X-ray diffraction studies of poly(I) . poly(C) analogues with substitution of the 2'-hydroxyl group by a fluorine atom.

From X-ray results of 2'-deoxy-2'-fluoronucleosides, characterization of the sugar conformation was summerized in comparison with the related ribo- and deoxyribonucleosides. It is emphasized that twisted forms of the sugar involving C(4')-exo puckering may be one of the characteristic feature of 2'-deoxy-2'-fluoronucleosides. In context of the characterization, molecular structure of duplex of poly(2'-deoxy-2'-fluoroinosinic acid) and poly(C), poly(dIf1) . poly(C), was analyzed by x-ray fiber diffraction methods. It is shown that the duplex has a strong preference of A'-RNA form than poly (I) . poly (C) and the preference could be interpreted by the sugar conformation of C(3') -endo-C(4')-exo pucker. Comparative studies of X-ray fiber diffraction by poly(I) . poly(C), poly(dIf1) . poly(C), poly(I) . poly(dCf1) and poly (dIf1) . poly (dCf1) are also given.