A novel method for the structural and configurational analysis of alkyl 3,4,6-tri-O-acetyl-2-deoxy-2-hydroxyimino-α--arabino- and-lyxo-hexopyranosides, using E.P.R. spectroscopy

Abstract

Alkyl 3,4,6-tri-O-acetyl-2-deoxy-2-hydroxyimino-α--arabino- and -lyxo-hexopyranosides were oxidised with lead(IV) acetate in solution, yielding the corresponding Z- and E-isomeric iminoxy radicals ( > C=N---O), which gave very intense and persistent electron paramagnetic resonance (e.p.r.) signals. Applyina previous results for cyclohexane iminoxy radicals and the differences between the spectra of the arabino and lyxo compounds, it has been possible to assign the observed, hydrogen hyperfine structure for both Z- and E-radicals to the hexopyranoid-ring hydrogen atoms at C-1,3,4, and 5 or 6. From Z- and E-oximes, the same Z/E-equilibrium mixture of iminoxy radicals is obtained. Also, conclusions on the conformation of the hexopyranoid ring have been drawn, based on solvent and temperature effects. The specificity and sensitivity ofthe novel e.p.r. method have been used to characterise α--oximes in μg-amounts in t.l.c. The presence of other (mainly β) oximes has also been demonstrated.