Novel phosphoramidite monomer for the site-selective incorporation of a diastereochemically pure phosphoramidate to oligonucleotide

Diastereochemically pure dithymidine phosphoramidates have been site-selectively incorporated into synthetic oligonucleotides by a phosphoramidite technique. By using the terminal amino residues bound to the chiral phosphoramidates, various functional residues have been attached to the oligonucleotides in stereospecific ways. No racemization takes place during these procedures. The dependence of the duplex- and tripler-forming activities of these tethered and functionalized oligonucleotides on the diastereochemistry of the phosphoramidate is shown.