Preparation and temperature-dependent enantioselectivities of homochiral phenolic crown ethers having aryl chiral barriers: thermodynamic parameters for enantioselective complexation with chiral amines |
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Institution: | 1. School of Pharmacy, South University, Savannah, Georgia;2. Department of Pharmacy Practice, Western New England University, Springfield, Massachusetts;1. College of Pharmaceutical Science, Zhejiang University of Technology, Chaowang Road 18, Chaohui No. 6 District, Hangzhou 310032, China;2. Pharmaceutical Informatics Institute, College of Pharmaceutical Sciences, Zhejiang University, Hangzhou 310023, China |
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Abstract: | Homochiral crown ether (S,S)-1 containing 1-naphthyl groups as chiral barriers together with the phenol moiety was prepared by using (S)-3 as a chiral subunit which was resolved in enantiomerically pure form by lipase-catalyzed enantioselective acylation of (±)-3. Homochiral phenolic crown ether (S,S)-2, containing phenyl groups as chiral barriers, was also prepared from (S)-5 which was derived from (S)-mandelic acid. The association constants for their complexes with chiral amines in CHCl3 were determined at various temperatures by the UV–visible spectroscopic method demonstrating that the crown ethers (S,S)-1 and (S,S)-2 displayed the large ΔR−SΔG values of 6.2 and 6.4 kJ mol−1, respectively, towards the amine 21 at 15°C. Thermodynamic parameters for complex formation were also determined and a linear correlation between TΔR−SΔS and ΔR−SΔH values was observed. |
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