Extensive Method Development Research Articles

A CD-MEKC Method Utilizing a Neutral Surfactant for Enantiomeric Purity Determination of an Oxazolidinone Drug Candidate

A method based on cyclodextrin-mediated micellar electrokinetic chromatography (CD-MEKC) was developed and validated for quantification of the minor, undesired enantiomer (distomer) in the drug candidate PHA-549184, an oxazolidinone that was under development as an antibiotic. The low intrinsic solubility of the compound (0.24 mg mL−1), combined with the poor solution concentration sensitivity of capillary electrophoresis, required extensive method development to enhance the solubility of PHA-549184 while minimally degrading electrophoretic performance. A number of approaches were investigated, including inclusion of neutral and charged cyclodextrins in the background electrolyte (BGE) and addition of both charged and neutral surfactants. The final BGE contains the nonionic surfactant Brij 35: pH 2.5, 18.8 mM lithium phosphate buffer/5% highly sulfated-γ-CD/7.5 mM Brij 35. Quantitation is versus an external standard in the presence of an internal standard. The assay is selective for the distomer and proved linear with a mean recovery of 104.0% over the range 0.25–2.0%. The LOD was 0.1, and the LOQ 0.2%, both slightly higher than customary in chiral analysis, a consequence of an upper bound of 1.5 mg mL−1 placed on the sample concentration in order to maintain high efficiency for the system. Precision examined over the range 0.2–1.0% varied between 3.8% and 8.0%. No batch of drug substance registered above the detection limit for the distomer.

Primärseitige Stickoxidminderung als Beispiel für die Optimierung des Verbrennungsvorgangs in Abfallverbrennungsanlagen abschlussbericht des HGF-Strategiefonds-Projektes

Under the umbrella of the HGF Strategy Fonds and in co-operation with a number of institutes of Forschungszentrum Karlsruhe, Cutec Institute, GSF and the universities of Karlsruhe and Stuttgart a research program was conducted aiming for primary reduction of nitrogen oxides in waste incineration. The release of the major nitrogen compounds from waste components under the conditions inside a combustion chamber was identified in laboratory scale experiments. These data were the basis for modelling the NO x formation. Validating experiments took place in a batch furnace and in TAMARA. Strategies for low NO x combustion were developed in combination with bum-up and combustion control models and tested in pilot and full scale in two plants each. Extensive development of analytical and monitoring methods were important prerequisites for the successful performance of the program.

Purification of antisense oligonucleotides

Chromatography is an effective tool for obtaining high-purity synthetic oligonucleotides for a variety of end uses, including antisense drug therapy. Reversed-phase and anion-exchange chromatographies are widely used techniques for this application. While selectivity of these techniques can be modified by methods such as ion-pair RP-HPLC or affinity chromatography, these are presently used only at small scales. RP chromatography makes use of terminal hydrophobic-protecting groups to increase retention and selectivity. The main advantages of the RP method are its utility for the purification of a wide variety of modified oligonucleotide structures, its applicability across a range of terminal hydrophobic groups, such as fluorescein, and its ready use from small scale to very large scale with a minimal requirement for process development. AX-HPLC can also give high-purity products at generally higher media capacities. A more extensive method development effort is typically required for the AX-HPLC purification of AO. The AX yield per unit operation can be lower, but the isolated yield of DMT-off desalted oligonucleotide can be equal to or higher than that from RP-HPLC. As additional AO drugs enter and mature in the market, there will be a potential need for ton-scale purification processes. AX provides a way to scale up production on somewhat less expensive equipment with reduced organic solvent requirements.

Markov chain models for threshold exceedances

In recent research on extreme value statistics, there has been an extensive development of threshold methods, first in the univariate case and subsequently in the multivariate case as well. In this paper, an alternative methodology for extreme values of univariate time series is developed, by assuming that the time series is Markovian and using bivariate extreme value theory to suggest appropriate models for the transition distributions. A new likelihood representation for threshold methods is presented which we apply to a Markovian time series. An important motivation for developing this kind of theory is the possibility of calculating probability distributions for functionals of extreme events. We address this issue by showing how a theory of compound Poisson limits for additive functionals can be combined with simulation to obtain numerical solutions for problems of practical interest. The methods are illustrated by application to temperature data.

Experimental charge densities in chemistry: what is next?

After extensive development of experimental and calculational methods and concepts, experimental charge densities from diffraction measurements are now being more widely applied to chemical and physical problems. Examples are the calculation of the Coulombic contribution to molecular interactions, the study of bonding-induced changes in transition-metal ligands, the establishment of the electronic ground state of transition-metal complexes, and the calibration of theoretical calculations. Further experimental advances may be expected from the availability of the new synchrotron sources, which allow the use of smaller crystals, harder radiation, and shorter data collection times

Exploratory Strategies and Graphical Displays

Exploratory Strategies and Graphical Displays The wide availability of computing machines and peripheral equipment such as line printers and cathode-ray-tube display devices has been accompanied by an extensive reassessment and fresh development of statistical concepts and methods. Numerical and graphical analyses of data that would have been prohibitive twenty-five years ago currently can be carried out as a matter of routine. With many enormously time-consuming computational tasks virtually eliminated, attention has focused on the questions of which calculations and pictures should be requested and how they can assist a historian in understanding masses of data based on many variables.

Analytic continuation of group representations. IV

The main problem, deforming a subalgebra of a Lie algebra, is treated algebraically, requiring an extensive development of methods of defining multiplications on Lie algebra cohomology cochains. Some applications to differential geometry are also presented.