Synthesis of 8-oxoguanosine phosphoramidite and its incorporation into Oligoribonucleotides

The detailed synthetic protocol for preparation of the phosphoramidite of an oxidatively damaged ribonucleotide, 8-oxoguanosine (8-oxo-G), and its incorporation into RNA are described. The O(6)- and N(7)-bisdiphenylcarbamoyl-protected 8-oxoguanosine phosphoramidite was synthesized as a new phosphoramidite precursor unit for the synthesis of RNA. It was successfully incorporated into the RNA sequences, and the synthesized RNAs were completely deprotected with 28% aqueous ammonia solution at 55°C for 24 hr. After purification using HPLC, they were identified by MALDI-TOF mass measurement. The base-pairing properties showed that 8-oxo-G forms base pairs not only with rC or dC in anti-conformation, but also with rA in syn conformation within the RNA duplexes or RNA/DNA heteroduplexes.