A New Cleavage Method for the Sugar – Aglycone Linkage in Saponin

A new cleavage method for the sugar – aglycone linkage in saponin is described. Treatment of [28‐hydroxy‐23,28‐dioxoolean‐12‐en‐3β‐yl‐ O ‐β‐D‐galactopoyranosyl‐(1 → 2)‐ O ‐α‐L‐arabinopyranosyl‐(1 → 3)‐β‐D‐glucopyranosid]uronic acid ( 1 ) with diazomethane – ether in methanol gave the aglycone 2 and the sugars 3 and 4 . On the basis of chemical and spectral evidence they were determined as methyl 3β,23α‐dihydroxy‐3‐ O ,23‐methylenolean‐12‐en‐28‐oate ( 2 ), methyl [methyl O ‐β‐D‐galactopyranosyl‐(1 → 2)‐ O ‐α‐L‐arabinopyranosyl‐(1 → 3)‐α‐D‐glucopyranosid]uronate ( 3 ), and methyl O ‐β‐D‐galactopyranosyl‐(1 → 2)‐ O ‐α‐L‐arabinopyranosyl‐(1 → 3)‐1,4‐anhydro‐α‐D‐glucopyranuronate ( 4 ). This method is useful for structure determination of some oleanane triterpenoid saponins and for yielding new oligosaccharides. The cleavage of the quillaic acid 3‐ O ‐glycoside 10 is also discussed.