Synthesis of oligoguanylates on oligocytidylate templates.

Short oligocytidylates can act as templates for the self-condensation of guanosine 5'-phosphorimidazolide. In the absence of a catalytic metal ion or in the presence of Pb2+ a noticeable template effect is already observed with the dimer and the yield of long oligomers reaches a plateau with a hexamer template. Short templates give oligomers longer than the template length. The products are predominantly 2'-5' linked for the Pb2+-catalyzed reaction while mixed linkages are observed in the uncatalyzed reaction. In the presence of Zn2+, a template effect is first observed with the pentamer and is maximal by the heptamer. The products are predominantly 3'-5' linked. Oligomers shorter than or as long as the template are obtained in substantial yield, and longer products in much lower yields.