Study of the Mechanism of Enantioseparation. X. Comparison Study of Thermodynamic Parameters on Separation of Phenylcarbamic Acid Derivatives Using Vancomycin and Teicoplanin CSPs

Abstract

The enantiomers of 1‐methyl‐2‐piperidinoethylesters of 3‐ and 4‐alkoxyphenylcarbamic acid were separated on vancomycin (CHIROBIOTIC V) and teicoplanin (CHIROBIOTIC T) columns isothermally in the range of 0–50°C at 10°C increments, using methanol containing 17.5 mmol/L acetic acid and 4.8 mmol/L diethylamine as the mobile phase. Lower temperatures produced the expected increase in retention of the studied enantiomers and improved their separation. The retention factors k i (as well as the resolutions R ij ) were higher on the teicoplanin chiral stationary phase (CSP) compared with the vancomycin CSP. Van't Hoff plots (dependence of ln k i on 1/T) were linear within the temperature interval studied, and they also were used to determine thermodynamic data, such as the (ΔH i ) and (ΔS i ) of transfer of the enantiomers between mobile and stationary phases. From these results, it is evident that the prolongation of carbon atoms in the alkoxy‐chain has a major influence on the values of Δ(ΔS 2,1) using the vancomycin CSP, and on the values of Δ(ΔH 2,1) using the teicoplanin CSP. However, when the alkoxy‐substituent on the phenylcarbamic acid ring system is in the 3‐ and 4‐positions, there seems to be little difference in the thermodynamic parameters.