Thaixylomolins O-R: four new limonoids from the Trang mangrove, Xylocarpus moluccensis

Two novel phragmalin 8,9,12-orthoesters, named thaixylomolins O-P (1-2), a 9,10-seco mexicanolide with a unique trans-orientation of H5 and Me-19, named thaixylomolin Q (3), and the first secomahoganin-type 7-nor-limonoid with a 6-oxabicyclo[3.2.1] octan-3-one motif, named thaixylomolin R (4), were isolated from the seeds of a Thai mangrove, Xylocarpus moluccensis collected from the mangrove swamps of the Trang Province. The absolute configurations of these limonoids were unambiguously determined by HRESIMS, extensive NMR investigations, single-crystal X-ray diffraction analyses with Cu K alpha radiation, and quantum-chemical electronic circular dichroism (ECD) calculations. Most notably, thaixylomolins O-P are unusual phragmalins with a 8,9,12-orthoacetate group reported for the second time. Thaixylomolin P exhibited antitumor activities against ovarian A2780 and A2780/T cells with an equal IC50 value of 37.5 mu M.