Effect of the C-2 hydroxyl group on the mesomorphism of alkyl glycosides: synthesis and thermotropic behavior of alkyl 2-deoxy-d-arabino-hexopyranosides

A homologous series of alkyl 2-deoxy-α-d-arabino-hexopyranosides and alkyl 2-deoxy-β-d-arabino-hexopyranosides were synthesized, upon glycosylation of 1-alkanols (from C8 to C18 alkanols) with ethyl 2-deoxy-3,4,6-tri-O-acetyl-1-thio-d-arabino-hexopyranoside, followed by a deprotection. The thermotropic behavior of these new types of alkyl glycosides was investigated. It was observed that the β-anomers of these alkyl glycosides, bearing nonyl to tetradecyl alkyl chain are mesomorphic, exhibiting monotropic smectic A phase. In contrast, the α-anomers are all non-mesomorphic. An effort to identify the liquid crystalline behavior of binary mixtures of the α- and β-anomers was undertaken and it was found that mixtures containing equimolar amounts of the anomers exhibited mesomorphic behavior. A fine balance of the hydrophilic and hydrophobic components within the molecule is also found to be important for the alkyl 2-deoxy glycosides to form the mesophase.