Automatic mass spectrometry method development for drug discovery: application in metabolic stability assays

High-throughput metabolic screening has been requested routinely to keep pace with high-throughput organic synthesis. Liquid chromatography/tandem mass spectrometry (LC/MS/MS) with a fast gradient has become the method of choice for the task due to its sensitivity and selectivity. We have developed an automated system that consists of a robotic system for in vitro incubation and a commercially available software package for automatic MS/MS method development. A short, generic LC gradient and MS conditions that are applicable to most compounds have been developed to minimize the method development time and data analysis. This system has been used to support a number of in vitro screening assays in early drug discovery phase including microsomal stability and protein binding.     

Lösungsmitteleinfluß auf das Redoxverhalten von Bistriphenylphosphinquecksilber(II)-perchlorat

The influence of solvents on the redox behaviour of bistriphenylphosphinomercury perchlorate has been investigated by polarographic, voltammetric and potentiometric methods. The electrode process was found to be reversible in acetonitrile, propylene carbonate, N,N-dimethylformamide and dimethyl sulfoxide. An irreversible process was observed in nitromethane employing the dropping mercury electrode as well as in N,N-dimethylthioformamide and N-methyl-2-thiopyrrolidinone employing the rotating platinum electrode. Half wave potentials and diffusion coefficients have been measured. A linear relationship between theE _1/2 and the donor number (DN) of the solvent has been found for the reversible electrode reactions. Ligand replacement occurs in N,N-dimethylthioformamide and N-methyl-2-thiopyrrolidinone.

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An Alternative to Automatic Titration

Automatic titrators are designed to do exactly what a lab-technician used to do. Much more sophisticated automation of volumetry is possible. Omegaphoresis [3] in buffer-free [2] sample solutions automatically creates a stationary multiple component titration curve or zoned pattern with normalized concentrations of each separated species. An automatic measurement of each zone length yields their quantity. Simultaneous automatic detection of all the zones in a 10–20 component solution in less than 2 minutes, with a precision of ±2%, a required amount of the order of less than one nanomol and a resolution of ±pK < 0.01 replaces acid-base, complexometric, and certain types of redox-titrimetry. An option of the method allows identification of the components as well.     

Atom promotion and bond properties in the hydrogen and the lithium molecules

In the process of forming the hydrogen molecule, the interacting atoms apparently undergo significant promotion, in the course of which there occurs contraction of each atom's electronic density distribution. Although this step in itself is energetically unfavourable, it appears to be a key factor in building up the charge density in the internuclear region. In forming the lithium molecule, the atoms apparently do not undergo promotion to any significant extent. It is suggested that the difference in the degrees of atom promotion in the formation of these two molecules is an important reason for the great disparity in the strengths of their bonds.

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Zusammenfassung Beim Prozeß der Wasserstoffmolekülbildung unterliegen die wechselwirkenden Atome offensichtlich einer deutlichen Promovierung, bei deren Verlauf eine Kontraktion der Elektronendichteverteilung von jedem der beiden Atome stattfindet. Obwohl dieser Schritt selbst energetisch ungünstig ist, scheint er ein Hauptfaktor beim Aufbau der Ladungsdichte im Gebiet zwischen den Kernen zu sein. Bei der Bildung des Lithiummoleküls unterliegen die Atome offenbar keiner irgendwie wesentlichen Promovierung. Man vermutet, daß die Verschiedenheit des Grades der Atompromovierung bei der Formation in diesen beiden Molekülen ein wichtiger Grund für die große Diskrepanz ihrer Bindungskräfte ist.

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Résumé Dans le processus de formation de la molécule d'hydrogène, les atomes qui interagissent subissent apparemment une promotion significative, au cours de laquelle il se produit une contraction de la densité électronique sur chaque atome. Quoique cette étape soit en elle même énergétiquement défavorable, elle apparaît comme un facteur clé dans la construction de la densité de charge de la région internucléaire. Lors de la formation de la molécule de lithium, les atomes ne semblent pas subir de promotion significative. On suggère que la différence dans les degrés de promotion atomique pour ces deux molécules est une des raisons importantes de la grande différence dans les énergies de liaison.

     

Searching of chemical structure data bases with parallel computer hardware

The use of two types of parallel computer hardware for increasing the efficiency of processing in chemical structure data bases is discussed. The distributed array processor can be used for the clustering of 2-D chemical structure data bases by using the Jarvis—Patrick clustering method and for the ranking of output in an experimental system for substructure searching in the 3-D macromolecules in the Protein Data Bank. The Inmos transputer can be used in the construction of PC-based systems for 2-D substructure searching and in the identification of the maximal substructures common to pairs of 3-D molecules.     

Survival paths for reaction dynamics in fluctuating environments

We study rate processes in general Gaussian fluctuating environments using a path integral formalism. We derive a variational equation for the dominant survival path when the fluctuations relax exponentially or according to a stretched exponential law. In the case of a slowly varying barrier, the equilibrium regression approximation which is used by Frauenfelder and coworkers emerges. In this approximation, the survival path follows the ordinary law of relaxation to equilibrium. If the rate coefficients vary rapidly with environmental variables, however, the dominant survival paths exhibit more complex behaviour. Many phenomena analogous to geometrical optics occur. These include reflection off of rapid variations in rate constant, as well as refraction, giving paths very different from the equilibrium relaxation properties. A model with a piece-wise linear rate exhibits the basic phenomena, and the survival path equation is exactly solved for the general stretched exponential relaxing environment.     

Syntheses and structures of structurally diverse potassium beta-diketiminates derived from the ligand [(N(SiMe3)C(Ph))2CH

The compounds [K((mu-N(SiMe3)C(Ph))2CH)(thf)2]infinity 1, [K(mu-N(SiMe3)C(Ph)C(H)C(Ph)NH)L]2 [L = (thf)2 2, tmen 3], [K(mu-NSi(Me)2C(Ph)C(H)C(Ph)N)(thf)3]2 4 and [K(N(H)C(Ph))2CH](thf)0.5 5 have been prepared from K[(N(SiMe3)C(Ph))2CH] and the X-ray structures of 1-4 are reported.     

Studies on Radical Cations I. Molecular and electronic structure of [3]radialene cation produced by γ-irradiation in condensed phase

γ-Irradiation of tris (methylidene)-cyclopropane (‘[3]radialene’) 1 in a rigid electron scavenging matrix (butylchoride/i-pentane, 1:1) at 77 K leads to formation of its molecular cation 1 ⁺. Slight softening of the matrix by a temperature increase of 3–5 K results in formation of a newly absorbing species, tentatively assigned arising from structrral relaxation of 1 ⁺ by π-bond rotation: