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

Abstract

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 (¹H, ¹³C) and 2D (¹H–¹H 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.

Keywords::

• marine ascidian; Didemnum species
• glycerides
• sterols

Acknowledgements

We thank Mr Volker Brecht (Nuclear Magnetics Resonance, Institute für Pharmazeutische Wissenschaften, Albert-Ludwigs-Universität Freiburg, Germany) for NMR and MS spectral measurements.