Convenient Preparation of Pheophytin b from Plant Extract through the C7-Reduced Intermediate

Article abstract of DOI:10.1246/bcsj.70.1905

A new method for the large scale preparation of Pheophytin (=Pheo) b is presented.The difficulty in chromatographic isolation of Pheo a and b, tetrapyrrole pigments, from the large amount of plant extract was overcome by an increase in polarity of the pigment given by a selective modification of Pheo b.Treatment of plant extract containing both Pheo a and b, carotenoids, lipids, etc. with a mild reductant t-BuNH2BH3 induced selective reduction of the C7-formyl group of Pheo b, but left unaffected other carbonyl moieties of the molecules.The resulting compound 7-hydroxymethyl-Pheo b was readily separated from intact Pheo a by silica gel column chromatography.Pure Pheo b was obtained by oxidation of the 7-hydroxymethyl-Pheo b with pyridinium chlorochromate.One of the reasons why the present method is superior to the previous ones is that Pheo a was obtained simultaneously as an intact form.Another is the utility of the intermediate compound, 7-hydroxymethyl-Pheo b: as the starting material for syntheses of various compounds as well as a model of ingredients in the photosynthetic systems, such as a light-harvesting apparatus of green photosynthetic bacteria.