Studies of synthesis and conformation in the D-ribopyranose series

Abstract

Reactions of tribenzoyl-α- and β- D-ribopyranosyl bromides with mercuric cyanide yielded 2,3,4-tri-O-benzoyl-β- D-ribopyranosyl cyanide. Its structure and configuration were proved by reduction with LAH to 6-amino-1,5-anhydro-6-deoxy- L-allitol, deamination of which gave 1,5-anhydro- L-allitol. The latter was identified by comparison with its D-enantiomer prepared from D-allose. The ring conformation of twelve 2,3,4-tribenzoyl- D-ribopyranose derivatives, and of two related acetyl compounds have been determined by PMR spectroscopy at 60 or 100 Mc/s. The operation, or non-operation of the anomeric effect appears to be the principal factor determining which particular chair conformation (Cl or 1C) predominates. The chemical shift and coupling constant differences in these derivatives and in their conformations are discussed. The anomeric proton in tribenzoyl β- D-ribopyranosyl iodide is unusually deshielded.