Sites of metabolic substitution: investigating metabolite structures utilising ion mobility and molecular modelling

Drug metabolism is an integral part of the drug development and drug discovery process. It is required to validate the toxicity of metabolites in support of safety testing and in particular provide information on the potential to form pharmacologically active or toxic metabolites. The current methodologies of choice for metabolite structural elucidation are liquid chromatography/tandem mass spectrometry (LC/MS/MS) and nuclear magnetic resonance (NMR) spectroscopy. There are, in certain cases, examples of metabolites whose sites of metabolism cannot be unequivocally identified by MS/MS alone. Utilising commercially available molecular dynamics packages and known quantum chemistry basis sets, an ensemble of lowest energy structures were generated for a group of aromatic hydroxylated metabolites of the model compound ondansetron. Theoretical collision cross–sections were calculated for each structure. Travelling‐wave ion mobility (IMS) measurements were also performed on the compounds, thus enabling experimentally derived collision cross‐sections to be calculated. A comparison of the theoretical and experimentally derived collision cross‐sections were utilised for the accurate assignment of isomeric drug metabolites. The UPLC/IMS‐MS method, described herein, demonstrates the ability to measure reproducibly by ion mobility, metabolite structural isomers, which differ in collision cross‐section, both theoretical and experimentally derived, by less than 1 Ų. This application has the potential to supplement and/or complement current methods of metabolite structural characterisation. Copyright © 2010 John Wiley & Sons, Ltd.     

Accreditation in the United Kingdom: responding to needs or 'changing the goalposts'?

 The requirements for establishing the competence of organisations involved in testing, calibration, certification and inspection, and the criteria for their assessment and accreditation are specified in international guides and European standards. As these guides and standards are intended for use by a range of organisations and accreditation bodies, operating in different disciplines, they are written in general terms in order to be widely applicable. It follows that some interpretation of the requirements is needed in order to address the different ways in which both organisations and accreditation bodies operate. This may be seen by accredited organisations as providing an opportunity for accreditation bodies to 'change the goalposts'; the needs of these organisations and of their clients must be accommodated as far as possible, without diminishing the value of, or undermining confidence in, accreditation. The United Kingdom Accreditation Service has been listening to its customers, reviewing its activities and is offering a more flexible pragmatic approach to assessment and accreditation; some of the new developments are described.     

Marine Toxins with Spiroimine Rings: Total Synthesis of Pinnatoxin A

This microreview provides a compilation of synthetic approaches and total syntheses of pinnatoxin A in a survey of the literature up to early 2010. Pinnatoxin A is the first discovered and representative member of a fascinating group of potent marine toxins that share a spiroimine subunit as a unifying structural element.     

Method of micro-sampling human dentine collagen for stable isotope analysis

Rationale

Sampling of dentine for stable carbon (δ¹³C) and nitrogen (δ¹⁵N) isotope ratios in the direction of tooth growth allows the study of temporal changes to the diet and physiological stress of an individual during tooth formation. Current methods of sampling permanent teeth using 1 mm increments provide temporal resolution of 6–9 months at best depending on the tooth chosen. Although this gives sufficient sample sizes for reliable analysis by mass spectrometry, sectioning the dentine across the incremental structures results in a rolling average of the isotope ratios. A novel method of incremental dentine collagen sampling has been developed to decrease the collagen increment size to 0.35 mm along the incremental structures, thus reducing averaging and improving the temporal resolution of short-term changes within the δ¹³C and δ¹⁵N values.

Methods

This study presents data for a MicroMill-assisted sampling method that allows for sampling at 0.35 mm width × 1 mm depth increments following the incremental growth pattern of dentine. A NewWave MicroMill was used to sample the demineralised dentine section of modern donated human third molars from Sudan and compared to data from the same teeth using the 1 mm incremental sectioning method 2 established by Beaumont et al.

Results

The δ¹³C and δ¹⁵N isotopic data showed an increased temporal resolution, with each increment providing data for 2–4 months of dentine formation.

Conclusions

The data show the potential of this method for studying dietary reconstruction, nutritional stress, and physiological change with greater temporal resolution potentially to seasonal level and with less attenuation of the δ¹³C and δ¹⁵N values than was previously possible from human dentine.