beta-Methoxy-gamma-methylene-alpha,beta-unsaturated-gamma-butyrolactones from Artabotrys hexapetalus

The dichloromethane extract of the aerial parts of Artabotrys hexapetalus afforded three beta-methoxy-gamma-methylene-alpha,beta-unsaturated-gamma-butyrolactones, which are proposed to be derived from a C(18) unsaturated fatty acid by a biosynthetic route similar to that proposed for the Annonaceous acetogenins. The structure of the unique beta-methoxy-gamma-methylene-substituted, alpha,beta-unsaturated-gamma-butyrolactone ring of artapetalins A-C (1-3) was determined by 2D-NMR spectroscopic analyses. Two unusual simple butyrolactones, (+)-tulipalin B and (2R,3R)- 3-hydroxy-2-methylbutyrolactone were also isolated from this species.