A remarkable stabilization of complexes formed by 2,6-diaminopurine oligonucleotide N3 '-> P5 ' phosphoramidates.

2'-Deoxyribo- and ribo-oligonucleotide N3'-->P5' phosphoramidates containin g 2,6-diaminopurine nucleosides were synthesized. Thermal denaturation expe riments demonstrated a significant stabilization of the complexes formed by these compounds with DNA and RNA complementary strands, relative to adenos ine-containing phosphoramidate counterparts. The increase in melting temper ature of the complexes reached up to 6.9 degreesC per substitution. The obs erved stabilization was attributed to the apparent synergistic effects of M -type sugar puckering of the oligonucleotide N3'-->P5' phosphoramidate back bone, and the ability of 2,6-diaminopurine bases to form three hydrogen bon ds.