C-13 NMR-SPECTRA OF NUCLEOSIDE 3',5'-CYCLIC PHOSPHATES - PROPOSITION FOR REVISED SIGNAL ASSIGNMENTS

On the basis of the data obtained from 13C NMR spectra of 8,2′‐S‐cycloadenosine 3′,5′‐cyclic phosphate and other nucleoside 3′,5′‐cyclic phosphate analogues, it is suggested that the published assignments of the C‐3′ and C‐4′ signals in nucleoside 3′,5′‐cyclic phosphates should be reversed. According to the revised assignments, C‐4′, which is fixed very closely to the diesterified phosphate group is markedly shielded (−12.5 to −15 ppm), and the C‐3′ signal shows a downfield shift (+6 to +8 ppm) which is comparable to that for the C‐5′ signal, for all compounds so far measured when compared with the chemical shifts for the corresponding nucleosides. The 3′,5′‐cyclic phosphates of thymidine and 8,2′‐S‐cycloadenosine, which have no α‐OH group on C‐2′, show similar chemical shift changes for the corresponding sugar carbons which are different from those observed for ribonucleoside derivatives. Copyright © 1979 Heyden & Son Ltd.