Synthesis of Oligoribonucleotides via the Phosphite-Triester Approach on a Polymer Support

Four ribonucleoside phosphoramidites bearing 5'-O-dimethoxytrityl and 2'-O-tetrahydrofuranyl groups were synthesized with the use of bis(diisopropylamino)-methoxyphosphine in yields of 68-92%. By the same procedure, the phosphoramidite derivatives of dimers were also prepared for block condensation.We measured the time course of the condensation reaction of ribonucleoside phosphoramidite and nucleoside linked to long-chain alkylamine-controlled pore glass (LCA-CPG) resin. It took 30 min for complete coupling if the nucleoside phosphoramidite was activated with 1-H-tetrazole. However, when 5-p-nitrophenyltetrazole was used for the activation, the condensation reaction was complete within 5 min. The behavior of the block condensation reaction using dimers was similar to that of monomers in the case of 5-p-nitrophenyltetrazole activation.We synthasized oligoribonucleotides UUUU, CUCUCUU and GGCGCGCC in yields of 51, 33 and 3%, respectively, by the phosphite-triester approach by means of either stepwise or block condensation on the LCA-CPG resin.