Cyclo(Dehydroala-L-Leu), an alpha-glucosidase inhibitor from Penicillium sp F70614

A diketopiperazine (1) has been isolated from the culture broth of Penicillium sp. F70614 and its structure has been determined to be cyclo(dehydroala-L-Leu) by various spectroscopic analyses. This compound selectively inhibited yeast alpha-glucosidase and porcine intestinal alpha-glucosidase with IC50 values of 35 and 50 mu g/ml, respectively. However, it did not show significant inhibitory effects against almond beta-glucosidase, Aspergillus alpha-galactosidase, Escherichia coli beta-galactosidase and jack bean alpha-mannosidase.