H. Katz et al., STRUCTURE OF A THYMINE-THYMINE ADDUCT FORMED BY MENADIONE PHOTOSENSITIZATION, Photochemistry and photobiology, 57(4), 1993, pp. 609-612
The structure of one of the dithymine adducts formed by near-UV photos
ensitization of aqueous oxygenated thymine in the presence of 2-methyl
-1,4-naphthoquinone is reported. The compound, methylpyrimidinyl-2,4-d
ione]-5'-6'-dihydrothymine, has one thymine ring (ring 1) linked throu
gh the 1-nitrogen atom to the C5' atom of a second thymine, which has
been hydroxylated at C6' (ring 11). Crystals are monoclinic, space gro
up I2/c, and the structure was refined to R(obs) = 0.036 for 2072 uniq
ue reflections with intensities I greater than 2.33sigma(I). Ring I is
planar, whereas ring II is not. Ring I and the OH group on ring 11 ar
e cis to ring II. The planar ring I and the OH group are attached, res
pectively, in an equatorial and axial manner to ring II (which is in t
he sofa conformation). The planar rings I of close-lying pairs of mole
cules stack parallel to each other. The structure is held together by
a hydrogen-bonding system consisting of the water molecules, the NH gr
oups, two of the C=O groups and the OH group. The chemical formula and
relative configurations at C5' and C6' are established by this analys
is.