Xylogranatins A-D: novel tetranortriterpenoids with an unusual 9,10-seco scaffold from marine mangrove Xylocarpus granatum.

[reaction: see text] Four novel tetranortriterpenoids, xylogranatins A-D (1-4), with an unusual 9,10-seco skeleton were isolated from the seeds of a Chinese marine mangrove Xylocarpus granatum. Their structures were determined by spectroscopic and chemical means. Xylogranatin A (1) featured by a unique 1,9-oxygen bridge was confirmed by single-crystal X-ray diffraction, and xylogranatin D (4) with an unprecedented skeleton of C-30-C-9 linkage was postulated biogenetically from 3 via an alpha-hydroxyl ketone rearrangement and was chemically mimicked.