Stereocontrolled synthesis of oleanolic saponin ladyginoside A isolated from Ladyginia bucharica.

Efficient stereocontrolled synthesis of ladyginoside A isolated from Ladyginia bucharica is described. The presented methodology bases on the β-selective glycosylation to construct oleanate-3-O-β-glycoside from selectively protected d-cellobiose comprising desired β-linkage in carbohydrate unit. By using this procedure, dimethyl ester of ladyginoside A (1) (methyl oleanate 3-O-(β-d-glucopyranosyl)-(1 → 4)-β-d-glucuronide methyl ester) was obtained in 16% overall yield. Elaborated synthesis is also demonstrated as useful methodology en route to saponin 2 with additional glucose unit, namely 3-O-[β-d-glucopyranosyl-(1 → 4)-β-d-glucuronide] oleanolic acid 28-O-β-d-glucopyranosyl ester.