Conformations of acyclic sugar derivatives. Acetylated methyl 5-hexulosonates and keto-hexuloses

Abstract

The conformations of the methyl 2,3,4,6-tetra-O-acetyl-5-hexulosonates have been determined by analysis of their N.M.R. spectra. The arabino and lyxo isomers are preponderantly in the planar zig-zag form, whereas in the xylo and ribo isomers rotation around the C2-C3 or C3-C4 bond had occurred to a gauche arrangement in order to relieve the steric interaction (in the zig-zag form) between the acetoxy groups on C2 and C4. The location of the gauche arrangement depends on the size of the groups attached to C2 and C4. Acylated derivatives of keto-D-fructose, keto-L-sorbose, and keto-D-psicose have similar conformations.