Commercially available 5′-DMT phosphoramidites as reagents for the synthesis of vinylphosphonate-linked oligonucleic acids

[GRAPHICS] Commercially available cyanoethyl phosphoramidites derived from T, d(C), d(A), and d(G) were hydrolyzed (1H-tetrazole, MeCN/H2O) to give the corresponding H-phosphonates in excellent yields. Palladium(0)-catalyzed cross-coupling of each of these with the thymidine-derived vinylbromide 2 afforded the corresponding vinylphosphonate-linked dimers T*T, d(C)*T, d(A)*T, and d(G)*T in modest to good yields. The T*T dimer was further elaborated to give a 5'-DMT-T*T-3'-CEP building block, and this was used in the automated synthesis of the TpT*TpT tetramer.