Identification of naturally occurringtrans,trans Δ5,9 fatty acids from the spongePlakortis halichondroides

The firsttrans fatty acids from a sponge have been isolated fromPlakortis halichondroides. The sponge was shown to contain theiso acids (5E,9E)-19-methyl-5,9-eicosadienoic, (5E,9E)-20-methyl-5,9-heneicosadienoic and (5E,9E)-21-methyl-5,9-docosadienoic acid, as well as theanteiso acids (5E,9E)-19-methyl-5,9-heneicosadienoic and (5E,9E)-20-methyl-5,9-docosadienoic acid together with the straight chain (5E,9E)-5,9-docosadienoic acid. The acids were shown by gas chromatography, Fourier transform infrared and¹³C nuclear magnetic resonance to contain thetrans configuration. An eicosadienoic acid, namely (6E,14E)-6,14-eicosadienoic acid, and 12-methyl-5-octadecenoic acid were also identified in a sponge for the first time. The fatty acids were shown to be the principal constituents of phosphatidylethanolamine and phosphatidylcholine. No sterols were found in the sponge. The results presented in this work should be helpful in taxonomy of Homoscleromorpha.