Dy. Ding et al., AN OLIGODEOXYRIBONUCLEOTIDE N3'-]P5' PHOSPHORAMIDATE DUPLEX FORMS AN A-TYPE HELIX IN SOLUTION, Nucleic acids research, 24(2), 1996, pp. 354-360
The solution conformations of the dinucleotide d(TT) and the modified
duplex d(CGCGAATTCGCG)(2) with N3'-->P5' phosphoramidate internucleosi
de linkages have been studied using circular dichroism (CD) and NMR sp
ectroscopy. The CD spectra indicate that the duplex conformation is si
milar to that of isosequential phosphodiester RNA, an A-type helix, an
d is different from that of DNA, a B-type helix. NMR studies of model
dimers d(TpT) and N3'-->P5' phosphoramidate d(TnpT) show that the suga
r ring conformation changes from predominantly C2'-endo to C3'-endo wh
en the 3'-phosphoester is replaced by a phosphoramidate group, Two-dim
ensional NMR (NOESY, DQF-COSY and TOCSY spectral studies of the duplex
provide additional details about the A-type duplex conformation of th
e oligonucleotide phosphoramidate and confirm that all furanose rings
of 3'-aminonucleotides adopt predominantly N-type sugar puckering.