Synthesis of a typical glucuronide-containing saponin, 28-O-beta-D-glucopyranosyl oleanate 3-O-beta-D-galactopyranosyl-(1 -> 2)-[beta-D-glucopyranosyl-(1 -> 3)]-beta-D-glucuronopyranoside

摘要

28-O-beta-D-Glucopyranosyl oleanate 3-O-beta-D-galactopyranosyl-(1-->2)-[beta-D-glucopyranosyl-(1-->3)]-beta-D-glucuronopyrano- side (1), a structurally typical glucuronide-containing triterpene saponin isolated from Aralia dasyphylla, was concisely synthesized in linear nine steps and 26% overall yield. The key features of the synthesis are: (1) attachment of the 28-glucosyl ester ahead of assembly of the 3-O-sugar chain; (2) elaboration of the glucuronide residue at a later stage via the TEMPO-mediated selective oxidation; (3) installation of 2-(azidomethyl)benzoyl group as a benzoylic neighboring participating group which is selectively removed afterwards for synthesis of the 1-->2 sugar linkage.