Collect. Czech. Chem. Commun. 1981, 46, 400-408

NMR and quantum chemical study of empiric 2',3'-cyclic sulphites of nucleosides

Zdeněk Havlas, Miroslava Synáčková, Hubert Hřebabecký, Jiří Farkaš and Jiří Beránek

Institute of Organic Chemistry and Biochemistry, Czechoslovak Academy of Sciences, 166 10 Prague 6


Quantum chemical calculations were applied to ethylene sulphite regarded as a model for the structures of 2',3'-cyclic sulphites of nucleosides. The structure of epimeric 2',3'-cyclic sulphites was investigated by spectroscopic methods including 1H-NMR, 1H-NMR with benzene-induced shifts and 13C-NMR. Five-membered cyclic sulphites are configurationally stable (barrier to inversion 180 kJ mol-1). The most stable conformation of the five-membered ring is represented by a twister envelope. According to 1H- and 13C-NMR measurements S configuration was assigned to those epimers of 5'-chloro-5'-deoxy-2',3'-sulphinyluridine and 5'-chloro-5'-deoxy-2',3'-sulphinyl-6-azauridine, which exhibit positive optical rotation. The both epimeric sulphites differ in the position and integral intensity of bands related to stretching vibrations of the S=O group. The epimer, which is more conformationally flexible (S configuration), is preferentially formed.