Template-directed synthesis of oligoguanylates in the presence of metal ions

Abstract

We have studied the condensation reaction of ImpG † † Abbreviations used: G, guanosine; Gp, guanosine 2′(3′)-phosphate; pG, guanosine 5′-phosphate; Gp!, guanosine cyclic 2′,3′-phosphate; ImpG, guanosine 5′-phosphorimidazolide; ImpA, adenosine 5′-phosphorimidazolide; pGp, 5′-phosphoguanosine 2′(3′)-phosphate; G 2pG, guanylyl-[2′-5′]-guanosine; G 3pG, guanylyl-[3′-5′]-guanosine; ImpGpG, 5′-phosphorimidazolide of GpG; (pG) n ( n = 2,3, …), oligomers of pG; GppG, P 1,P 2-diguanosine 5′-diphosphate; GppGpG, P 1,P 2-guanosine 5′-diphosphate derivative of guanylyl guanosine; NH 2pG, guanosine 5′-phosphoramidate; (pG) 4+, tetramer and higher oligoguanylates with 5′-terminal phosphate; poly(C), polycytidylic acid; poly(U), polyuridylic acid. on a poly(C) template, in the presence of various metal ions. With Mg 2+ as co-catalyst we confirmed that Pb 2+ and Zn 2+ are effective catalysts. A catalytic effect was also observed for Bi 3+, Sb 3+ and Mn 2+. Bi 3+ and Sn 2+, like Pb 2+, favored the formation of 2′-5′ linkages. With Mn 2+ a rather complex mixture of oligomers is formed, some of which contain pyrophosphate linkages. None of the metal ions investigated behaved like Zn 2+ in favoring the formation of the naturally occurring 3′-5′ linkages.