Synthesis and characterization of (2′-5′)ppp3′dA(p3′dA)_n, an analogue of (2′-5′)pppA(pA)_n

Abstract

The secretion of Interferon after viral infection enhances antiviral resistance in other cells characterized by increased activity of certain enzymes, a protein kinase, an endoribonuclease and a (2′-5′) (A)_n synthetase^1–6. The biochemical function of the synthetase is to convert ATP into oligonucleotides called genetically (2′-5′)pppA(pA)_n, which are characterized by the 2′,5′-phosphodiester bond (see Table 1 legend for abbreviations used). The function of these (2′-5′) oligonucleotides seems to be the activation of the latent endoribonuclease whose consequence is to inhibit protein synthesis. As part of our study of the development of the antiviral/antitumour state, we have set out to synthesize analogues of (2′-5′)pppA(pA)_n, in the expectation that these analogues would also activate a latent endoribonuclease, yet be metabolically more stable. We now describe the enzymatic conversion of 3′dATP (cordycepin 5′-triphosphate) to the 5′-triphosphate trimer, (2′-5′)ppp3′dA(p3′dA)₂, the effectiveness of the latter in the inhibition of translation and its resistance to hydrolysis by 2′,5′-phosphodiesterase⁷. The enzymatic synthesis of the 2′,5′-phosphodiester bond with 3′dATP by (2′-5′) (A)_n synthetase is an extension of our earlier report on the formation of a 2′,5′-phosphodiester bond following the incorporation of 3′dAMP from [G-³H]cordycepin into the internucleotide linkage of RNA of H.Ep. 1 cells⁸.