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A series of cyano- and amidino-substituted imidazo[4,5-b]pyridines were synthesized using standard methods of organic synthesis, and their biological activity was evaluated. Biological evaluation included in vitro assessment of antiproliferative effects on a diverse selection of human cancer cell lines, antibacterial activity against chosen Gram-positive and Gram-negative bacterial strains, and antiviral activity on a broad panel of DNA and RNA viruses. The most pronounced antiproliferative activity was observed for compound 10, which contained an unsubstituted amidino group, and compound 14, which contained a 2-imidazolinyl amidino group; both displayed selective and strong activity in sub-micromolar inhibitory concentration range against colon carcinoma (IC50 0.4 and 0.7 μM, respectively). All tested compounds lacked antibacterial activity, with the exception of compound 14, which showed moderate activity against E. coli (MIC 32 μM). Bromo-substituted derivative 7, which contained an unsubstituted phenyl ring (EC50 21 μM), and para-cyano-substituted derivative 17 (EC50 58 μM) showed selective but moderate activity against respiratory syncytial virus (RSV).

We present the synthesis of a range of benzimidazole/benzothiazole-2-carboxamides with a variable number of methoxy and hydroxy groups, substituted with nitro, amino, or amino protonated moieties, which were evaluated for their antiproliferative activity in vitro and the antioxidant capacity. Antiproliferative features were tested on three human cancer cells, while the antioxidative activity was measured using 1,1-diphenyl-picrylhydrazyl (DPPH) free radical scavenging and ferric reducing antioxidant power (FRAP) assays. Trimethoxy substituted benzimidazole-2-carboxamide 8 showed the most promising antiproliferative activity (IC50 = 0.6−2.0 µM), while trihydroxy substituted benzothiazole-2-carboxamide 29 was identified as the most promising antioxidant, being significantly more potent than the reference butylated hydroxytoluene BHT in both assays. Moreover, the latter also displays antioxidative activity in tumor cells. The measured antioxidative capacities were rationalized through density functional theory (DFT) calculations, showing that 29 owes its activity to the formation of two [O•∙∙∙H−O] hydrogen bonds in the formed radical. Systems 8 and 29 were both chosen as lead compounds for further optimization of the benzazole-2-carboxamide scaffold in order to develop more efficient antioxidants and/or systems with the antiproliferative activity.

New trans- and cis-o-stilbene-methylene-sydnones 3a,b were synthesized by transforming the trans- and cis-o-aminomethylstilbene derivative, obtained by reduction of corresponding o-cyano derivatives, into glycine ester derivatives (43 and 31% yield) followed by hydrolysis (90 and 96% yield), nitrosation and ring closure with acetic acid anhydride (30 and 40% yield). The products were submitted to photochemical and thermal intramolecular [3 + 2] cycloadditions to afford diverse heteropolycyclic compounds. Photochemical reactions afforded cis-3-(4-methylphenyl)-3a,8-dihydro-3H-pyrazolo[5,1-a]isoindole (11, 12.5% yield) and trans-3-(4-methylphenyl)-3a,8-dihydro-3H-pyrazolo[5,1-a]isoindole (12, 5% yield). Thermal reactions afforded 3-(4-methylphenyl)-3,3a,8,8a-tetrahydroindeno[2,1-c]pyrazole (14, 50% yield) and 11-(4-methylphenyl)-9,10-diazatricyclo[7.2.1.02,7]dodeca-2,4,6,10-tetraene (15, 22% yield).