After oligonucleotide synthesis:
5-Chloro-saligenyl-
N,N-diisopropylphosphoramidite (Reagent I,
C3326) is coupled to the 5'-end of the DMT-off oligonucleotide. Oxidation of the formed 5'-phosphite using the same oxidizing reagent used in standard oligonucleotide synthesis leads to support-bonded 5'-
cycloSal-oligonucleotides. Reaction with
pyrophosphate (Reagent II, B5440) yields the corresponding 5'-triphosphates. The 5'-triphosphorylated oligonucleotides are obtained after cleavage from the support in high purity and excellent yields. The whole reaction sequence was adapted to be used on a standard oligonucleotide synthesizer.