Mechanism-Based Inactivation of Cytochromes by Furan Epoxide: Unraveling the Molecular Mechanism

Abstract

Drugs carrying an unsaturated C═C center (such as furans) form reactive epoxide metabolites and cause irreversible mechanism-based inactivation (MBI) of cytochrome P450 (CYP450) activity, through covalent modification of amino acid residues. Though this reaction is confirmed to take place in the active site of CYPs, the details of the reactions of furan (epoxidation and epoxide ring opening), the conditions under which MBI may occur, the residues involved, the importance of the heme center, etc. have yet to be explored. A density functional theory (DFT) study was carried out (i) to elucidate the reaction pathways for the generation of furan epoxide metabolite from furan ring by the model oxidant Cpd I (iron(IV)-oxo heme-porphine radical cation, to mimic the catalytic domain of CYPs) and (ii) to explore different reactions of the furan epoxide metabolite. The energy profiles of the competitive pathways and the conditions facilitating MBI of CYPs by the reactive epoxide metabolite are reported. The rate-determining step for the overall metabolic pathway leading to MBI was observed to be the initial epoxidation, requiring ∼12 kcal/mol under the enzymatic conditions. The covalent adducts (inactivator complexes) are highly stable (∼-46 to -70 kcal/mol) and may be formed due to the reaction between furan epoxide and nucleophilic amino acid residues such as serine/threonine, preferably after initial activation by basic amino acids.

Applications of density functional theory to iron-containing molecules of bioinorganic interest

“…Rather, one must use quantum mechanical methods such as DFT. In recent years, several research groups have reported DFT studies of P450 MBI (de Visser et al, 2004; Rydberg and Olsen, 2011; Hirao et al, 2012, 2013a,b; Taxak et al, 2012, 2013a,b). …”

Chloroperoxidase‐Catalyzed Achmatowicz Rearrangements

“…Our study towards an enzyme‐catalyzed version of the well‐established Achmatowicz rearrangement commenced with the identification of biological systems that would resemble the key step in the transformation, that is, the oxygenative cleavage of furans to form ketoenal intermediates (Scheme ) . Here, investigations on the in vivo degradation of furans by cytochrome P450 monooxygenases indicated that heme‐dependent oxygenation biocatalysts might provide the required reactivity to be utilized in the title reaction , . As relatively cheap commercial alternative to the P450s, we envisaged that heme peroxidases could potentially serve this purpose, and initial studies aimed to elucidate the oxygenating abilities of a set of peroxidases with regard to the conversion of 1‐furylethanol ( 1a ).…”

The Achmatowicz Rearrangement – Oxidative Ring Expansion of Furfuryl Alcohols

“…In particular, the heme-dependent cytochrome P450 proteins were studied in detail and epoxidation activity was observed for a variety of these monooxygenases. [144][145][146][147] Here, Nelson's investigations on the detoxification pathway of menthofuran by human liver enzymes gave very strong indications for the presence of furan epoxides that, in analogy to what Adam observed, 72 cleave to the ketoenal species before being trapped by nucleophiles (Scheme 44). 144…”