He Hua, Liu Yang, Sun Cheng, Wang Xiaorong, Pham-Huy Chuong
State Key Laboratory of Pollution Control and Resource Reuse, School of the Environment, Nanjing University, Nanjing 210093, China.
J Chromatogr Sci. 2004 Feb;42(2):62-6. doi: 10.1093/chromsci/42.2.62.
A reversed-phase high-performance liquid chromatography (HPLC) method with beta-cyclodextrin (beta-CD) derivatized as chiral stationary phase is used to directly separate oxazepam (Oxa) and lorazepam (Lor) enantiomers. The effect of temperature on the direct HPLC separation of Oxa and Lor enantiomers is studied for the commercially available beta-CD derivatized bonded chiral stationary phase. Chromatographic peak coalescence, appearing as a plateau between the resolved peaks, is observed at column temperatures of above 13 degrees C. Peak coalescence on the beta-CD derivatized bonded column is attributable to racemization of the Oxa enantiomer. By reducing the column temperature to 13 degrees C, the enantiomeric composition of Oxa and Lor could be determined on the chiral column. This method is expected to be useful for the resolution of 3-hydroxybenzodiazepines. At the same time, the separation mechanism is studied by calculating the thermodynamic parameters. The results reveal that the separation of Oxa and Lor enantiomer is a case of enthalpy-controlled separation, inclusion mechanism does not control the separation. The interaction between Oxa and beta-CD is an additionally strong pi-pi interaction or hydrogen bonding, but that between Lor or beta-CD derivatized is a weak pi-pi interaction or hydrogen bonding.
采用以β-环糊精（β-CD）衍生化作为手性固定相的反相高效液相色谱（HPLC）方法直接分离奥沙西泮（Oxa）和劳拉西泮（Lor）对映体。针对市售的β-CD衍生化键合手性固定相，研究了温度对Oxa和Lor对映体直接HPLC分离的影响。在高于13℃的柱温下观察到色谱峰合并，表现为分离峰之间的一个平台。β-CD衍生化键合柱上的峰合并归因于Oxa对映体的外消旋化。通过将柱温降至13℃，可在手性柱上测定Oxa和Lor的对映体组成。该方法有望用于3-羟基苯二氮䓬类药物的拆分。同时，通过计算热力学参数研究了分离机理。结果表明，Oxa和Lor对映体的分离是焓控分离的情况，包合机理不控制分离。Oxa与β-CD之间的相互作用是额外的强π-π相互作用或氢键，但Lor或β-CD衍生化之间的相互作用是弱π-π相互作用或氢键。
