Preparation of short oligonucleotides via the phosphoramidite method using a tetrazole promoter in a catalytic manner

A facile phosphoramidite method using a tetrazole promoter in a catalytic manner has been developed for the condensation of a nucleoside 3'-phosphoramidite and a nucleoside, This method is particularly useful for a large-scale synthesis of short oligonucleotides, For example, dinucleoside phosphates are prepared on a multigram scale in 92-99% yields through the reaction of nucleoside 3'-N,N-diethylphosphoramidites (1.05 equiv) and 5'-O-free nucleosides (1.00 equiv) with 5-(p-nitrophenyl)-1H-tetrazole (NPT) (0.05 equiv) in the presence of molecular sieves 13X in acetonitrile (40 degrees C, 60 min) followed by trimethylsilyl triflate-catalyzed oxidation with bis(trimethylsilyl) peroxide in dichloromethane (40 degrees C, 10 min). The NPT-catalytic approach is also effective for the synthesis of longer deoxyribonucleotides such as d((5')CTACCTGT(3')) and 2'-5'- or 3'-5'-linked ribonucleotides.