1H-nmr studies on the dinucleoside monophosphates containing 2′-halogeno-2′-deoxypurinenucleosides: Effects of 2′-substitutes on conformation

Seven dinucleoside monophosphates containing 2′-halogeno-2′-deoxypurine nucleoside residue, dAfl-U, dAcl-U, dAbr-U, dAio-U, dGfl-U, and dIfl-C, were chemically synthesized and investigated by ¹H-nmr spectroscopy at 300 MHz. The sugar and backbone conformations of these compounds were analyzed by the spectral pattern of furanose proton resonances; and the extents of base-base interaction were estimated from chemical shifts and their temperature-dependent changes of base-proton resonances. It is found that the population of C_3′-endo conformer and the extent of base-base interaction decrease as the electronegativity of 2′-substituent decreases in dAx-U (x = fl, cl, br, and io) series. The C_3′-endo (³E) population and the base-base interaction in Nfl-U (N = A,G)-type dimers as well as dIfl-C are relatively higher than the corresponding natural ribo-dimers but can be recognized as grossly similar to the conformation of regular RNA dimers.