Structure of a thymine-thymine adduct formed by menadione photosensitization.
The structure of one of the dithymine adducts formed by near-UV photosensitization of aqueous oxygenated thymine in the presence of 2-methyl-1,4-naphthoquinone is reported. The compound, 6' beta-hydroxy-5' beta-1-[5-methylpyrimidinyl-2,4-dione]-5'- 6'-dihydrothymine, has one thymine ring (ring I) linked through the 1-nitrogen atom to the C5' atom of a second thymine, which has been hydroxylated at C6' (ring II). Crystals are monoclinic, space group I2/c, and the structure was refined to R(obs) = 0.036 for 2072 unique reflections with intensities I greater than 2.33 sigma(I). Ring I is planar, whereas ring II is not. Ring I and the OH group on ring II are cis to ring II. The planar ring I and the OH group are attached, respectively, in an equatorial and axial manner to ring II (which is in the sofa conformation). The planar rings I of close-lying pairs of molecules stack parallel to each other. The structure is held together by a hydrogen-bonding system consisting of the water molecules, the NH groups, two of the C = O groups and the OH group. The chemical formula and relative configurations at C5' and C6' are established by this analysis.
Institute for Cancer Research, Fox Chase Cancer Center, Philadelphia, PA 19111.
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D006860:Hydrogen Bonding; D008958:Models, Molecular; D017319:Photosensitizing Agents; D013941:Thymine / Q000737:chemistry*; D014812:Vitamin K
D017319:Photosensitizing Agents; D014812:Vitamin K; D013941:Thymine