Structure and conformation of N-benzoyl derivatives of the biologically important 3-amino-2,3,6-trideoxy- L -hexoses and their synthetic precursor γ- and δ-lactones; a ¹ H and ¹³ C nuclear magnetic resonance study

The 3-benzoylamino-2,3,6-trideoxy-L-xylo- and L-arabino-hexoses have been shown to exist in the α- and β-pyranose forms, whereas the compounds with the L-ribo- and L-lyxo-configurations exist as mixtures of α- and β-pyranose and α- and β-furanose tautomers. All the pyranoid compounds are stable in the 1C4(L) conformation except the L-xylo-α-derivative, which exists in a conformational equilibrium with about 15% of the 4C1(L) form. The L-ribo-α- and β-furanoses adopt the 1T2(or E2) and 2T1(or 2E) conformation, respectively. The γ-lactones exist in a conformational equilibrium except the L-arabino-γ-lactone, which exists in the 4T3(or E3) conformation. The δ-lactones preferentially adopt the half-chair conformation although some distortions must be invoked for the L-arabino-δ-lactone to account for the observed coupling constants.