The analysis and characterization of isomeric metabolites of temelastine by the combined use of thermospray liquid chromatography/mass spectrometry and liquid chromatography/tandem mass spectrometry.

This paper describes the development and application of a combined thermospray liquid chromatographic/mass spectrometric and liquid chromatographic/tandem mass spectrometric method for distinguishing between five isomeric metabolites of Temelastine, comprising four hydroxylated metabolites and one N-oxide. The method allows the unambiguous characterization of all of the isomers either on their own or in the presence of each other. Clear results were obtained for the characterization of these metabolites in biological samples. Temelastine showed extensive phase I and phase II metabolism and the methodology was used to study the aglycone structures of the glucuronide conjugates derived from the hydroxylated metabolites. Photo-diode array ultraviolet spectroscopy was used as a complementary technique to help elucidate the site of glucuronidation in these species.

The structural identification of drug metabolites using thermospray liquid chromatography/mass spectrometry.

The structural identification of drug metabolites has been carried out using thermospray liquid chromatography/mass spectrometry (LC/MS). It has allowed the direct analysis of biological samples, in this case in vitro hepatocyte incubations, with the minimum of sample preparation. The technique also provided molecular weight information on several conjugates including glucuronides, a glutathione conjugate and one unidentified conjugate. A number of minor metabolites were also successfully identified using this method. The examples discussed in this paper illustrate the value of LC/MS in identifying unknown drug metabolites covering a wide polarity range in a complex biological mixture. However, this would not have been possible, if the interface had been unable to handle gradient separations.

Rapid structural analysis of the in vitro and in vivo metabolism of SK & F 95448 by the combined use of thermospray liquid chromatography/mass spectrometry and liquid chromatography/tandem mass spectrometry.

The thermospray liquid chromatography/mass spectrometry (LC/MS) interface has had a major impact on the direct analysis of the metabolic fate of xenobiotics in complex biological media. This paper outlines the rapidity and power of the LC/MS approach, and shows how detailed structural information can be obtained without recourse to individual compound isolation. This provides a great saving in time and effort. The additional specificity of liquid chromatography/tandem mass spectrometry is highlighted in identifying the sites of metabolic transformation. The ability to handle biological samples with little or no clean-up using wide high-performance liquid chromatographic gradients is a key feature of the success of this methodology.

Application of thermospray liquid chromatography-mass spectrometry and liquid chromatography-tandem mass spectrometry for the identification of cynomolgus monkey and human metabolites of SK & F 101468, a dopamine D2 receptor agonist.

A combination of thermospray liquid chromatography-mass spectrometry (LC-MS) and LC MS MS has allowed the structural elucidation of a number of metabolites of 4-[2-(dipropylamino)ethyl]-1,3-dihydro-2H-indol-2-one (SK & F 101468) in monkey urine. By using LC-MS-MS with the third quadrupole (Q3) set up in multiple ion detection (MID) mode, a number of metabolites were subsequently detected in the human urine and plasma samples despite very low dosing regimes. This was achieved with minimal sample preparation, e.g. for the urine sample centrifugation was the only preparative step, in order to remove particulate matter, prior to analysis. The good signal-to-noise ratio obtained for the human samples, using LC MS MS with Q3 set up for MID, raised the possibility of a LC-MS-MS quantitative assay. As a result, the detection limit of this method for SK&F 101468 when dissolved in methanol was determined to be in the region of 20 pg on column.

The disposition of SK&F L-94901, a selective thyromimetic in rat, dog and cynomolgus monkey.

SK&F L-94901 is a novel thyromimetic, structurally related to thyroxine. The absorption, distribution, excretion and metabolism of radiochemically labelled [14C]-SK&F L-94901 has been investigated in the rat, dog and cynomolgus monkey. Oral absorption from solution was low or moderate in all three species. The compound was widely distributed and rapidly excreted, although traces of radioactivity were still evident in some tissues at 7 days post-dose, particularly in the kidney where radioactivity was located in an area approximating to the corticomedullary junction. Elimination of [14C]-SK&F L-94901 was both metabolic, mediated by the liver, and renal. The major metabolic routes of elimination were via oxidative deamination to lactate and acetate derivatives.