Limonoids from the seeds of the marine mangrove Xylocarpus granatum

Five new limonoids, granaxylocarpins A-E (1-5), were isolated from the seeds of the Chinese marine mangrove Xylocarpus granatum. Granaxylocarpins A (1) and B (2) are mexicanolide-type limonoids with a 9,10-seco skeleton, and granaxylocarpin C (3) possesses an 8 alpha,30 alpha-epoxy ring and a rare 1,29-oxygen bridge. The structures of these limonoids were characterized on the basis of extensive spectroscopic methods and single-crystal X-ray diffraction analysis performed on 4. The structure of xyloccensin U (4a) was revised as 4b by comparison with granaxylocarpin D (4). The cytotoxicity of these isolates was evaluated against the P-388 and A-549 tumor cell lines.