A H-1-NMR SPECTROSCOPIC INVESTIGATION OF THE CONFORMATION OF THE ACETAMIDO GROUP IN SOME DERIVATIVES OF N-ACETYL-D-ALLOSAMINE AND N-ACETYL-D-GLUCOSAMINE
P. Fowler et al., A H-1-NMR SPECTROSCOPIC INVESTIGATION OF THE CONFORMATION OF THE ACETAMIDO GROUP IN SOME DERIVATIVES OF N-ACETYL-D-ALLOSAMINE AND N-ACETYL-D-GLUCOSAMINE, Helvetica Chimica Acta, 79(1), 1996, pp. 269-287
The population of the conformations obtained by rotation around the C(
2)-N and the N-C(O) bonds of AllNAc, GlcNAc, and GlcNMeAc derivatives
was investigated by H-1-NMR spectroscopy. The AllNAc-derived alpha-D-
and beta-D-pyranosides 4-7, the AllNAc diazirine 16, and the GlcNAc-de
rived axial anomers alpha-D-8-10 prefer the (Z)-anti-conformation. A s
ignificant population of the (Z)-syn-conformer in the (Z)-syn/(Z)-anti
-equilibrium for the equatorial anomers beta-D-8-10 and the GlcNAc dia
zirine 17 was evidenced by an upfield shift of H-C(2), downfield shift
s of H-C(I) and H-C(3), and by NOE measurements. The population of the
(Z)-syn-conformation depends on the substituent at C(1) and is highes
t for the hexafluoroisopropyl glycoside. The population of the (Z)-syn
-conformation of beta-D-14 decreases with increasing polarity of the s
olvent, but a substantial population is still observed for solutions i
n D2O. Whereas the alpha-D-anomers of the hemiacetal 22 and the methyl
glycoside 21 prefer the (Z)-anti-conformation in D2O solution, the co
rresponding beta-D-anomers are mixtures of the (Z)-anti-and (Z)-syn-co
nformers. The diazirine 17 self-associates in CD2Cl2 solution at conce
ntrations above 0.005m at low temperatures. The axial anomers of the G
lcNMeAc derivatives alpha-D-26- 28 are 2:1 to 3:1 mixtures of (Z)-anti
- and (E)-anti-conformers, whereas the corresponding beta-D-glycosides
are ca. 1:3:6 mixtures of(Z)-syn-, (Z)-anti-, and (E)-anti-conformers
.