Dehydrogenation of Indoline by Cytochrome P450 Enzymes: A Novel “Aromatase” Process

Abstract

Indoline derivatives possess therapeutic potential within a variety of drug candidates. In this study, we found that indoline is aromatized by cytochrome P450 (P450) enzymes to produce indole through a novel dehydrogenation pathway. The indole products can potentially be bioactivated to toxic intermediates through an additional dehydrogenation step. For example, 3-substituted indoles like 3-methylindole and zafirlukast [4-(5-cyclopentyloxy-carbonylamino-1-methyl-indol-3-ylmethyl)-3-methoxy-N-o-tolylsulfonylbenzamide] are dehydrogenated to form 3-methyleneindolenine electrophiles, which react with protein and/or DNA nucleophilic residues to cause toxicities. Another potentially significant therapeutic consequence of indoline aromatization is that the product indoles might have dramatically different therapeutic potency than the parent indolines. In this study, indoline was indeed efficiently aromatized by human liver microsomes and by several P450s, but not by flavin-containing monooxygenase (FMO) 3. CYP3A4 had the highest aromatase activity. Four additional indoline metabolites [2,3,4,7-tetrahydro-4,5-epoxy-1H-indole (M1); N-hydroxyindole (M2), N-hydroxyindoline (M3), and M4 ([1,4,2,5]dioxadiazino[2,3-a:5,6-aЈ]diindole)] were characterized; none was a metabolite of indole. M1 was an arene oxide from P450 oxidation, and M2, M3, and M4 were produced by FMO3. Our data indicated that indoline was oxidized to M3 and then to an intermediate indoline nitrone, which tautomerized to form M2, and subsequently dimerized to a di-indoline. This dimer was immediately oxidized by FMO3 or atmospheric oxygen to the final product, M4. No evidence was found for the P450-mediated production of an aliphatic alcohol from indoline that might dehydrate to produce indole. Therefore, P450 enzymes catalyze the novel "aromatase" metabolism of indoline to produce indole. The aromatase mechanism does not seem to occur through N-oxidation or dehydration of an alcohol but rather through a formal dehydrogenation pathway.Indoline, 2,3-dihydroindole, is a "saturated" structural analog of indole. Indoline-containing drugs have been utilized as drug candidates in a variety of therapeutic fields and are more frequently employed in new therapeutic entities in recent years. Indolines have been widely investigated as serotonin receptor agonists or antagonists. Examples include: SB-242084, a selective 5-HT 2C receptor antagonist with anxiolytic activity (Bromidge et al., 1997); SB-224289, a selective 5-HT 1B receptor antagonist with negative intrinsic activity (Selkirk et al., 1998); and 1-(1-indolinyl)-2-propylamine, a 5-HT 2C receptor agonist for the treatment of obesity (Bentley et al., 2004). A series of potent factor Xa inhibitors, the indoline derivatives of DX-9065a, could be novel antithrombotics for the treatment and prevention of thromboembolic diseases . Another indoline derivative, 5-amino-1-(3,5-dimethylphenyl)-indoline, was reported as a selective cyclooxygenase-1 inhibitor for its antiangiogenic property (Sano et al., 2006). Other...

Colorectal Cancer-Specific Cytochrome P450 2W1: Intracellular Localization, Glycosylation, and Catalytic Activity

“…Supernatant was collected and analyzed by HPLC. In brief, the separation was carried out on the reverse-phase C18 column (150 ϫ 2 mm, 5 m; Phenomenex Inc., Torrance, CA) using the gradient system consisting of acetonitrile and 1 mM ammonium acetate as described by Sun et al (2007). The metabolite peaks were monitored at 250 nm using a Varian UV detector (Varian Inc., Palo Alto, CA).…”

Assymmetric Ir-catalyzed hydrogenation of 2-methylindole using phosphite-type ligands

“…Initially we studied the hydrogenation of 2 methyl indole (1) with [Ir(COD) 2 Cl] 2 (COD is cycloocta 1,5 diene) as a precatalyst and a chiral phosphoramidite ligand L1 (PipPhos) or a chiral phosphite ligand L2 (Scheme 1) in ethanol or CH 2 Cl 2 for 24 hours. The conversion of 1 varied from 0 to 10% and the product 2 was formed as a racemate (Table 1, entries 1-4).…”

“…1 Some compounds are used as antihypertensive drugs, neuroprotectors and for cancer treatment. 2 There is a range of successful preparations of indolines, but the methods of their enantioselective synthesis are extremely limited. 3, 4 One of the promising ways to obtain chiral in dolines is a catalytic metal complex hydrogenation of prochiral indoles because it uses inexpensive hyrdogen and allows one step synthesis with small amounts of catalyst.…”

Excretion, Metabolism, and Pharmacokinetics of 1-(8-(2-Chlorophenyl)-9-(4-Chlorophenyl)-9H-Purin-6-yl)-4-(Ethylamino)Piperidine-4-Carboxamide, a Selective Cannabinoid Receptor Antagonist, in Healthy Male Volunteers

“…It has also been shown that two Arabidopsis P450s, CYP79B2 and CYP79B3, metabolized an important intermediate indole-3-acetaldoxime, implicated in auxin biosynthesis, by decarboxylation and subsequent dehydrogenation (Halkier et al, 1989;Zhao et al, 2002). Another possibility is via the hydroxylamine and nitrone formation pathway; for example, a previous study found indoline was biotransformed to an indoline nitrone that was tautomerized to produce N-hydroxyindole (Sun et al, 2007). It seems that the M4 formation may be initiated from the nitrogen radical cation formation and then the oxygen rebound due to the lack of the vicinal carbon hydrogens, followed by the nitrone formation and decarboxylation.…”