©IUPAC THE HOPANOIDS PALAEOCHEMISTRY AND BIOCHEMISTRY OF A GROUP OF NATURAL PRODUCTS

Abstract- More than 100 individual derivatives of hopane have been isolated from sedimentary organic matter of most varied origin. They are ubiquitous molecular fossils derived from cellular cons-tituents of micro-organisms. Hopanoids are shown to be widely distributed among Bacteria and Cyanobacteria (blue-green algae). Their function in cells is probably equivalent to that of sterols in the eucaryote cell: to act as optimizers of the fluid lipid membranes. They are even probably phylogenetic precursors of sterols. In procaryotes containing no hopanoids, other mechanisms of fluidity control of biomembranes are probably operating; they imply acyclic di- or tetraterpenes (carotenoids or isomers), the molecular fossils of which are also present in sediments. These terpenes may in turn be phylogenetic precursors of hopanoids