Synthesis of 1,2,4-Oxadiazole Sulfonamide Derivatives and Their Biological Investigation as Monoamine Oxidase Inhibitors

Monoamine oxidase (MAO) enzymes catalyze the catabolism of neurotransmitter amines, and MAO inhibitors are therefore of much clinical value. Based on the continued interest in MAO inhibitors, the present study examined the MAO inhibition properties of 1,2,4-oxadiazole sulfonamide derivatives. While we previously investigated benzenesulfonamides as MAO inhibitors, the incorporation of the 1,2,4-oxadiazole ring as the heteroaromatic ring is novel. 1,2,4-Oxadiazole sulfonamide derivatives were prepared from the corresponding carboxylic acids and amidoximes by an acylation–cyclization reaction under basic conditions, and MAO inhibition properties were determined using recombinant human enzymes. The derivatives potently inhibited MAO-B, with seven compounds exhibiting IC50 values lower than 0.02 µM. In contrast, comparatively weak MAO-A inhibition was observed with IC50 values greater than 6.04 µM. Mechanistic studies indicated that a representative compound acted as a reversible and competitive inhibitor. It may be concluded that 1,2,4-oxadiazole sulfonamide derivatives exhibit promising, isoform-selective MAO-B inhibition that may be of value for future therapeutic application.