Optical enrichment of dansyl-rac-amino acids by formation of crystalline inclusion complexes with cyclodextrins.
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.
Jin
H L
HL
Department of Chemistry, University of Missouri-Rolla 65401.
Stalcup
A
A
Armstrong
D W
DW
D000596:Amino Acids / Q000032:analysis*; D003460:Crystallization; D003505:Cyclodextrins; D003619:Dansyl Compounds / Q000032:analysis*; D006863:Hydrogen-Ion Concentration; D007930:Leucine / Q000302:isolation & purification; D009646:Norleucine / Q000302:isolation & purification; D009904:Optical Rotation; D013056:Spectrophotometry, Ultraviolet
D000596:Amino Acids; D003505:Cyclodextrins; D003619:Dansyl Compounds; D009646:Norleucine; D007930:Leucine