Chemical synthesis of 5′-pyrophosphate and triphosphate derivatives of 3′–5′ ApA, ApG, GpA and GpG. CD study of the effect of 5′-phosphate groups on the conformation of 3′–5′ GpG

A simple, two-step method is described for the synthesis of the 5'-pyro- and triphosphate derivatives of 3'-5' ApA, ApG, GpA and GpG. The readily accessible 2'(3')-5' ApA, ApG, GpA and GpG were converted in one step to the corresponding 5'-phosphoramidate derivatives which were then transformed to the 5'-pyro- and triphosphates. CD spectra of 3'-5' pn GpG (n = 0,1,2 or 3) derivatives, measured at pH 1, indicated stabilization of the (syn) G+p (anti)G conformation by the 5'-phosphate groups.