α-Glucosidase inhibitor from Buthus martensi Karsch

► An α-glucosidase inhibitor (compound S) was isolated from Buthus martensi Karsch. ► The structure of compound S was elucidated as harmanyl β-d-glucopyranoside. ► Compound S inhibited α-glucosidase activity with an IC50 value of 24 μM. ► Compound S was an uncompetitive inhibitor with a Ki value of 16.1 μM.