Synthesis of short RNA fragments by the benzotriazolyl phosphotriester approach

Analytical and experimental evidence will be presented to show that addition of a slight excess of 2-chlorophenyl-0,0-bis[1-benzotriazolyl]phosphate to a properly 2',5'-protected ribonucleoside gives an intermediate 3'-phosphotriester, which, after addition of a 2'-protected ribonucleoside, affords a dimer containing solely a 3'-5'-internucleotide linkage. The above phosphorylation procedure has been used in the synthesis of the pentamer UpApCpGpC.