Studies on high carbon number geoporphyrins by tandem mass spectrometry

Abstract

High carbon number geoporphyrins (>C 33) aetio and DPEP porphyrins were isolated from Boscan oil (Cretaceous, W. Venezuela) and analysed by tandem mass spectrometry (MS/MS). The results provide the first structural information on individual high carbon number porphyrins which were not generated from chlorobium chlorophylls. These porphyrins are present in high abundance, ca 25% of the total geoporphyrin content. There are a number of isomers of both aetio and DPEP porphyrins present, but there is a marked difference between the isomeric composition of the two classes. In addition to the true DPEP components, other geoporphyrins which bear an isocyclic ring may also be abundant. There are at least two sites on the chlorophyll a macrocycle which can be converted to extended (>C 2) alkyl substituents assuming that it is the precursor of the geoporphyrins.