Characterization of a γ-radiation-induced decomposition product of thymidine. Crystal and molecular structure of the (−)cis(5R,6S) thymidine glycol

Abstract
X-ray crystallography was used to determine the structure of (-)cis(5R,6S)-5,6-dihydroxy-5,6-dihydrothymidine, a .gamma.-radiation induced product of thymidine. The crystals belong to the orthorhombic space group P212121 and have cell dimensions a = 8.420(1) .ANG., b = 10.422(1) .ANG., and 13.552(1) .ANG.. 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 .ANG., .theta. = 62.degree., and .vphi. = 272.degree.. The conformation about the N-glycosyl bond is anti; the .chi. angle (-111.6(5).degree.) lies at extreme of the range previously seen for nucleosides (-180 to -115.degree.). The pucker 2T1 of the sugar (P = 151.2.degree.; .tau.m =36.5.degree.) 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 structre is similar to that determined in aqueous solution by 1H nmr.

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