[Synthesis and biological activity of isomeric 5- and 6-nitro-1-alkylbenzimidazoles]

Either the alkylation of 5(6)-nitro-benzimidazoles (R = H, CH3) or the nitration of 1-alkyl-benzimidazoles afforded corresponding mixtures of 1-alkyl-5-nitro- and 1-alkyl-6-nitro-benzimidazoles (III, IV, VII, VIII, XI). Fractional crystallization from water was employed for isolation of 6-nitro isomers V, VI and IX from mixtures III, IV and VII. On the other hand, application of this isolation method to mixtures VIII and XI proved unsuccessful. 6-Nitro-compound X and 5-nitro derivatives XIII and XV were obtained by direct syntheses. From calibration curves depicting dependence of absorbance of the mixtures upon their composition, percentage ratios of 5-nitro to 6-nitro isomers in the mixtures were estimated. Usefulness of thin-layer chromatography, and UV and IR spectrometry for identification of 5-nitro and 6-nitro isomers was stated; e. g. 5-nitro isomers have higher epsilon values, while 6-nitro isomers exhibit two vmax values of the benzene ring. Compounds IV, IX and X proved to exert antihelminthic, antibacterial and antiphlogistic activities.