N-Acyl-β-D-glycopyranosylamines containing 1,4-disubstituted cyclohexyl and phenyl rings: mesomorphism and molecular structure relationships

Abstract

A variety of N-acyl-β-d-glycopyranosylamines incorporating aliphatic and/or aromatic groups has been prepared regiospecifically and in good yield in a one step reaction of the required acid chloride with commercially available d-glycosylamines. The dependence of mesophase behaviour on the degree and nature of intermolecular hydrogen bonding, as well as the size and nature of the hydrophilic and hydrophobic parts of the core and the linking groups between the two have been studied. Of the compounds investigated only the N-(4-alkoxybenzoyl)-β-d-glucopyranosylamines and N-(trans-4-pentylcyclohexylacetyl)-β-d-glucopyranosylamine exhibited an observable thermotropic liquid crystal phase. The compounds synthesized were essentially insoluble in water and no lyotropic mesomorphism was observed. It is clear that it is the number of groups on the hydrophilic carbohydrate part of the molecule capable of hydrogen bonding, after a crucial length of the hydrophobic part of the molecule has been attained, that primarily determines thermotropic mesophase behaviour. However, it has also been found that an odd number of units in the central linkage between the hydrophilic and lipophilic parts of the molecule leads to significantly higher transition temperatures than those of compounds incorporating linkages with an even number of units. X-Ray diffraction studies imply that there is no intercalation of the hydrophobic parts of the molecule in the crystalline state. However, some intercalation is thought to occur after melting to form the bilayer structure of the smectic A* phase.