Metabolites of the mangrove fungus Xylaria sp. BL321 from the South China Sea.

Two new lactones, 1 and 2, together with five known compounds, 3-7, were isolated from the marine mangrove fungus Xylaria sp. BL321. Their structures were determined by comprehensive analysis of their MS and NMR spectroscopic data. The absolute configurations of 1 and 2 were established on the basis of electronic circular dichroism calculations. It was found that the exocyclic double bond of 1 rearranged into a cyclic double bond to form a new crystal compound (1a) in diluted NaOH solution. Compound 3 was isolated for the first time as a natural product; its absolute configuration was determined by single-crystal X-ray crystallography. Compounds 4-7 displayed cytotoxicity against human breast cancer cell lines MCF-7 and MDA-MB-435, while compounds 1- 3 were inactive (IC(50) > 50 µM).