Proanthocyanidins from the leaves of Machilus philippinensis.

Seven proanthocyanidins (2-8) together with epicatechin (1) were isolated from the EtOH extract of the leaves of Machilus philippinensis. Of these, machiphilitannins A (7) and B (8) are new natural products, with respective IC(50) values of 31.3 (7) and 18.4 microM (8) against alpha-glucosidase type IV from Bacillus stearothermophilus. Their structures were elucidated mainly on the basis of CD and 2D NMR analyses. In addition, aesculitannin B (2) showed inhibitory activity against alpha-glucosidase with an IC(50) value of 3.5 microM. This work demonstrates for the first time that the purified proanthocyanidins possess inhibitory activity against alpha-glucosidase type IV.