Structural identification of steryl alkyl ethers in marine sediments

Steryl alkyl ethers have been reported to occur in immature marine sediments up to Cretaceous age. Here, we report their unambiguous structural identification in Holocene sediments from the Arabian Sea, Pleistocene sediments from the southeast Atlantic and a Miocene sediment from the Monterey formation through chemical degradation experiments and synthesis. We show that the main steryl alkyl ethers in sediments from the southeast Atlantic are cholest-5-enyl 3β-(2-dodecanyl) ether and cholest-5-enyl 3β-(3-dodecanyl) ether together with their 24-methyl and 24-ethyl pseudo-homologues. Steryl alkyl ethers in sediments from the Arabian Sea are dominated by cholest-5-enyl 3β-(5-decanyl) ether and cholest-5-enyl 3β-(4-decanyl) ether together with their 24-methyl and 24-ethyl pseudo-homologues. The structures suggest that these compounds are formed by direct biosynthesis by as yet unknown marine organisms.