Modelling the enantiorecognition of structurally diverse pharmaceuticals on O-substituted polysaccharide-based stationary phases.

This study aims to develop models to predict the retention, separation and elution sequence of the enantiomers of structurally diverse pharmaceuticals. More specifically, Quantitative Structure Retention Relationships (QSRR) models are built that describe the relationship between molecular descriptors and retention. Eighteen structurally diverse chiral mixtures, each consisting of a pair of enantiomers, were analyzed on two polysaccharide chiral stationary phases, Chiralcel OD-RH (cellulose tris(3,5-dimethylphenylcarbamate)) and Lux amylose-2 (amylose tris(5-chloro-2-methylphenylcarbamate)), applying either a basic or an acidic mobile phase, and their retention factor and elution sequence were determined. Both achiral and, in-house defined, chiral descriptors were used as descriptive variables to build the models. Linear regression techniques, i.e. stepwise multiple linear regression (sMLR) and partial least squares (PLS) regression, were applied to model the retention or separation as a function of the descriptors. In a first step, models were built with only achiral descriptors to model the global retention of both enantiomers of a chiral molecule. Subsequently, models were built with only chiral descriptors to predict the enantioseparation and elution sequence, and finally, models were considered with both descriptor types to predict the retention, the separation and the elution sequence of the enantiomers. The global retention was predicted well by the sMLR models with only achiral descriptors. The models with only chiral descriptors were not found suitable to predict the enantioseparation and elution sequence. Finally, the models containing both chiral and achiral descriptors allowed predicting the retention well, but their ability to predict the elution sequence and separation of the enantiomers differed widely for the chromatographic systems considered.

Modelling approaches for chiral chromatography on polysaccharide-based and macrocyclic antibiotic chiral selectors: A review.

An overview of molecular modelling approaches, related to chiral separations on polysaccharide-based and macrocyclic antibiotic chiral selectors, is presented. Both atomistic calculations and empirical fitting procedures are discussed. Atomistic calculations, such as docking and molecular dynamics can be used to model the interactions between enantiomers and the chiral stationary phase. This may help obtaining information about the chiral recognition mechanism. Conversely, in empirical fitting procedures, mathematical models for relevant separation parameters are fitted to experimental observations. The latter use theoretical molecular descriptors, calculated from the molecular structure, which are combined into a model to predict a given response, for example, retention. Such relationships, when used in chiral separations, are often called quantitative structure enantioselective retention relationships (QSERR) and an increased interest in them can be observed in the literature. Different regression models are discussed, such as multiple linear regression and partial least squares.