Biomedical subjects

M R Euerby

Publications and source records attributed to M R Euerby.

12 recordsLinked to original sources

PubMed2000

Comparison of different packing methods for capillary electrochromatography columns.

A study was carried out in which 50 microm I.D. fused-silica capillaries were packed with 3 microm octadecylsilane bonded silica, from the same batch, by four methods; liquid slurry and carbon dioxide supercritical carrier, each with and without the use of an ultrasonic probe. A neutral test mixture was analysed by capillary column in reversed-phase mode, and the reproducibility of the electroosmotic flow and of migration time, column efficiency and retention factors, was determined. Initially results suggested that there was no significant difference between properties of columns packed by different methods, and a more thorough statistical evaluation confirmed this; differences observed in the column performance were attributed to random variations between replicate columns, and not between packing methods. However, the variation was least when applying the ultrasonication during liquid slurry.

Carbon Dioxide↗

PubMed1997

Step-gradient capillary electrochromatography.

The analytical benefits of using a step-gradient in capillary electrochromatography (CEC) are demonstrated. The application of step-gradient CEC to the analysis of six diuretics of widely differing lipophilicities was evaluated and shown to result in a marked reduction in the analysis time and an improvement in the peak shape for later-eluting lipophilic components. When the step-gradient approach was performed in an automated mode, the retention time RSD for repeated injections was below 1%.

Diuretics↗

PubMed1996

The S-oxidative degradation of a novel corticosteroid tipredane (INN) Part III. Detailed investigations into the disulphoxidation of tipredane.

The methyl- and ethylsulphoxide diastereoisomers (V and VI) of the corticosteroid tipredane (INN, I) have been shown to undergo further stereoselective S-oxidation to yield diastereoisomeric disulphoxides (II). Interactive computer optimisation software was employed to develop semi-preparative chromatography conditions for the isolation of the disulphoxide diastereoisomers (II) and to develop a multiselective gradient HPLC analysis of tipredane (I), the four monosulphoxide diastereoisomeric pairs (V, VI, IX and X), the four disulphoxide diastereoisomers (II), the vinyl methyl and ethyl derivatives (XI and XII) and the methylsulphone of tipredane (VII). The four diastereoisomeric disulphoxides (II) have been isolated by semi-preparative HPLC and their structures unambiguously confirmed by high resolution multinuclear NMR and mass spectrometry. The stereochemical assignment of the four disulphoxide diastereoisomers (II), the ethylsulphoxide diastereoisomeric pair (VI), and the vinyl methyl and ethylsulphoxide diastereoisomeric pairs (IX and X) was determined by degradation/synthesis and relation to the S/R-disulphoxide (II) whose stereochemistry was determined by X-ray crystallography. The monosulphoxides (V and VI) showed a high degree of site and stereoselectivity towards further S-oxidation. S-Oxidation on the C-17 beta-substituent of tipredane occurred at a rate approximately 50-fold faster than that on the alpha-substituent. The disulphoxides (II) have been shown to be susceptible to thermolysis yielding the vinyl methylsulphoxide diastereoisomers (IX) preferentially. The loss of the ethylsulphenic acid from the disulphoxide diastereoisomers (II) could be rationalised in terms of the preferred rotamers of the C-17 substituents.

Administration, Topical↗

PubMed1994

The S-oxidative degradation of a novel corticosteroid tipredane (INN). Part II--Detailed investigations into the primary S-oxidation of tipredane using achiral oxidants.

The C-17 dithioketal moiety of the corticosteroid tipredane (INN,I) has been shown to undergo site and stereoselective S-oxidations with a range of achiral oxidants. S-Oxidation was favoured on the methylthio substitutent (beta-plane) in preference to the ethylthio substituent (alpha-plane) in a ratio of 1.8-3.5:1. S-Oxidation on both substituents appeared to be stereoselective yielding an approximate ratio of 4:1 and 1:3.5-6 for the S-:R-methyl and ethylsulphoxide diastereoisomers, (II and VI) respectively. The preferred sites for S-oxidation have been explained in terms of the preferred rotamers of the C-17 substituents and the steric factors imposed on the attack of the oxidant on the lone pair of electrons at each sulphur atom. Optimized HPLC conditions using a Hypersil ODS column and an acetonitrile-0.025 M NH4OAc pH 7.2 gradient at 26 degrees C were developed to prevent degradation of the ethylsulphoxide diastereoisomers (VI) occurring during chromatographic analysis, via elimination of ethylsulphenic acid to yield the corresponding C-17 vinylmethylthio derivative (VII).

Administration, Topical↗

PubMed1992

The S-oxidative degradation of a novel corticosteroid tipredane (INN). Part I: Preliminary investigations into the hydrogen peroxide S-oxidation of tipredane.

The C-17 dithioketal moiety of the corticosteroid tipredane (INN, I) has been shown to undergo peroxide oxidation yielding an array of sulphoxide epimers. All epimers have been isolated and characterized by spectroscopic techniques. Oxidation of the C-17 beta methylthio-substituent appeared to occur exclusively giving a 4:1 ratio of the S:R configuration at the sulphoxide moiety. Both methylthiosulphoxide epimers (V) have been shown to be susceptible to thermolysis yielding the monoethylthio- derivative (VI) via elimination of methylsulphenic acid. As expected from stereochemical considerations at the C-17 position the S epimer has been found to be more susceptible than its corresponding R epimer towards thermolysis. The monomethylthiosulphoxide epimers (III) were produced in a 1:1 ratio, indicating that they were formed from the oxidation of the corresponding monomethylthio- derivative (VII). This probably arose from the elimination of ethylsulphenic acid from the alpha-ethylthiosulphoxide (VIII).

Administration, Topical↗

PubMed1990