Pivaloylated glucoconjugates with heterocyclic oximes

Condensation of tetra-O-pivaloyl-α-d-glucopy-ranosyl bromide (1) with three heterocyclic oximes: 3-hydroxyiminoquinuclidine (2), 4-hydroxyiminomethyl-pyridine (3) and N-methyl-2-hydroxyiminomethylimidazole (4) leads to the β-N-glucoconjugates. Conjugates 6 and 7 were synthesized using aromatic compounds 3 and 4 as the starting material. They were obtained in two isomeric forms (E and Z) due to the restricted rotation around the oxime's double bond. The presence of E and Z isomers was proved by comparison of NMR spectra with calculated GIAO/DFT NMR spectra on B3LYP/6-31G(d) level of theory and by X-ray structural analysis of starting oxime reagents. Isomery was not observed in the quinuclidinium glucoconjugate 5.