Specific inhibitors of human pancreatic alpha-amylase (HPA) have potential as oral agents for the control of blood glucose levels in the treatment of diabetes and obesity. In a search for novel inhibitors, a library of 30 000 crude biological extracts of terrestrial and marine origin has been screened. A number of inhibitory extracts were identified, of which the most potent was subjected to bioassay-guided purification. A family of three glycosylated acyl flavonols, montbretins A-C, was thereby identified and characterized as competitive amylase inhibitors, with K(i) values ranging from 8.1-6100 nM. Competitive inhibition by myricetin, which corresponds to the flavone core, and noncompetitive inhibition by a second fragment, ethyl caffeiate, suggest a binding mode for these inhibitors.