Synthesis of DNA templates containing the fifth base, 2-amino-6-(dimethylamino)purine, for specific transcription involving unnatural base pairs

An unnatural nucleobase, pyridin-2-one (denoted as y), can be specifically incorporated into RNA opposite 2-amino-6-(dimethylamino)purine (denoted as x) in DNA templates by T7 RNA polymerase. For the easy preparation of DNA t emplates containing x, protecting groups for the 2-amino group of x were ex amined. Although the general N2 protecting groups, such as isobutyryl and a cetyl, resisted removal by the usual treatment with concentrated ammonia at 55 degreesC for 6 h, the N2-phenoxyacetyl group was successfully removed f rom the protected oligomers. This DNA synthesis would be a useful method fo r preparation of DNA templates toward enzymatic incorporation of unnatural nucleosides into RNA at desired positions.