Algal Pheromone Biosynthesis: Stereochemical Analysis and Mechanistic Implications in Gametes of Ectocarpus siliculosus

During sexual reproduction, female gametes or eggs of brown algae release pheromones to attract their male mating partners. The biologically active compounds comprise linear or alicyclic unsaturated hydrocarbons derived from the aliphatic terminus of C-20 polyunsaturated fatty acids (PUFAs) by oxidative cleavage. The current study addresses the stereochemical course of the pheromone biosynthesis using female gametes of the marine brown alga E. siliculosus and chiral deuterium-labeled arachidonic acids. The biosynthetic sequence is likely to proceed via an intermediary 9-hydroperoxyarachidonic acid, which is cleaved with loss of the C(16)-H-R into the C-II-hydrocarbon dictyopterene C and 9-oxonona-(5Z,7E)-dienoic acid.