Inhibitors of hepatic mixed function oxidases--V. Inhibition of aminopyrine N-demethylation and enhancement of aniline hydroxylation by benzoxazole derivatives

Asymmetric Olefin Isomerization via Photoredox Catalytic Hydrogen Atom Transfer and Enantioselective Protonation

Asymmetric olefin isomerization can be appreciated as an ideal synthetic approach to access valuable enantioenriched C═C-containing molecules due to the excellent atom economy. Nonetheless, its occurrence usually requires a thermodynamic advantage, namely, a higher stability of the product to the substrate. It has thus led to rather limited examples of success. Herein, we report a photoredox catalytic hydrogen atom transfer (HAT) and enantioselective protonation strategy for the challenging asymmetric olefin isomerization. As a paradigm, by establishing a dual catalyst system involving a visible light photosensitizer DPZ and a chiral phosphoric acid, with the assistance of N-hydroxyimide to perform HAT, a wide array of allylic azaarene derivatives, featuring α-tertiary carbon stereocenters and β-C═C bonds, was synthesized with high yields, ees, and E/Z ratios starting from the conjugated α-substituted alkenylazaarene E/Z-mixtures. The good compatibility of assembling deuterium on stereocenters by using inexpensive D2O as a deuterium source further underscores the broad applicability and promising utility of this strategy. Moreover, mechanistic studies have provided clear insights into its challenges in terms of reactivity and enantioselectivity. The exploration will robustly inspire the development of thermodynamically unfavorable asymmetric olefin isomerizations.

Traceless directing group for stereospecific nickel-catalyzed alkyl-alkyl cross-coupling reactions

Stereospecific nickel-catalyzed cross-coupling reactions of benzylic 2-methoxyethyl ethers are reported for the preparation of enantioenriched 1,1-diarylethanes. The 2-methoxyethyl ether serves as a traceless directing group that accelerates cross-coupling. Chelation of magnesium ions is proposed to activate the benzylic C-O bond for oxidative addition.

Induction of the cytochrome P450 I and IV families and peroxisomal proliferation in the liver of rats treated with benoxaprofen. Possible implications in its hepatotoxicity

Administration of the non-steroidal anti-inflammatory drug benoxaprofen to rats gave rise to significant increases in the hepatic O-dealkylations of ethoxyresorufin and methoxyresorufin and in the 12-hydroxylation of lauric acid but, in contrast, the N-demethylation of dimethylnitrosamine was inhibited. Immunoblot studies employing solubilized microsomes from benoxaprofen-treated rats revealed that benoxaprofen increased the apoprotein levels of P450 IA1 and A2 and of P450 IVA1. The same treatment with benoxaprofen increased the beta-oxidation of palmitoyl CoA determined in liver homogenates, and immunoblot analysis showed an increase in the apoprotein levels of the trans-2-enoyl CoA hydratase bifunctional protein. It is concluded that benoxaprofen is a peroxisomal proliferator which selectively induces the hepatic cytochrome P450 I and IV families. The possible implications of these findings to the well-known hepatotoxicity of this drug are discussed.

Benoxaprofen induced toxicity in isolated rat hepatocytes

The toxicity of benoxaprofen, a non-steroidal anti-inflammatory compound was investigated using rat hepatic microsomal and isolated hepatocyte suspensions. In microsomes, benoxaprofen produced a Type I binding spectra and competitively inhibited (ki 380 microM) the oxidative metabolism of aminopyrine. Marked toxicity was observed following incubation of benoxaprofen with isolated hepatocytes from either untreated, phenobarbitone (PB) or 3-methylcholanthrene (3-MC) pretreated male rats. In untreated hepatocytes increases in the intracellular lactate/pyruvate (L/P) ratio and alanine aminotransferase (ALT) release were related to the benoxaprofen concentration and duration of incubation. Alterations in L/P ratio preceded the release of cytosolic ALT and at 4 h a well defined dose-response relationship existed between the benoxaprofen concentration and the observed increases in the L/P ratio and ALT release. Pretreatment of animals with either PB or 3-MC did not affect the temporal nature nor the magnitude of the hepatocyte response to benoxaprofen. In addition, inhibitors of cytochrome P-450 isozymes (SKF-525A, metyrapone and alpha-napthoflavone) were ineffective with regard to modifying the observed toxicity. The results of this study suggest that hepatic cytochrome P-450 mediated metabolism may not be implicated in the toxicity of benoxaprofen in isolated hepatocytes. However, alterations in the cellular redox state and evidence of plasma membrane bleb formation suggest that benoxaprofen may uncouple oxidative phosphorylation and disturb intracellular calcium ion homeostasis.

New heterocyclic modifiers of oxidative drug metabolism--I. 6-Substituted-2-aminobenzothiazoles

A series of 6-substituted-2-aminobenzothiazoles(2-AB) was synthesized and evaluated as in vitro inhibitors of microsomal mixed-function oxidase activity (as aminopyrine N-demethylase) from phenobarbitone-induced rat liver. Using physiochemical parameters and multiple regression analysis a quantitative structure-activity relationship (QSAR) was derived in which 82% of the data variance was accounted for in terms of the hydrophobic character of the inhibitor and the molar refractivity of the 2-AB 6-substituent. In contrast, literature equations derived from earlier studies with heterocyclic systems possessing non-polar substitutents underestimated by up to an order of magnitude the potency of the present compounds. Kinetic studies revealed that 6-n-propoxy-2-AB, one of the more potent compounds, was a pure competitive inhibitor of aminopyrine N-demethylase activity (Ki = 60 microM from Dixon analysis), suggesting that the binding of substrate and inhibitor is mutually exclusive at the cytochrome P-450 active site. Binding studies indicated that most 2-AB derivatives elicited mixed type I/reverse type I optical difference spectra in phenobarbitone-induced microsomes. The overlap of these components resulted in non-linear double reciprocal plots of the spectral titrations and precluded the determination of binding parameters. In contrast, the more potent inhibitors (the 6-propoxy and 6-butoxy derivatives of 2-AB) were type I ligands with quite high affinity for ferric cytochrome P-450. Although no quantitative relationship was apparent between inhibition and spectral binding affinity a good correlation (r = 0.93) was observed between inhibition potency (I50) and the capacity of ten 2-AB derivatives to prevent substrate(aminopyrine) binding to cytochrome P-450. These findings suggest that 2-AB derivatives may inhibit microsomal oxidation via a direct competitive effect on substrate binding to cytochrome P-450. The present study also demonstrates that substitution of heterocyclic systems with hydrophilic groups does not necessarily produce weak inhibitors of mixed-function oxidase activity, and that extrapolation of existing QSAR equations to new inhibitor series must be interpreted with caution.

Inhibition of tolbutamide metabolism by substituted imidazole drugs in vivo: evidence for a structure-activity relationship

Tolbutamide has been used as a model drug for an examination of the effects of eleven substituted imidazole compounds on hepatic metabolism in vivo. The 1-substituted compounds 1-methylimidazole, miconazole, clotrimazole and ketoconazole produced marked alterations in tolbutamide kinetics (increased half-life, decreased clearance). However, if there was substitution in the 2- position, irrespective of a substituent on N-1, then the compound did not appear to inhibit metabolism (e.g. 2-methylimidazole, 1,2-dimethylimidazole, methimazole, metronidazole). The 4- substituted compounds, 4-methylimidazole and cimetidine were inhibitors. A structure-activity relationship for the inhibitory actions of the substituted imidazoles is thus evident in vivo.