Aromatic rings, hydroxylation

Rieske-type clusters are found in aromatic-ring hydroxylating dioxygenase systems (20). These enzymes catalyze the conversion of different aromatic compounds into cis-arene diols ... 

Martin VJJ, WW Mohn (1999) A novel aromatic ring-hydroxylating dioxygenase from the diterpenoiddegrading Pseudomonas abietaniphila BKME-9. J Bacteriol 181 2675-2682. 

Inspired by the results of aromatic-ring hydroxylation from the laboratory of Karlin and co-workers, a few groups provided further examples of such reactivity, including some structurally characterized complexes of modified m-xylyl-based pyridine-donor ligands (Schiff base and non-Schiff base acyclic ligands), as well as aliphatic amine donor ligands (179) (Cu-Cu 2.990 A),169 (180) (Cu-Cu 3.015 A),170 and (181) (Cu-Cu 2.999 A).171 172 A m-xylyl-based ligand system that was used by Mukherjee and co-workers in the formation of complex (181) also resulted in the isolation of a bis(/i-hydroxo)dicopper(II) complex (182) (Cu-Cu 3.004 A).171,172 Casella and co-workers demonstrated that when their dicopper(I) complex... 

Increased Efficiency of Aromatic-Ring Hydroxylating Dioxygenases... 

Butler, C.S. and Mason, J.R. (1997) Structure-function analysis of the bacterial aromatic ring-hydroxylating dioxygenases. Advances in Microbial Physiology, 38, 47-84. 

Aromatic amines are initially metabolized by aromatic and A -hydroxylation (oxidation reactions) and Y-acetylation. Following aromatic ring hydroxylation, the ring structure may be further conjugated with glucuronic acid or sulfate (Parkinson 1996). N-hydroxylation results in the potential methemoglobin-generating metabolite,... 

The selective hydroxylation, in the presence of aqueous H2O2, of aromatic hydrocarbons such as benzene, toluene, and xylene to phenol, cresols, and xylenols, respectively, occurs easily on TS-1 (33,165,224). Again, a significant contrast between TS-2 and VS-2 in the oxidation of toluene is that when the catalyst is the former, only aromatic ring hydroxylation takes place, although when the catalyst is VS-2, the side chain C-H bonds are also hydroxylated (165, 218,219,225,226) (Table XXVIII). 

The microbiological transformation of several yohimbines and derivatives resulted almost exclusively in aromatic-ring hydroxylated compounds (298, 299). 

Several syntheses exist for vanillin. A process recently developed by Rhodia seems to be superior [11]. The process (Scheme 5.2) involves four catalytic steps starting from phenol aromatic ring hydroxylation, O-methylation, hydroxymethyl-ation, and oxidation. The process combines elegance and precision in organic synthesis. 

Preston BD, Miller JA, Miller EC. 1983. Non-arene oxide aromatic ring hydroxylation of 2,2,5,5 -tetrachlorobiphenyl as the major metabolic pathway catalyzed by phenobarbital-induced rat liver microsomes. J Biol Chem 258 8304-8311. 

Whereas the reactive species under acidic conditions are the [H2OOH] and [HO] cations, the reactive species under alkaline conditions is the [H02]e anion. Whereas the cationic oxidation species are stronger oxidants, with oxidation potential rising with increasing acidity favoring aromatic ring hydroxylation by electrophilic substitution (3,13), the anionic species mediate a nucleophilic attack on quinones according to the scheme illustrated in Fig. 6 (3,10,11). The formation of new acidic functionality results in a rapid decline in pH. 

In addition to these classical aromatic ring hydroxylations, many nitrogen heterocycles are substrates for molybdenum-containing enzymes, such as xanthine oxidase and aldehyde oxidase, which are present in the hepatic cytosolic fractions from various animal species. The molybdenum hydroxylases (B-75MI10902) catalyze the oxidation of electron-deficient carbons in aromatic nitrogen heterocycles. The reactions catalyzed by these enzymes are generally represented by equations (2) and (3). 

R. E. Parales, D. T. Gibson, H. Eklund, and S. Ramaswamy, Structure of an aromatic ring-hydroxyl-dioxygenase-naphthalene-... 

The xylyl hydroxylating system appears to possess a number of elements seen in enzyme catalyzed reactions, and the presence of a dicopper moiety, which effects a specific aromatic ring hydroxylation, identifies it as a tyrosinase model system. Analogous to the enzyme, either dieopper(I)/02 or met dicopper(II)/ H202 reactions result in xylyl hydroxylation. Although not yet proved absolutely, [Cu2(R—XYL—Y)(02)]2+ (11) is suggested to possess a p.-ii2 Ti2-022 structure, the one now favored for oxy-Hc and oxy-Tyr. Very likely, it acts as an electro-... 

SCHEME 11.14 Propranolol is an example of a compound that forms multiple alternative metabolites. Two different aromatic ring hydroxylated metabolites and the AT-dealkylated metabolite are excreted in urine. 

Aromatic Ring hydroxylation glucuronic acid conjugation glycine conjugation... 

Vanadium-substituted heteropolymolybdates Alkylbenzenes Range of oxidation products, aromatic ring hydroxylation products... 

A Hydroxylation of the aromatic ring Hydroxylation of the p-carbon atom Conjugation with glucuronic acid of the... 

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