How does the 3′-phosphate drive the sugar conformation in DNA?
Abstract
While the 3JC(4′)P, 3JC(2′)P, 3JH(3′)P, 3JCH3P and 3JCH2P coupling constants in simple model systems 13–16 remain unchanged over 278–358 K, considerable changes of endocyclic 3JHH coupling constants have been found to take place, which, for the first time, unequivocally show that the change of the North (3′-endo-2′-exo)⇄ South (3′-exo-2′-endo) sugar pseudorotamer equilibrium is independent of the change of the phosphate backbone torsion, it is also found that the gauche effects between O(4′) and 3′-OPO3H- in 9–12 and between O(4′) and 3′-OPO3Et– in 13–16 are responsible for the stabilization of the South sugar conformer by ΔH°=–1.5 kJ mol–1 compared to 3′-OH in 5–8.