Novel ring A rearranged isomers with γ-lactone from the fruits of Aphanamixis grandifolia

Aphagranols A (1) and B (2), a pair of isomers with a novel limonoid carbon skeleton, were isolated from the fruits of Aphanamixis grandifolia. Their structures were determined by spectroscopic analyses and further confirmed by their unique acetylated derivative aphagranol C (3). The possible equilibrium system of the enol interconversion was presented using the polarizable continuum model (PCM). The absolute configuration of 3 was established via experimental and calculated ECD spectra comparison. The γ-lactone moiety in ring A system was first found in this class of limonoids.