Stilbenoids Isolated from the Seeds of Melinjo (Gnetum gnemon L.) and Their Biological Activity

A 50% EtOH extract of the dried endosperms of melinjo (Gnetum gnemon L.) was purified by a combination of column chromatography, including highly porous polymer, octadecylated silica (ODS), hydroxypropylated dextran (LH-20), and silica gel, resulting in the isolation of a new stilbenoid 1, named gnetin L, along with five previously identified stilbenoids 2-6 (gnetin C, gnemonosides A, C, and D, and resveratrol). All of these stilbenoids showed 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity similar to that of ascorbic acid and dl-alpha-tocopherol. With the exception of gnemonoside A (3), these stilbenoids showed moderate antimicrobial activity. Inhibition of lipase from porcine pancreas was recognized in four stilbenoids excluding gnemonoside A (3) and resveratrol (6). Gnetin C (2), gnemonoside C (4), and gnemonoside D (5) inhibited the hydrolysis of starch by alpha-amylase from porcine pancreas. An EtOH extract containing these stilbenoids also showed DPPH radical scavenging effect, lipase and alpha-amylase inhibition activity, and antimicrobial activity against food microorganisms and enterobacteria. The present study indicates that melinjo and extracts containing these constituents are useful as health supplements.