Chiral hplc-cd studies of the antituberculosis drug (+)-ethambutol

Biomimetic sensor for ethambutol employing β-cyclodextrin mediated chiral copper metal organic framework and carbon nanofibers modified glassy carbon electrode

Stereochemical configuration of the drug is responsible for racemic switch with enantiomers in presence of chiral environment for human beings. Therefore, its determination in racemic and pharmaceutical samples becomes a challenge. Addressing this issue, an enantioselective electrochemical biomimetic sensor for discrimination of isomers of ethambutol (ETB) employing square wave voltammetry (SWV) is reported for the first time. For this purpose, a chiral host, β-Cyclodextrin based copper metal organic framework (CD-CuMOF) was synthesized and used for chelate complexation of ETB isomers (SS-ETB/RR-ETB). A glassy carbon electrode (GCE) is chemically modified using CD-CuMOF and carbon nanofibers (CNF) composite material to construct a sensor in the form of (CD-CuMOF-CNF-GCE). The behaviour of CD-CuMOF for ETB isomers on GCE is postulated to be an artificial enzyme model (AEM) as it mimics the catalytic activity similar to enzyme alcohol dehydrogenase for ETB. The biosensor exhibits excellent peak potential difference (ΔEp (SS-RR) = 108 mV) between ETB isomers using SWV showing a clear distinction in the racemic mixture. It showed a linear response in the range of 1.0 x 10^-7 to 1 x 10^-4 M and 5.0 x 10^-7 to 2.5 x 10^-4 M with low detection limit of 3.10 x 10^-8 M and 8.52 x 10^-8 M for RR-ETB and SS-ETB isomers respectively. The sensor was applied for the estimation of ETB isomers in racemic mixture and real samples viz., blood, urine and pharmaceutical. The CD-CuMOF is a low-cost material with higher stability than enzyme and offers an advantage for sensing and catalysis in future.

Directly coupled HPLC-NMR and HPLC-NMR-MS in pharmaceutical research and development

The methodology for the direct coupling of HPLC with NMR spectroscopy and the simultaneous double coupling of HPLC with NMR and mass spectrometry (MS) is described. Indications of the necessary technical developments to achieve this are given, and the applications of these new techniques to studies of pharmaceutical relevance are reviewed. These include studies of combinatorial chemistry libraries, synthetic chemical impurities, characterisation of drug mixtures, identification of natural products of possible pharmaceutical interest and identification of xenobiotic metabolites in human, animal and in vitro systems. In addition, HPLC-NMR has been used to investigate xenobiotic metabolite reactivity. Finally, the potential future directions of the techniques are discussed.