title: Dynamic Behavior of Clobazam on High-Performance Liquid Chromatography Chiral Stationary Phases.
abstract: Clobazam, a 1,5-benzodiazepin-2,4-dione, is a chiral molecule because its ground state conformation features a nonplanar seven-membered ring lacking reflection symmetry elements. The two conformational enantiomers of clobazam interconvert at room temperature by a simple ring-flipping process. Variable temperature HPLC on the Pirkle type (R)-N-(3,5-dinitronenzoyl)phenylglycine and (R,R)-Whelk-O1 chiral stationary phases (CSPs) allowed us to separate for the first time the conformational enantiomers of clobazam and to observe peak coalescence-decoalescence phenomena due to concomitant separation and interconversion processes occurring on the same time scale. Clobazam showed temperature dependent dynamic high-performance liquid chromatography (HPLC) profiles with interconversion plateaus on the two CSPs indicative of on-column enantiomer interconversion. (enantiomerization) in the column temperature range between Tcol = 10°C and Tcol = 30°C, whereas on-column interconversion was absent at temperature close to or lower than Tcol = 5°C. Computer simulation of exchange-deformed HPLC profiles using a program based on the stochastic model yielded the apparent rate constants for the on-column enantiomerization and the corresponding free energy activation barriers. At Tcol = 20°C the averaged enantiomerization barriers, ΔG(‡), for clobazam were found in the range 21.08-21.53 kcal mol(-1) on the two CSPs. The experimental dynamic chromatograms and the corresponding interconversion barriers reported in this article are consistent with the literature data measured by DNMR at higher temperatures and in different solvents.
authors.affiliation: Department of Drug Chemistry and Technologies, Sapienza University of Rome, Rome, Italy.
authors.forename: Rocchina
authors.initials: R
authors.lastname: Sabia
authors.affiliation: Department of Drug Chemistry and Technologies, Sapienza University of Rome, Rome, Italy.
authors.forename: Michela
authors.initials: M
authors.lastname: De Martino
authors.affiliation: Department of Chemistry, University of Ferrara, Ferrara, Italy.
authors.forename: Alberto
authors.initials: A
authors.lastname: Cavazzini
authors.affiliation: Department of Drug Chemistry and Technologies, Sapienza University of Rome, Rome, Italy.
authors.forename: Claudio
authors.identifier: http://orcid.org/0000-0002-3253-3608
authors.initials: C
authors.lastname: Villani
mesh_terms: D001569:Benzodiazepines / Q000737:chemistry*; D002851:Chromatography, High Pressure Liquid / Q000379:methods*; D000078306:Clobazam; D003198:Computer Simulation; D015394:Molecular Structure; D013237:Stereoisomerism
chemical_list: D001569:Benzodiazepines; D000078306:Clobazam
keywords: atropisomers; benzodiazepines; conformational enantiomers; dynamic chiral chromatography; enantiomerization barriers