- Tautomerism and isomerism in some antitrichinellosis active benzimidazoles: Morphological study in polarized light, quantum chemical computations
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The morphology of the crystal structure of some antitrichinellosis active benzimidazole derivatives including (1H-benzimidazol-2-ylthio)acetic acids, [1,3]thiazolo[3,2-a]benzimidazol-3(2H)-ones, 1H-benzimidazol-2-ylthioacetylpiperazines and starting 2-mercapto benzimidazoles, was studied by the use of Polarized Light Microscopy (PLM). Characterization of the crystal phase was complimented by Differential scanning calorimetry analysis (DSC) and spectroscopic data. DFT computations were performed in order to investigate the prototropic tautomerism and the geometry of the molecule of the synthesized compounds. One distinct type of crystal structure for each one of 5 or 6-methyl-(1H-benzimidazol-2-ylthio)acetic acid 6 was observed by PLM – dendritic and needle-shaped formations. Compound 14, containing a methyl substituent in the benzimidazole ring crystallized also into two phases; while for the unsubstituted compound 13 a separation of phases does not take place. The influence of the both solvents - chloroform and ethanol on the phase separation and the formation of the crystalline structure of compound 14 was investigated. The morphological study showed that the cyclization of 6 in the presence of acetic anhydride in pyridine medium led to a mixture of 6-methyl-[1,3]tiazolo[3,2-a]benzimidazol-3(2H)-one (10a) and 7-methyl-[1,3]thiazolo[3,2-a]-benzimidazole-3(2H)-one (10b), which crystallized in the form of fibrils and spherulites respectively. It was found that a difference in the crystal structures of substituted and unsubstituted benzimidazol-2-thiones, respectively benzimidazol-2-thiol derivatives exists, which may be due not only to the thiol-thione tautomerism but to the prototropic properties of the hydrogen atom in first position of the ring. The calculation results indicated that the thione form is more stable than the thiol tautomer by 51–55 kJ mol?1. But at the same time ΔG for the two thiol tautomers is below 0.5 kJ mol?1. In solid phase the 5(6)-substituted-1H-benzimidazol-2-thiols crystallized in two different crystal structures while the unsubstituted 1H-benzimidazol-2-thiol possess one type of crystal structure.
- Anichina, Kameliya,Mavrova, Anelia,Yancheva, Denitsa,Tsenov, Jordan,Dimitrov, Rasho
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p. 179 - 187
(2017/09/05)
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- Antihelminthic activity of some newly synthesized 5(6)-(un)substituted-1H-benzimidazol-2-ylthioacetylpiperazine derivatives
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Piperazine derivatives of 5(6)-substituted-(1H-benzimidazol-2-ylthio)acetic acids were synthesized by using two methods and studied for antihelminthic activity. The antiparasitic screening showed that compounds 18-24 exhibited higher activity against Trichinella spiralis in vitro in comparison to methyl 5-(propylthio)-1H-benzimidazol-2-yl-carbamate (albendazole). Most active were compounds 2-({2-[4-(4-chlorophenyl)piperazin-1-yl]-2-oxoethyl}thio)-1H-benzimidazo le 21 and 2-{[2-oxo-2-(4-benzhydrylpiperazin-1-yl)ethyl]thio}-5(6)-methyl-1(H)-ben zimidazole 19 as well as 2-({2-[4-(4-chlorophenyl)piperazin-1-yl]-2-oxoethyl}thio)-5(6)-methyl-1( H)-benzimidazole 23 with efficacy of 96.0%, 98.4% and 100%, respectively. The tested derivatives 15-19 and 20-23 were less active against Syphacia obvelata in vivo than albendazole and exhibited the same efficacy as piperazine, but in twice lower concentration.Compounds 2-({2-[4-(4-chlorophenyl)piperazin-1-yl]-2-oxoethyl}thio)-1H-benzimidazo le 21, 1,4-bis[(5(6)-methyl-1(H)-benzimidazol-2-ylthio)acetyl]piperazine 17 and 2-({2-[4-(4-chlorophenyl)piperazin-1-yl]-2-oxoethyl}thio)-5(6)-methyl-1( H)-benzimidazole 23 had higher efficacies of 73%, 76%, and 77%, respectively.
- Mavrova, Anelia Ts.,Anichina, Kamelya K.,Vuchev, Dimitar I.,Tsenov, Jordan A.,Denkova, Pavletta S.,Kondeva, Magdalena S.,Micheva, Mitka K.
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p. 1412 - 1420
(2007/10/03)
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- Synthesis and antitrichinellosis activity of some 2-substituted-[1,3] thiazolo[3,2-a]benzimidazol-3(2H)-ones
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Some new thiazolo[3,2-a]benzimidazolone derivatives were synthesized using two methods. The structures of the synthesized compounds were proved by means of IR, 1H NMR and mass spectral data. Ab initio computations were performed in order to determine the electronic structure and geometry of the investigated molecules and to compare it to the geometry of albendazole. Biologically, experiments in vitro and in vivo were accomplished in order to identify the efficacy of the obtained thiazolobenzimidazolones against Trichinella spiralis. The effectiveness of compounds 4a-c in the intestinal phase of trichinellosis was 100% and in the muscle phase were 88% and 80% at a concentration of 100 mg/kg mw for the compounds 4a and 4c. The results of the hepatotoxicity test showed that the compounds 4a and 4b possess hepatotoxicity comparable to that of albendazole.
- Mavrova, Anelia Ts.,Anichina, Kamelya K.,Vuchev, Dimitar I.,Tsenov, Jordan A.,Kondeva, Magdalena S.,Micheva, Mitka K.
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p. 5550 - 5559
(2007/10/03)
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- HETEROCYCLIC SYSTEMS CONTAINING BRIDGEHEAD NITROGEN ATOM-7
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The synthesis of 6-methyl- , 8- methyl- , 6,7- dimethyl- , and 5,8- dimethyl-thiazolo !3,2- alpha! benzimidazol- c(2H)- ones and 2H- 7,8-dimethyl !1,3! thiazino !3,3- alpha! benzimidazol- 4(3H)- one have been accomplished by the cyclization with acetic anhydride of the corresponding acid. The orientation of the product formed, wherever two isomeric products are likely to be obtained on cyclization, has been established through NMR spectral data. The condensation of some thiazolidinoines with aldehydes and their bromine derivatives have also been studied.
- CHAUDHARY HS,PANDA CS,PUJARI HK
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