Chemistry of the annonaceae, Part 29. Structure of mezzettiaside-2, -4, -5, -6 and -7, new partially esterified 1-O-octyl tri- and tetra-rhamnosyl derivatives from Mezzettia leptopoda

Abstract

Extensive NMR and MS studies have led to the characterization of mezzettiasides-2, -4, -5, -6 and -7 from the stem bark of Mezzettia leptopoda(Annonaceae). All mezzettiasides isolated to date are based on an octyl 4-O-acetyl-α-L-rhamnopyranosyl-(1 → 3)-2,4-di-O-acetyl-α-L-rhamnopyranosyl(1 → 3)-4-O-hexanoyl-α-L-rhamnopyranoside nucleus (= mezzettiaside-4). Mezzettiaside-2 has an additional O-acetyl substituent at C-2 of the terminal hexose and mezzettiasides-5 to -7 an additional 1 → 3-linked α-L-rhamnose unit at C-3 of that hexose (=mezzettiaside-7). Mezzettiaside-5 has C-3 of the additional hexose unit O-acetylated; in mezzettiaside-6 C-2 of that unit is O-acetylated