Limonoids from the Seeds of a Hainan Mangrove, <i>Xylocarpus granatum</i>

Ten new limonoids, hainangranatumins A−J (1−10), and 25 known compounds were isolated from seeds of a Chinese mangrove, Xylocarpus granatum, collected on Hainan Island. Hainangranatumins A−E (1−5) and I and J (9 and 10) are 9,10-seco-mexicanolides, whereas hainangranatumin F (6) is a limonoid possessing an 8α,30α-epoxy ring and a C1−C29 oxygen bridge. Hainangranatumin G (7) is a limonoid with a central pyridine ring, and hainangranatumin H (8) is a phragmalin 1,8,9-ortho ester. The relative configurations of hainangranatumins A and B were established by means of single-crystal X-ray diffraction analysis, and their absolute configurations were assigned on the basis of the specific rotation of the free acids obtained from alkaline hydrolysis. This is the first report of X-ray crystallographic structures of 9,10-seco-mexicanolides with a flexible C2−C30−C8 linkage. Hainangranatumins I and J (9 and 10), unusual 9,10-seco-mexicanolides with a C9−C30 linkage, are proposed to be artifacts derived from hainangranatumin C and xylomexicanin A, respectively.