Hydroxylations reactions catalyzed

Martin G, S Dijols, C Capeillere-Blandin, 1 Arnaud (1999) Hydroxylation reaction catalyzed by the Burk-holderia cepacia ACllOO bacterial strain. Involvement of the chlorophenol-4-monooxygenase. Eur J Bioichem 261 533-538. 

BH4 is converted to 4a-hydroxytetrahydrobiopterin (95) with incorporating one atom of dioxygen in the C(4a) position of pterin by the hydroxylation reaction catalyzed by aromatic amino acid hydroxylases (Scheme 32). The formation of 95 was observed in the reaction catalyzed by all three hydroxylases using UV spectroscopy [151]. Dehydration of 95 was carried out by the action... 

May, S. W., and Abbott, B. J. 1973. Enzymatic Epoxidation. 2. Comparison between Epoxidation and Hydroxylation Reactions Catalyzed by Omega-Hydroxylation System of Pseudomonas oleovorans. J. Biol. Chem., 248,1725-1730. 

Logan, D. T, deMarE, F., Persson, B. O., Slaby, A., Sj berg, B.-M., and Nordlund, P., 1998, Crystal structures of two self-hydroxylating ribonucleotide reductase protein R2 mutants Structural basis for the oxygen-insertion step of hydroxylation reactions catalyzed by diiron proteins. Biochemistry 37 10798nl0807. 

Husain, M., B. Entsch, D.P. Ballou, V. Massey, and P.J Chapman. 1980. Fluoride elimination from substrates in hydroxylation reactions catalyzed by p-hydroxy-benzoate hydroxylase. /. Biol. Chem. 255 4189-4197. 

Neurons that secrete norepinephrine synthesize it from dopamine in a hydroxylation reaction catalyzed by dopamine (3-hydroxylase (DBH). This enzyme is present only within the storage vesicles of these cells. Like tyrosine hydroxylase, it is a mixed-function oxidase that requires an electron donor. Ascorbic acid (vitamin C) serves as the electron donor and is oxidized in the reaction. Copper (Cu ) is a bound cofactor required for the electron transfer. 

These results show that it is unlikely that the hydroxylation reaction catalyzed by dopamine -hydroxylase occurs as depicted in Reactions 5 and 6. A -substituted hydroperoxide of the substrate could still be involved in the mechanism if the formation of the hydroperoxide required the participation of ascorbate. 

Scheme 18.17 Hydroxylation reaction catalyzed by cytochrome P450s.

Baciocchi, E., T. Boschi, E. CassioU, C. GaUi, A. Lapi, and P. TagUatesta (1997). Epoxidation and hydroxylation reactions catalyzed by yS-telrahalo and 8-octahalo manganese porphyrins. Tetrahedron Lett. 38, 7283-7286. 

Scheme 5.1 General hydroxylation reaction catalyzed by P450 monooxygenases. RH indicates the substrate.

Some hydroxylation reactions catalyzed by cytochromes P450. Hydroxylation of camphor 1 by P450 g from P. putida [6] Hydroxylation of (S)-/V-methylcoclaurine 3 by CYP80B1 in morphine biosynthesis [7] Hydroxylation of 6-deoxyerythronolide B 5 by P450j from Saccharopolyspora erythraea [8] Hydroxylation of cinnamic acid 7 by CYP73 from Arabidopsis thaliana [9] Hydroxylation of diclofenac 9 by human CYP3A4 [10],... 

The importance of the o-hydroxyl moiety of the 4-benzyl-shielding group of R,R-BOX/o-HOBn-Cu(OTf)2 complex was indicated when enantioselectivities were compared between the following two reactions. Thus, the enantioselectivity observed in the reaction of O-benzylhydroxylamine with l-crotonoyl-3-phenyl-2-imi-dazolidinone catalyzed by this catalyst was 85% ee, while that observed in a similar reaction catalyzed by J ,J -BOX/Bn.Cu(OTf)2 having no hydroxyl moiety was much lower (71% ee). In these reactions, the same mode of chirality was induced (Scheme 7.46). We believe the free hydroxyl groups can weakly coordinate to the copper(II) ion to hinder the free rotation of the benzyl-shielding substituent across the C(4)-CH2 bond. This conformational lock would either make the coordination of acceptor molecules to the metallic center of catalyst easy or increase the efficiency of chiral shielding of the coordinated acceptor molecules. 

Analogous side-chain oxidations occur in various biosynthetic pathways. The neurotransmitter norepinephrine, for instance, is biosynthesized from dopamine by a benzylic hydroxylation reaction. The process is catalyzed by the copper-containing enzyme dopamine /3-monooxygenase and occurs by a radical mechanism. A copper-oxygen species in the enzyme first abstracts the pro-R benzylic hydrogen to give a radical, and a hydroxyl is then transferred from copper to carbon. 

Step 3 of Figure 29.3 Alcohol Oxidation The /3-hydroxyacyl CoA from step 2 is oxidized to a /3-ketoacyl CoA in a reaction catalyzed by one of a family of L-3-hydroxyacyl-CoA dehydrogenases, which differ in substrate specificity according to the chain length of the acyl group. As in the oxidation of sn-glycerol 3-phosphate to dihydroxyacetone phosphate mentioned at the end of Section 29.2, this alcohol oxidation requires NAD+ as a coenzyme and yields reduced NADH/H+ as by-product. Deprotonation of the hydroxyl group is carried out by a histidine residue at the active site. 

The overall hydroxylation or epoxidation reaction catalyzed by cytochrome P450s involves the insertion of one oxygen atom, derived from molecular oxygen, into a C-H bond or into the Jt-system of an olefin, with the concomitant reduction of the... 

Peptidyl hydroxyprohne and hydroxylysine are formed by hydroxylation of peptidyl proline or lysine in reactions catalyzed by mixed-function oxidases that require vitamin C as cofactor. The nutritional disease scurvy reflects impaired hydroxylation due to a deficiency of vitamin C. 

Hydroxylation is the chief reaction involved in phase 1. The responsible enzymes are called monooxygenases or cytochrome P450s the human genome encodes at least 14 families of these enzymes. Estimates of the number of distinct cytochrome P450s in human tissues range from approximately 35 to 60. The reaction catalyzed by a monooxygenase (cytochrome P450) is as follows ... 

May SW, BJ Abbott (1973) Enzymatic epoxidation. II. Comparison between the epoxidation and hydroxyl-ation reactions catalyzed by the omega-hydroxylation system of Pseudomonas oleovorans. J Biol Chem 248 1725-1730. 

Brune A, B Schink (1990) Pyrogallol-to-phloroglucinal conversion and other hydroxyl-transfer reactions catalyzed by cell extracts of Pelobacter acidigallici. J Bacterial 172 1070-1076. 

Pure parathion is a pale yellow, practically odorless oil, which crystallizes in long white needles melting at 6.0° C. (17). It is soluble in organic solvents, except kerosenes of low aromatic content, and is only slightly soluble in water (15 to 20 p.p.m. at 20° to 25° C.). Peck (35) measured its rate of hydrolysis to diethyl thiophosphate and nitro-phenate ions in alkaline solutions. He found that the reaction kinetics are first order with respect to the ester and to hydroxyl ion. In normal sulfuric acid the rate of hydrolysis was the same as in distilled water. Peck concluded that hydrolysis takes place by two mechanisms—a reaction catalyzed by hydroxyl ions and an independent uncatalyzed reaction with water. He calculated that at a pH below 10 the time for 50% hydrolysis at 25° C. is 120 days in the presence of saturated lime water the time is 8 hours. The over-all velocity constant at 25° C. is k = 0.047 [OH-] + 4 X 10-6 min.-1... 

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