THE ABNORMAL CONFORMATIONS OF PYRIDINIUM α-GLYCOPYRANOSIDES

The nuclear magnetic resonance spectra for N-(tetra-O-acetyl-α-D-glucopyranosyl)-pyridinium and 4-methylpyridinium bromides and N-(tri-O-acetyl-2-deoxy-2-iodo-α-D-mannopyranosyl)-pyridinium perchlorate (V) require these compounds to exist in the 1C-conformation wherein the pyridinium group is in equatorial orientation. The highly strained condition of V was evidenced by its high reactivity as compared to the β-D-gluco diastereoisomer (IV). It is suggested that the instability of the C1-conformation is partly attributable to the reverse of the anomeric effect, and the probable importance of this phenomenon is discussed. The optical rotatory dispersion properties of these and a number of other pyridinium glycosides are presented.