Liquid chromatography-mass spectrometry and related techniques for purity assessment in early drug discovery

Nonlinear behavior in preparative liquid chromatography: A method-development case study for hydroxytyrosol purification

Preparative liquid chromatography has become an important purification method owing to its advantages of high separation efficiency, good reproducibility, and low solvent consumption. Because overloading in preparative liquid chromatography must be performed to increase the throughput in a cycle, nonlinear chromatographic behavior is observed. Therefore, it is crucial to carefully study nonlinear chromatography for the purification of a given product, which facilitates the efficient optimization of the purification parameters. In this work, a method for the development of a purification method using preparative liquid chromatography based on nonlinear chromatography is proposed. Hydroxytyrosol was selected as the subject for method demonstration. Using methanol and ethanol as organic modifiers, the optimum flow rate was determined on three commercial columns entitled C₈ TDE, C₁₈ ME, and C₁₈ TDE, respectively. The curves were fitted with the van Deemter equation, with thorough analysis of the A, B, and C terms. Adsorption isotherms were subsequently studied to explore the distribution of solutes between the stationary and mobile phases at equilibrium. C₁₈ TDE, 5 vol% ethanol-water, and 0.2 mL/min were selected as the optimal separation material, elution solvent, and flow rate, respectively. Purification of hydroxytyrosol was tentatively confirmed on a C₁₈ TDE column with 1.6% sample loading, 90.98% recovery, and 98.01% purity.

Impurity profiling of drug candidates: Analytical strategies using reversed-phase and mixed-mode high-performance liquid chromatography methods

The development of new active pharmaceutical ingredients (API) requires accurate impurity profiling. Nowadays, reversed-phase HPLC (RPLC) on C18 stationary phase is the method of first choice for this task and usually employed in generic screening methods. However, this method sometimes fails, especially when the target analyte is not sufficiently retained, making impurity analysis difficult or even impossible. In such cases, a second method must be available. In the present paper, we compare the merits of RPLC on C18 phase to those of previously optimized alternative methods, based on the analysis of a large and diverse set of small-molecule drug candidates. Various strategies are considered: RPLC on C18 phase but with different mobile phase composition (acidic or basic), RPLC with a pentafluorophenyl stationary phase, or mixed-mode HPLC with both bimodal and trimodal stationary phases. First, method performances were compared in terms of response rate (proportion of compounds eluted) and peak shapes for a large set of synthetic drugs (140) with structural diversity and their orthogonality was evaluated. Then a subset of compounds (25) containing varied impurity profiles was used to compare the methods based on the capability to detect impurities and evaluate the relative purity of the API.

Capillary electrophoresis and small molecule drug discovery: a perfect match?

Capillary electrophoresis (CE) is an analytical technique based on the separation of the analytes within a capillary owing to their different electrophoretic mobilities. It is widely used in pharmaceutical analyses owing to its versatility and high separation power. However, its penetration into the drug discovery scene has been relatively limited until recent years. Several factors have contributed to this low implementation, including the maturity of liquid chromatography, the scarcity of experienced CE practitioners, and certain limitations intrinsic to the technique. Recently, instrumental improvements and the growing demand for analytical information have lead to a continuously expanding range of routine electrophoretic applications throughout pharmaceutical discovery and development. In this article we review CE fundamentals, review well-established CE methodologies in drug discovery of small molecules and discuss trends that, in our opinion, might emerge in the coming years.

An approach to speed up the isolation of hydrophilic metabolites from natural sources at semipreparative level by using a hydrophilic-lipophilic balance/mixed-mode strong cation exchange-high-performance liquid chromatography/mass spectrometry system

An approach to speed up the isolation of hydrophilic metabolites in complex natural matrixes by using a HLB/MCX-HPLC/MS system based on the retention properties of hydrophilic-lipophilic and cation exchange polymeric cartridges was developed. This methodology was successfully applied to the re-isolation of small water soluble compounds with completely different structures from two different natural extracts such as a dipeptide (vanchrobactin) from a bacterium culture broth and a pyrrolidine bearing a carboxylic acid moiety (clionapyrrolidine A) from a sponge. This method improved not only the efficiency of the isolation methodology but also the isolation time in relation to the existing methods.