Conformational analysis of the trinucleoside diphosphate 3'd(A2'-5'A2'-5'A). An NMR and CD study

A 500 MHz and 300 MHz NMR study of the trinucleoside diphosphate 3'd(A2'-5'A2'-5'A) is presented. In addition, circular dichroism is used to study base stacking in the title compound. The complete 1H-NMR spectral assignment of the sugar ring proton signals is given. Information about the sugar ring (N- or S-type conformation) and about the backbone geometry along C4'-C5' and C5'-O5' bonds is obtained from the NMR coupling constants. It is shown that the trimer mainly occurs in the N-N-N stacked state at low temperatures; the presence of a minor amount of N-N-S conformational sequence is indicated.