Hopanoids

Hopanoids are a diverse subclass of triterpenoids with the same hydrocarbon skeleton as the compound hopane. This group of pentacyclic molecules therefore refers to simple hopenes, hopanols and hopanes, but also to extensively functionalized derivatives such as bacteriohopanepolyols (BHPs) and hopanoids covalently attached to lipid A.^[1][2]

The first known hopanoid, hydroxyhopanone, was isolated by two chemists at The National Gallery, London working on the chemistry of dammar gum, a natural resin used as a varnish for paintings.^[3] While hopanoids are often assumed to be made only in bacteria, their name actually comes from the abundance of hopanoid compounds in the resin of plants from the genus Hopea. In turn, this genus is named after John Hope, the first Regius Keeper of the Royal Botanic Garden, Edinburgh.

Since their initial discovery in an angiosperm, hopanoids have been found in plasma membranes of bacteria, lichens, bryophytes, ferns, tropical trees and fungi.^[4] Hopanoids have stable polycyclic structures that are well-preserved in petroleum reservoirs, rocks and sediment, allowing the diagenetic products of these molecules to be interpreted as biomarkers for the presence of specific microbes and potentially for chemical or physical conditions at the time of deposition.^[5] Hopanoids have not been detected in archaea.^[6][7]