Exclusive observation of the (13R)-enantiomer of chlorophyll-c from a diatom Chaetoseros calcitrans.

Chiral high-performance liquid-chromatography (HPLC) for quantitative analysis of optically active chlorophyll(Chl)-c molecules, which are seen in many marine photosynthetic organisms, was developed. Chls-c have a single asymmetric carbon at the 13(2)-position, so their stereoisomers are (13(2)R)- and (13(2)S)-enantiomers. After the separation of each enantiomer, the stereochemistry was unambiguously characterized using its circular dichroism spectrum in comparison with that of the structure-related compound, protochlorophyllide-a. Moreover, Chls-c were carefully extracted from the cells of a diatom Chaetoseros calcitrans without racemization and were subjected to the chiral HPLC. The results clearly demonstrated that naturally occurring Chl-c molecules are enantiomerically pure (13(2)R)-forms, which are generally found in photosynthetically active chlorophyllous pigments.