Kinetics and mechanism of hydrolysis of 1-naphthyl N-methyl- and N,N-dimethylcarbamates

Vontor, T.; Socha, J.; Večeřa, M.

doi:10.1135/cccc19722183

Cited by 28 publications

(16 citation statements)

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“…It is noteworthy that no other carbamate is known to react by such a mechanism, which until now seemed almost exclusive of certain types of amides. For instance, the basic hydrolysis of 4‐nitrophenyl N,N ‐dimethylcarbamates follows a regular B AC 2 mechanism,51 and a similar behaviour was obtained for the basic hydrolysis of 1‐naphthyl N,N ‐dimethylcarbamate,52 despite the many similarities shared with the quinolinyl N , N ‐dimethylcarbamates presented in this paper.…”

Section: Resultssupporting

confidence: 77%

Basic hydrolysis of quinolinyl N,N‐dimethylcarbamates: a two‐step mechanism

Silva

Norberto

Santos

et al. 2011

J of Physical Organic Chem

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The reactivity of 6-quinolinyl and 8-quinolinyl N,N-dimethylcarbamates was examined in several aqueous basic media. A quadratic dependence was observed for the constant rates upon hydroxide concentration for both compounds, which is a typical behaviour of a mechanism involving a base-catalysed deprotonation of the tetrahedral intermediate with the formation of a dianion at high concentrations of hydroxide ion, while at lower concentrations a specific-base catalysed addition-elimination mechanism seems to be predominant. The reactivity of 8-quinolinyl N,N-dimethylcarbamate was also studied in several amine buffers, showing specific base catalysis. The reactivity of 6-quinolinyl N,N-dimethylcarbamate was studied in H 2 O and in D 2 O and the solvent isotope effect supports the proposal of a mechanism involving a specific-base hydrolysis. All results confirm the existence of a mechanism with a rate determining step involving the substrate anion and a second mole of hydroxide ion. This mechanism was so far unknown for carbamate reactivity, being only known to occur with amides. In the present study, the hydrolysis 8-quinolinyl and 6-quinolinyl N,N-dimethylcarbamates (compounds 1 and 2, respectively) were studied in several basic media, and a similar behaviour to the one showed by activated anilides was observed, in which kinetic constants show a quadratic dependence on hydroxide concentration.(wileyonlinelibrary.com)

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Section: Resultssupporting

confidence: 77%

Basic hydrolysis of quinolinyl N,N‐dimethylcarbamates: a two‐step mechanism

Silva

Norberto

Santos

et al. 2011

J of Physical Organic Chem

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“…Carbamate pesticides generally do not persist in the environment for a long time. In aqueous solutions, carbaryl hydrolyzes to 1-naphthol, methylamine, and CO 2 (30). Bacteria capable of degrading carbamate pesticides have been isolated from the soil (3,6,7,13,16,25).…”

mentioning

confidence: 99%

Metabolism of Carbaryl via 1,2-Dihydroxynaphthalene by Soil Isolates Pseudomonas sp. Strains C4, C5, and C6

Swetha

Phale

2005

Appl Environ Microbiol

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Pseudomonas sp. strains C4, C5, and C6 utilize carbaryl as the sole source of carbon and energy. Identification of 1-naphthol, salicylate, and gentisate in the spent media; whole-cell O 2 uptake on 1-naphthol, 1,2-dihydroxynaphthalene, salicylaldehyde, salicylate, and gentisate; and detection of key enzymes, viz, carbaryl hydrolase, 1-naphthol hydroxylase, 1,2-dihydroxynaphthalene dioxygenase, and gentisate dioxygenase, in the cell extract suggest that carbaryl is metabolized via 1-naphthol, 1,2-dihydroxynaphthalene, and gentisate. Here, we demonstrate 1-naphthol hydroxylase and 1,2-dihydroxynaphthalene dioxygenase activities in the cell extracts of carbaryl-grown cells. 1-Naphthol hydroxylase is present in the membrane-free cytosolic fraction, requires NAD(P)H and flavin adenine dinucleotide, and has optimum activity in the pH range 7.5 to 8.0. Carbaryl-degrading enzymes are inducible, and maximum induction was observed with carbaryl. Based on these results, the proposed metabolic pathway is carbaryl 3 1-naphthol 3 1,2-dihydroxynaphthalene 3 salicylaldehyde 3 salicylate 3 gentisate 3 maleylpyruvate.Carbamate insecticides, such as carbaryl (1-naphthyl-Nmethylcarbamate), are highly toxic, have a wide range of activity, and comprise a major portion of pesticides used in the agriculture industry. Widespread and repeated use leads to pollution of soil and groundwater (5). The ester bond between N-methylcarbamic acid and 1-naphthol is responsible for carbaryl toxicity. Carbamates are competitive inhibitors of neuronal nicotinic acetylcholine receptors and acetylcholinesterase (28). N-Nitrosocarbamates and the 1-naphthol that they generate are potent mutagens and are more toxic and recalcitrant than carbaryl itself (8,22,26,27,32). Carbamate pesticides generally do not persist in the environment for a long time. In aqueous solutions, carbaryl hydrolyzes to 1-naphthol, methylamine, and CO 2 (30). Bacteria capable of degrading carbamate pesticides have been isolated from the soil (3,6,7,13,16,25). The first step in degradation is the hydrolysis of carbaryl to 1-naphthol by carbaryl hydrolase, which has been purified and characterized from various organisms (3,5,10,11,20,24). Depending on the strain, 1-naphthol is metabolized via salicylate to either gentisate or catechol (4,7,9,16,17). It has been proposed that prior to ring cleavage, 1-naphthol is hydroxylated either to 4-hydroxy-1-tetralone (1), 3,4-dihydro-dihydroxy-1(2H)-naphthalenone (31), or 1,4-naphthoquinone (25). Though 1-naphthol, salicylate, and gentisate are well-established intermediates in carbaryl degradation, the steps and enzymes responsible for the conversion of 1-naphthol to salicylate have not been demonstrated so far.In this study, we report isolation of three soil bacterium Pseudomonas sp. strains, C4, C5, and C6, utilizing carbaryl as the carbon source via 1-naphthol, salicylate, and gentisate. The aim of this study is to investigate the catabolic pathway and its regulation, with emphasis on the enzymes involved in the conversion of 1-naphthol to ...

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“…The ester bond between Nmethylcarbamic acid and 1-naphthol is responsible for its toxicity. In aqueous solutions, carbaryl hydrolyzes to 1-naphthol, methylamine, and CO 2 (41). A few microbes have been reported to transform 1-naphthol by hydroxylation to either 4-hydroxy-1-tetralone (5), 3,4-dihydro-dihydroxy-1(2H)-naphthalenone (42), or 1,4-naphthoquinone (33).…”

mentioning

confidence: 99%

Purification and Characterization of 1-Naphthol-2-Hydroxylase from Carbaryl-Degrading Pseudomonas Strain C4

2007

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Pseudomonas sp. strain C4 metabolizes carbaryl (1-naphthyl-N-methylcarbamate) as the sole source of carbon and energy via 1-naphthol, 1,2-dihydroxynaphthalene, and gentisate. 1-Naphthol-2-hydroxylase (1-NH) was purified 9.1-fold to homogeneity from Pseudomonas sp. strain C4. Gel filtration and sodium dodecyl sulfate-polyacrylamide gel electrophoresis showed that the enzyme is a homodimer with a native molecular mass of 130 kDa and a subunit molecular mass of 66 kDa. The enzyme was yellow, with absorption maxima at 274, 375, and 445 nm, indicating a flavoprotein. High-performance liquid chromatography analysis of the flavin moiety extracted from 1-NH suggested the presence of flavin adenine dinucleotide (FAD). Based on the spectral properties and the molar extinction coefficient, it was determined that the enzyme contained 1.07 mol of FAD per mol of enzyme. Although the enzyme accepts electrons from NADH, it showed maximum activity with NADPH and had a pH optimum of 8.0. The kinetic constants K m and V max for 1-naphthol and NADPH were determined to be 9.6 and 34.2 M and 9.5 and 5.1 mol min ؊1 mg ؊1 , respectively. At a higher concentration of 1-naphthol, the enzyme showed less activity, indicating substrate inhibition. The K i for 1-naphthol was determined to be 79.8 M. The enzyme showed maximum activity with 1-naphthol compared to 4-chloro-1-naphthol (62%) and 5-amino-1-naphthol (54%). However, it failed to act on 2-naphthol, substituted naphthalenes, and phenol derivatives. The enzyme utilized one mole of oxygen per mole of NADPH. Thin-layer chromatographic analysis showed the conversion of 1-naphthol to 1,2-dihydroxynaphthalene under aerobic conditions, but under anaerobic conditions, the enzyme failed to hydroxylate 1-naphthol. These results suggest that 1-NH belongs to the FAD-containing external flavin mono-oxygenase group of the oxidoreductase class of proteins.Polyaromatic compounds are highly reduced, toxic, and recalcitrant in nature due to a resonance-stabilized benzene ring. However, microorganisms have evolved or adapted the ability to utilize polycyclic aromatic compounds as a sole source of carbon and energy. This is achieved by increasing the oxidation level of the compound followed by breaking the aromaticity by incorporating molecular oxygen, with this reaction being catalyzed by the oxygenase group of the oxidoreductase class of enzymes. Oxygenases are subgrouped into ring-hydroxylating mono-oxygenases and ring-cleaving or ring-hydroxylating dioxygenases (13,16,(23)(24)(25). Hence, these enzymes are important in the metabolism of polyaromatic compounds and responsible for releasing the locked carbon from these pollutants. One such recalcitrant compound is 1-naphthol, a high-volume industrial product widely used in the production of synthetic dyes, perfumes, and pesticides such as carbaryl (Sevin) (8,14). It is also released by microbes into the environment as a metabolic intermediate of various polycyclic aromatic compounds, including carbaryl (6,9,32,36).Carbaryl (1-naphthyl-N-methylcarbamate...

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Kinetics and mechanism of hydrolysis of 1-naphthyl N-methyl- and N,N-dimethylcarbamates

Cited by 28 publications

References 0 publications

Basic hydrolysis of quinolinyl N,N‐dimethylcarbamates: a two‐step mechanism

Basic hydrolysis of quinolinyl N,N‐dimethylcarbamates: a two‐step mechanism

Metabolism of Carbaryl via 1,2-Dihydroxynaphthalene by Soil Isolates Pseudomonas sp. Strains C4, C5, and C6

Purification and Characterization of 1-Naphthol-2-Hydroxylase from Carbaryl-Degrading Pseudomonas Strain C4

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