Direct assignment of the absolute configuration of a distinct class of deoxyribonucleoside cyclic N-acylphosphoramidites at phosphorus by M-GOESY nuclear magnetic resonance spectroscopy.
The determination of the absolute configuration of deoxyribonucleoside cyclic N-acylphosphoramidites at phosphorus toward the synthesis of P-stereodifined phosphorothioated oligodeoxyribonucleotides is easily accomplished with computer-assisted molecular modeling and M-GOESY NMR spectroscopy. Specifically, computer-modeling diasteromeric phosphoramidite 3 has identifed a proximal (2.55 A) through-space interaction between benzylic H-5 and sugar H-2' ', which can predictably be detected by M-GOESY NMR in SP-3 but not in RP-3 because of being too distant (5.85 A). Consistent with computer-assisted modeling predictions, M-GOESY NMR spectra of SP-3 and RP-3 revealed NOE signals generated from nuclei near the selectively excited H-2' ' that are common to both SP-3 and RP-3, namely those of H-2', H-4', H-3', and H-1'. In addition, a diagnostic NOE signal at 5.5 ppm (benzylic H-5) is, as predicted, only detected in SP-3 and thus provides an unequivocal assessment of the configuration of the diastereomer at phosphorus. M-GOESY NMR data also confirm that the condensation of deoxyribonucleoside cyclic N-acylphosphoramidites with base-activated nucleosidic or nucleotidic 5'-hydroxyls proceeds via a single nucleophilic event.
Wilk
Andrzej
A
Division of Therapeutic Proteins, Center for Biologics Evaluation and Research, Food and Drug Administration, 8800 Rockville Pike, Bethesda, Maryland 20892, USA.
Grajkowski
Andrzej
A
Bull
Thomas E
TE
Dixon
Ann M
AM
Freedberg
Darón I
DI
Beaucage
Serge L
SL
D008956:Models, Chemical; D019906:Nuclear Magnetic Resonance, Biomolecular / Q000379:methods*; D009690:Nucleic Acid Conformation; D009838:Oligodeoxyribonucleotides / Q000737:chemistry*; D009943:Organophosphorus Compounds / Q000737:chemistry*; D010758:Phosphorus / Q000737:chemistry
D009838:Oligodeoxyribonucleotides; D009943:Organophosphorus Compounds; C434331:phosphoramidite; D010758:Phosphorus