Collection of Czechoslovak Chemical Communications - digital archive 

Abstract

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.