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）withβ-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）withβ-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 usingβ-cyclodextrin derivatives as chiral selectors.Thenβ-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,α-cyclopentyl mandelic acid andα-methylmandelic acid;fourβ-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-β-CD or SBE-β-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 betweenβ-cyclodextrin derivatives and aromatic acids was studied by HPLC.Experimental results showed that the stoichiometry between the HP-β-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-β-CD or SBE-β-CDas CMPA.The results showed that 5-10 mg of racemicα-cyclopentylmandelic acid orα-methylmandelic acid could be successfully enantioseparated by preparative HPLC with HP-β-CD or SBE-β-CD as CMPA,while 250 mg ofracemicα-cyclopentylmandelicacidcouldbecompletely enantioseparated by HSCCC with HP-β-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 racemicβ-subsitituted-2-phenylpropionic acids were enantiosepared by preparative HSCCC withβ-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-β-CD or SBE-β-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-β-CD and enantiomers instead of inclusion capacity between HP-β-CD and racemates.