title: Generation of thymine radicals from 6-alkoxy-5-bromo-5,6-dihydrothymine derivatives by radiolytic reduction and photolytic dehalogenation.
abstract: The reduction of 6-alkoxy-5-bromo-5,6-dihydrothymine derivatives ( 1a, b) by hydrated electrons (e aq (-)) generated in the radiolysis of deoxygenated aqueous solution was investigated. As the major products, 1-(6'-alkoxy-5',6'-dihydrothymin-5'-yl)thymines ( 6a, b), 5-(hydroxymethyl)uracil ( 8), 6-alkoxy-5,6-dihydrothymines ( 9a, b), and thymine ( 10) were produced in sufficient yields. This product distribution is indicative of the generation of 6-alkoxy-5,6-dihydrothymin-5-yl radicals ( 2a, b) as primary intermediates that undergo elimination of alkoxide ions (RO (-)) into thymine radical cations ( 3) followed by deprotonation at the N1 to form N-centered thymine radicals ( 4). The transient absorption spectra of the 5-yl radicals 2a- c were observed by means of nanosecond laser flash photolysis of 1a, b and 5-bromo-6-ethoxy-5,6-dihydrothymidine ( 1c) in deoxygenated aqueous solution, in which homolytic C5-Br bond dissociation occurred. In contrast to the reaction characteristics in aqueous solutions, the dimeric products were not obtained in acetonitrile, probably because in-cage hydrogen abstraction from the C5 methyl group by bromine atom leads to formation of methide type intermediates 20.
authors: Department of Energy and Hydrocarbon Chemistry, Graduate School of Engineering, Kyoto University, Nishikyo-ku, Kyoto 615-8510, Japan.
authors: Mayuko
authors: M
authors: Mori
authors: Takeo
authors: T
authors: Ito
authors: Mitsunobu
authors: M
authors: Kawano
authors: Yukinari
authors: Y
authors: Takao
authors: Hiroshi
authors: H
authors: Hatta
authors: Sei-ichi
authors: S
authors: Nishimoto
mesh_terms: D005720:Gamma Rays; D010084:Oxidation-Reduction; D010782:Photolysis; D013941:Thymine / Q000031:analogs & derivatives* / Q000528:radiation effects*
chemical_list: D013941:Thymine