Dealkylation, oxidative

It was not their reactivity but their chemical inertness that was the true surprise when diazirines were discovered in 1960. Thus they are in marked contrast to the known linear diazo compounds which are characterized by the multiplicity of their reactions. For example, cycloadditions were never observed with the diazirines. Especially surprising is the inertness of diazirines towards electrophiles. Strong oxidants used in their synthesis like dichromate, bromine, chlorine or hypochlorite are without action on diazirines. Diazirine formation may even proceed by oxidative dealkylation of a diaziridine nitrogen in (186) without destruction of the diazirine ring (75ZOR2221). The diazirine ring is inert towards ozone simple diazirines are decomposed only by more than 80% sulfuric acid (B-67MI50800). 

Electrochemical oxidation of alkyl aryl ethers results m oxidative dealkylation and coupling of the intermediate radicals ElectrooxidaUon m the presence of hydrogen fluonde salt leads to fluonnated dienones [66] (equation 58)... 

The numerous biotransformations catalyzed by cytochrome P450 enzymes include aromatic and aliphatic hydroxylations, epoxidations of olefinic and aromatic structures, oxidations and oxidative dealkylations of heteroatoms and as well as some reductive reactions. Cytochromes P450 of higher animals may be classified into two broad categories depending on whether their substrates are primarily endogenous or xenobiotic substances. Thus, CYP enzymes of families 1-3 catalyze... 

The oxidation of OPs can bring detoxication as well as activation. Oxidative attack can lead to the removal of R groups (oxidative dealkylation), leaving behind P-OH, which ionizes to PO . Such a conversion looks superficially like a hydrolysis, and was sometimes confused with it before the great diversity of P450-catalyzed biotransformations became known. Oxidative deethylation yields polar ionizable metabolites and generally causes detoxication (Eto 1974 Batten and Hutson 1995). Oxidative demethy-lation (0-demethylation) has been demonstrated during the metabolism of malathion. 

Whatever the true details of the metabolic pathway shown in Scheme 1 might be, there are certain facts which are very secure. Among these are that the nitrosamines are oxidatively dealkylated, that electrophilic intermediates which alkylate proteins and nucleic acids are formed, and that one of the... 

Combined treatment of atrazine with ozone and H2O2 resulted in retention of the triazine ring, and oxidative dealkylation with or without replacement of the 2-chloro group by hydroxyl (Nelieu et al. 2000). Reaction with ozone and hydroxyl radicals formed the analogous products with the additional formation of the acetamido group from one of the N-alkylated groups (Acero et al. 2000). 

Treatment of methano-dimer 28 with elemental bromine revealed a remarkable reactivity at low temperatures it proceeded quantitatively to the furano-spiro dimer 29, by analogy with the ethano-dimer 12 giving spiro dimer 9 upon oxidation. With increasing temperatures, the reaction mechanism changed, however, now affording a mixture of 5-bromo-y-tocopherol (30) and spiro dimer 9 (Fig. 6.24). Thus, the methano-dimer 28 fragmented into an a-tocopherol part, in the form of o-QM 3 that dimerized into 9, and a /-tocopherol part, which was present as the 5-bromo derivative 30 after the reaction. Thus, the overall reaction can be regarded as oxidative dealkylation. 

Organic Lead. Alkyl lead compounds are actively metabolized in the liver by oxidative dealkylation catalyzed by cytochrome P-450. 

Tetraethyl and tetramethyl lead under oxidative dealkylation metabolize to the highly neurotoxic metabolites, triethyl and trimethyl lead, respectively. In the liver, the reaction is catalyzed by a cytochrome P-450 dependent monoxygenase system (Kimmel et al. 1977). Complete oxidation of alkyl lead to inorganic lead also occurs (Bolanowska 1968). 

Nitration versus oxidative dealkylation with nitrogen dioxides. The reaction of various substituted hydroquinone ethers with nitrogen oxides leads to either oxidation (i.e. 1,4-benzoquinones) or nitration (i.e. nitro-p-dimethoxybenzenes) depending on the reaction conditions239 (equation 84). 

The stoichiometries for the nitration and oxidative dealkylation with nitrogen dioxide are established both in dichloromethane and acetonitrile,239 i.e.,... 

Aryl and alkyl hydroxylations, epoxide formation, oxidative dealkylation of heteroatoms, reduction, dehalogenation, desulfuration, deamination, aryl N-oxygenation, oxidation of sulfur Oxidation of nucleophilic nitrogen and sulfur, oxidative desulfurization Oxidation of aromatic hydrocarbons, phenols, amines, and sulfides oxidative dealkylation, reduction of N-oxides Alcohol oxidation reduction of ketones Oxidative deamination... 

While most alkaloids do not contain aldehydes when they enter mammalian, microbial, or plant tissues, this functional group may become important when formed as a metabolite of alcohols (via alcohol dehydrogenase) or amines (via oxidative dealkylation and oxidative deamination). Aldehyde dehydrogenases catalyze oxidation of aldehydes to the corresponding carboxylic acids. The physical properties, catalytic mechanism, and specificity of this group of enzymes has been reviewed (99). The general reaction catalyzed by aldehyde dehydrogenase is seen in Eq. (9). 

In the presence of hydroxy or perhydroxy radicals generated from Fenton s reagent, atrazine undergoes oxidative dealkylation in aqueous solutions (Kaufman and Kearney, 1970). Major products identified by GC/MS included deisopropylatrazine (2-chloro-4-ethylamino-6-amino-s-triazine), 2-chloro-4-amino-6-isopropylamino-5-triazine, and a dealkylated dealkylatrazine (2-chloro-4,6-diamino-s-triazine) (Kaufman and Kearney, 1970). 

As a result of our previous work on the scope and mechanism of tertiary amine nitrosation (X), we became interested in the behavior of N-alkylaziridines toward nitrous acid. Possible modes of reaction are illustrated in Scheme 1. The operation of either path A or C would be consistent with our previous studies of oxidative dealkylation of tertiary amines (1 ), while pathway B would be akin to the observed cheleotropic transformation of N-nitroso-aziridines (2). 

It may be followed by oxidation to form a ketone or in the case of oxidative dealkylation to form an unstable intermediate, examples... 

Oxidative Dealkylation of 1.1-Dialkoxy-X -phosphorins 4-Hydroxy-phos-phinic Acids... 

The ax-membered spiro compound 210 reacts with H202/LiBr/HAc to form besides some byproducts the stereoisomeric 4-hydroxy-3 -bromopropyl-phosphinic esters 211 Z and E. This experiment of Stade strengthens the proposed mechanism for oxidative dealkylation formulated above. 

Oxidation reactions can produce hydroxylation on the aromatic rings, such as in the case of the steroids and thiabendazole, or on the aliphatic carbon chain such as in the case of pentobarbitone. They can also cause epoxidation, which leads to normally unstable intermediates that can be hydrolyzed by epoxide hydrolase to dihydrodiols. In addition, they can produce oxidative dealkylation at the alpha carbons of the alkyl groups attached to a nitrogen, sulfur, or oxygen atom of the drug molecule, as in the case of the macrolide antibiotics and trimethoprim. Moreover, they can induce oxidation of sulfur atoms to the corresponding sulfox-... 

Major oxidations are aromatic, aliphatic, alicyclic, heterocyclic, N-oxidation, S-oxidation, dealkylation. Other enzymes also catalyze phase 1 reactions microsomal flavin monooxygenases, amine oxidases, peroxidases, and alcohol dehydrogenase. 

Figure 1. Two possible routes of oxidative dealkylation of the glycidyl moiety of bisphenol A diglycidyl ether...

Electrochemical oxidation of alkyl aryl ethers results in oxidative dealkylation and coupling of the intermediate radicals. Electro-oxidation of alkyl (4-fluorophenyl) ethers in the presence of a hydrogen fluoride double salt leads to 4,4-difluorocyclohexa-2,5-dienone in 50% yield (Table 10).182 In the electrochemical oxidation of methyl tetrafluorophenyl ethers with a hydrogen atom at the para position, coupled products 6 arc obtained.183 If the para position in the substrate is occupied by a fluorine substituent, then no reaction occurs. 

Oxidative dealkylation N-Dealkylation rhhch3->rnh2+ch2o Morphine, et benzphetam caffeine, the ... 

When heteroatom-substituted alkyl groups (Y = electronegative heteroatom) are oxidized, all three mechanisms lead to a common, cationic intermediate, 8.1 (Scheme 8.2). Water either attacks or deprotonates intermediate 8.1 depending on the identity of Y (Scheme 8.3). If water attacks as a nucleophile, an alkyl group will be lost from the parent drug. This process is known as an oxidative dealkylation. Two specific dealkylations of drugs are shown in Scheme 8.4. 

The primary metabolite of sertraline (Zoloft, 8.62), an antidepressant, arises from oxidative dealkylation of the amine group by CYP enyzmes in the liver (Figure 8.1). The metabolite, /V-desmethylsertraline (8.63), is essentially inactive and is readily eliminated by the kidneys. Other metabolites of sertraline include 8.64 and 8.65, both of which involve modification of the amine. Neither is an effective inhibitor of the serotonin transporter, the target of sertraline.10... 

Turn to Appendix A and pick five different drugs to demonstrate the following phase I metabolic processes oxidation (dealkylation, arene/alkene, heteroatom), reduction, and... 

The heme-thiolate cytochromes P450 (P450) catalyze regio- and stereospecific reactions under physiological conditions [18-20], including the hydrox-ylation of hydrocarbons (Equation Eq. 1), alkene epoxidation, heteroatom (N,S) oxidation, dealkylation, and (anaerobic) dehalogenation [21]. 

While the term biotransformation generally implies inactivation and detoxification, there are exceptional cases where a metabolite is more chemically active or more toxic than the parent compound. In these situations, the processes of bioactivation and biotoxification are said to have occurred, respectively. An example of bioactivation is the formation of the commonly used drug acetaminophen from phenacetin in the liver (see Figure 3.2). The latter drug was once widely used as an analgesic agent but because of kidney toxicity has been replaced by other more potent, less toxic substitutes including, of course, acetaminophen itself. In this particular bioactivation pathway the process occurs via normal oxidative dealkylation. 

Oxidative dealkylation of tert-amines.1 Oxidation of tert-N-methylamines with f-BuOOH (2 equiv.) catalyzed by this ruthenium complex results in a-(t-butyl-dioxy)alkylamines. N-Methyl groups are oxidized selectively in the presence of... 

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