α-Glucosidase inhibitor from Buthus martensi Karsch

A bioassay-guided fractionation of an ethanol extract of Buthus martensi Karsch led to the isolation of a potent α-glucosidase inhibitor (compound S). The structure was elucidated as a novel β-carboline glucoalkaloid, harmanyl β-d-glucopyranoside, on the basis of spectral data, including 1H NMR, 13C NMR, 1H-1H COSY, NOESY, and HMBC. Compound S showed potent inhibitory activity against α-glucosidase, with an IC50 value of 24 μM. A Lineweaver–Burk plot indicated that its inhibition of α-glucosidase was uncompetitive, with a Ki value of 16.1 μM.