Preparative Enantioseparation Of Aromatic Acids By Counter-current Chromatography With Cyclodextrin Derivatives As Chiral Selectors

This work concentrates on the preparative enantioseparation of racemic aromatic acids by high speed counter-current chromatography?HSCCC?with?-cyclodextrin derivatives as chiral selectors.For the aim of preparative enantioseparation of racemic aromatic acids,the analytical enantioseparation of aromatic acids was performed by reverse phase high performanceliquidchromatography?HPLC?with?-cyclodextrin derivatives as chiral mobile phase additives?CMPA?,and the application and comparison of preparative HPLC and preparative HSCCC were carried out with aromatic acids as experiment racemates using?-cyclodextrin derivatives as chiral selectors.Then?-cyclodextrin derivatives were used as chiral selectors in the preparative enantioseparation of aromatic acids by HSCCC.The following thirteen racemates were used:nine mandelic acid derivatives:mandelic acid,4-bromomandelic acid,4-methoxymandelic acid,3-chloromandelicacid,4-hydroxy-3-methoxymandelicacid,2-chloromandelic acid,4-hydroxymandelic acid,?-cyclopentyl mandelic acid and?-methylmandelic acid;four?-substituted-2-phenylpropionic acids derivatives:2-phenylbutyric acid,2,3-diphenylpropionic acid,tropic acid and 2-phenyl-3-methylbutyric acid.1.The enantioseparation of mandelic acid derivatives was established by using HPLC with HP-?-CD or SBE-?-CD as the CMPA and a C₁₈reversed-phase column as the stationary phase.The main influence factors for retention factor and peak resolution were investigated,and the mechanism of inclusion complex between?-cyclodextrin derivatives and aromatic acids was studied by HPLC.Experimental results showed that the stoichiometry between the HP-?-CD host and the guest molecule was 1:1.2.The application and comparison of preparative HPLC and preparative HSCCC in preparative enantioseparation of aromatic acids were carried out with HP-?-CD or SBE-?-CDas CMPA.The results showed that 5-10 mg of racemic?-cyclopentylmandelic acid or?-methylmandelic acid could be successfully enantioseparated by preparative HPLC with HP-?-CD or SBE-?-CD as CMPA,while 250 mg ofracemic?-cyclopentylmandelicacidcouldbecompletely enantioseparated by HSCCC with HP-?-CD as CMPA.As a fact,HSCCC could be selected as a highly efficient enantioseparation alternative method with high capacity but lower cost,if a higher enantioseparation factor was available for enantiomers.3.Four racemic?-subsitituted-2-phenylpropionic acids were enantiosepared by preparative HSCCC with?-cyclodextrin derivatives as chiral selectors.The enantioseparation conditions were optimized by enantioselective liquid-liquid extraction.The two-phase solvent system was composed of n-hexane-ethyl acetate-0.10 mol/L of phosphate buffer solution at pH 2.68 containing 0.10 mol/L HP-?-CD or SBE-?-CD.Under the optimum separation conditions,100 mg of 2-phenylbutyric acid,100mg of tropic acid and 50 mg of 2,3-diphenylpropionic acid were successfully enantioseparated by HSCCC,purity of the?±?-enantiomers was over 96%with recovery of over 85%.The results of UV spectrophotometry showed that the different enantioselectivity for a certain racemate was mainly caused by different enantiorecognition between HP-?-CD and enantiomers instead of inclusion capacity between HP-?-CD and racemates.