SYNTHESIS OF OLIGODEOXYRIBONUCLEOTIDE N3'-]P5' PHOSPHORAMIDATES

An efficient synthesis of the novel nucleic acid analogs oligodeoxyrib onucleotide N3'-->P5' phosphoramidates, where the 3'-oxygen is substit uted by a 3'-nitrogen, is described, Synthesis of the title compounds was accomplished by the following synthetic steps, First, 5'-O-DMT bas e-protected-3'-amino-2',3'-dideoxynucleosides were prepared, The 3'-am inopyrimidines were obtained via the corresponding 2,3'-anhydronucleos ides, whereas 3'-aminopurines were derived via 2'-deoxyxylo precursors , Second, using the prepared 3'-aminonucleosides, oligonucleotide N3'- ->P5' phosphoramidates were synthesized on a solid support, Oligonucle otide chain assembly was based upon a carbon tetrachloride-driven oxid ative coupling of the appropriately protected 3'-aminonucleosides with the 5'-H-phosphonate diester group, resulting in the formation of an internucleoside phosphoramidate link, Fully deprotected oligonucleotid e N3'-->P5' phosphoramidates were characterized by ion exchange and re versed phase HPLC, capillary and slab gel electrophoresis and by P-31 NMR analysis, Oligonucleotide N3'-->P5' phosphoramidates form remarkab ly stable duplexes with complementary RNA strands and also with themse lves, where the melting temperature of the complexes exceeded that for the parent phosphodiester compounds by 26-33 degrees C, Additionally, duplexes formed by oligonucleotide phosphoramidates with single-stran ded DNA were also more thermally stable than those formed by phosphodi esters, The described properties indicate that these compounds may hav e great potential in oligonucleotide-based diagnostics and therapeutic applications.