Unusual C24, C25, C26 and C27 polyunsaturated fatty acids of the marine sponge Microciona prolifera

(1) Complete characterization of the fatty acids of the marine sponge Microciona prolifera, including double bond positional isomers, has identified 95 different acids in amounts of 0.1% or more. Trace amounts of 23 other acids were found. (2) 48% of the fatty acids present have C24--C28 chain lengths. These are all saturates, monoenes, dienes and trienes; the tetraene, pentaene and hexaene acids possess the usual C18--C22 carbon chains. The numerous C24--C28 acids present apparently originate within the sponge itself, indicating a highly active chain elongation system. (3) A new family of C24, C25, C26 and C27 polyunsaturated acids with isolated double bonds has been discovered. All contain delta 5,9 unsaturation. Specific acids identified were 5,9-24:2; 5,9-25:2; 5,9-26:2; 5,9,17-26:3; 5,9,19-26:3; 5,9,19-27:3 and 5,9,20-27:3. Biosynthetic pathways for such acids are proposed, based on intermediates found in our fatty acid analyses.