Conformational analysis of 3'-S-PO3-linked ribo- and deoxyribodinucleosidemonophosphates

The conformations of two phosphodiester-linked dinucleotides and their anal ogues containing a 3'-S-phosphorothiolate linkage were investigated using H -1 NMR spectroscopy. The phosphorus decoupled H-1 NMR spectrum of each comp ound was simulated and values for the vicinal proton-proton coupling consta nts of the sugar ring hydrogens abstracted at several different temperature s, for use in full conformational analyses. The UV absorbance temperature p rofiles of the dimers were also analysed. It was found that in both the deo xyribo and ribo analogues the sugar ring conformations are affected by the phosphorothiolate modification, with a large increase in the percentage of north-type puckering. This change is mainly due to the decrease in the infl uence of the gauche effect between the 3'-substituent and the O4'-ring oxyg en experienced when substituting an oxygen atom for the less electronegativ e sulphur atom. Copyright (C) 1999 John Wiley & Sons, Ltd.