Aphanamixoid A, a Potent Defensive Limonoid, with a New Carbon Skeleton from Aphanamixis polystachya

Aphanamixoid A (1), a limonoid with a new carbon skeleton, along with its biogenetically related limonoid aphanamixoid B (2), was isolated from the leaves and twigs of Aphanamixis polystachya . Their structures with the absolute stereochemistry were determined by spectroscopic analysis, X-ray crystallography and computational methods. The significant antifeedant activity of 1 against the generalist plant-feeding insect Helicoverpa armigera (EC50 = 0.015 μmol/cm(2)) suggested it may be a potent defensive component of A. polystachya.