Isolation and structure determination of the unstable 132, 173-Cyclopheophorbide a enol from recent sediments
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We observed that the unstable 13(2), 17(3)-cyclopheophorbide a enol is one of the most abundant pigments in recent sediments (Black Sea, Mediterranean Sea, Peru margin) and here we report its isolation and structure determination (high-performance liquid chromatography, ultraviolet-visible spectrometry, mass spectrometry, and nuclear magnetic resonance). This enol has been considered as the precusor of sedimentary chlorins and porphyrins bearing either a seven + five- or a seven-membered ring system. Analysis of sediment trap samples collected from the Peru Upwelling area revealed relatively high concentrations of 13(2), 17(3)-cyclopheophorbide a enol in trap samples containing high concentrations of metabolically derived carotenoid transformation products. The abundance of 13(2), 17(3)-cyclopheophorbide a enol in sediment trap samples and recent sediments suggests that formation of an exocyclic seven-membered ring is a major diagenetic pathway for chlorophylls. Biologically mediated transformations of chlorophylls can therefore yield products not included in the classical Triebs degradation scheme for cyclic tetrapyrroles. Copyright (C) 1999 Elsevier Science Ltd.