Isoprenoid thiophenes: Novel products of sediment diagenesis?

Abstract

Sulphur is a significant component of the organic matter in recent and ancient sediments and in petroleums, yet the precise nature of its association and incorporation is poorly understood. Various sulphur-containing compounds have been recognized in petroleums, but little is known about their origins and mode of generation during sediment burial, and for only a few organo-sulphur compounds with >15 carbon atoms have the structures been determined. Here we identify one of the alkyl thiophenes which occur widely in both recent and ancient deep-sea sediments as 3-methyl-2-(3, 7, 11-trimethyldodecyl)-thiophene, occurring as a limited number of the possible stereoisomers. This compound is presumed to originate from the incorporation of sulphur into chlorophyll-derived phytol, or archaebacterial phytenes or their diagenetic products. Its recognition suggests a novel diagenetic pathway for acyclic isoprenoids involving the introduction of sulphur into specific lipid moieties. Similar, but intermolecular, sulphur incorporation might give rise to sulphurlinked macromolecular materials and thereby contribute significantly to the formation of kerogens.