Efficient activation of nucleoside phosphoramidites with 4,5-dicyanoimidazole during oligonucleotide synthesis.

A new activator for the coupling of phosphoramidites to the 5'-hydroxyl group during oligonucleotide synthesis is introduced. The observed time to complete coupling is twice as fast with 4, 5-dicyanoimidazole (DCI) as the activator, compared with 1 H -tetrazole. The effectiveness of DCI is thought to be based on its nucleophilicity. DCI is soluble in acetonitrile up to 1.1 M at room temperature and can be used as the sole coupling activator during routine automated solid phase synthesis of oligonucleotides. The addition of 0.1 M N -methylimidazole to 0.45 M 1 H -tetrazole also results in higher product yields during oligonucleotide synthesis than observed with 1 H -tetrazole alone.