A mass spectrometric study on meloxicam metabolism in horses and the fungus Cunninghamella elegans,and the relevance of this microbial system as a model of drug metabolism in the horse

This paper describes a study where the metabolism of the non‐steroidal anti‐inflammatory drug meloxicam was investigated in six horses and in the filamentous fungus Cunninghamella elegans. The metabolites identified were compared between the species, and then the fungus was used to produce larger amounts of the metabolites for future use as reference material. C. elegans proved to be a good model of phase I meloxicam metabolism in horses since all four metabolites found were the same in both species. Apart from the two main metabolites, 5′‐hydroxymethylmeloxicam and 5′‐carboxymeloxicam, a second isomer of hydroxymeloxicam and dihydroxylated meloxicam were detected for the first time in horse urine and the microbial incubations. Phase II metabolites were not discovered in the C. elegans samples but hydroxymeloxicam glucuronide was detected intact in horse urine for the first time in this study. Urine from six horses was further analyzed in a semi‐quantitative sense and 5′‐hydroxymethylmeloxicam gave peaks with much higher intensity compared to the parent drug and the other metabolites, and was detected for at least 14 days after the last given dose in some of the horses. From the results presented in this article, we suggest that analytical methods developed for the detection of meloxicam in horse urine after prohibited use should focus on the 5′‐hydroxymethyl metabolite and that C. elegans can be used to produce large amounts of this metabolite for potential future use as a reference compound. Copyright © 2009 John Wiley & Sons, Ltd.     

Characterization of calixarene‐bonded stationary phases

Calixarene‐bonded stationary phases received growing interest in HPLC as stationary phases with special retention characteristics and selectivity. The commercially available unsubstituted and p‐tert‐butyl‐substituted Caltrex^® columns have been intensively studied and characterized in our workgroup. They can be used as reversed phases, yet they support additional interactions. Especially, their steric, polar and ionic properties differ from conventional alkyl‐bonded phases. However, also the hydrophobic interaction shows differences since adsorption and partition interactions on or in a bonded layer of calixarenes are not similar to those of alkyl‐bonded layers. The relative strength of the hydrophobic properties of the stationary phases has been found depending on the methanol concentration of the mobile phase. Generally, the dependencies of their interaction strengths on mobile‐phase conditions, e.g. the change of the intensity of the hydrogen‐bonding abilities with decreasing methanol content, are not similar from phase to phase either. This probably gives calixarene‐bonded stationary phases enhanced suitability for analyses at extreme compositions of the mobile phase. An overview about the synthesis, retention and selectivity properties of Caltrex^® columns is given here.     

Reductive openings of benzylidene acetals revisited: a mechanistic scheme for regio- and stereoselectivity

Despite the importance of regioselective reductive openings of cyclic acetals, mechanistic details are scarce. In this study 4,6-O-benzylidene acetals were used as model compounds for deciphering the mechanism of regioselective openings using a variety of reducing agents. Competitive isotopic studies aiming at primary and secondary isotope effects, as well as an electron-deficient substrate, were used to evaluate stereo- and regioselectivity. We show that there are three distinctly different mechanistic pathways. In nonpolar solvents, such as toluene, the acetal is activated by the very reactive naked Lewis acid to give a fully developed oxocarbenium ion that is then reduced by the borane, with low stereoselectivity. In THF the reactivity of the Lewis acid is moderated by complex formation with the solvent. These reactions are thus much slower and proceed through an intimate ion pair and thereby show high stereoselectivities. The regioselectivity in these reactions is directed by the interaction between the Lewis acid and the most nucleophilic oxygen of the acetal, thus yielding a free 6-hydroxyl group. Finally, boranes such as BH(3)·NMe(3) are activated by Lewis acid, which results in the borane being the most electrophilic species, and consequently the reaction shows inversed regioselectivity to give a free 4-hydroxyl group. These reactions proceed through an oxocarbenium ion and thus show low stereoselectivity.     

Pseudo-Hyperkähler Geometry and Generalized Kähler Geometry

We discuss the conditions for additional supersymmetry and twisted super-symmetry in N = (2, 2) supersymmetric nonlinear sigma models described by one left and one right semi-chiral superfield and carrying a pair of non-commuting complex structures. Focus is on linear non-manifest transformations of these fields that have an algebra that closes off-shell. We find that additional linear supersymmetry has no interesting solution, whereas additional linear twisted supersymmetry has solutions with interesting geometrical properties. We solve the conditions for invariance of the action and show that these solutions correspond to a bi-hermitian metric of signature (2, 2) and a pseudo-hyperkähler geometry of the target space.     

Big elements in irreducible linear groups

Let V be a linear space over a field K of dimension n > 1, and let \({G \leq {\rm GL}(V)}\) be an irreducible linear group. In this paper we prove that the group G contains an element g such that rank \({(g - \alpha E_{n}) \geq \frac{n}{2}}\) for every \({\alpha \in K}\) , where E _n is the identity operator on V. This estimate is sharp for any \({n = 2^{m}}\) . The existence of such an element implies that the conjugacy class of G in GL(V) intersects the big Bruhat cell \({B\dot{w}_{0}B}\) of GL(V) non-trivially (here B is a fixed Borel subgroup of G). The latter fact is equivalent to the existence of a complete flag \({\mathfrak{F}}\) such that the flags \({g(\mathfrak{F}), \mathfrak{F}}\) are in general position for some g ∈ G.     

Insights into sulfinate formation from tosyl hydrazides

Benzylation of 1,2-ditosylhydrazine in DMF under various basic conditions results in a benzyl sulfone via intermediary sulfinate formation, providing new insights and allowing practical conclusions to be drawn. The half-lives of 1,2-ditosylhydrazine and several monotosylated hydrazides with 1,1,3,3-tetramethylguanidine in DMSO have been determined by ¹H NMR spectroscopy and are found to vary from a few minutes to several months. In the course of this work a benzylated, partly detosylated compound has been identified and a 1,1,3,3-tetramethyl guanidine-containing side-product characterized. A contradictory report is also commented on.     

QSAR with experimental and predictive distributions: an information theoretic approach for assessing model quality

We propose that quantitative structure–activity relationship (QSAR) predictions should be explicitly represented as predictive (probability) distributions. If both predictions and experimental measurements are treated as probability distributions, the quality of a set of predictive distributions output by a model can be assessed with Kullback–Leibler (KL) divergence: a widely used information theoretic measure of the distance between two probability distributions. We have assessed a range of different machine learning algorithms and error estimation methods for producing predictive distributions with an analysis against three of AstraZeneca’s global DMPK datasets. Using the KL-divergence framework, we have identified a few combinations of algorithms that produce accurate and valid compound-specific predictive distributions. These methods use reliability indices to assign predictive distributions to the predictions output by QSAR models so that reliable predictions have tight distributions and vice versa. Finally we show how valid predictive distributions can be used to estimate the probability that a test compound has properties that hit single- or multi- objective target profiles.