Identification and characterization of two new methylicosadienoic acids from Erylus formosus.

The novel fatty acids 18-methyl-5,9-icosadienoic acid [1] and 19-methyl-5,9-icosadienoic acid [2] were identified in the Caribbean sponge Erylus formosus. Other interesting fatty acids identified were the branched acids 3-methylpentadecanoic acid and 3-methylhexadecanoic acid, which are known to possess larvicidal activity. The most stable conformation of the new acid 19-methyl-5,9-icosadienoic acid is also presented as predicted by Molecular Mechanics (MM2) calculations. The sterol composition of E. formosus is also reported.