C-32 C-36 POLYMETHYL ALKENES IN BLACK-SEA SEDIMENTS

A series of novel C32-C36 polymethylhentriacontenes has been identifie d in near-surface sediments of the Black Sea. Hydrogenation of these c omponents 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- an d 15-methylhentriacontane C skeletons, which was confirmed by synthesi s of an authentic standard of the C34 member. The dominant C36 member of this series contains double bonds. The C-13 content of these polyme thylhentricontenes indicated that they are probably biosynthesized by photoautotrophs and that blooming or bicarbonate pumping affected the C-13 content of the fixed C. Their structures suggest that they were b iosynthesized by methylation of an unsaturated n-C31 precursor at spec ific positions in a well-defined sequence. This biosynthetic pathway r epresents an alternative for the biosynthesis of isoprenoid-like compo nents.