Equilibrium study on enantioselective distribution of amlodipine besilate enantiomers in a biphasic recognition chiral extraction system

The objective of this paper is to present the enantioselective distribution of amlodipine besilate enantiomers (ADB) in a biphasic recognition chiral extraction (BRCE) system. In the BRCE system, hydrophobic tartrate was added in organic phase and hydrophilic β-cyclodextrins in aqueous phase. Tartrate and β-cyclodextrins preferentially recognize (−)-ADB and (+)-ADB, respectively. Impacts of the type and concentration of chiral selectors, the pH value of the aqueous phase solution as well as temperature on the separation efficiency were investigated. Sulfobutyl ether-β-cyclodextrin (SBE-β-CD) and d-isobutyl tartrate (d-IBTA) were found to be the most suitable chiral selectors. By substituting the monophasic recognition chiral extraction (MRCE, with chiral selector in only one phase) system with BRCE system, the distribution ratios of the ADB enantiomers are remarkably increased with a little increase of enantioselectivity. The optimized conditions that are 5 °C of temperature, 7.2 of pH value, 0.05 mol/L of SBE-β-CD as well as 0.1 mol/L of d-IBTA are identified. The experimental results demonstrated that BRCE with strong chiral separation ability possesses good prospect in separation of enantiomers.