Stigmastane-type steroid saponins from the leaves of Vernonia amygdalina and their α -glucosidase and xanthine oxidase inhibitory activities.

Two new vernonioside K ( 1 ) and vernonioside L ( 2 ) and four known Δ 7,9(11) stigmastane-type steroidal saponins-vernonioside B2 ( 3 ), vernoniacum B ( 4 ), vernonioside B1 ( 5 ), and vernoamyoside A ( 6 )-were isolated from the leaves of Vernonia amygdalina . Their structures were determined by comprehensive spectroscopic analysis with one-dimensional nuclear magnetic resonance, two-dimensional nuclear magnetic resonance, and high-resolution mass spectrometry. All isolated compounds ( 1 - 6 ) were evaluated to determine their inhibitory effects on α -glucosidase and xanthine oxidase. Among them, two new compounds 1 and 2 showed significant inhibition of α -glucosidase with IC 50 values of 78.56 ± 7.28 and 14.74 ± 1.57 (μM), respectively, comparable with acarbose as a positive control (127.53 ± 1.73 μM); none of these compounds inhibited xanthine oxidase activity. Compounds 1 and 2 are promising candidates for the development of antidiabetic agents from natural sources.