Long-range Spin–Spin Coupling in Pyrimidine Nucleosides

Abstract

A study has been made of the 100 MHz p.m.r. spectra of a number of pyrimidine nucleosides in aqueous solution. Long-range five-bond spin–spin coupling interactions between the H-5 and H-1′ hydrogens were noted in uridine, 2′-deoxyuridine, 6-azauridine, and 6-azacytidine and rationalized by a predominantly anti conformation for each nucleoside. The absence of a detectable five-bond coupling in orotidine suggested that the syn conformation is preferred in this instance. The relative magnitudes of the four-bond and five-bond interactions in uridine and pseudouridine were shown to be consistent with the calculated mobile π-bond orders of the C6—N1 and C6—C5 bonds of the uracil base.