Novel extended side-chain-unsaturated hopenes released from the kerogen macromolecules under artificial conditions

A novel family of hopanoids present in pyrolysates of solvent-extracted peat from Caohai Basin, Southwest China, has been tentatively identified on the basis of GC-MS data as C32---C35 extended side-chain-unsaturated hopenes. These unsaturated pentacyclic triterpenoid compounds are produced by laboratory thermal decomposition of kerogen. The results of our pyrolysis experiments suggest that these structures result from thermal release of bound C35 bacteriohopanepolyols which are bonded to the kerogen macromolecule via polyether or polyester linkages. The finding of these new hopenes indicates that pyrolysis can provide information about the types of linkings and sites of bonding of hopane units to the macromolecular network. Meanwhile, this study also provides valuable information on the way that these hopane skeletons are released from a kerogen structure under thermal stress. These novel extended side-chain-unsaturated hopenes may act as intermediates in the transformation of bound C35 hopanoid precursors to free C27---C35 hopanes under artificial conditions.