Synthesis of two bidesmosidic ursolic acid saponins bearing a 2,3-branched trisaccharide residue

The focus of this work was on the synthesis of two bidesmosidic ursolic acid saponins bearing a 2,3-branched trisaccharide residue. Therefore, 3-O-{[β-d-glucopyranosyl-(1→2)]-[α-l-arabinopyranosyl-(1→3) ]-α-l-arabinopyranosyl}ursolic acid-28-O-[β-d-glucopyranosyl] ester 1 was concisely synthesized by two strategies in 22% and 41% overall yield, respectively, and another congener 3-O-{[β-d-xylopyranosyl-(1→2)]- [β-d-glucopyranosyl-(1→3)]-α-l-arabinopyranosyl}ursolic acid-28-O-[β-d-glucopyranosyl] ester 2 was also efficiently prepared in 81% overall yield. The ¹H NMR and ¹³C NMR signals of saponin 2 are all consistent with those reported for the natural product.