4,5-Dimethylthiazole-N-oxide-S-oxide: a metabolite of chlormethiazole in man

Reactive Metabolites from Thiazole-Containing Drugs: Quantum Chemical Insights into Biotransformation and Toxicity

Drugs containing thiazole and aminothiazole groups are known to generate reactive metabolites (RMs) catalyzed by cytochrome P450s (CYPs). These RMs can covalently modify essential cellular macromolecules and lead to toxicity and induce idiosyncratic adverse drug reactions. Molecular docking and quantum chemical hybrid DFT study were carried out to explore the molecular mechanisms involved in the biotransformation of thiazole (TZ) and aminothiazole (ATZ) groups leading to RM epoxide, S-oxide, N-oxide, and oxaziridine. The energy barrier required for the epoxidation is 13.63 kcal/mol, that is lower than that of S-oxidation, N-oxidation, and oxaziridine formation (14.56, 17.90, and 20.20, kcal/mol respectively). The presence of the amino group in ATZ further facilitates all the metabolic pathways, for example, the barrier for the epoxidation reaction is reduced by ∼2.5 kcal/mol. Some of the RMs/their isomers are highly electrophilic and tend to form covalent bonds with nucleophilic amino acids, finally leading to the formation of metabolic intermediate complexes (MICs). The energy profiles of these competitive pathways have also been explored.

In silico, in vitro and in vivo metabolite identification of brexpiprazole using ultra-high-performance liquid chromatography/quadrupole time-of-flight mass spectrometry

RATIONALE

Brexpiprazole is a novel serotonin-dopamine activity modulator approved by the USFDA in July 2015 for the treatment of schizophrenia and as an adjunctive therapy with other antidepressants for major depressive disorder in adults. However, limited numbers of metabolites are reported in the literature for brexpiprazole. Our prime intent behind this study is to revisit metabolite profiling of brexpiprazole and to identify and characterize all possible in vitro and in vivo metabolites.

METHODS

Firstly, the site of metabolism for brexpiprazole was predicted by a Xenosite web predictor model. Secondly, in vitro metabolite profiling was performed by incubating the drug individually with rat liver microsomes, human liver microsomes and rat S9 fraction at 37°C for 1 h in incubator shaker. Finally, for in vivo metabolite identification, a 50 mg kg^-1 dose of brexpiprazole was administered to male Sprague-Dawley rats and the presence of various metabolites was confirmed in rat plasma, urine and feces.

RESULTS

The predicted atomic site of metabolism was obtained as a color gradient by the Xenosite web predictor tool and, from this study, probable metabolites were listed. In total, 14 phase I and 2 phase II metabolites were identified and characterized in the in vitro and in vivo matrices using ultra-high-performance liquid chromatography/quadrupole time-of-flight tandem mass spectrometry (UHPLC/QTOF-MS/MS). The majority of metabolites were found in the sample incubated with human liver microsomes and in rat urine, while in the other matrices only a few metabolites were detected.

CONCLUSIONS

All the 16 metabolites were identified and characterized using UHPLC/QTOF-MS/MS. The study revealed that brexpiprazole is metabolized via hydroxylation, glucuronidation, S-oxidation, N-oxidation, dioxidation, oxidative deamination, N-dealkylation, etc.

Identification of Key Odorants in Used Disposable Absorbent Incontinence Products

PURPOSE

The purpose of this study was to identify key odorants in used disposable absorbent incontinence products.

DESIGN

Descriptive in vitro study SUBJECTS AND SETTING:: Samples of used incontinence products were collected from 8 residents with urinary incontinence living in geriatric nursing homes in the Gothenburg area of Sweden. Products were chosen from a larger set of products that had previously been characterized by descriptive odor analysis.

METHODS

Pieces of the used incontinence products were cut from the wet area, placed in glass bottles, and kept frozen until dynamic headspace sampling of volatile compounds was completed. Gas chromatography-olfactometry was used to identify which compounds contributed most to the odors in the samples. Compounds were identified by gas chromatography-mass spectrometry.

RESULTS

Twenty-eight volatiles were found to be key odorants in the used incontinence products. Twenty-six were successfully identified. They belonged to the following classes of chemical compounds: aldehydes (6); amines (1); aromatics (3); isothiocyanates (1); heterocyclics (2); ketones (6); sulfur compounds (6); and terpenes (1).

CONCLUSION

Nine of the 28 key odorants were considered to be of particular importance to the odor of the used incontinence products: 3-methylbutanal, trimethylamine, cresol, guaiacol, 4,5-dimethylthiazole-S-oxide, diacetyl, dimethyl trisulfide, 5-methylthio-4-penten-2-ol, and an unidentified compound.

In vitro microsomal metabolic studies on a selective mGluR5 antagonist MTEP: characterization of in vitro metabolites and identification of a novel thiazole ring opening aldehyde metabolite

In vitro liver microsomal studies revealed that [14C] MTEP (3-[2-methyl-1,3-thiazol-4-yl)ethynyl] pyridine) was metabolized into three major oxidative metabolites. Metabolite 1 (M1) was shown to be a hydroxymethyl metabolite; M2 was shown to be a pyridine oxide. Moreover, a novel aldehyde metabolite (M3) was identified from mouse liver microsomes. The structure of the aldehyde M3 was elucidated by LC/MS/MS. In addition, methoxyamine, an aldehyde-trapping agent, and accurate mass measurement using a high-resolution quadrupole-time of flight (Q-TOF) instrument, were used to confirm the proposed thiazole ring-opening structure of M3. A mechanism for aldehyde M3 formation was postulated based on MTEP incubation studies with 18O2 and H2 18O using mouse liver microsomes. MTEP was initially oxidized at sulfur, followed by subsequent C4-C5 of thiazole epoxidation, thiozole ring opening and further oxidative desulfation. This proposed thiazole ring-opening mechanism might represent a novel metabolism pathway for xenobiotics containing a thiazole moiety. Species differences in the metabolism of MTEP were observed in mouse, rat, dog, monkey and human liver microsomes. Mouse appears to generate all three oxidative metabolites to a greater extent than other species examined.

The pharmacology of chlormethiazole: a potential neuroprotective agent?

Chlormethiazole is a thiazole derivative with a long history of use as a sedative agent. The mode of action of the drug has been partly worked out and has been established with recognition that its mechanism of action involves potentiation of GABA activity, the major intrinsic inhibitory neurotransmitter. Animal models of stroke ranging from rodents to primates have suggested an optimistic role for chlormethiazole in preventing both anatomical and functional deleterious effects of stroke. Phase III clinical trials, therefore, proceeded but unfortunately with very little success. Recently, the animal models have been revisited in an attempt to identify causes for this discrepancy between the results from preclinical and clinical studies. This review studies the pharmacological roots of chlormethiazole from its origin through to its licensed and novel applications. Emphasis is placed on discussing the animal experiments which led to its grooming as a neuroprotective agent and also on the human trials. The review seeks to explain the discrepancies between animal and human studies, which include short survival times of experimental subjects, speed of drug administration and fundamental differences between species. The primate model of stroke perhaps offers the nearest alternative to phase III trials and has recently been used to compare a number of newer neuroprotective agents with greater efficacy than chlormethiazole. In addition, novel approaches involving human neurochemical analyses in vivo are described which may help bridge the gap between animal models and future phase III trials.

CHARACTERIZATION OF NOVEL DIHYDROTHIENOPYRIDINIUM AND THIENOPYRIDINIUM METABOLITES OF TICLOPIDINE IN VITRO: ROLE OF PEROXIDASES, CYTOCHROMES P450, AND MONOAMINE OXIDASES

Ticlopidine is an agent that inhibits adenosine diphosphate-induced platelet aggregation. Metabolic studies with ticlopidine have indicated that the principal routes of metabolism are N-dealkylation, N-oxidation, and oxidation of the thiophene ring. However, ticlopidine shares some structural features that are similar to those of cyclic tertiary amines such as 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine and tetrahydroisoquinolines, which are converted to neurotoxic pyridinium metabolites, via the iminium (dihydropyridinium) species. The current in vitro studies examined the potential of ticlopidine to undergo a similar conversion by cytochrome P450 (P450), peroxidases, and monoamine oxidase (MAO). The results from these studies have suggested that ticlopidine undergoes an overall 4-electron oxidation to the novel thienopyridinium metabolite (M6) via the intermediate 2-electron oxidation product, the thienodihydropyridinium metabolite (M5) by P450, horseradish peroxidase, and myeloperoxidase and, to a lesser extent, by MAO. The structures of these metabolites were characterized by liquid chromatography (LC)-tandem mass spectrometry and LC-NMR. Qualitative studies with baculovirus-expressed P450s revealed the involvement of P450 3A4 in this conversion. Interestingly, M5 was the primary metabolite in the peroxidase-mediated reactions and was quite stable to air oxidation or disproportionation. It was less electrophilic and did not form cyanide, glutathione, or N-acetylcysteine adducts. On the other hand, M6 was the major metabolite in P450-catalyzed oxidation of ticlopidine. The results from this study have revealed that in addition to metabolism of the thiophene ring of ticlopidine, the tetrahydropyridine moiety of the compound is susceptible to a 2-electron and a 4-electron oxidation like other cyclic tertiary amines.

Metabolism of benzothiazole. I. Identification of ring-cleavage products

1. The metabolic fate of benzothiazole in guinea pig has been investigated following i.p. administration at a dose of 30 mg/kg. 2. Five ring-cleavage products were identified in urinary extracts by g.l.c.-mass spectra. By reference to authentic compounds the three major metabolites were shown to be 2-methylmercaptoaniline (I), 2-methylsulphinylaniline (II) and 2-methylsulphonylaniline (III). On the basis of the mass spectrometric evidence the remaining two metabolites were postulated to be 2-methylsulphinylphenylhydroxylamine (IV) and 2-methylsulphonylphenylhydroxylamine (V). 3. I, II and III were present in conjugated and unconjugated forms; IV and V were identified only after hydrolysis with sulphatase.