NMR and molecular modelling studies of two photoproducts of 2′-deoxy-4- thiouridylyl-(3′,5′)- thymidine.

Abstract Preparation, spectroscopic analysis and molecular modelling of dYo(4-α;p)dTand dhs 4 U(6-α;p)dt, two photoproducts of 2′-deoxy-4-thioridylyl-(3′,5′)-thymidine are described. The 6(S) configuration of the additional chiral centre of dhs 4 U(6-α;p)dT has been determined using 2D-NMR spectroscopy. NMR data also provided conformational information on the deoxyribose and glycosidic torsion angles of dYo(4-α;p)dT and dhs 4 U(6-α;p)dT. The two fragments of dYo(4-a;p)dT have an anti type glycosidic conformation. The furanose conformation of the 5′-end is exclusively C3′-endo and that of -pdT is mainly C2′-endo. A syn/anti glycosidic torsion angle is found for both sugar in dhs 4 U(6-α;p)dT. A C2′-endo/C3′-endo conformation blend exists for the 5′-furanose whereas the second sugar prefers a C2′-endo geometry. The detailed three-dimensional reconstruction of the solution state was performed using NMR guided molecular modelling.