Synthesis, purification and liquid-crystalline behaviour of several alkyl 1-thio-d-glycopyranosides

This paper describes the synthesis, purification, and liquid-crystalline behaviour of a series of alkyl 1-thioglycopyranosides. The synthesis of these derivatives was carried out via a Lewis acid mediated coupling of the fully acetylated monosaccharide with an alkanethiol. The choice of the Lewis acid depends on the configuration of AcO-2. The carbohydrate-derived surfactants exhibit thermotropic liquid-crystalline behaviour. The alkyl l-thioglycopyranosides form the expected smectic A phases upon heating. The clearing temperatures vary with alkyl chain length which is in accordance with the accepted model for the SA phase of amphiphilic carbohydrate mesogens. For the alkyl l-thiotalopyranosides, the clearing points are much lower than expected, presumably due to the formation of an intramolecular hydrogen bond in the talose moiety.