Aryl hydroxylation

Oxidative Reactions. The majority of pesticides, or pesticide products, are susceptible to some form of attack by oxidative enzymes. For more persistent pesticides, oxidation is frequently the primary mode of metaboHsm, although there are important exceptions, eg, DDT. For less persistent pesticides, oxidation may play a relatively minor role, or be the first reaction ia a metaboHc pathway. Oxidation generally results ia degradation of the parent molecule. However, attack by certain oxidative enzymes (phenol oxidases) can result ia the condensation or polymerization of the parent molecules this phenomenon is referred to as oxidative coupling (16). Examples of some important oxidative reactions are ether cleavage, alkyl-hydroxylation, aryl-hydroxylation, AJ-dealkylation, and sulfoxidation. 

Dinitroaniline herbicides show minimal plant systematic translocation properties with the majority of the absorbed residues in the root tissues. Metabolites identified include traces of Al-dealkylation, alkyl and aryl hydroxylation and nitro reduction products. Low levels of dinitroaniline herbicide residues have been reported in raw agricultural commodities according to Good Agricultural Practice. 

Previously, it was mentioned that the steric characteristics of the carbon atom (primary, secondary, tertiary) should be considered it becomes clear with the new classes of compounds studied that the electronic characteristic of the substituent groups—aryl, hydroxyl, alkoxyl— must also be taken into account. Thus, whereas trisalkylperoxy radicals have weak recombination constants, dialkylhydroxy or dialkylalkoxy have much higher recombination constants, occasionally similar to values observed for secondary alkyl radicals. 

Eine Aminoxy-Cope-Umlagerung wird bei der Cyclisierung von N-Acyl-N-aryl-hydroxyl-aminen mit Bromcyan beobachtet. Zunachst wird die Hydroxy-Funktion zum Cyanat I acyliert, das sich zum Isocyanat II umlagert unter Addition bilden sich schlieBlich 2-Hydroxy-benz-imidazolelll595 ... 

Chemical Oxidants That Cause the N1H Shift and Aryl Hydroxylations... 

Indol 1-Acetyl-4,6-dibrom- E6b/1, 706 [N-Acyl-N-aryl-hydroxyl-amin -I- H2C = CH —O —Ac/ Pd(II)]... 

Aryl-Hydroxylation, This is occasionally observed as the initial transformation of aromatic pesticides. The vast majority of aromatic pesticide degradation products are susceptible to aryl-hydroxylation, representing either cometaboHsm or the initial step in mineralization (17). Numerous genera of bacteria and fungi possess the monooxygenases and dioxygenases responsible for hydroxylation of aromatic products. Examples of aromatic products susceptible to aryl-hydroxylation include 2,4-dichlorophenol [120-83-2] (from 2,4-D) (eq. 3), 4-nitrophenol (from parathion) (eq. 4), 3,4-dichloroaniHne [95-76-1] (from propanil), and 3,6-dichlorosaHcyHc acid [3401-80-7] (from dicamba). 

Together with cinchona-PTC-mediated a-alkylations, the asymmetric nucleophilic a-substitution of carbonyl derivatives by using cinchona alkaloids as organocatalysts in nonbiphasic homogeneous conditions also have been extensively studied (e.g., arylation, hydroxylation, amination, hydroxyamination, and sulfenylation). 

Ozone has been found to cleave Si-X bonds, where X = silicon, alkyl, aryl, hydroxyl and alkoxyl, to give siloxanes as major products (10,11). 

Furanocoumarins are rapidly catabolized in mammals. In rodents, xanthotoxin (19) is metabolized by O-demethyl-ation, aryl hydroxylation at position 5, oxidation of the 5,8-dihydroquinone to the quinone, hydrolysis of the pyrone ring, oxidative opening of the furan ring, and sulfate and glucuronide conjugation (Ivie, 1987 Ivie et al., 1987). 

Rearrangements of 0-Vinyl-A/-Aryl hydroxyl amines to Indoles, 2-Amino-2 -Hydroxy-l,rBiaryls, and a-Arylated Carbonyl Compounds... 

In vitro (a) Inhibition of aryl hydroxylation, W-demethylation, (3-deethylation, and glucuronidation in vitro by piperine [8]... 

Once interest in polyaniline as a most suitable conducting polymer was established, several strategies were worked out to induce solubility and processability in polyaniline [115-35]. One method to achieve solubility is by substituting one or more hydrogens by an alkyl, an alkoxy, an aryl hydroxyl, an amino group or a halogen in an aniline nucleus. We will briefly consider these aspects in this chapter. 

Aryl hydroxylation (1) Deesterification (2) Homoglutathione 1 conjugation (3) S02NHCNH— (N) i y / Aliphatic T hydroxylation (4) / Sulfonamide Urea Cleavage (7) hydrolysis (6) 0-Demethylation (5) ... 

Under normal physiological conditions the bulk of L-phenylalanine is oxidatively metabolised by its initial transformation to L-tyrosine which is then oxidised to acetoacetate, fumarate and carbon dioxide Figure 4.1). The aryl hydroxylation reaction probably takes place in all higher animals and occurs in the liver . The same conversion... 

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