Triterpene glycosides ofAstragalus and their genins. XII. Askendoside B fromAstragalus taschkendicus

Abstract

On the basis of chemical transformations and with the aid of physicochemical characteristics it has been established that a new glycoside of the cycloartane series — askendoside B (I) — isolated from the roots ofAstragalus taschkendicus Bge., is 20S,24R-epoxycycloartane-3β,6α,16β,25-tetraol 3-0-[0-α-L-arabinopyranosyl-(1 → 2)-(3′-0-acetyl-β-D-xylopyranoside)] 6-0-β-D-xylopyranoside, C₄₇H₇₆O₁₈, mp 215–218°C, [α] ²⁰_D −45.5° (c 1.1; pyridine). The acid hydrolysis of (I) yielded cyclosiversigenin (II) with mp 239–241°C, [α] ²⁰_D +54.5° (c 1.2; MeOH), and cyclosiversigenin 3-0-β-D-xylopyranoside (III) with mp 262–264°C, [α] ²⁰_D +41° (c 0.4; MeOH). The periodate oxidation of glycoside (I) followed by acid hydrolysis likewise led to (II) and to D-xylose. The alkaline hydrolysis of (I) yielded askendoside D (IV), with mp 235–236°C, [α] ²³_D −8.5° (c 1.0; pyridine). The Smith degradation of (I) led to (III). The IR and PMR spectra of (I) are given.