Optical enrichment of dansyl-rac-amino acids by formation of crystalline inclusion complexes with cyclodextrins |
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Authors: | H L Jin A Stalcup D W Armstrong |
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Institution: | Department of Chemistry, University of Missouri-Rolla 65401. |
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Abstract: | Optical enrichment from racemic dansyl-leucine, dansyl-norleucine, and dansyl-phenylalanine with both beta- and gamma-cyclodextrins in water is reported. Initial crystallization yielded the dansyl-L-Leucine isomer complexed in excess with beta-cyclodextrin with an optical purity of 62-78% depending on experimental conditions. The optical purities obtained for L-norleucine and L-phenylalanine were 71 and 64%, respectively. The optical purity can be increased with continued recrystallization. The dansyl-D-leucine isomer was obtained in the mother liquor with an optical purity of 54-93% depending on experimental conditions. The optical purities obtained for D-norleucine and D-phenylalanine were 72 and 58%. The optical purity of the isomer depended on the molar ratio of host:guest and the pH value of the solution. Optimum enrichment of both enantiomers was achieved with host:guest ratios of 2:1 and 3:1. Although maximum crystalline yield of the dansyl-leucine/CD inclusion complex was obtained at a pH of 3.5, optical purity of both enantiomers was less than that obtained at other pHs. The influence of the molar ratio of host:guest and the pH value of the solution are discussed. This method is suitable for large-scale enantiomeric separations. |
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Keywords: | resolution by crystallization racemic mixture dansyl-D-leucine dansyl-L-leucine dansyl-D-norleucine dansyl-L-norleucine dansyl-D-phenylalanine dansyl-L-phenylalanine β-cyclodextrin γ-cyclodextrin |
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