Synthesis of Novel C4-Linked C_2-Imidazole RibonucleosidePhosphoramidite and Its Application to Probing the CatalyticMechanism of a Ribozyme

摘要

The synthesis of a novel C4-linked C2-imidazole ribonucleoside phosphoramidite (ICN-C2-PA 1) with atwo-carbon linker between imidazole and ribose moieties is described. In the phosphoramidite, POMand 2-cyanoethyl groups were selected to protect the endocyclic amine function of imidazole and the2'-hydroxyl function of D-ribose, respectively. The C2-imidazole nucleoside, a flexible structural mimicof a purine nucleobase, was successfully incorporated using ICN-C2-PA 1 into position 638 of the VSribozyme through 2'-TBDMS chemistry to study the role of G638 in general acid—base catalysis. Themodified VS ribozyme (G638C2Imz) exhibited significantly greater catalytic activity than observed withthe C0-imidazole that has no carbon atoms linking the ribose and the C4-imidazole. Imidazole nucleosideanalogues with variable spacer lengths could provide a valuable general methodology for exploring thecatalytic mechanisms of ribozymes.