Synthesis and anticancer activity of 5-(3-indolyl)-1,3,4-thiadiazoles

A series of 5-(3-indolyl)-2-substituted-1,3,4-thiadiazoles 5a-m were synthesized and their cytotoxicity analyzed against six human cancer cell lines. The reaction of indole-3-carboxylic acid 3 with aryl or heteroaryl hydrazides afforded the N,N'-diacylhydrazines 4, which upon treatment with Lawesson's reagent resulted in the formation of indolyl-1,3,4-thiadiazoles 5a-m in good yields. Indolyl-1,3,4-thiadiazole 5m with 4-benzyloxy-3-methoxyphenyl and 5-bromo indolyl substituents is the most active in suppressing the growth of cancer cells (IC(50) 1.5 muM, PaCa2). The compounds 5b, 5e and 5h bearing C-2 substituent as benzyl, 3,4-dimethoxyphenyl and 4-benzyloxy-3-methoxyphenyl, respectively, have shown significant cytotoxicity against multiple cancer cell lines. Introduction of 4-dimethylamino (5d and 5k) and 3,4,5-trimethoxy (5l) groups in the C-2 phenyl ring induced selectivity against MCF7 and MDA-MB-231 cancer cell lines (compounds 5d, 5k and 5l).