Nucleic Acids Research, Vol 26, Issue 4 1099-1106, Copyright © 1998 by Oxford University Press
K Pongracz and SM Gryaznov
The synthesis and hybridization properties of novel nucleic acid analogs,
alpha-anomeric oligodeoxyribonucleotide N3'-->P5' phosphoramidates, are
described. The alpha-3'-aminonucleoside building blocks used for
oligonucleotide synthesis were synthesized from 3'- azido-3'-deoxythymidine
or 3'-azido-2',3'-dideoxyuridine via acid catalyzed anomerization or
transglycosylation reactions. The base- protected
alpha-5'-O-DMT-3'-aminonucleosides were assembled into dimers and
oligonucleotides on a solid support using the oxidative phosphorylation
method.1H NMR analysis of the alpha-N3'-->P5' phosphoramidate dimer
structures indicates significant differences in the sugar puckering of
these compounds relative to the beta-N3'-->P5' phosphoramidates and to
the alpha-phosphodiester counterparts. Additionally, the ability of the
alpha-oligonucleotide N3'-->P5' phosphoramidates to form duplexes was
studied using thermal denaturation experiments. Thus the N3'-->P5'
phosphoramidate decamer containing only alpha-thymidine residues did not
bind to poly(A) and exhibited lower duplex thermal stability with poly(dA)
than that for the corresponding beta-anomeric phosphoramidate counterpart.
A mixed base decamer alpha-CTTCTTCCTT formed duplexes with the RNA and DNA
complementary strands only in a parallel orientation. Melting temperatures
of these complexes were significantly lower, by 34-47 or 15-25 degrees C,
than for the duplexes formed by the isosequential beta- phosphoramidates in
antiparallel and parallel orientations respectively. In contrast, the
alpha-decaadenylic N3'-->P5' phosphoramidate formed duplexes with both
RNA and DNA complementary strands with a stability similar to that of the
corresponding beta- anomeric phosphoramidate. Moreover, the
self-complementary oligonucleotide alpha-ATATATATAT did not form an
alpha:alpha homoduplex. These results demonstrate the effects of
3'-aminonucleoside anomeric configuration on sugar puckering and
consequently on stability of the duplexes.
ARTICLES
alpha-Oligodeoxyribonucleotide N3'-->P5' phosphoramidates: synthesis and duplex formation
Lynx Therapeutics Inc., 3832 Bay Center Place, Hayward, CA 94545, USA.
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