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Relevant academic research and scientific papers

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

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.

Synthesis and self-assembly of zinc methyl bacteriopheophorbide-f and its homolog

Zinc methyl bacteriopheophorbide-f, zinc 3-(1-hydroxyethyl)-7-formyl-chlorin, and its 31-demethyl derivative were prepared by modification of naturally occurring chlorophyll-b. The former complex was a 31-epimeric mixture and separated to pure stereoisomers by HPLC, while such a separation was unnecessary for the latter possessing the 3-hydroxymethyl group. The absolute configuration at the 31 -position of the separated samples was determined by transformation of the 7-formyl to the 7-methyl group because the 31 -stereochemistry of zinc methyl bacteriopheophorbide-d (3-(1-hydroxyethyl)-7-methyl-chlorin) has been confirmed. All the synthetic zinc chlorins self-aggregated in 0.5% (v/v) THF-hexane as well as in 6% (v/v) THF-water to form oligomers which absorbed longer-wavelength lights by the J-aggregation than the monomers in THF. Diastereomeric control in the self-aggregation of the 31-epimers was observed. The 31-demethyl compound interacted more tightly in the self-aggregates than the 31-epimers. Comparing with the corresponding 7-methyl analogs, zinc 7-formyl-chlorins have red-shifted Soret and blue-shifted Q(y) bands in both the monomeric and aggregated states. Visible, circular dichroism and resonance Raman spectra showed that the supramolecular structures of self-aggregates of the 7-formyl and 7-methyl derivatives were similar and highly ordered, and were built-up by 13-C = O···H(3-CHR)O···Zn and π-π interaction of the chlorin chromophores. The coordinatable 7-formyl group did not disturb the special bondings of the composite molecules in the self-aggregates. (C) 2000 Elsevier Science Ltd.