The enantiomers of chiral molecules differ in their biological activity, therefore there is a large interest in the production of pure enantiomers in the pharmaceutical, fine chemical, food and agrochemical industries. Molecular chirality includes a variety of closely interconnected static and dynamic stereochemical aspects that are all related to the three-dimensional structure of molecules. While static stereochemistry focuses on the spatial arrangement of atoms and groups in molecules and the corresponding chemical and physical properties, dynamic stereochemistry stresses structural changes as observed in asymmetric reactions as well as during interconversion of con¿gurational and conformational isomers. While static stereochemistry and its consequences on biological activity of drugs are well recognized and understood, the dynamic counterparts of stereochemistry and chirality are less studied and their impact on drug action are studied to a lesser extent. Diazepam (an anticonvulsant, skeletal muscle relaxant, anxiolytic drug) and other structurally related 1,4-benzodiazepin-2-ones (BDZ) lacking a chiral center exist in the form of conformational enantiomers. The two enantiomers interconvert quickly at room temperature by a ¿ring-flip¿ mechanism, and can be separated by chromatography (HPLC) on chiral stationary phases (CSPs) at low temperatures. Depending on the substitution pattern on the N1 of the azepine ring, enantiomerization rate can be slowed compared to diazepam and the half-life of the individual enantiomers raised up to the minute or hour time scales. Here we propose to investigate by chromatographic, spectroscopic, kinetic and computational methods the dynamic stereochemistry of chiral benzodiazepine-2-ones related to diazepam. The new data generated by the project can give useful insights for a better understanding of the dynamic aspects of drug-receptor interaction and guide the design of new drugs with improved properties.
Conformational enantiomers are a class of stereoisomers that are frequently encountered within chiral drugs or drug-like molecules. While stereoisomers of drugs arising from central chirality are easily produced, separated, analyzed and characterized by standard methods, conformational enantiomers pose additional challenges as they are prone to interconvert on time scales that span several orders of magnitude. Depending on the stereoelectronic and steric features of the molecular fragments close to the stereogenic axis, enantiomerization can be slow on the pharmacodynamic time-frame, and the individual enantiomers can survive longer than their duration of action. On the other hand, fast enantiomerization is potentially involved in induced-fit or conformational selection processes. The present study will offer improved and refined techniques to study these interesting phenomena, using benzodiazepines as model compounds. The project is based largely on dynamic techniques like DHPLC or DNMR that use racemic compounds to extract kinetic informations, and has the clear advantage over thermal equilibrations procedures requiring enriched samples. The two dynamic techniques are complemetary with respect to the rate of the processes investigated, and offers structural information (NMR) and the potential for physical isolation (HPLC). In addition, the project will generate chiroptical data and stereochemical assignment for this compound class, these data in turn will be useful for drug-target interaction studies and drug design. Further innovative aspects of the project are related to: 1) the ability of the DHPLC approach to yield kinetic data also for processes occurring in water-rich media and 2) the potential for studying drug-protein association using immobilized protein CSPs, and include in the study the dyamic aspects related to stereolability.