The role of intramolecular reactions and chemical degradation in the apparent biotransformation pathways of a series of SYK inhibitors.

In vitro metabolism studies of the SYK inhibitors AZ-A and AZ-B identified four unusual metabolites. M1 (m/z 411) was formed by both molecules and was common to several analogues (AZ-C to AZ-H) sharing the same core structure, appearing to derive from the complete loss of a pendent 3,4-diaminotetrahydropyran ring and pyrazole ring cleavage resulting in a non-obvious metabolite. M2-M4 were formed by AZ-A and a subset of the other compounds only and apparently resulted from a sequential loss of H2 from parent. Initial attempts to isolate M3 for identification were unsuccessful due to sample degradation and it was subsequently found that M2 and M3 underwent sequential chemical degradation steps to M4. M4 was successfully isolated and shown by mass spectrometry and NMR spectroscopy to be a tricyclic species incorporating the pyrazole and the 3,4-diaminotetrahydropyran groups. We propose that this arises from an intramolecular reaction between the primary amine on the tetrahydropyran and a putative epoxide intermediate on the adjacent pyrazole ring, evidence for which was generated in a b-mercaptoethanol trapping experiment. The loss of the THP-moiety observed in M1 was found to be enhanced in an analogue which was unable to undergo the intra-molecular reaction step leading us to propose two possible reaction pathways originating from the reactive intermediate. Ultimately, we conclude that the apparently complex and unusual metabolism of this series of compounds likely resulted from a single metabolic activation step forming an epoxide intermediate which subsequently underwent intramolecular rearrangement and/or chemical degradation to form the final observed products. Significance Statement The current work provides an unusual biotransformation example showing the potential for intramolecular reactions and chemical degradation to give the appearance of complex metabolism arising from a single primary route of metabolism.

Impact of the physical-chemical properties of poly(lactic acid)-poly(ethylene glycol) polymeric nanoparticles on biodistribution.

Nanoparticle (NP) formulations are inherently polydisperse making their structural characterization and justification of specifications complex. It is essential, however, to gain an understanding of the physico-chemical properties that drive performance in vivo. To elucidate these properties, drug-containing poly(lactic acid) (PLA)-poly(ethylene glycol) (PEG) block polymeric NP formulations (or PNPs) were sub-divided into discrete size fractions and analyzed using a combination of advanced techniques, namely cryogenic transmission electron microscopy, small-angle neutron and X-ray scattering, nuclear magnetic resonance, and hard-energy X-ray photoelectron spectroscopy. Together, these techniques revealed a uniquely detailed picture of PNP size, surface structure, internal molecular architecture and the preferred site(s) of incorporation of the hydrophobic drug, AZD5991, properties which cannot be accessed via conventional characterization methodologies. Within the PNP size distribution, it was shown that the smallest PNPs contained significantly less drug than their larger sized counterparts, reducing overall drug loading, while PNP molecular architecture was critical in understanding the nature of in vitro drug release. The effect of PNP size and structure on drug biodistribution was determined by administrating selected PNP size fractions to mice, with the smaller sized NP fractions increasing the total drug-plasma concentration area under the curve and reducing drug concentrations in liver and spleen, due to greater avoidance of the reticuloendothelial system. In contrast, administration of unfractionated PNPs, containing a large population of NPs with extremely low drug load, did not significantly impact the drug's pharmacokinetic behavior - a significant result for nanomedicine development where a uniform formulation is usually an important driver. We also demonstrate how, in this study, it is not practicable to validate the bioanalytical methodology for drug released in vivo due to the NP formulation properties, a process which is applicable for most small molecule-releasing nanomedicines. In conclusion, this work details a strategy for determining the effect of formulation variability on in vivo performance, thereby informing the translation of PNPs, and other NPs, from the laboratory to the clinic.

Identification and optimisation of a pyrimidopyridone series of IRAK4 inhibitors.

In this article, we report the discovery of a series of pyrimidopyridones as inhibitors of IRAK4 kinase. From a previously disclosed 5-azaquinazoline series, we found that switching the pyridine ring for an N-substituted pyridone gave a novel hinge binding scaffold which retained potency against IRAK4. Importantly, introduction of the carbonyl established an internal hydrogen bond with the 4-NH, establishing a conformational lock and allowing truncation of the large basic substituent to a 1-methylcyclopyl group. Subsequent optimisation, facilitated by X-ray crystal structures, allowed identification of preferred substituents at both the pyridone core and pyrazole. Subsequent combinations of optimal groups allowed control of lipophilicity and identification of potent and selective inhibitors of IRAK4 with better in vitro permeability and lower clearance.

Caudate hyperactivation during the processing of happy faces in borderline personality disorder.

BACKGROUND: Emotion dysfunction and anhedonia are main problems in borderline personality disorder (BPD). In the present functional magnetic resonance imaging (fMRI) study, we investigated neural activation during the processing of happy faces and its correlates with habitual emotion acceptance in patients with BPD. METHODS: 22 women with BPD and 26 female healthy controls watched movie clips of happy and neutral faces during fMRI without any instruction of emotion regulation. To associate neural activation with habitual emotion acceptance, we included individual scores of the Emotion Acceptance Questionnaire (EAQ) as a covariate in brain data analysis. RESULTS: All participants showed amygdala, temporal and occipital activation during the processing of happy compared to neutral faces. Compared with healthy controls, patients with BPD showed significantly more activation within the bilateral caudate. We did not find significant correlations with emotion acceptance. CONCLUSIONS: Our results indicate caudate hyperactivation in patients with BPD during the processing of happy faces. Although patients reported significantly less emotion acceptance of positive emotions, an association with neural activation was not detectable.

Potent and Selective Inhibitors of the Epidermal Growth Factor Receptor to Overcome C797S-Mediated Resistance.

The epidermal growth factor receptor (EGFR) harboring activating mutations is a clinically validated target in non-small-cell lung cancer, and a number of inhibitors of the EGFR tyrosine kinase domain, including osimertinib, have been approved for clinical use. Resistance to these therapies has emerged due to a variety of molecular events including the C797S mutation which renders third-generation C797-targeting covalent EGFR inhibitors considerably less potent against the target due to the loss of the key covalent-bond-forming residue. We describe the medicinal chemistry optimization of a biochemically potent but modestly cell-active, reversible EGFR inhibitor starting point with sub-optimal physicochemical properties. These studies culminated in the identification of compound 12 that showed improved cell potency, oral exposure, and in vivo activity in clinically relevant EGFR-mutant-driven disease models, including an Exon19 deletion/T790M/C797S triple-mutant mouse xenograft model.

The Stroop Negative Priming Matching Task: A New Task for the Direct Comparison of Interference Control and Inhibition.

Inhibition processing is an inherent part of cognitive and behavioral control. The aim of the present study was to develop and investigate psychometric criteria of an experimental paradigm that combines Stroop interference and negative priming, both of which involve inhibitory processes. We adopted a Stroop matching paradigm assessing interference control and implemented a negative priming condition. A nonclinical community sample of 94 volunteers performed this Stroop Negative Priming Matching paradigm. Since timing plays a role in priming, the interval between the prime and the probe has been varied in length (500 ms, 800 ms, and 3000 ms). The main results showed both, effects of Stroop interference and negative priming, as indicated by reaction times and incorrect responses. Reduced time pressure showed an effect on response speed and accuracy, but no interaction with interference and priming effects occurred. Reliability computed as internal consistency was generally high and did not differ between Stroop interference and negative priming scales. Retest-reliability was best for the prime-probe interval of 3000 ms. Concluding, the Stroop negative priming matching task provides reliable and directly comparable assessment of Stroop interference and negative priming effects.

Symbol Comprehension in Patients With Alzheimer Disease Dementia, Mild Cognitive Impairment, and Major Depressive Disorder.

INTRODUCTION: Previous research suggests that specific symbol features attenuate symbol comprehension deficits in seniors suffering from Alzheimer disease dementia (ADD). However, it remains unclear whether these findings also apply to other disorders associated with cognitive dysfunctions. METHODS: Ninety healthy controls, 30 patients with major depressive disorder (MDD), 35 patients with mild cognitive impairment (MCI), and 55 patients with ADD performed a Symbol Processing Task with 4 different symbol categories. Nonparametric between×within subjects analyses were conducted to examine the impact of different symbol categories on performance accuracy in all experimental groups. RESULTS: Analyses revealed a higher symbol comprehension accuracy in healthy seniors than in MDD, MCI, and ADD patients, with the lowest accuracy rates shown by ADD patients. Although the type of symbol hardly affected performance accuracy in healthy seniors and MDD patients, different symbol categories influenced the performance of MCI and ADD patients significantly. CONCLUSIONS: Our findings indicate that symbols with distracting features impede symbol comprehension in ADD and MCI. Symbols with visual cues, by contrast, facilitate symbol comprehension in ADD and may even be advantageous over standardized symbols used in public life.

Discovery of a Series of 5-Azaquinazolines as Orally Efficacious IRAK4 Inhibitors Targeting MyD88L265P Mutant Diffuse Large B Cell Lymphoma.

In this article, we report the discovery of a series of 5-azaquinazolines as selective IRAK4 inhibitors. From modestly potent quinazoline 4, we introduced a 5-aza substitution to mask the 4-NH hydrogen bond donor (HBD). This allowed us to substitute the core with a 2-aminopyrazole, which showed large gains in cellular potency despite the additional formal HBD. Further optimization led to 6-cyanomethyl-5-azaquinazoline 13, a selective IRAK4 inhibitor, which proved efficacious in combination with ibrutinib, while showing very little activity as a single agent up to 100 mg/kg. This contrasted to previously reported IRAK4 inhibitors that exhibited efficacy in the same model as single agents and was attributed to the enhanced specificity of 13 toward IRAK4.

Optimization of permeability in a series of pyrrolotriazine inhibitors of IRAK4.

We have developed a series of orally efficacious IRAK4 inhibitors, based on a scaffold hopping strategy and using rational structure based design. Efforts to tackle low permeability and high efflux in our previously reported pyrrolopyrimidine series (Scott et al., 2017) led to the identification of pyrrolotriazines which contained one less formal hydrogen bond donor and were intrinsically more lipophilic. Further optimisation of substituents on this pyrrolotriazine core culminated with the discovery of 30 as a promising in vivo probe to assess the potential of IRAK4 inhibition for the treatment of MyD88 mutant DLBCL in combination with a BTK inhibitor. When tested in an ABC-DLBCL model with a dual MyD88/CD79 mutation (OCI-LY10), 30 demonstrated tumour regressions in combination with ibrutinib.

Expanding the Armory: Predicting and Tuning Covalent Warhead Reactivity.

Targeted covalent inhibition is an established approach for increasing the potency and selectivity of potential drug candidates, as well as identifying potent and selective tool compounds for target validation studies. It is evident that identification of reversible recognition elements is essential for selective covalent inhibition, but this must also be achieved with the appropriate level of inherent reactivity of the reactive functionality (or "warhead"). Structural changes that increase or decrease warhead reactivity, guided by methods to predict the effect of those changes, have the potential to tune warhead reactivity and negate issues related to potency and/or toxicity. The half-life to adduct formation with glutathione (GSH t1/2) is a useful assay for measuring the reactivity of cysteine-targeting covalent warheads but is limited to synthesized molecules. In this manuscript we assess the ability of several experimental and computational approaches to predict GSH t1/2 for a range of cysteine targeting warheads, including a novel method based on pKa. Furthermore, matched molecular pairs analysis has been performed against our internal compound collection, revealing structure-activity relationships between a selection of different covalent warheads. These observations and methods of prediction will be valuable in the design of new covalent inhibitors with desired levels of reactivity.

Organocatalytic Stereoconvergent Synthesis of α-CF3 Amides: Triketopiperazines and Their Heterocyclic Metamorphosis.

The highly enantioselective alkylation of α-CF3 enolates, generated from triketopiperazines, has been accomplished through use of a bifunctional thiourea organocatalyst to facilitate 1,4-addition to varied enone acceptors. On treatment with appropriate nitrogen nucleophiles, the chiral triketopiperazine products undergo a metamorphosis, to provide novel fused heterocyclic lactams such as extended pyrazolopyrimidines.

Methanol adducts leading to the identification of a reactive aldehyde metabolite of CPAQOP in human liver microsomes by ultra-high-performance liquid chromatography/mass spectrometry.

RATIONALE: The incubation of CPAQOP (1-[(2R)-2-[[4-[3-chloro-4-(2-pyridyloxy)anilino]quinazolin-5-yl]oxymethyl]-1-piperidyl]-2-hydroxy) with human liver microsomes generated several metabolites that highlighted the hydroxyacetamide side chain was a major site of metabolism for the molecule. The metabolites were derived predominantly from oxidative biotransformations; however, two unexpected products were detected by liquid chromatography/ultraviolet/mass spectrometry (LC/UV/MS) and identified as methanol adducts. This observation prompted further LC/MS investigations into their formation. METHODS: Three separate incubations of CPAQOP were conducted in human liver microsomes; Naïve, fortified with methoxyamine and fortified with glutathione. Separation was achieved via ultra-high-performance liquid chromatography with either methanol or acetonitrile gradients containing formic acid. MS analysis was conducted by electrospray ionisation LTQ Orbitrap mass spectrometry acquiring accurate mass full scan, data-dependent MS2 and all ion fragmentation. RESULTS: No methanol adducts were detected by MS when acetonitrile was used in the mobile phase instead of methanol, verifying that a metabolite was reacting with methanol on column. Although this reactive metabolite could not be isolated or structurally characterised by LC/MS directly, product ion spectra of the methanol adducts confirmed addition of methanol on the hydroxyacetamide side chain. Additional experiments using methoxyamine showed the disappearance of the two methanol adducts and appearance of a methoxyamine adduct, confirming the presence of an aldhyde. Product ion spectra of the methoxyamine adduct confirmed addition of methoxyamine to the hydroxyacetamide side chain. CONCLUSIONS: The proposed bioactivation of CPAQOP occurred via the reactive aldehyde intermediate, which readily reacted with methanol in the mobile phase to form a pair of isomeric hemiacetal methanol adducts. In acidified methanol the equilibrium favoured the methanol adduct and in acidified acetonitrile it favoured the hydrate; therefore, the reactive aldehyde metabolite was not detected and could not be structurally characterised directly. Copyright © 2016 John Wiley & Sons, Ltd.

Discovery of a Potent, Selective, Orally Bioavailable, and Efficacious Novel 2-(Pyrazol-4-ylamino)-pyrimidine Inhibitor of the Insulin-like Growth Factor-1 Receptor (IGF-1R).

Optimization of cellular lipophilic ligand efficiency (LLE) in a series of 2-anilino-pyrimidine IGF-1R kinase inhibitors led to the identification of novel 2-(pyrazol-4-ylamino)-pyrimidines with improved physicochemical properties. Replacement of the imidazo[1,2-a]pyridine group of the previously reported inhibitor 3 with the related pyrazolo[1,5-a]pyridine improved IGF-1R cellular potency. Substitution of the amino-pyrazole group was key to obtaining excellent kinase selectivity and pharmacokinetic parameters suitable for oral dosing, which led to the discovery of (2R)-1-[4-(4-{[5-chloro-4-(pyrazolo[1,5-a]pyridin-3-yl)-2-pyrimidinyl]amino}-3,5-dimethyl-1H-pyrazol-1-yl)-1-piperidinyl]-2-hydroxy-1-propanone (AZD9362, 28), a novel, efficacious inhibitor of IGF-1R.

Metabolism by conjugation appears to confer resistance to paracetamol (acetaminophen) hepatotoxicity in the cynomolgus monkey.

1. Paracetamol overdose remains the leading cause of acute liver failure in humans. This study was undertaken in cynomolgus monkeys to study the pharmacokinetics, metabolism and the potential for hepatotoxic insult from paracetamol administration as a possible model for human toxicity. 2. No adverse effects were observed for doses of up to 900 mg/kg/d for 14 d. Only minor sporadic increases in alanine aminotransferase, aspartate aminotransferase and glutamate dehydrogenase in a number of animals were observed, with no clear dose response. 3. Toxicokinetic analysis showed good plasma exposure, albeit with less than proportional rises in Cmax and AUC, with increasing dose. The Cmax values in monkey were up to 3.5 times those associated with human liver toxicity and the AUC approx. 1000 times those associated with liver enzyme changes in 31-44% of human subjects. 4. Metabolite profiling of urine by (1)H NMR spectroscopy revealed paracetamol and its glucuronide and sulphate metabolites. Glutathione-derived metabolites, e.g. the cysteinyl conjugate, were only present in very low concentrations whilst the mercapturate was not detected. 5. These in vivo observations demonstrated that the cynomolgus monkey is remarkably resistant to paracetamol-induced toxicity and a poor model for investigating paracetamol-related hepatotoxicity in humans.

Identification of the reactive metabolites of fenclozic acid in bile duct cannulated rats.

Fenclozic acid (Myalex) was developed by ICI pharmaceuticals in the 1960s for the treatment of rheumatoid arthritis and was a promising compound with a good preclinical safety profile and efficacy. While it did not show adverse hepatic effects in preclinical animal tests or initial studies in man [ Chalmers et al. Ann. Rheum. Dis. 1969 , 28 , 595 and Chalmers et al. Ann. Rheum. Dis. 1969 , 28 , 590 ], it was later withdrawn from clinical development. Hepatotoxicity was observed in humans at daily doses of 400 mg but was not replicated in any of the animal species tested. Rodrigues et al. [ Arch. Toxicol. 2013 , 87 , 1569 ] published a mechanistic investigation using modern in vitro assays/techniques in order to investigate the hepatotoxicity; however, only the covalent binding in rat, dog, and human microsomes was identified as a potential indicator for hepatoxicity. Metabolites associated with or responsible for covalent binding could not be detected, likely due to the low in vitro metabolic turnover of fenclozic acid in microsomes. Foulkes [ J. Pharmacol. Exp. Ther. 1970 , 172 , 115 ] investigated the in vivo metabolism of fenclozic acid which included a rat bile duct cannulated (BDC) study characterizing the biliary and urinary metabolites; however, no reactive metabolites were identified. This study aimed to reinvestigate the in vivo metabolism of fenclozic acid in rat, with a focus on identifying any reactive metabolites that could explain the in vitro covalent binding in microsomes observed across the species. Using modern analytical techniques, we were successful in identifying an epoxide reactive metabolite, which upon conjugation with glutathione (GSH), formed up to 16 GSH-related products including positional and diastereoisomers. Not including the GSH related conjugates, 7 additional metabolites were identified compared to these previous metabolism studies.

Reactive metabolite trapping screens and potential pitfalls: bioactivation of a homomorpholine and formation of an unstable thiazolidine adduct.

Successful early attrition of potential problematic compounds is of great importance in the pharmaceutical industry. The lead compound in a recent project targeting neuropathic pain was susceptible to metabolic bioactivation, which produced reactive metabolites and showed covalent binding to protein. Therefore, as a part of the backup series for this compound several structural modifications were explored to mediate the reactive metabolite and covalent binding risk. A homomorpholine containing series of compounds was identified without compromising potency. However, when these compounds were incubated with human liver microsomes in the presence of GSH, Cys-Gly adducts were identified, instead of intact GSH conjugates. This article examines the formation of the Cys-Gly adduct with AZX ([M+H]+ 486) as a representative compound for this series. The AZX-Cys-Gly-adduct ([M+H]+ 662) showed evidence of ring contraction by formation of a thiazolidine-glycine and was additionally shown to be unstable. During its isolation for structural characterization by 1H NMR spectroscopy, it was found to have decomposed to a product with [M+H]+ 446. The characterization and identification of this labile GSH-derived adduct using LC-MS/MS and 1H NMR are described, along with observations around stability. In addition, various structurally related trapping reagents were employed in an attempt to further investigate the reaction mechanism along with a methoxylamine trapping experiment to confirm the structure of the postulated reactive intermediate.

Reassortment of NS segments modifies highly pathogenic avian influenza virus interaction with avian hosts and host cells.

Highly pathogenic avian influenza viruses (HPAIV) of subtypes H5 and H7 have caused numerous outbreaks in diverse poultry species and rising numbers of human infections. Both HPAIV subtypes support a growing concern of a pandemic outbreak, specifically via the avian-human link. Natural reassortment of both HPAIV subtypes is a possible event with unpredictable outcome for virulence and host specificity of the progeny virus for avian and mammalian species. NS reassortment of H5N1 HPAIV viruses in the background of A/FPV/Rostock/1934 (H7N1) HPAIV has been shown to change virus replication kinetics and host cell responses in mammalian cells. However, not much is known about the virus-host interaction of such viruses in avian species. In the present study, we show that the NS segment of A/Vietnam/1203/2004 (FPV NS VN, H5N1) HPAIV significantly altered the characteristics of the H7 prototype HPAIV in tracheal organ cultures (TOC) of chicken and turkey in vitro, with decreased replication efficiency accompanied by increased induction of type I interferon (IFN) and apoptosis. Furthermore, species-specific differences between chicken and turkey were demonstrated. Interestingly, NS-reassortant FPV NS VN showed an overall highly pathogenic phenotype, with increased virulence and replication potential compared to the wild-type virus after systemic infection of chicken and turkey embryos. Our data demonstrate that single reassortment of an H5-type NS into an H7-type HPAIV significantly changed virus replication abilities and influenced the avian host cell response without prior adaptation.

Reaction of homopiperazine with endogenous formaldehyde: a carbon hydrogen addition metabolite/product identified in rat urine and blood.

Drug reactivity and bioactivation are of major concern to the development of potential drug candidates in the pharmaceutical industry (Chem Res Toxicol 17:3-16, 2004; Chem Res Toxicol 19:889-893, 2006). Identifying potentially problematic compounds as soon as possible in the discovery process is of great importance, so often early in vitro screening is used to speed up attrition. Identification of reactive moieties is relatively straightforward with appropriate in vitro trapping experiments; however, on occasion unexpected reactive intermediates can be found later during more detailed in vivo studies. Here, we present one such example involving a series of compounds from an early drug discovery campaign. These compounds were found to react with endogenous formaldehyde from a rat in vivo study, resulting in the formation of novel +13-Da bridged homopiperazine products (equivalent to the addition of one carbon and one hydrogen atom), which were detected in urine and blood. The identification of these +13-Da products and their origin and mechanism of formation are described in detail through analyses of a representative homopiperazine compound [N-(3-(3-fluorophenyl)-1,2,4-thiadiazol-5-yl)-4-(4-isopropyl-1,4-diaze-pane-2-carbonyl)piperazine-1-carboxamide (AZX)] by liquid chromatography-UV-mass spectrometry, (1)H NMR, and chemical tests.

Disposition and metabolism of the specific endothelin A receptor antagonist zibotentan (ZD4054) in healthy volunteers.

Zibotentan (ZD4054) is a specific endothelin A (ET(A)) receptor antagonist that is in clinical development for the treatment of castration-resistant prostate cancer (CRPC) and has shown a promising signal for improvement in overall survival compared with placebo in a Phase II study of patients with metastatic CRPC. In this study, the pharmacokinetics, disposition and metabolism of zibotentan were evaluated following administration of a single oral dose of [(14)C]-zibotentan 15 mg to six healthy subjects. Zibotentan was rapidly absorbed, with the maximum zibotentan plasma concentration being observed 1 hour after administration. Excretion was rapid with the majority of the dose being excreted in the urine (71-94%). Total recovery of radioactivity over the 5 days of the study was high (mean 93%), with 78% of the dose being recovered within 24 hours. Concentrations of radioactivity in the plasma were similar up to 12 hours post dose, and diverged thereafter, indicating the presence of circulating metabolites. The main circulating component was zibotentan with a number of metabolites being identified in excreta. Zibotentan was well absorbed and was cleared via metabolism and urinary excretion with zibotentan-related material predominantly excreted via the urine.

The metabolism of [14C]-zibotentan (ZD4054) in rat, dog and human, the loss of the radiolabel and the identification of an anomalous peak, derived from the animal feed.

This paper presents an overview of a cross-species investigation of the metabolic fate of [(14)C]-zibotentan (ZD4054), with particular focus on the main analytical challenges encountered during the study. A combination of detection methods were used including HPLC coupled to UV, RAD and/or MS(MS), and (1)H NMR spectroscopy. The objective was to characterise and identify the major metabolites found in the circulation and excreta of rat and dog for comparison with those produced in human. Initial investigations in rat, using [(14)C]-labelled zibotentan positioned on the oxadiazole ring and HPLC-UV-RAD analysis, revealed seven labelled resolved metabolite peaks. Parallel analysis by HPLC-UV-MS (with in-source fragmentation) uncovered two additional metabolites, indicating loss of the radiolabel during biotransformation. Hence, in subsequent studies in rat, dog and human, dual-radiolabelled zibotentan was employed with the (14)C-label positioned on the pyridine ring, which was shown to be less prone to metabolism. A total of 12 metabolites were found in the excreta and plasma in all species. One of these metabolites was found in the circulation in humans, which warranted further investigations. Characterisation of the isolated human circulating metabolite by (1)H NMR was complicated by the co-extraction of a matrix component with a similar UV-chromophore to zibotentan, which was identified as daidzein, an isoflavone derived from the animal feed.