Designing novel anticancer sulfonamide based 2,5-disubstituted-1,3,4-thiadiazole derivatives as potential carbonic anhydrase inhibitor

Abstract A series of sulfonamide derivatives bearing 2,5-disubstituted-1,3,4-thiadiazole (5a–j) have been synthesized. Thiosemicarbazide was reacted with CS2 to get 2-amino-5-mercapto-1,3,4-thiadiazole 1. The intermediate thiadiazole (1) was alkylated by reacting with different halides (2a–c) to afford the alkylated thiadiazoles (3a–c). The title sulfonamide bearing derivatives (5a–j) have been prepared by condensation of sulfonyl chlorides (4a–d) with thiadiazole derivatives (3a–c). The molecular docking studies of target molecules showed strong binding of compounds (5a–j) with target enzyme (PDBID 1V9E) particularly for compound 5f containing fluoro and methoxy groups. The carbonic anhydrase (CA) inhibitory activity showed derivative 5h to be the most potent (IC50 0.60 ± 0.02 µM) as compared to acetazolamide (IC50 0.984 ± 0.12 µM) used as standard. Free radical scavenging activity was measured using ascorbic acid as a reference. It was observed that just like CA inhibition the compound 5h showed greater free radical scavenging activity than all other target molecules. Enzyme inhibition kinetics (Lineweaver-Burk plots) showed a compound (5h) to inhibit the enzyme by mixed type of inhibition (Ki and Kiʹ values 2.91 µM and 3.88 µM, respectively). Compound 5h was further investigated that a smaller value of Ki than Ki′ showed preferred competitive binding over non-competitive manners. The anticancer activity performed against the MCF-7 cell line showed that the compound 5h inhibits 40% cell growth at 125 µM concentration. The mechanism of anticancer potential was further investigated by DNA binding studies through electrochemical methods. The UV-Vis spectroscopy and Cyclic voltammetry results suggested that 5h was weakly bound to DNA (binding constant 30–32 M−1). It is thus proposed that anticancer activity of 5h may be through carbonic anhydrase inhibition rather than by DNA binding. Our investigations suggested the derivative 5h to serve as a lead structure in designing potentially more active carbonic anhydrase inhibitors.