C40 monoaromatic lycopane derivatives as indicators of the contribution of the alga Botryococcus braunii race L to the organic matter of Messel oil shale (Eocene, Germany)

A novel series of sedimentary aromatic lycopane derivatives, cyclolycopatrienes, has been found in an outcrop sample from the Messel oil shale. The predominant monoaromatic compound 4 from this hydrocarbon series has been isolated using reversed phase HPLC and its structure determined using 1D and 2D 1H NMR spectroscopy, as well as from identification of the RuO4 degradation products. From examination of its structure, related to that of lycopane, and from its stable carbon isotopic composition, this compound and related isomers can be considered as new proxies for Botryococcus braunii race L in sediments deposited under freshwater and/or brackish conditions.