Patent ID: 7807821

Claim:
A phosphoramidite method for the synthesis of a nucleic acid oligomer without protecting the base moiety, which comprises: reacting a 3′ or 5′ hydroxyl group of a nucleotide, optionally attached to a solid phase support, with a nucleoside phosphoramidite, a cyclonucleoside phosphoramidite, a 2′-substituted nucleoside phosphoramidite, a 4′-substituted nucleoside phosphoramidite, or a 2′,4′-di-substituted nucleoside phosphoramidite to produce a phosphodiester linkage; wherein the phosphoramidite is contacted with an activator, and the activator comprises both a) an alcohol-type compound selected from the group consisting of hydroxybenzotriazole-1-ol (HOBt), a mono-substituted or d-substituted HOBt and a di-substituted phenol and b) an acid catalyst selected from the group consisting of imidazole, tetrazole, benzimidazoletriflate (BIT), 4-ethylthiotetrazole, imidazolium triflate(trifluoromethane sulfonate) and 4,5-dicyanoimidazole.