title: Photooxidative cleavage of zinc 20-substituted chlorophyll derivatives: conformationally P-helix-favored formation of regioselectively 19-20 opened linear tetrapyrroles.
abstract: Photoreaction of zinc methyl 20-substituted meso(pyro)pheophorbide-a prepared by modifying naturally occurring chlorophyll-a in the presence of oxygen molecules gave its C19-C20 oxidative cleavage (1-carbonyl-19-oxo-bilatrienes) as the major products and the regioisomeric C1-C20 cleavage (19-carbonyl-1-oxo-bilatrienes) as the minor products. The resulting zinc complexes of linear tetrapyrroles took a helical conformation and the P-conformers were preferential over the M-stereoisomers due to the presence of their 17S,18S-chiral centers. The helical conformers (diastereomers) of the corresponding nickel complexes were separated by reverse-phase or chiral HPLC and their conformational changes were observed in solution.
authors.affiliation: Department of Bioscience and Biotechnology, Faculty of Science and Engineering, Ritsumeikan University, Kusatsu, Shiga, 525-8577, Japan. tamiaki@se.ritsumei.ac.jp
authors.forename: Hitoshi
authors.initials: H
authors.lastname: Tamiaki
authors.forename: Yukihiro
authors.initials: Y
authors.lastname: Okamoto
authors.forename: Yuji
authors.initials: Y
authors.lastname: Mikata
authors.forename: Sunao
authors.initials: S
authors.lastname: Shoji
mesh_terms: D002734:Chlorophyll / Q000031:analogs & derivatives / Q000138:chemical synthesis / Q000737:chemistry*; D000077194:Chlorophyll A; D056831:Coordination Complexes / Q000737:chemistry; D018360:Crystallography, X-Ray; D008027:Light; D008968:Molecular Conformation; D010084:Oxidation-Reduction; D013237:Stereoisomerism; D045725:Tetrapyrroles / Q000737:chemistry*; D015032:Zinc / Q000737:chemistry*
chemical_list: D056831:Coordination Complexes; D045725:Tetrapyrroles; D002734:Chlorophyll; C032623:pheophorbide a; D015032:Zinc; D000077194:Chlorophyll A