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-3β,5α,6β-26-tetrol (5), were isolated from the Red Sea ascidian Didemnum sp. Their structures were elucidated by using extensive 1D ((1)H, (13)C) and 2D ((1)H-(1)H 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.