Immunomodulatory and Anticancer Activities of Some Novel 2-Substituted-6-bromo-3-methylthiazolo[3,2-a]benzimidazole Derivatives

Ethyl 6‐bromo‐3‐methyl‐1,3‐thiazolo[3,2‐a]benzimidazole‐2‐carboxylate 2 was prepared by the ambient temperature bromination of ethyl 3‐methyl‐1,3‐thiazolo[3,2‐a]benzimidazole‐2‐carboxylate 1. The acid hydrazide 4 was obtained by the reaction of ester 2 with hydrazine hydrate. Treatment of compound 4 with benzaldehyde or 2‐thiophenaldehyde yielded the corresponding hydrazones 6a and 6b, respectively, while the reaction of acid hydrazide 4 with ethoxymethylene malononitrile (7a) or with ethyl ethoxymethylene cyanoacetate (7b) in refluxing ethanol afforded pyrazole derivatives 9a and 9b, respectively. Taken together, from the biological investigations compounds 9a and 9b were the most significant inhibitors of LPS‐stimulated NO generation from Raw murine macrophage 264.7, and, as another result, compounds 2 and 4 had a weak radical scavenging activity against DPPH radicals. Moreover, 2, 4, and 9a had a concomitant strong cytotoxicity against both colon carcinoma cells (HCT‐116) and hepatocellular carcinoma cells (Hep‐G2) while 9b showed specific cytotoxicity only against colon carcinoma cells.