8-Furylimidazolo-2 `-deoxycytidine: crystal structure, packing, atropisomerism and fluorescence

Abstract

8-Furylimidazolo-2'-deoxycytidine ((fur)ImidC), C14H14N4O5, is a fluorescent analogue of 2'-deoxycytidine, also displaying the same recognition face. As a constituent of DNA, (fur)ImidC forms extraordinarily strong silver-mediated self-pairs. Crystal structure determination revealed that (fur)ImidC adopts two types of disordered residues: the sugar unit and the furyl moiety. The disorder of the sugar residue amounts to an 87:13 split. The disorder of the furyl ring results from axial chirality at the C8 -C2 `' bond connecting the nucleobase to the heterocycle. The two atropisomers are present in unequal proportions [occupancies of 0.69 (2) and 0.31 (2)], and the nucleobase and the furyl moiety are coplanar. Considering the atomic sites with predominant occupancy, an anti conformation with chi = - 147.2 (7)degrees was found at the glycosylic bond and the 2'-deoxyribosyl moiety shows a C2'-endo (S, T-2(1)) conformation, with P = 160.0 degrees. A H-1 NMR-based conformational analysis of the furanose puckering revealed that the S conformation predominates also in solution. In the solid state, two neighbouring (fur)ImidC molecules are arranged in a head-to-tail fashion, but with a notable tilt of the molecules with respect to each other. Consequently, one N-H center dot center dot center dot N hydrogen bond is found for neighbouring molecules within one layer, while a second N-H center dot center dot center dot N hydrogen bond is formed to a molecule of an adjacent layer. In addition, hydrogen bonding is observed between the nucleobase and the sugar residue. A Hirshfeld surface analysis was performed to visualize the intermolecular interactions observed in the X-ray study. In addition, the fluorescence spectra of (fur)ImidC were measured in solvents of different polarity and viscosity. (fur)ImidC responds to microenvironmental changes (polarity and viscosity), which is explained by a hindered rotation of the furyl residue in solvents of high viscosity.