Biomimetic modeling of oxidative drug metabolism

Fluorinated isatin derivatives. Part 3. New side-chain fluoro-functionalized pyrrolidinyl sulfonyl isatins as potent caspase-3 and -7 inhibitors

Background: Dysregulation of type I programmed cell death (apoptosis) leads to a variety of diseases, among which cancer, cardiovascular and neurodegenerative disorders are the most prominent and widespread. Effector caspases such as caspases-3 and -7 get activated during the apoptotic signaling cascade and hence represent a biological target for the diagnosis and therapy of apoptosis-associated diseases. Methods: Synthesis of potent fluorinated analogs of the lead compound (S)-(+)-5-[1-(2-methoxymethylpyrrolidinyl)sulfonyl]isatin facilitates the aim-oriented identification of precursor candidates for 18F-radiofluorination resulting in radiolabeled compounds that could be employed as tracers for the specific imaging of apoptosis in vivo, using positron-emission tomography. Conclusion: Within a series of new mono-, di- and trifluoromethylated pyrrolidine ring analogs of the lead compound, high inhibition potencies were found for caspases-3 and -7 with IC50 values up to 30 and 37 nM, respectively. A new oxidative desulfurization–fluorination protocol was shown to be a versatile technique for fluorine incorporation.

A microfluidic chip for electrochemical conversions in drug metabolism studies

We have designed a microfluidic microreactor chip for electrochemical conversion of analytes, containing a palladium reference electrode and platinum working and counter electrodes. The counter electrode is placed in a separate side-channel on chip to prevent unwanted side-products appearing in the measured spectrograms. Using this chip, cyclic voltammograms are measured in volumes of 9.6 nL. Furthermore the conversion efficiency of ferricyanide is characterized using UV/vis-spectroscopy. We have obtained an on-line conversion of 97% using a flow rate of 1 microL/min. We have used the microreactor chip to study the electrochemical metabolism pathway of amodiaquine using electrochemistry (EC)-liquid chromatography (LC)-mass spectrometry (MS). We have compared our results with measurements obtained with commercially available electrochemical flow-through cells. Using our chip it was possible to obtain similar results. Therefore, we have fabricated an electrochemical cell on-chip which is used successfully in EC-UV/vis and EC-LC-MS experiments.

Metabolic studies of tetrazepam based on electrochemical simulation in comparison to in vivo and in vitro methods

During the last 2 years, the knowledge on the metabolic pathway of tetrazepam, a muscle relaxant drug, was expanded by the fact that diazepam was identified as a degradation product of tetrazepam. The present study demonstrates that this metabolic conversion, recently discovered by in vivo studies, can also be predicted on the basis of a purely instrumental method, consisting of an electrochemical cell (EC) coupled to online liquid chromatography (LC) and mass spectrometry (MS). By implementing a new electrochemical cell type into the EC-LC-MS set-up and by an enhanced oxidation potential range up to 2V, one limitation of the electrochemical metabolism simulation, the hydroxylation of alkanes and alkenes, has been overcome. Instead of commonly used flow-through cell with a porous glassy carbon working electrode, a wall-jet cell with exchangeable electrode material was used for this study. Thereby, the entire metabolic pathway of tetrazepam, in particular including the hydroxylation of the tetrazepam cyclohexenyl moiety, was simulated. The electrochemical results were not only compared to microsomal incubations, but also to in vivo experiments, by analysing urine samples from a patient after tetrazepam delivery. For structure elucidation of the detected metabolites, MS/MS experiments were performed. The comparison of electrochemistry to in vitro as well as to in vivo experiments underlines the high potential of electrochemistry as a fast screening tool in the prediction of metabolic transformations in drug development.

On-line electrochemistry/liquid chromatography/mass spectrometry for the simulation of pesticide metabolism

On-line electrochemistry/liquid chromatography/mass spectrometry (EC/LC/MS) was employed to mimic the oxidative metabolism of the fungicide boscalid. High-resolution mass spectrometry and MS/MS experiments were used to identify its electrochemical oxidation products. Furthermore, the introduction of a second electrochemical cell with reductive conditions provided important additional information on the oxidation products. With this equipment, hydroxylation, dehydrogenation, formation of a covalent ammonia adduct, and dimerization were detected after initial one-electron oxidation of boscalid to a radical cation. On-line reaction with glutathione yielded different isomeric covalent glutathione adducts. The results of the electrochemical oxidation are in good accordance with previously reported in vivo experiments, showing that EC/LC/MS is a useful tool for studying biotransformation reactions of various groups of xenobiotics.

Use of an electrochemically synthesised metabolite of a selective androgen receptor modulator for mass spectrometry-based sports drug testing

The elucidation of the metabolism of new therapeutics is a major task for pharmaceutical companies and of great interest for drug testing laboratories. The latter in particular need to determine the presence or absence of drugs or their metabolic products in urine to test for a misuse of these compounds. Commonly, in vitro or animal models are used to mimic the human metabolism and produce potential targets in amounts allowing for method development. An alternative route based on electrochemical reactions of drugs was reported to allow for the generation of selected metabolites. The utility of this approach for doping control purposes was demonstrated with a novel class of anabolic agents termed selective androgen receptor modulators (SARMs). An arylpropionamide- derived drug candidate was subjected to electrochemical "metabolism" and a major phase-I- metabolite, resulting from the elimination of a substituted phenol residue as identified in in vitro experiments, was generated and characterised using liquid chromatography/nuclear magnetic resonance spectroscopy and high resolution/high accuracy mass spectrometry. The metabolite was included in routine doping control procedures based on liquid chromatography/tandem mass spectrometry and has served as a reference compound for 5000 doping control specimens.