Addressing the metabolic activation potential of new leads in drug discovery: a case study using ion trap mass spectrometry and tritium labeling techniques

Metabolic activation of drug candidates to electrophilic reactive metabolites that can covalently modify cellular macromolecules may result in acute and/or idiosyncratic immune system-mediated toxicities in humans. This presents a significant potential liability for the future development of these compounds as safe therapeutic agents. We present here an example of an approach where sites of metabolic activation within a new drug candidate series were rapidly identified using online liquid chromatography/multi-stage mass spectrometry on an ion trap mass spectrometer. This was accomplished by trapping the reactive intermediates formed upon incubation of compounds with rat and human liver microsomes as their corresponding glutathione conjugates and mass spectral characterization of these thiol adducts. Based on the structures of the GSH adducts identified, potential sites and mechanisms of bioactivation within the chemical structure were proposed. These metabolism studies were interfaced with iterative structural modifications of the chemical series in order to block these bioactivation sites within the molecule. This strategy led to a significant reduction in the propensity of the compounds to undergo metabolic activation as evidenced by reductions in the irreversible binding of radioactivity to liver microsomal material upon incubation of tritium-labeled compounds with this in vitro system. With the efficiency and throughput achievable with such an approach, it appears feasible to identify and address the metabolic activation potential of new drug leads during routine metabolite identification studies in an early drug discovery setting.     

Zur Fehlerermittlung bei der photometrischen Eisenbestimmung in Glassanden

Zusammenfassung Zur Bestimmung des Eisengehaltes in Glassanden eignet sich die o-Phenanthrolinmethode, da diese Methode frei ist von störenden Einflüssen der im Sand neben dem Eisen vorliegenden Fremdionen.Der Analysenfehler wird dabei aus den Eichmessungen nach den Methoden der Ausgleichsrechnung und mathematischen Statistik rechnerisch ermittelt und bei der Auswertung des Analysenergebnisses in geeigneter Form berücksichtigt.

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Summary For the determination of the iron content in glass sands the o-phenanthroline method is suitable because it is unaffected by foreign ions occuring in the sand besides iron.The analytical error is calculated from the calibrating measurements according to the methods of balancing computation and mathematical statistics, and is taken into account on interpreting the analytical result in a suitable form.

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Herrn Dr. Moritz danken wir für die Anregung zu dieser Arbeit, Herrn Dr.-Ing. habil. Klaus Doerffel für wertvolle Hinweise zur mathematischen Auswertung.     

Catalytic end-point detection in titrimetric analysis

In catalytic end-point detection, the first drop of titrant in excess is not used for a stoichiometric reaction with the indicator (as in conventional titrations) but acts as, or liberates, a catalyst for the indicator reaction. A very small excess of titrant thus suffices to catalyze large amounts of the indicator reaction mixture. Such catalytic end-points are therefore very sensitive. Terminology is discussed briefly. The various types of titration (direct, with a “brake”, reversed, indirect and substitution) and of end-point detection (visual, olfactory, photometric, thermometric and electrometric) are described. Applications of these techniques are summarized.     

Square-planar coordinated polyanions of palladium, platinum, and gold stannaborate [SnB11H11]2- coordination chemistry

The tetrasubstituted polyanions of platinum, palladium, and gold [M(SnB(11)H(11))(4)](x-) (x=6, M=Pd, Pt; x=5, M=Au) have been prepared and characterized by single-crystal X-ray diffraction, elemental analysis, IR, Raman, (11)B, and (119)Sn heteronuclear NMR spectroscopy. In the case of the platinum derivative [Bu(3)MeN](6)[Pt(SnB(11)H(11))(4)] (2) (119)Sn M?ssbauer spectroscopy has been carried out. The isolated salts are stable towards moisture and air and the complexes 2 and 3 were treated with 1,3-bis(diphenylphosphino)propane (dppp) to give the respective substitution products [Bu(3)MeN](2)[(dppp)M(SnB(11)H(11))(2)] (M=Pd, Pt).     

Application of fluorescence reactions in the ring oven segment technique

Summary The ring oven segment technique already described earlier has been applied to the determination of ng- tog-amounts of organic and inorganic substances using fluorescence reactions. The methods proposed here are based either on self-fluorescence or on appearance or disappearance of fluorescence following a chemical reaction.

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Anwendung von Fluoreszenzreaktionen in der Ringofen-Segmenttechnik

Zusammenfassung Die bereits früher beschriebene Ringofen-Segmenttechnik wurde auf die Bestimmung organischer und anorganischer Substanzen im ng- bisg-Bereich mit Hilfe von Fluoreszenzreaktionen angewendet. Die hier vorgeschlagenen Methoden beruhen entweder auf Eigenfluoreszenz oder aber auf der Bildung bzw. dem Verschwinden von Fluoreszenz nach einer chemischen Reaktion.

     

Catalytic-kinetic absorptiostat technique with the indigo carmine—hydrogen peroxide reaction as the indicator reaction

The absorptiostat method previously described is used for the catalytic-kinetic determination of sulphur compounds (sulphide, thioacetamide. thiourea and thiosulphate) in the micromolar range by means of their catalytic action for the indigo carmine—hydrogen peroxide indicator reaction. The thiosulphate catalyst is activated by iron(III) or aluminium(III); aluminium(III) is deactivated by fluoride. On this basis, iron(III) is determined in the ng range, and aluminium(III) and fluoride in the μg range.     

Delta-electron emission in fast heavy ion — atom collisions: observations of new phenomena and breakdown of common scaling laws

Double differential cross sections for the emission of Delta-electrons have been measured in fast uranium-rare gas collisions. The well-known Binary Encounter peak reveals unexpected structures for certain observation angles and its intensity increases towards smaller angles, which is in contradiction to results and scaling laws obtained by experiments with light ion impact. The observed dependencies are fairly well described by recent calculations in the framework of IA and CTMC. From systematic experimental as well as theoretical studies we can derive that the potential of the partially stripped projectile ion gives rise to rainbow and glory scattering of the target electron in the field of the projectile. The rainbow scattering is observed in the laboratory frame as pronounced interference structures, whereas the glory scattering is responsible for the steep increase of the cross sections for binary-encounter electrons towards small laboratory ejection angles. The observed effects have a dramatic influence on the commonq ² scaling laws derived from experiments with light ions. Furthermore, since the binary-encounter electrons ejected at forward angles have approximately twice the projectile velocity, these new phenomena have an important influence on the electronic stopping power of heavy ions and therefore have to be taken into account for the investigation of radiation damage by these ions e.g. in biological matter.     

Electron-electron interaction in strong electromagnetic fields: the two-electron contribution to the ground-state energy in He-like uranium

Radiative recombination transitions into the ground state of cooled bare and hydrogenlike uranium ions were measured at the storage ring ESR. By comparing the corresponding x-ray centroid energies, this technique allows for a direct measurement of the electron-electron contribution to the ionization potential in the heaviest He-like ions. For the two-electron contribution to the ionization potential of He-like uranium we obtain a value of 2248+/-9 eV. This represents the most accurate determination of two-electron effects in the domain of high-Z He-like ions, and the accuracy reaches already the size of the specific two-electron radiative QED corrections.