Medicinal Foodstuffs. XVI. Sugar Beet. (3). Absolute Stereostructures of Betavulgarosides II and IV, Hypoglycemic Saponins Having a Unique Substituent, from the Roots of Beta vulgaris L.

Abstract

The absolute stereostructures of betavulgaroside II having a dioxolane-type substituent and betavulgaroside IV having an acetal-type substituent, which were isolated from the roots of Beta vulgaris L. (sugar beet, Chenopodiaceae) and exhibited hypoglycemic activity on glucose-loaded rats, were determined by the chemical correlations of betavulgarosides II and IV with a known saponin, momordin I. In these chemical correlations, the α-L-arabinopyranosyl moiety of momordin I was converted to a dioxolane-type substituent of betavulgaroside II or to an acetal-type substituent of betavulgaroside IV. Additionally, the 2'-diastereoisomer of betavulgaroside IV was synthesized from momordin I, and four acetal-type substituent analogues were also synthesized from L- and D-arabinose.