STEROIDAL ETHER LIPIDS WITH LIQUID-CRYSTALLINE PROPERTIES

Steroidal ether lipids, e.g. various 3-beta-alkoxycholest-5-enes (cholesteryl alkyl ethers) with saturated and unsaturated alkoxy moieties having 9-30 carbon atoms or an R-(+)-13-(cyclopent-2-en-1-yl)tridecoxy moiety as well as 3-beta-[rac-1,2-di-(tridecoxy)-propoxy]-cholest-5-ene [rac-1,2-di-(tridecoxy)glyceryl cholesterylether; rac-1,2-di-O-tridecyl-3-O-(3-beta-cholest-5-enyl)-glycerol], and 3-beta-(3-beta-cholest-5-enoxy) cholest-5-ene (3-beta, 3'beta-bicholest-5-enyl ether; dicholesteryl ether), were prepared and examined for liquid crystalline properties. Both smectic A and cholesteric phases were found for most of these cholesteryl ether lipids, whereas blue phases as well as tilted and ordered smectic phases were not detected. No indication was found for the occurrence of alpha-phases. The crystal phase of the higher homologues of 3-beta-alkoxycholest-5-enes, however, corresponded to the beta-phase of lipids, as was evident from the form of the melting point curves and the modest supercooling of the melting temperatures. The cholesteryl ether lipids demonstrated liquid crystalline properties similar to cholesteryl ester lipids except for lower phase transition temperatures as well as lack of blue phases. Comparison of 3-beta-alkoxycholest-5-enes with the corresponding 3-beta-alkoxy-5-alpha-cholestanes (5-alpha-cholestanyl alkyl ethers) showed quite different phase transitions for these two structurally related classes of steryl ether lipids. Both smectic A and cholesteric phases were found for saturated 3-beta-alkoxy derivatives of the cholestane series. The appearance or non-appearance of particular mesophases can be explained by steric structure and molecular ordering of the various steroidal ether lipids.