title: Nucleophilic ring opening of meso-substituted 5-oxaporphyrin by oxygen, nitrogen, sulfur, and carbon nucleophiles.
abstract: Nucleophilic ring opening of 23H-[21,23-didehydro-10,15,20-tris(4-methoxycarbonylphenyl)-5-oxaporphyrinato](trifluoroacetato)zinc(II) with various nucleophiles such as alkoxide, amine, thiolate, and enolate gave 19-substituted bilinone zinc complexes, and they were isolated as free base bilinones. An X-ray crystallographic study demonstrated that the product of 5-oxaporphyrin with sodium methoxide was 21H,23H-(4Z,9Z,15Z)-1,21-dihydro-19-methoxy-5,10,15-tris(4-methoxycarbonylphenyl)bilin-1-one with a helicoidal conformation. The structure of the product of 5-oxaporphyrin with an enolate of ethyl acetoacetate was 21H,22H,24H-(4Z,9Z,15Z,19E)-19-(1-ethoxycarbonyl-2-oxopropylidene)-5,10,15-tris(4-methoxycarbonylphenyl)-1,19,21,24-tetrahydrobilin-1-one, with three inner NH groups. The product with SH(-) was also the same tautomer, 21H,22H,24H-19-thioxo-bilin-1-one, with three NH groups, while the products with RO(-), RNH2, and RS(-) nucleophiles were 21H,23H-bilin-1-ones with two inner NH groups. The first-order rate constants of the ring opening reaction of 5-oxaporphyrin with 1 M BnOH and BnSH in toluene at 303 K were 3.0 × 10(-4) and 6.1 × 10(-4) s(-1), respectively. The ratio of the rate of alcohol to thiol was much higher than that with methyl iodide, suggesting that 5-oxaporphyrin reacted as a hard electrophile in comparison to methyl iodide. UV-visible spectra of 19-substituted bilinones in CHCl3 at 298 K showed that the absorption maximum of the lower energy band was red-shifted in increasing order of O-substituted (645 nm), S-substituted (668 nm), N-substituted (699 nm), and C-substituted bilinones (706 nm).
authors.affiliation: Department of Molecular Chemistry and Biochemistry, Faculty of Science and Engineering, and Center for Nanoscience Research, Doshisha University , Kyotanabe, Kyoto 610-0321, Japan.
authors.forename: Kazuhisa
authors.initials: K
authors.lastname: Kakeya
authors.forename: Masakatsu
authors.initials: M
authors.lastname: Aozasa
authors.forename: Tadashi
authors.initials: T
authors.lastname: Mizutani
authors.forename: Yutaka
authors.initials: Y
authors.lastname: Hitomi
authors.forename: Masahito
authors.initials: M
authors.lastname: Kodera
mesh_terms: D001663:Bilirubin / Q000031:analogs & derivatives* / Q000737:chemistry*; D056831:Coordination Complexes / Q000737:chemistry*; D018360:Crystallography, X-Ray; D008968:Molecular Conformation; D015394:Molecular Structure; D009584:Nitrogen / Q000737:chemistry*; D010100:Oxygen / Q000737:chemistry*; D011166:Porphyrins / Q000737:chemistry*; D013455:Sulfur / Q000737:chemistry*; D015032:Zinc / Q000737:chemistry*
chemical_list: C121881:21-oxaporphyrin; C000592417:23H-(21,23-didehydro-10,15,20-tris(4-methoxycarbonylphenyl)-5-oxaporphyrinato)(trifluoroacetato)zinc(II); D056831:Coordination Complexes; D011166:Porphyrins; D013455:Sulfur; D015032:Zinc; D009584:Nitrogen; D001663:Bilirubin; D010100:Oxygen