ABSTRACT: A novel series of 2,4,5- and 2,3,4-trisubstituted thiazole hybrids with 1,3,4-thiadiazolylbenzenesulfonamide was designed following the tail approach as possible hCAIX inhibitors. The key intermediate 1 was condensed with thiosemicarbazide 2a to give 1,3,4-thiadiazolylthiosemicarbazone 3, which upon hetero-cyclization with substituted α-haloketones and esters afforded 2,4,5-trisubstituted thiazole-1,3,4-thiadiazole conjugates 4-8. Furthermore, the trisubstituted thiazole-1,3,4-thiadiazole hybrids 12a-d were synthesized via the regioselective cyclization of 4-substituted-1,3,4-thiadiazolylthiosemicarbazones with phenacyl bromide. The cyclized 2,4-disubstituted thiazole 4 enhanced cytotoxicity by nine, four and two times against HepG-2, Caco2, and MCF-7, respectively. Moreover, the si
