Constituents from the botanical dietary supplement wild yam

Abstract

Dioscorea villosa, its rhizomes/roots known as “wild yam”, is a species of a twining tuberous vine that is native to North America. The general fame of Dioscorea species is based on their steroidal saponins which can be chemically converted to progesterone contraceptives and cortisone. Almost all previous phytochemical and pharmacological research on wild yam focused on the isolation and bioactivity evaluation of steroids. So far, twelve steroidal saponins and two flavan-3-ol glycosides have been reported as major secondary metabolites from the rhizomes/roots of D. villosa. This narrow spectrum of known phytoconstituents limits the current understanding of the significance of wild yam as an important dietary supplement. Aimed at the metabolomic mining of potentially interesting bioactive constituents, this study explored a new fractionation methodology on the basis of 1D-1H and 2D-COSY NMR and diversified chromatography. The resulting isolation of ten diarylheptanoids including both open-chain and new cyclized (pyranoid) species from the MeOH extract marks the first report of this metabolite class from D. villosa. LC-MS profiling confirmed that diarylheptanoids represent genuine secondary metabolites of wild yam. To date, the only other report of the occurrence of diarylheptanoids in the genus Dioscorea came from D. spongiosa. Well-known from the Zingiberaceae and prominent for their pharmacological activities such as anti-cancer, estrogenic, anti-bacterial, anti-oxidative, anti-inflammation, and anti-osteoporotic activity, the metabolomic mining of a variety of diarylheptanoids in wild yam might offer a new lead for the development of this and possibly other Dioscorea botanicals.