C32-C36 polymethyl alkenes in Black Sea sediments

Abstract

A series of novel C32-C36 polymethylhentriacontenes has been identified in near-surface sediments of the Black Sea. Hydrogenation of these components indicated that they possess the 5,8,14,24,27-pentamethyl-, 8,14,24,27-tetramethyl-, 8,14,24-trimethyl-, 8,14-dimethyl-, and 14- and 15-methylhentriacontane C skeletons, which was confirmed by synthesis of an authentic standard of the C34 member. The dominant C36 member of this series contains eight double bonds. The 13C content of these polymethylhentricontenes indicated that they are probably biosynthesized by photoautotrophs and that blooming or bicarbonate pumping affected the 13C content of the fixed C. Their structures suggest that they were biosynthesized by methylation of an unsaturated n-C31 precursor at specific positions in a well-defined sequence. This biosynthetic pathway represents an alternative for the biosynthesis of isoprenoid-like components.