Studies into the preparation of 1-deoxy-1-thiocyanato- d-glycopyranosyl cyanides and the anomeric effect of the thiocyanate group

Abstract

The reaction of per- O-acetylated 1-bromo-1-deoxy-α- d-arabinopyranosyl cyanide with thiocyanate ions gave the corresponding 1-deoxy-1-thiocyanato-α- and β- d-arabinopyranosyl cyanides. In the reaction of the per- O-acetylated 1-bromo-1-deoxy-β- d-xylopyranosyl cyanide and its per- O-benzoylated β- d-glucopyranosyl analogue the corresponding 2-hydroxy-glycal esters formed in addition to the anomeric pair of thiocyanato-cyanides. The formation of 2,3,4,6-tetra- O-benzoyl-α- d-glucopyranosyl thiocyanate was demonstrated in the reaction of benzobromoglucose with thiocyanate ions. The equilibrium constant between 2,3,4,6-tetra- O-acetyl-1-deoxy-1-thiocyanato-α- and β- d-galactopyranosyl cyanides was determined. Based on this value, the equilibrium ratio for the 2,3,4,6-tetra- O-acetyl-α- and β- d-galactopyranosyl thiocyanates was calculated to be 94:6, and the anomeric effect of the SCN group was estimated to exceed 3 kcal/mol. X-Ray crystallographic data support endo- and exo-anomeric effects of the SCN moiety.