Andhraxylocarpins A-E: Structurally Intriguing Limonoids from the True Mangroves Xylocarpus granatum and Xylocarpus moluccensis

Five new limonoids, including andhraxylocarpins A and B (1 and 2) which contain a 9-oxa-tricyclo[3.3.2.17,?10]undecane-2-ene motif, andhraxylocarpins C and D (3 and 4), which contain a (Z)-bicyclo[5.2.1]dec-3-en-8-one substructure, and andhraxylocarpin E (5), which contains a tricyclo[3.3.1.13,?6]decane-9-one scaffold, were isolated from the seeds of two true mangroves, Xylocarpus granatum and Xylocarpus moluccensis, that were collected in the estuaries of Andhra Pradesh, India. The absolute configurations of these compounds were determined by extensive NMR investigations, single-crystal X-ray diffraction analysis, and by circular dichroism and optical rotatory dispersion spectroscopy, in combination with quantum-chemical calculations. The pronounced structural diversity of limonoids from these mangroves might originate from environmental factors.