New acylated triterpenoid saponins from Maesa lanceolata

Abstract

Ten new acylated triterpenoid saponins were isolated from the leaves of Maesa lanceolata. For their structure elucidation extensive use was made of homo- and heteronuclear 2D NMR techniques such as COSY, NOESY, HSQC and HMBC. All saponins identified contained the same tetraglycosidic side chain, but the triterpenoid moiety showed a variable esterification pattern. Monoester, diester and triester derivatives were present. Maesasaponin I was a 21-monoester derivative, i.e. {3β- O-[α- l-rhamnopyranosyl-(1→2)-β- d-galactopyranosyl-(1→3)]-[β- d-galactopyranosyl-(1→2)]-β- d-glucuronopyranosyl}-21β-angeloyloxy-13β,28-oxidoolean-16α, 22α, 28α-triol. Maesasaponins III, IV 3, V 3 and VI 2 had an additional acetyl, propanoyl, n-butanoyl and angeloyl substituent, respectively, in position 22. Maesasaponins II, IV 2, V 2, VI 3 and VII 1 were characterised as the 16-acetyl derivatives of maesasaponins I, III, IV 3, V 3 and VI 2, respectively. Structures of saponins previously reported in M. lanceolata had to be revised.