SYNTHESIS OF OLIGODEOXYNUCLEOTIDES CONTAINING 6-N-([C-13]METHYL)ADENINE AND 2-N-([C-13]METHYL)GUANINE

Oligonucleotides containing 6N-([C-13]methyl)adenine and 2-N-([C-13]me thyl)guanine have been prepared for NMR studies using the deprotection step to introduce the [C-13]methylamine group. For this purpose, the use of 2'-deoxy-6-O-(pentafluorophenyl)inosine 1 and deoxy-2-fluoro-6- O-[2-(4-nitrophenyl)ethyl]inosine 2 as precursors of the N-methylated nucleosides is described. Preliminary NMR characterization of the C-13 -labelled oligonucleotides shows that the C-13 chemical shift of the m ethyl group in N-methylguanine is sensitive to duplex formation, makin g it a useful local probe.