Syn- and anti-conformations of 5'-deoxy- and 5'-O-methyl-uridine 2',3'-cyclic monophosphate.

Two uridine 2',3'-cyclic monophosphate (cUMP) derivatives, 5'-deoxy (DcUMP) and 5'-O-methyl (McUMP), were studied by means of quantum chemical methods. Aqueous solvent effects were estimated based on the isodensity-surface polarized-continuum model (IPCM). Gas phase calculations revealed only slight energy differences between the syn- and anti-conformers of both compounds: the relative energies of the syn-structure are -0.9 and 0.2 kcal mol(-1) for DcUMP and McUMP, respectively. According to the results from the IPCM calculations, however, both syn-conformers become about 14 kcal mol(-1) more stable in aqueous solution than their corresponding anti-structures. Additionally, the effects of a countercation and protonation on DcUMP were studied, revealing that the syn-structure is also favored over the anti-one for these systems.