Aphanalides A-H, Ring A-seco Limonoids from the Fruits of Aphanamixis polystachya

The genus Aphanamixs is mainly distributed in the tropical areas of Asia such as southern China, India, Malaysia and Indonesia. A. polystachya (Wall.) R. N. Parker is a large evergreen and timber tree that has been comprehensively investigated since the 1960s for a myriad of activities of its extracts. Previous chemical investigations on this plant revealed many structurally complex limonoids. Recently, we reported the isolation and characterization of a novel limonoid with unusual skeleton from the fruits of A. polystachya collected in Yunnan Province of P. R. China, from which, in this study, eight novel limonoids, aphanalides A-H (1-8), were further isolated. Compounds 1-3 featured a highly strained four-membered oxetane ring between C-7 and C-14, unprecedented in ring A-seco limonoids; compound 4 possessed a ring A-seco C-15 ketone carbon skeleton, whereas 5-8 possessed a 14,15-epoxide in ring D with a modified ester at C-12. The structures and absolute configurations of 1 and 3 were confirmed by single-crystal X-ray studies using Cu Kα diffraction. A possible biosynthetic pathway for compounds 1-8 has been proposed.