Abstract:Several examples of a new class of lariat ethers, those having steroidal side arms, are reported. These include the following carbon-pivot and nitrogen-pivot structures: 2-(3-dihydrocholesteryloxymethyl)-15-crown-5, mp 61-63 °C; N-(3-cholesteryloxycarbonylmethyl)aza-15-crown-5, mp 85-86 °C; N-(3-cholesteryloxycarbotiylmethyl)aza-18-crown-6, mp 66-67 °C; Ñ-(3-dihydrocholesteryloxycarbonylmethyl)aza-15-crown-5, mp 60-61 °C; jV-(3-dihydrocholesteryloxycarbonylmethyl)aza-18-crown-6, mp 55-56 °C; jV-(3-cholesterylo… Show more
“…Lehn and Ringsdorf have explored the use of this concept in a number of areas: photochemical control of phase changes, optical memory devices, “one-dimensional” conductors and photoconductors. The synthesis and cation binding properties of steroidal aza-crown ethers were reported by Gokel et al − also reported the synthesis of cholesteric liquid crystals bearing crown ethers.…”
The cholesteryl esters (3b and 3a) of 5-carboxy-1,3-phenylene-16-crown-5 and 5-carboxy-4,6-dichloro-1,3-phenylene-16-crown-5 show cholesteric liquid crystalline behavior but only upon heating samples that were rapidly cooled from the isotropic melt in the case of 3a and a monotropic phase for 3b. The dichloro compound 3a was formed by treatment of the corresponding acid 2 with SOCl 2 first and then cholesterol; it is believed that the SOCl 2 was contaminated with SO 2 Cl 2 , leading to the chlorination of the aromatic ring. The dichloro compound 3a was structurally characterized using single crystal X-ray diffraction. 3a crystallizes in the orthorhombic space group P2 1 2 1 2 1 with unit cell parameters of a ) 12.76(4) Å, b ) 17.511(5) Å, and c ) 18.213 Å. Use of freshly opened SOCl 2 produced 3b. The reaction of the acid 2 and cholesterol in the presence of dicyclohexylcarbodiimide yielded the acylisourea 4 as the major product (64%) along with 3b (36%) upon treatment with cholesterol. The dicholesteryl ester 9 of bis(5-carboxy-1,3-phenylene)-32-crown-10 (8a) was also synthesized, and by differential scanning calorimetry (DSC) and polarized optical microscopy no liquid crystalline behavior was observed with this system. Apparently the presence of the semirigid crown in the molecule prevents the two cholesteryl moieties from organizing in independent helices. The complexation ability of this cholesteryl crown (9) with methyl viologen bis(hexafluorophosphate) ([paraquat]‚2[PF 6 ]) (12) in acetone has been examined by 1 H NMR spectroscopy; it showed weaker binding than its simple dimethyl ester analog 8b.
“…Lehn and Ringsdorf have explored the use of this concept in a number of areas: photochemical control of phase changes, optical memory devices, “one-dimensional” conductors and photoconductors. The synthesis and cation binding properties of steroidal aza-crown ethers were reported by Gokel et al − also reported the synthesis of cholesteric liquid crystals bearing crown ethers.…”
The cholesteryl esters (3b and 3a) of 5-carboxy-1,3-phenylene-16-crown-5 and 5-carboxy-4,6-dichloro-1,3-phenylene-16-crown-5 show cholesteric liquid crystalline behavior but only upon heating samples that were rapidly cooled from the isotropic melt in the case of 3a and a monotropic phase for 3b. The dichloro compound 3a was formed by treatment of the corresponding acid 2 with SOCl 2 first and then cholesterol; it is believed that the SOCl 2 was contaminated with SO 2 Cl 2 , leading to the chlorination of the aromatic ring. The dichloro compound 3a was structurally characterized using single crystal X-ray diffraction. 3a crystallizes in the orthorhombic space group P2 1 2 1 2 1 with unit cell parameters of a ) 12.76(4) Å, b ) 17.511(5) Å, and c ) 18.213 Å. Use of freshly opened SOCl 2 produced 3b. The reaction of the acid 2 and cholesterol in the presence of dicyclohexylcarbodiimide yielded the acylisourea 4 as the major product (64%) along with 3b (36%) upon treatment with cholesterol. The dicholesteryl ester 9 of bis(5-carboxy-1,3-phenylene)-32-crown-10 (8a) was also synthesized, and by differential scanning calorimetry (DSC) and polarized optical microscopy no liquid crystalline behavior was observed with this system. Apparently the presence of the semirigid crown in the molecule prevents the two cholesteryl moieties from organizing in independent helices. The complexation ability of this cholesteryl crown (9) with methyl viologen bis(hexafluorophosphate) ([paraquat]‚2[PF 6 ]) (12) in acetone has been examined by 1 H NMR spectroscopy; it showed weaker binding than its simple dimethyl ester analog 8b.
“…Gokel and co-workers prepared the lariat ethers , 156 and 157 (Figure ) by linking hydrophobic 3-cholestanol or cholesterol to crown ethers. − The amphiphilic compound 157a was shown to form vesicles in aqueous solutions . Other vesicles, including redox-switchable molecular aggregates, were obtained by attachment of a ferrocenyl group to cholesterol and derivatives. , 34 Steroidal lariat ethers prepared by Gokel and co-workers. − …”
Section: B Steroids As Hosts In Supramolecular
Assembliesmentioning
“…So, the combination of steroids and crown ethers might be expected to bind ion species accompanied with the ordering property of the steroid moiety. Several examples of synthetic cholesteric liquid crystals having crown ethers have been reported [28][29][30][31][32][33]. Extending these studies, Marand and Gibson have published the synthesis and properties of cholesteryl esters bearing 32-and 16-membered crown ethers [34].…”
Section: Cholesteryl Esters and Liquid Crystalsmentioning
Cholesterol is one of the most widely distributed natural materials and has a unique chemical structure such as a steroid skeleton. Many types of chemical transformations of cholesterol functional groups have been developed. There is an interest in the derivatization of cholesterol and to introduce alkyl branched fatty acids into the molecule. These have found applications in the formulation of cosmetics and toiletries over the past few decades. An extraordinary interesting case is related to cholesteryl esters and their use in gene therapy delivery systems. These results can be attributed to their potential for forming cell-mimic membranes, because cholesterol is the most important building block of living cell membranes. In terms of organic synthesis, cholesterol is a strategically useful material. A typical case is remote functionalization by chemical reactions or by biocatalysis. In the future, cholesterol should be considered as a key compound, a building block for the construction of artificial lipid-like membranes by self-assembly. Also, as cholesterol is one of the members of the fat and oil family, fat and oil chemists should study and develop cholesterol chemistry even further.
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