N Matthijs

Screening approach for chiral separation of pharmaceuticals: Part II. Reversed-phase liquid chromatography

A screening strategy for the rapid separation of drug enantiomers by reversed-phase liquid chromatography was developed using three cellulose/amylose stationary phases. The key point to achieve enantioselectivity is the control of the compound ionisation. Only two mobile phases, i.e. an acidic phosphate buffer (pH 2.0) containing a chaotropic salt (KPF6) and a borate buffer (pH 9.0) mixed with acetonitrile, are used in the proposed strategy. This strategy was successfully applied to a set of 37 diverse chiral pharmaceuticals. Satisfactory enantioselectivity was achieved for 89% of them.

Exploratory analysis of chromatographic fingerprints to distinguish rhizoma Chuanxiong and rhizoma Ligustici.

Identification and quality control of products of natural origin, used for preventive and therapeutical goals, is required by regulating authorities, as the World Health Organization. This study focuses on the identification and distinction of the rhizomes from two Chinese herbs, rhizoma Chuanxiong (from Ligusticum chuanxiong Hort.) and rhizoma Ligustici (from Ligusticum jeholense Nakai et Kitag), by chromatographic fingerprints. A second goal is using the fingerprints to assay ferulic acid, as its concentration provides an additional differentiation feature. Several extraction methods were tested, to obtain the highest number of peaks in the fingerprints. The best results were found using 76:19:5 (v/v/v) methanol/water/formic acid as solvent and extracting the pulverized material on a shaking bath for 15 min. Then fingerprint optimization was done. Most information about the herbs, i.e. the highest number of peaks, was observed on a Hypersil ODS column (250 mm × 4.6 mm ID, 5 μm), 1.0% acetic acid in the mobile phase and employing within 50 min linear gradient elution from 5:95 (v/v) to 95:5 (v/v) acetonitrile/water. The final fingerprints were able to distinguish rhizoma Chuanxiong and Ligustici, based on correlation coefficients combined with exploratory data analysis. The distinction was visualized using Principal Component Analysis, Projection Pursuit and Hierarchical Clustering Analysis techniques. Quantification of ferulic acid was possible in the fingerprints of both rhizomes. The time-different intermediate precisions of the fingerprints and of the ferulic acid quantification were shown to be acceptable.

Multi-way modelling of high-dimensionality electroencephalographic data

Abstract The aim of this study is to investigate whether useful information can be extracted from an electroencephalographic (EEG) data set with a very high number of modes, and to determine which model is the most appropriate for this purpose. The data was acquired during the testing phase of a new drug expected to have effect on the brain activity. The implemented test program (several patients followed in time, different doses, conditions, etc.…) led to a six-way data set. After it was confirmed that the exploratory analysis of this data set could not be handled with classical principal component analysis (PCA), and it was verified that multidimensional structure was present, multi-way methods were used to model the data. It appeared that Tucker 3 was the most suited model. It was possible to extract useful information from this high-dimensionality data. Non-relevant sources of variance (outlying patients for instance) were identified so that they can be removed before the in-depth physiological study is performed.

18 – Chiral Separations

The chiral separation of drug molecules and of their precursors, in the case of the synthesis of enantiomerically pure drugs, is one of the important application areas of HPLC in pharmaceutical analysis. Besides HPLC, capillary electrophoresis is another technique of choice for chiral separations. In this chapter we give an overview of the different modes (e.g., direct and indirect ones) by which it is possible to obtain a chiral separation in HPLC and CE. The direct approaches, i.e., those where the compound of interest is not derivatized prior to separation, are discussed in more detail since they are the most frequently used approaches nowadays. The latter approaches require the use of so-called chiral selectors to enable enantioselective recognition and enantiomeric separation. Many different molecules have been used as chiral selectors, both in HPLC and CE. They can be classified into three selectors, and iii) macromolecular selectors. The different classes are discussed, including their subclasses, while examples of chiral separations obtained with them are given. Finally, some practical guidelines about screening conditions to test the enantioselectivity of a given compound on a limited number of chromatographic systems, and about method optimization when an initial separation has already been obtained, are given briefly.