El. Cavalieri et al., The glycosyl C-1 '-N-9 bond of deoxyadenosine and deoxyguanosine: responseto electrophilic attacks on the purinic nitrogen atoms, THEOR CH AC, 104(3-4), 2000, pp. 235-239
Self-consistent-field computations shed light on two relevant conformations
of deoxyadenosine (dA) and deoxyguanosine (dG): one with a pseudoequatoria
l C1'N9 glycosyl bond and the other, a slightly more stable one, with its C
1'N9 bond in a bisectional orientation. In dA, both the N-3 and N-7 nitroge
ns are plausible sites for electrophilic attack, but only N-7 is a plausibl
e site in dG. The addition of H+, CH3+, C2H5+ or tert-C4H9+ onto N-7 does n
ot provoke notable structural modifications and leaves the base of dA and d
G in an antiperiplanar (or nearly antiperiplanar) position with respect to
the sugar C1'O4' bond, but N-3 additions cause the base to adopt a synperip
lanar or strongly chiral position. This produces strong interactions betwee
n the purine and deoxyribose moieties, whose relief could aid the eventual
cleavage of the glycosyl bond of dA. addition of a radical cation onto N-7
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.