Novel Bioactivation Mechanism of Reactive Metabolite Formation from Phenyl Methyl-Isoxazoles

Abstract

ABSTRACT:Recently, we described a series of phenyl methyl-isoxazole derivatives as novel, potent, and selective inhibitors of the voltage-gated sodium channel type 1.7 (Bioorg Med Chem Lett 21:3871-3876, 2011). The lead compound, 2-chloro-6-fluorobenzyl [3-(2,6-dichlorophenyl)-5-methylisoxazol-4-yl]carbamate, showed unprecedented GSH and cysteine reactivity associated with NADPH-dependent metabolism in trapping studies using human liver microsomes. Additional trapping experiments with close analogs and mass spectra and NMR analyses suggested that the conjugates were attached directly to the 5-methyl on the isoxazole moiety. We propose a mechanism of bioactivation via an initial oxidation of the 5-methyl generating a stabilized enimine intermediate and a subsequent GSH attack on the 5-methylene. Efforts to ameliorate reactive metabolite generation were undertaken to minimize the potential risk of toxicity. Formation of reactive metabolites could be significantly reduced or prevented by removing the 5-methyl, by N-methylation of the carbamate; by replacing the nitrogen with a carbon or removing the nitrogen to obtain a carboxylate; or by inserting an isomeric 5-methyl isoxazole. The effectiveness of these various chemical modifications in reducing GSH adduct formation is in line with the proposed mechanism. In conclusion, we have identified a novel mechanism of bioactivation of phenyl 5-methylisoxazol-4-yl-amines. The reactivity was attenuated by several modifications aimed to prevent the emergence of an enimine intermediate. Whether 5-methyl isoxazoles should be considered a structural alert for potential formation of reactive metabolites is dependent on their context, i.e., 4-nitrogen.

Deep Learning to Predict the Formation of Quinone Species in Drug Metabolism

“…103 Top right, a voltage-gated sodium channel inhibitor drug candidate. 104 Bottom center, an imiloxan metabolite. 105 Bottom right, a brimonidine metabolite.…”

Isoxazoles: synthesis, evaluation and bioinformatic design as acetylcholinesterase inhibitors

“…Details for pharmacological experiments are described in Materials and Methods as well as in previous works. [21] The series of compounds with 1-ethynylcyclohexene used as alkyne (7)(8)(9) showed the highest activity with IC50 values upper to 200 μm. Although the activity of compounds is deficient comparable with the reference employed, it is Table 1 Aldehydes and alkynes required for the synthesis of compounds 1-10 and structure to obtain show as interesting pharmacophores to be used for the design of new biologically active compounds against enzymes related with neurodegenerative diseases.…”

“…The isoxazoles also form the basis for a number of specific drugs, including the cyclooxigenase‐2 inhibitor valdecoxib (Bextra, Omaha, NE, USA) . Thus, the isoxazoles have been widely used and studied in the modern drug discoveries …”

“…[6] Thus, the isoxazoles have been widely used and studied in the modern drug discoveries. [7] The isoxazoles can be prepared in many ways, but the most widely reported and researched synthesis of isoxazoles is via [3 + 2] cycloaddition of a nitrile oxide and an alkyne. The conventional generation of a nitrile oxide requires the dehydration of a nitroalkane or a similar starting material.…”

Formation of A Novel Purine Metabolite through CYP3A4 Bioactivation and Glutathione Conjugation

“…There are, however, instances where mass spectrometry is not sufficient in fully determining the metabolic soft spots on a molecule due to inadequate fragmentation data [ 4 ]. In such cases, after isolation of a metabolite structural elucidation has been conducted using Nuclear Magnetic Resonance (NMR) in preclinical [ 5 ] and clinical settings [ 6 ].…”