Isoprenoid thiophenes: novel products of sediment diagenesis?

Abstract

Sulphur is a significant component of the organic matter in recent and ancient sediments and in petroleums1,2, yet the precise nature of its association and incorporation is poorly understood. Various sulphur-containing compounds have been recognized in petroleums2–4, 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 determined5,6. Here we identify one of the alkyl thiophenes which occur widely in both recent and ancient deep-sea sediments7–13 as 3-methyl-2-(3,7,l l-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 sulphur-linked macro molecular materials and thereby contribute significantly to the formation of kerogens.