Studies of para-quinomethane formation during the tyrosinase-catalyzed oxidation of 4-alkylcatechols

Land, Edward J.; Ramsden, Christopher A.; Riley, Patrick A.; Stratford, and Michael R. L.

doi:10.3998/ark.5550190.0009.228

Cited by 5 publications

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References 34 publications

(35 reference statements)

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“…6 We have described other examples of 4-alkylortho-quinones that readily rearrange in aqueous buffer but are relatively stable in organic solvents, with slow formation of complex mixtures. 7 Clearly, the aqueous environment favours proton transfer and para-quinomethane formation. These results for ortho-quinones 9 (Y = Me, NH 2 ) therefore show a consistent pattern of behaviour for derivatives in which the catechol side chain is neither sufficiently nucleophilic to cyclise onto the ortho-quinone ring (Scheme 1) nor sufficiently basic to catalyse rearrangement.…”

Section: Resultsmentioning

confidence: 99%

Dopamine quinone chemistry: a study of the influence of amide, amidine and guanidine substituents [-NH-CX-Y] on the mode of reaction

et al. 2009

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The influence of N-substituents on the mode of reaction of ortho-quinones generated by oxidation of N-substituted dopamine derivatives has been studied. Ortho-quinones with amide, urea or guanidine side chains are relatively stable, with evidence of rearrangement to para-quinomethanes. The N-methylthiourea derivative rapidly cyclises giving a bicyclic product . The trichloromethylamidine derivative also rapidly cyclises but in this case gives a spirocyclic derivative . In contrast to the transient formation of spirocyclic products by other ortho-quinones derived from dopamine derivatives, e.g., , the product is stable and has been isolated and fully characterised.

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Section: Resultsmentioning

confidence: 99%

Dopamine quinone chemistry: a study of the influence of amide, amidine and guanidine substituents [-NH-CX-Y] on the mode of reaction

et al. 2009

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“…In a previous study, related to the suicide inhibition of tyrosinase by catechols, − we demonstrated the clean rearrangement of 4- n -alkyl- ortho -quinones 2 to para -quinomethanes 3 over a period of 10−20 min in aqueous buffer . Fresh tyrosinase rapidly oxidizes 4- n -alkylcatechols 1 to the corresponding ortho -quinones 2 (Scheme ).…”

Section: Introductionmentioning

confidence: 87%

“…We have had a long-standing interest in the toxicity of ortho-quinones generated by tyrosinase [E.C.1.14. 18.1] activity, in particular because of the possibility of utilizing the action of quinones in selective toxicity to pigment cells in targeted chemotherapy for disseminated malignant melanoma. It was shown that the major cytotoxic product of the noncyclizing tyrosinase substrate 4-hydroxyanisole is the corresponding ortho-quinone, 2,3 and the use of melanogenesis as a targeting strategy in melanoma was proposed.…”

Section: ' Introductionmentioning

confidence: 99%

“…In a previous study, related to the suicide inhibition of tyrosinase by catechols, [15][16][17] we demonstrated the clean rearrangement of 4-nalkyl-ortho-quinones 2 to para-quinomethanes 3 over a period of 10-20 min in aqueous buffer. 18 Fresh tyrosinase rapidly oxidizes 4-nalkylcatechols 1 to the corresponding ortho-quinones 2 (Scheme 1). Monitoring the UV-vis spectrum of the reaction solution at 30 s intervals shows a steady decay of the initially formed orthoquinone 2 (λ max 400 nm) with well-defined isosbestic points corresponding to the formation of the para-quinone isomer 3.…”

Section: ' Introductionmentioning

confidence: 99%

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Rapid Halogen Substitution and Dibenzodioxin Formation during Tyrosinase-Catalyzed Oxidation of 4-Halocatechols

Stratford

Riley

Ramsden

2011

Chem. Res. Toxicol.

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4-Fluoro-1,2-benzoquinone, generated by tyrosinase oxidation of 4-fluorocatechol in aqueous buffer, rapidly undergoes substitution by O-nucleophiles (water or catechols) with release of fluoride. 4-Chloro- and 4-bromocatechol behave similarly. The reactions, which have toxicological implications, have been monitored by spectrophotometry and HPLC/MS, and intermediate and final products, including dibenzodioxins, identified.

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Latent and active aurone synthase from petals of C. grandiflora: a polyphenol oxidase with unique characteristics

Molitor

Mauracher

Pargan

et al. 2015

Planta

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Main conclusionAurone synthase belongs to the novel group 2 polyphenol oxidases and the presented kinetic characterization suggests a differing aurone biosynthesis in Asteraceae species compared to snapdragon.Aurone synthases (AUS) are polyphenol oxidases (PPO) physiologically involved in the formation of yellow aurone pigments in petals of various Asteraceae species. They catalyze the oxidative conversion of chalcones into aurones. Latent (58.9 kDa) and active (41.6 kDa) aurone synthase from petals of C. grandiflora was purified by a quantitative removal of pigments using aqueous two-phase separation and several subsequent chromatographic steps. The purified enzymes were identified as cgAUS1 (A0A075DN54) and sequence analysis revealed that cgAUS1 is a member of a new group of plant PPOs. Mass determination experiments of intact cgAUS1 gave evidence that the C-terminal domain, usually shielding the active site of latent polyphenol oxidases, is linked to the main core by a disulfide bond. This is a novel and unique structural feature of plant PPOs. Proteolytic activation in vivo leads to active aurone synthase possessing a residual peptide of the C-terminal domain. Kinetic characterization of purified cgAUS1 strongly suggests a specific involvement in 4-deoxyaurone biosynthesis in Coreopsis grandiflora (Asteraceae) that differs in various aspects compared to the 4-hydroxyaurone formation in Antirrhinum majus (Plantaginaceae): cgAUS1 is predicted to be localized in the thylakoid lumen, it possesses exclusively diphenolase activity and the results suggest that aurone formation occurs at the level of chalcone aglycones. The latent enzyme exhibits allosteric activation which changes at a specific product concentration to a constant reaction rate. The presented novel structural and functional properties of aurone synthase provide further insights in the diversity and role of plant PPOs.Electronic supplementary materialThe online version of this article (doi:10.1007/s00425-015-2261-0) contains supplementary material, which is available to authorized users.

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Studies of para-quinomethane formation during the tyrosinase-catalyzed oxidation of 4-alkylcatechols

Cited by 5 publications

References 34 publications

Dopamine quinone chemistry: a study of the influence of amide, amidine and guanidine substituents [-NH-CX-Y] on the mode of reaction

Dopamine quinone chemistry: a study of the influence of amide, amidine and guanidine substituents [-NH-CX-Y] on the mode of reaction

Rapid Halogen Substitution and Dibenzodioxin Formation during Tyrosinase-Catalyzed Oxidation of 4-Halocatechols

Latent and active aurone synthase from petals of C. grandiflora: a polyphenol oxidase with unique characteristics

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