Phosphoramidate-linked oligonucleotides

Carbodi-imides are used to mediate the formation of amide linkage betwen a carboxylate and an amine or phosphoramidate linkages between a phosphate and an amine [12]. The following is essentially the method of Rockwood [13] and is modified to give a phospho-diester link between the terminal monophosphate of the oligonucleotide and the hydroxyl group of 2-hydroxyethyl disulfide (HEDS) [14]. 

In the fragment reaction, the ability of puromycin to mimic the aminoacyl-tRNA in the peptidyl transferase reaction was exploited to measure catalytic activity. Puromycin was subsequently used to design a transition-state analog for the peptidyl transferase reaction, known as the Yarns inhibitor, in which it is linked to the oligonucleotide CCdA by a phosphoramide group [73]. In a complex with the 50S ribosomal subunit, the Yarns inhibitor was used to define the catalytic site in a high-resolution crystal structure. No protein was found within 18 A of this site [74]. This result demonstrated conclusively that the catalytic activity indeed resides in the ribosomal RNA. 

Workers at Isis Pharmaceuticals have developed methods for the synthesis of chimeric oligonucleotides containing blocks of phosphodiester, phos-phorothioate and phosphoramidate intemucleosidic links. H-Phosphonate... 

There have been two reports of the synthesis of di- and oligonucleotides with P-NH-5 -phosphoramidate intemucleotide links 134.135 in one approach 135 a Staudinger-type reaction is used to form the link (Scheme 15). Another paper has reported the synthesis of building blocks for 5 -amino- and 5 -mercapto-ollgodeoxy nucleotides. 136... 

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