Didemnacerides A and B: two new glycerides from Red Sea ascidian Didemnum species

Two new glycerides, didemnacerides A (1) and B (2), together with three known sterols, 24-ethyl-25-hydroxycholesterol (3), cholest-6-en-3,5,8-triol (4) and cholestane-3 beta,5 alpha,6 beta-26-tetrol (5), were isolated from the Red Sea ascidian Didemnum sp. Their structures were elucidated by using extensive 1D (H-1, C-13) and 2D (H-1-H-1 COSY, HSQC and HMBC) NMR studies and mass spectroscopic data (GC-MS and HR-MS) as well as alkaline hydrolysis followed by GC-MS and NMR spectral analyses of the fatty acid methyl esters. This is the first report of compounds 3-5 from the Red Sea ascidian Didemnum species.