Selective 2′-benzoylation at the 2′, 3′-diols of protected ribonucleosides. New solid phase synthesis of RNA and DNA-RNA mixtures

5′–0–(Dimethoxytrityl)–2′–0–(benzoyl or 3, 4, 5–trimethoxybenzoyl)–base protected ribonucleosides have been prepared by selective benzoylation of the 2′–hydroxyl group. The isomerization of the 2′–benzoates to the 3'–benzoates was studied. The protected ribonucleosides have been converted to either methylphosphochloridites or methylphosphoamidites and used to synthesize oligoribonucleotides on silica gel solid support. The synthetic RNA were deprotected and isolated using conditions that minimize inter-nucleotide cleavage. The use of 2′–benzoates as protecting groups for ribonucleosides has made it possible to easily prepare and isolate mixtures of DNA and RNA.