Characterization of a γ-radiation-induced decomposition product of thymidine

X-ray crystallography was used to determine the structure of (-)cis(5R,6S)-5,6-dihydroxy-5,6-dihydrothymidine, a γ-radiation induced product of thymidine. The crystals belong to the orthorhombic space group P212121 and have cell dimensions a = 8.420(1) angstrom, b =10.422(1) angstrom, and 13.552(1) angstrom. The half-chair pucker of the 5,6-saturated pyrimidine ring is similar to that observed for the isolated base with the cis configuration, and is described by the Cremer-Pople parameters Q = 0.48 angstrom, θ = 62o, and φ = 272o. The conformation about the N-glycosyl bond is anti; the χ angle (-111.6(5)o) lies at one extreme of the range previously seen for nucleosides (-180 to -115o). The pucker 2T1 of the sugar (P = 151.2o; τm = 36.5o) contrasts with the O4'-endo type of pucker seen in 5,6-dihydrothymidine (0T4) and (5S)-5-hydroxy-5,6-dihydrothymidine (0T1). The conformation about the C4'--C5' bond is gauche+. The solid state structure is similar to that determined in aqueous solution by 1H nmr