Self-consistent-field computations shed light on two relevant conformations of deoxyadenosine (dA) and deoxyguanosine (dG): one with a pseudoequatorial C1′N9 glycosyl bond and the other, a slightly more stable one, with its C1′N9 bond in a bisectional orientation. In dA, both the N3 and N7 nitrogens are plausible sites for electrophilic attack, but only N7 is a plausible site in dG. The addition of H+, CH+3, C2H+5 or tert-C4H+9 onto N7 does not provoke notable structural modifications and leaves the base of dA and dG in an antiperiplanar (or nearly antiperiplanar) position with respect to the sugar C1′O4′ bond, but N3 additions cause the base to adopt a synperiplanar or strongly chiral position. This produces strong interactions between the purine and deoxyribose moieties, whose relief could aid the eventual cleavage of the glycosyl bond of dA. Addition of a radical cation onto N7 reduces the dissociation energy of the glycosyl bond by an estimated 8 kcal mol-1 in dA and 4 kcal mol-1 in dG - a bond weakening likely to concur to a depurination of DNA induced by radical cations.
- Glycosyl CN bond
ASJC Scopus subject areas
- Physical and Theoretical Chemistry