Porphyrin and chlorin distributions in a Late Pliocene lacustrine sediment

The tetrapyrroles in a highly immature Late Pliocene lacustrine sediment (Willershausen, Germany) show a simple distribution of both chlorin and porphyrin components as the free bases. The major components are C[sub 32] desoxophylloerythroaetioporphyrin (DPEP), a C[sub 33] bicycloalkano porphyrin, the chlorine analogue of the latter, and desoxophylloerythrin and its chlorin counterpart. The structure of the novel bicycloalkano chlorin was determined using a combination of two-dimensional phase-sensitive COSY NMR and nOe studies. Measurements of [delta][sup 13]C and other data indicate that DPEP and the bicycloalkano porphyrin were derived from the chlorophyll(s) of photosynthetic organisms utilizing a common source of CO[sub 2], probably diatoms. The occurrence of DPEP and other minor alkyl porphyrins indicates that the chlorophyll defunctionalization pathway leading to these components can occur at low temperature and was probably biologically mediated, as was the condensation reaction leading to the fused ring components.