Non-Amphiphilic Carbohydrate Liquid Crystals Containing an Intact Monosaccharide Moiety
摘要:
A chiral rigid moiety which forms the basis of a new class of non-amphiphilic carbohydrate liquid crystals has been developed. This moiety contains a fully intact glucopyranose ring embedded in a trans-decalin structure. The original carbohydrate is substituted so that only two hydroxyl groups are left, resulting in derivatives with reduced hydrophilicity. The substituents R and X-R' on the 4,6-O-ylidene beta-D-glucopyranoside are in the equatorial position and can be varied extensively, using straightforward synthetic procedures. Investigations as to the requirements for R and X-R' for inducing liquid-crystalline behavior have shown that at least one of the substituents should contain a large, polarizable aromatic moiety. An aromatic Schiff base fulfils this requirement.
The perfluorohexyl-aryl-thioethers 3 and 4, building blocks for the synthesis of the chiral target mesogens 12-15, were prepared by dithionite-mediated S-perfluoroalkylation of the p-substituted thiophenols 1 and 2. The phenolic HO- group of 3 was O-glucosylated with pentaacetyl-D-glucopyranose to 5 followed by deacetylation forming the tetrol 6 and by acetalizing with 4-(4-perfluorohexylsulfanylbenzoyloxy)-benzaldehyde-dimethylacetal (8) generating the dihydroxy-intermediate 9. The latter contains two perfluorohexylthio chains. Alternatively, the dimethylacetal 8 was linked to p-octylphenyl-beta-(D)-glucopyranoside (10) giving the mixed octyl/perfluorohexyl substituted p-octylphenyl-4,6-O-[4'-(4"-perfluorohexylsulfanyl)-benzoyloxy]-benzylidene-beta-(D)-glucopyranoside (11). Compound 8 was obtained via esterification of 4 with p-hydroxy-benzaldehyde to 4-(4-perfluorohexylsulfanyl-benzoyloxy)-benzaldehyde (7). Finally, the diols 9 and 11 were dehydroxylated to 12 and 13 followed by hydrogenation yielding 14 and 15, respectively. Tetrol 6, diols 9, 11 and the non-amphiphilic compounds 7, 12-15 are thermotropic liquid crystals. (C) 2002 Elsevier Science B.V. All rights reserved.