 126.93, 128.14, 128.67, 128.79, 129.30, 129.49, 129.74, 129.77, 130.11, 130.46, 130.85, 130.93, 131.70, 132.18, 132.80, 134.47, 134.65, 138.32, 142.50, 142.70, 149.20, 150.83, 151.85, 151.96, 154.41, 155.77. IR (KBr), cm : n(C=N) 1546, 1587. LC/MS (ESI+); m/z: 363.1605 experimental + + ([C H N + H] = 363.1604 theor.); m/z: 385.1425 exp. ([C H N + Na] = 385.1424 theor.); 24 18 4 24 18 4 exit time 140–170 s. The ratio of isotopic peaks corresponds to the theoretical m/z: 363.16 (100%), 364.16 (27%), 365.16 (4%). Molbank 2021, 2021, x FOR PEER REVIEW 5 of 5 stirring for 2 h. The reaction was monitored by TLC (eluent: chloroform). After cooling, the precipitate was filtered out and washed with EtOH. The title compound 3 was ob- tained as yellow crystals (yield 89%); M.p. 195–196 °C (from ethanol). H NMR (400 MHz, CDCl3), δ, ppm: 1.23–1.34 (m, 3H, CH2CH3), 2.69–2.80 (m, 2H, CH2CH3), 7.49–7.68 (m, 2H, H-2, H-3), 7.73–7.86 (m, 2H, H-7, H-8), 8.09 (d, 1H, J  4 Hz, H- 9), 8.18 (d, 1H, J  6 Hz, H-6), 8.25–8.34 (m, C6H4), 8.32 (d, 1H, J  4 Hz, H-4), 8.74 (d, 1H, J   4 Hz, H-1), 8.85 (s, 0.15 H, H-12), 8.91 (s, 0.85 H, H-12) (atom numbering is shown in Scheme 3). C NMR (100 MHz, CDCl3), δ, ppm: 15.34, 15.50, 29.16, 29.29, 122.59, 126.93, 128.14, 128.67, 128.79, 129.30, 129.49, 129.74, 129.77, 130.11, 130.46, 130.85, 130.93, 131.70, 132.18, 132.80, 134.47, 134.65, 138.32, 142.50, 142.70, 149.20, 150.83, 151.85, 151.96, 154.41, −1 155.77. IR (KBr), cm : ν(C=N) 1546, 1587. LC/MS (ESI+); m/z: 363.1605 experimental + + ([C24H18N4 + H] = 363.1604 theor.); m/z: 385.1425 exp. ([C24H18N4 + Na] = 385.1424 theor.); Molbank 2021, 2021, M1299 5 of 7 exit time 140–170 s. The ratio of isotopic peaks corresponds to the theoretical m/z: 363.16 (100%), 364.16 (27%), 365.16 (4%). Scheme Scheme 3 3.. Atom numberi Atom numbering ng for N for NMR MR as assignments signments i in n mol molecule ecule 3 3. . Molbank 2021, 2021, xM FO olb Ra n Pk EE 20 R 2 1 R, EV 202 IEW 1, x FOR PEER REVIEW 5 of 5 5 of 5 1 13 1 13 The H NMR and C NMR spectrum are shown in Figures S1 and S2. The H NMR and C NMR spectrum are shown in Figures S1 and S2. 3.2. DFT Calculations 3.2. DFT Calculations The ORCA 5.0 computational chemistry software [24] was used for DFT calculations The ORCA 5.0 computational chemistry software [24] was used for DFT calculations of E,E-, E,Z-, Z,E- and Z,Z-isomers of compound 3. Before the calculations, conforma- of E,E-, E,Z-, Z,E- and Z,Z-isomers of compound 3. Before the calculations, conformation tion searches were performed for geometric isomers using the VConf 2.0 program of searches were performed for geometric isomers using the VConf 2.0 program of the Ver- the VeraChem suite software (VeraChem LLC, Germantown, MD, USA). For the best ten aChem suite software (VeraChem LLC, Germantown, MD, USA). For the best ten confor- conformations found for each isomer, singlet state geometry optimizations were carried mations found for each isomer, singlet state geometry optimizations were carried out with out with ORCA 5.0 employing the BLYP functional and def2-SVP basis set. Afterwards, ORCA 5.0 employing the BLYP functional and def2-SVP basis set. Afterwards, the lowest- Scheme 2. SynthesSche is of t m ite le 2 c . omp Synto hund esis 3 o.f title compound 3. the lowest-energy conformation of each isomer was re-optimized with the use of the energy conformation of each isomer was re-optimized with the use of the B3LYP/G func- B3LYP/G functional, ma-def2-SVP basis set, and D3BJ dispersion correction. Solvation According to the A NM ccoR rd d in at g a to (CDCl the NM 3), th Re dre atcr a ys (CDCl talliz 3ed ), th ce om repo crys un ta dl l3 iz w ed as co ob m ta po inun edd a s 3 was obtained as tional, ma-def2-SVP basis set, and D3BJ dispersion correction. Solvation effects were taken effects were taken into account using the CPCM model with chloroform as a solvent. Fre- 1 1 a Z,E-isomer mix ature Z,E. -The isom er H m NM ixture R spec . The tru m H (NM Figure R spec S1) tru con m ta (iFi ns gure two S d 1i)st co inn ct talio n w s -tw fieo ld d istinct low-field into account using the CPCM model with chloroform as a solvent. Frequency calculations quency calculations were performed for the optimized geometries in order to establish the signals of the imsi ingn e pr als oto ofn th N= e iCH mina e t pr 8.9 o1 to a n n N= d 8CH .85 ppm at 8.9wi 1 a th n d re 8 l.a 8ti 5v ppm e integr with al i re ntens lativie ties in tegral intensities were performed for the optimized geometries in order to establish the nature of the sta- nature of the stationary points. For CI-NEB calculations of the isomerization paths and 0.35/0.65, as well0 a .3 s 5typi /0.65 ca , l as siwell gnal s as oftypi the ca ethy l sign l gro als up of a th t e 1.ethy 30 (tw l gro o oup vera la t i1 d. 3tr 0i p (tw lets o o fro ver ml aid triplets from tionary points. For CI-NEB calculations of the isomerization paths and barriers, the DFT barriers, the DFT approximation indicated different iso above mersd )with ia fn fer d ent 2 B3L .75 iso ppm YP/G mers (m ) functional a ul nti dpl 2.et 75 ). ppm Sign was a (l m s applied ul ofti th pl e et in ).d S eno ignq aui ls n oo f xa the lin in e d h eno etero qui cycl noxa e line heterocycle approximation indicated above with B3LYP/G functional was applied using 10 interme- were observed bet were wee o nb 7 ser .5 v an ed d b 8et .5 wee ppm. n 7 S.ep 5 aa n ra dti 8o .5 n ppm. of the Siep soa m ra er tis owa n os f th im e po iso ss m iber le s pr wa ob s -impossible prob- using 10 intermediate images for each isomerization. Analysis and visualization of the diate images for each isomerization. Analysis and visualization of the DFT results were ably due to a rela ab tilv y eld y ue low to ener a relgy ati v ba elrr y iler ow foener r the gy is o ba m rr er ier iz afti oo r n th of e ith soe mca errb izo ati n– on ni tro of gen the carbon–nitrogen DFT results were made with Chemcraft 1.8 program. The ORCA 5.0 output files for the made with Chemcraft 1.8 program. The ORCA 5.0 output files for the lowest-energy con- double bond (seed , o e. ub g.,l e [1b 7o ] n ad n d (see our , e. DF g.,T [1 re 7s ] ul an ts d d oescr ur DF ibed T re bs el ul ots w )d . escribed below). lowest-energy conformations, CIs, and minimum energy path trajectories are available in formations, CIs, and minimum energy path trajectories are available in the Supplemen- The main characte The rist m ics ain o fch th ae ra ti cte tle ric st oim cs po of un th d e 3 ti : tl yel e c lo om w po crys untd al s, 3: M yel .p. lo w 195 cr –ys 196 ta l° s, С,M .p. 195–196 °С, the Supplementary Materials. soluble in acetonso e a ln ub dl chl e in o ro ace fo to rm. ne a The nd chl NM oR ro d fo arm. ta a re The prNM esen R ted da ita n a Sre ec tio prn ese 3.n 1ted , Fig in ure Sec S1 tio , n 3.1, Figure S1, tary Materials. and Figure S2. and Figure S2. 3.3. ADME Predictions 3.3. ADME Predictions The physicochemical properties of selected compounds were computed using Swis- 2.2. DFT Study of 2 Ald .2. az DFT ine Stud Isomy e rof ism Ald azine Isomerism The physicochemical properties of selected compounds were computed using sADME (http://www.swissadme.ch) (accessed on 20 September 2021). Azines can exhibA it z Z i,n E es -iso cam n er exih sm ib id t ue Z,E to -i so thm e pr eri ese smn d ce ue of to tw th oe C= prN ese bn oce nd o s. f We twos C= tudi N ed bo nds. We studied SwissADME (http://www.swissadme.ch) (accessed on 20 September 2021). the relative stabilth ity e re ofl f ao tiur ve po sta ss biib lilty e geo of fm our etr po ic i ss so ib m le er geo s of m cetr om ic po iso un m der 3s in o fchl coo m ro po foun rm dus- 3 in chloroform us- 4. Conclusions ing the DFT meth in o g dth . The e DFT lowest meth -ener od. gy The coln of west orm- aener tiongy s o fco th ne fo irm som ati er os ns were of th fe o u iso nd m wi ers thwere found with 4. Conclusions In this work, we presented the synthesis of the previously unknown compound 3 B3LYP/G functioB n3 aL l Y im P/ pl G e m fuented nction ia nl O im Rpl CA em 5ented .0 sof tw in a O re R . CA The 5m .0 a so -def2 ftwa -S re VP . The basi m sa set -def2 [18 -S ] VP basis set [18] (11H-indeno[1,2-b]quinoxalin-11-one 2-(4-ethylbenzylidene)hydrazone). The compound In this work, we presented the wa syn s used the fo si r sf of ina wa lthe geo s p used mretr ev f y ious oo r pti fin ly m al i unkno geo zatim on etr s. w Thi y n com opti s ba m si ip z s set oun ation d in s. cl 3 Thi ude s s ba dsi iff s set use fiun nclctio ude n s s d pe iffrti use - functions perti- nent for an adequa nent te tre for aa tm n ent adeq of ua az te in tre e la otn m e ent paio r fi n atzer ina e cti lo o n n e s. pa The ir in ot pti era m citi zo ed ns. stThe ructure opti s mized structures structure was confirmed by NMR, IR, and LC/MS methods. According to the DFT results, (11H-indeno[1,2-b]quinoxalin-11-one 2-(4-ethylbenzylidene)hydrazone). The compound of the geometric o iso f th me er geo s ar m e etr prese ic iso nted mer in s a Fi re gure prese S3n . ted The in E ,Fi E- gure isom S er 3 .wa Ths e fE o,un E-d iso to m b er e wa the s found to be the compound 3 has a thermodynamically favorable E,E-configuration. The calculated isomer- structure was confirmed by NMR, IR, and LC/MS methods. According to the DFT results, most thermodynm am oi st ca th lly erst m ao bd le yn (h aer me ica an lld y st bel ab olw, e (h th er e e fia rst ndsy bel mo bw, ol ith n e iso first mer sy nm ota bo tilo in n d iso e-mer notation de- ization paths suggest that the E,Z-isomerization occurs via in-plane inversion of the azine scribes the configura scrib ties onth oe f th coe na fiz gura ine C= tioN n o bfo th nd e a att zia n ce hC= ed N to b th oe nd in a d tt eno ach qed ui n to o x th al e in in e d m eno oiety quinoxaline moiety nitrogen atoms. An in silico estimation of ADME characteristics indicates that compound 3 while the secondwh syim le bth ole ref seco ers nto d sy thm e b C= olN ref ber on s dto n ea thr e th C= e N p-b ethy ond l phen nearyl th f e ra pgm -ethy enltphen ). The yl fragment). The can cross the blood–brain barrier and thus has perspectives to be used for the treatment Z,E-, E,Z- and ZZ ,Z ,E -i-so , E m ,Z er - sa h na dv e Z,th Z-e iso ca m lcul ersa ted hav e Gth ibb e sc a fre lcul e ener atedgi G es ibb 3s .1 f 6re , 4 e .9 ener 1 an gi des 7.1 33 .1 6, 4.91 and 7.13 of neuroinflammation and ischemia–reperfusion injury like other indenoquinoxaline ana- kJ/mol, respectivkJ/ ely, mh oilgh , re er spec thati nv tel hy, e E h ,E igh -iso erm th er a.n B ta hsed e E ,o En -i so thm ese er re . B sul ased ts, o we n th pr ese opo re se sul th ts a,t we propose that logues [12]. Despite using classic methods to obtain azine derivatives, we have discovered a the synthesized c th oe msy pon un thd esi 3z ed con c si ost ms po ofun rel da 3 ti v co eln y sim sto s re of st rel ab alti e vE el ,E y - m an od re Z st ,E a- b ilso e m E,er E-s, an as d Z,E-isomers, as new class of azines based on the heterocyclic system of 11H-indeno[1,2-b]quinoxalin-11-one, the other two isoth me er o s th wi erth tw Zo - o iri so enta merti s owi n th of th Z-e ori p- enta ethy ti lo phen n ofyl th subs e p-ethy tituent lphen are yl c h subs aracte tituent r- are character- which is of great interest for further study of possible biologically active compounds. ized by higher G ii zbb eds b fre y e hiener ghergi G es. ibb It s sh fre o e ul ener d be gin es. ote It d sh tho aul t o dn b ly e th no e te E d ,E th -iso at m on er ly hth as e th Ee ,E -isomer has the optimized structure opti wi mith zed a fst ul ruc ly c ture opl a wi na th r a a rr fa ul nlge y c m oent pla n oa fr m arr ola ec nul gea m r ent mo io eti f m es. o lecular moieties. Supplementary Materials: The following are available online. Figure S1: The H NMR spectrum of To evaluate the ener To ev gy alba uarte rier ths e fener or Zg ,E y iba sor m rier eris za fo tir on Z ,of E ib so oth mer az iz in ati e o C= n N of b bo on th d s, azwe ine C=N bonds, we recrystallized compound 3; Figure S2: The C NMR spectrum of compound 3; Figure S3: The struc- applied the climba ippl ng iim ed a ge the nc udge limbd in e g la im sta ic ge ba n n udge d (CId -NE elaB st)i c mb etho andd (CI olo -NE gy, B wh ) m ich etho is d efo flo icigy ent , wh ich is efficient tures of E,E-, Z,E-, E,Z-, and Z,Z-isomers of compound 3 optimized by the DFT method; Figure S4: at finding minimat um fi n ener ding gy mpa int im hs ua m n d ener sadg d y le pa poi thn s ts an [d 19 s]a . d The dle cli poi m n b ts in [g 19 im ]. a The ges cli (CIs mb ) io nb g -images (CIs) ob- The energy diagrams and the climbing image conformations for E,E Z,E and E,E E,Z iso- tained for E,E ta in Zed ,E a fo nr dE E ,E ,E Z E,,E Z a in so dm Eer ,Ei zatio n E ,o Zf icso om mpo eriun zad ti o 3n ca of n cb oe m co po nun sid d er 3ed ca n be considered merization of compound 3; Figure S5: goBioavailability od approximati go radar on od s of appr plots the oco xiof m rra espo compound tionn s d of in th g tra e 3co n and rr siespo tio SP600125. n st nd ates. ing tra The nsi CI tis oa nn st da o tes. ther The inter CIm s a ed nd i- other intermedi- Files: ORCA 5.0 output files for fourageometric te images o isomers n the ate miof in m im a the ge um s o title ener n th compound, gy e m p ia ntih m s a um re XYZ ener shown files gy p in a for tFi hs a gure CIre s Sh 4o , wn wh er ine Fi th gure e inter S4po , wh lated ere the interpolated energy diagrams ener are gy pr ese dian gra ted m . s Ba ased re pr oese n th nted e ca . lB cul ased ated o n DF th T e ener calcul gies ated of DF CIs, T ener we h gi av es e of CIs, we have conformations and isomerization trajectories. estimated the barr esti ierm s a as ted 89 ta h n e dba 84 rr kJ/ ierm s a os l 8 fo 9r aE n,d E 84 kJ/ Z m ,E ol a fn od r E E,,E E Z E,,E Z a iso nd m Eer ,Ei zatio n E,, Z isomerization, respectively. The re ob spec tainti ed vel re y. sul The ts sug obta gest ined th re at sul the tsi n sug tergest conv ter hasi t o th ne ii n n b ter oth co pa nvier rs si oo f n is io nm ber oth s pairs of isomers occurs via in-plan oe cc in urs ver vsi ia o in n o -pl f th an e en iin tro ver gen sion ato of m th le ike niin tro o gen ther a to sim mi lla ike r co in m opo thun er si ds m[i1 la 7r ,2co 0]m , pounds [17,20], i.e., without rotai ti .e. on , wi arou tho nd ut C= rota N tid oo nub arlou e b nd on d C= s. N Thus doub , th le e bva on ld ues s. Thus of N,- N= the C va va lues lence of aN n- -N=C valence an- gles in CIs are clo gl se es to in 1 CIs a 60° (Fi regure close S4 to ). 160° (Figure S4). The calculated iso The mer ca izla cul tio an ted ba rr iso ier ms er aire za h tiio gn h b eno arrug ierh s a to re ex hipl gh a ieno n thug e d hi st to i n ex ct pl sia gn ina th ls e distinct signals of isomers in the o NM f iso Rm spec ers tra in th of e c NM ompo R spec undtra 3. H of o c weve ompo r,un they d 3a . re H o cl weve ose ir, n m tha ey gn aire tude clo , se for in magnitude, for Molbank 2021, 2021, M1299 6 of 7 Author Contributions: Conceptualization was conducted by A.R.K. and A.I.K.; methodology and experimental work were conducted by A.R.K. and E.I.S.; data analysis, writing and editing of the paper were conducted by A.R.K. and A.I.K.; project administration and supervision was conducted by A.I.K. All authors have read and agreed to the published version of the manuscript. Funding: This research was supported by the Ministry of Science and Higher Education of the Russian Federation (project no. Nauka FSWW-2020-0011) and by the Tomsk Polytechnic University development program. The synthesis and DFT study of compound 3 were funded by the Russian Science Foundation (grant No. 17-15-01111). Institutional Review Board Statement: Not applicable. Informed Consent Statement: Not applicable. Data Availability Statement: The data presented in this study are available in this article. Acknowledgments: The authors wish to thank Alexander A. Bondarev for the MS analysis of compound 3. Conflicts of Interest: The authors declare no conflict of interest. References 1. Outirite, M.; Lebrini, M.; Lagrenée, M.; Bentiss, F. New one step synthesis of 3,5-disubstituted pyrazoles under microwave irradiation and classical heating. J. Heterocycl. Chem. 2008, 4, 503–505. [CrossRef] 2. Regitz, M.; Weise, G.; Lenz, B.; Förster, U.; Urgast, K.; Maas, G. Diazo Compounds. Part 67. Electrophilic Diazoalkane Substitution with Donor-substituted Cations. Bull. Soc. Chim. Belg. 1985, 94, 499–520. [CrossRef] 3. Zhao, M.-N.; Liang, H.; Ren, Z.-H.; Guan, Z.-H. Copper-Catalyzed N–N Bond Formation by Homocoupling of Ketoximes via N–O Bond Cleavage: Facile, Mild, and Efficient Synthesis of Azines. Synthesis 2012, 1501–1506. [CrossRef] 4. Nanjundaswamy, H.; Pasha, M. Rapid, Chemoselective and Facile Synthesis of Azines by Hydrazine/I . Synth. Commun. 2007, 37, 3417–3420. [CrossRef] 5. Diamant, S.; Agranat, I.; Goldblum, A.; Cohen, S.; Atlas, D. -adrenergic activity and conformation of the antihypertensive specific 2-agonist drug, guanabenz. Biochem. Pharmacol. 1985, 34, 491–498. [CrossRef] 6. Ramakrishnan, A.; Chourasiya, S.S.; Bharatam, P.V. Azine or hydrazone? The dilemma in amidinohydrazones. RSC Adv. 2015, 5, 55938–55947. [CrossRef] 7. Chourasiya, S.S.; Kathuria, D.; Nikam, S.S.; Ramakrishnan, A.; Khullar, S.; Mandal, S.K.; Chakraborti, A.K.; Bharatam, P.V. Azine-Hydrazone Tautomerism of Guanylhydrazones: Evidence for the Preference Toward the Azine Tautomer. J. Org. Chem. 2016, 81, 7574–7583. [CrossRef] 8. Sundberg, R.J.; Dahlhausen, D.J.; Manikumar, G.; Mavunkel, B.; Biswas, A.; Srinivasan, V.; Musallam, H.; Reid, W.A., Jr.; Ager, A.L. Cationic antiprotozoal drugs. Trypanocidal activity of 2-(4 -formylphenyl)imidazo[1,2-a]pyridinium guanylhydrazones and related derivatives of quaternary heteroaromatic compounds. J. Med. Chem. 1990, 33, 298–307. [CrossRef] 9. Davydov, V.; Sokol, V.; Polyanskaya, N.; Linko, R.; Ryabov, M.; Sergienko, V. Synthesis, crystal structure, and spectral studies of 10-(2-Benzothiazolylazo)-9-phenanthrol. Crystallogr. Rep. 2012, 57, 227–234. [CrossRef] 10. Giorgi, G.; Ponticelli, F.; Savini, L.; Chiasserini, L.; Pellerano, C. On the isomerism/tautomerism of hydrazones. Crystal structures, study in solution and theoretical calculations of new series of -N-heterocyclic hydrazones. J. Chem. Soc. Perkin Trans. 2 2000, 11, 2259–2264. [CrossRef] 11. Ganga, M.; Sankaran, K.R. Synthesis, spectral characterization, DFT, molecular docking and biological evaluation of some newly synthesized asymmetrical azines of 3,5-dimethoxy-4–hydroxy benzaldehyde. Chem. Data Collect. 2020, 28, 100475–100489. [CrossRef] 12. Schepetkin, I.A.; Khlebnikov, A.I.; Potapov, A.S.; Kovrizhina, A.R.; Matveevskaya, V.V.; Belyanin, M.L.; Quinn, M.T. Synthesis, biological evaluation, and molecular modeling of 11H-indeno[1,2-b]quinoxalin-11-one derivatives and tryptanthrin-6-oxime as c-Jun N-terminal kinase inhibitors. Eur. J. Med. Chem. 2019, 161, 179–191. [CrossRef] [PubMed] 13. Kotharkar, S.A.; Shinde, D.B. Synthesis of antimicrobial 2,9,10-trisubstituted-6-oxo-7,12-dihydrochromeno[3,4-b]quinoxalines. Bioinorg. Med. Chem. Let. 2006, 16, 6181–6184. [CrossRef] 14. Tseng, C.-H.; Chen, Y.-R.; Tzeng, C.-C.; Liu, W.; Chou, C.-K.; Chiu, C.-C.; Chen, Y.-L. Discovery of indeno[1,2-b]quinoxaline derivatives as potential anticancer agents. Eur. J. Med. Chem. 2016, 108, 258–273. [CrossRef] 15. Pearson, B.D. Indenoquinolines. III. Derivatives of 11H-Indeno-[1,2-b]quinoxaline and related indenoquinolines. J. Org. Chem. 1962, 27, 1674–1678. [CrossRef] 16. Balamurugan, G.; Velmathi, S. Quinoxaline based redox relay receptor for iodide ions and its application towards real sample analysis and logic gate function. Sens. Actuators B 2018, 256, 126–134. 17. Warren, C.H.; Wettermark, G.; Weiss, K. Cis-trans isomerization about the carbon-nitrogen double bond. Structures of the isomers of N-benzylideneaniline. J. Am. Chem. Soc. 1971, 93, 4658–4663. 18. Zheng, J.; Xu, X.; Truhlar, D.G. Minimally augmented Karlsruhe basis sets. Theor. Chem. Acc. 2011, 128, 295–305. [CrossRef] Molbank 2021, 2021, M1299 7 of 7 19. Ásgeirsson, V.; Birgisson, B.O.; Bjornsson, R.; Becker, U.; Neese, F.; Riplinger, C.; Jónsson, H. Nudged Elastic Band Method for Molecular Reactions Using Energy-Weighted Springs Combined with Eigenvector Following. J. Chem. Theory Comput. 2021, 17, 4929–4945. [CrossRef] 20. Blanco, F.; Alkorta, I.; Elguero, J. Barriers about Double Carbon-Nitrogen Bond in Imine Derivatives (Aldimines, Oximes, Hydrazones, Azines). Croat. Chem. Acta 2009, 82, 173–183. 21. Gasparro, F.P.; Kolodny, N.H. NMR Determination of the Rotational Barrier in N,N-dimethylacetamide. J. Chem. Educ. 1977, 54, 258–261. [CrossRef] 22. Daina, A.; Michielin, O.; Zoete, V. SwissADME: A free web tool to evaluate pharmacokinetics, drug-likeness and medicinal chemistry friendliness of small molecules. Sci. Rep. 2017, 7, 42717. [CrossRef] [PubMed] 23. Bennett, B.L.; Sasaki, D.T.; Murray, B.W.; O’Leary, E.C.; Sakata, S.T.; Xu, W.; Leisten, J.C.; Motiwala, A.; Pierce, S.; Satoh, Y.; et al. SP600125, an anthrapyrazolone inhibitor of Jun N-terminal kinase. Proc. Natl. Acad. Sci. USA 2001, 98, 13681–13686. [CrossRef] [PubMed] 24. Neese, F.; Wennmohs, F.; Becker, U.; Riplinger, C. The ORCA quantum chemistry program package. J. Chem. Phys. 2020, 152, 224108. [CrossRef] [PubMed]

Journal

Molbank – Multidisciplinary Digital Publishing Institute

Published: Nov 23, 2021

Keywords: azine; aldazine; 11H-indeno[1,2-b]quinoxalin-11-one; DFT; ADME

There are no references for this article.