Ab initio Theoretical Study of the Structures of Thymine Glycol and Dihydrothymine

Abstract

The structures of all diastereoisomers of 5,6-dihydroxy-5,6-dihydrothymine (thymine glycol) and 5,6-dihydrothymine, two important DNA lesions, have been optimized with ab initio quantum chemical methods at a 6–31G level of calculations. The methyl group on C₅ of thymine glycol shows a strong preference for a pseudo axial orientation. In contrast, in 5,6-dihydrothymine a pseudo equatorial methyl is preferred. Consequently, the thymine glycol lesion is much more bulky than 5,6-dihydrothymine. This observation may explain the different biological consequences observed for the two lesions.