- pH stability and antioxidant power of CycloDOPA and its derivatives
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CycloDOPA (leukodopachrome), a well known metabolite of tyrosine, is a precursor of melanine in mammalian organisms and of the pigment betalain in plants. However, the isolation of cycloDOPA from natural sources has not been widely reported. In the present work, the stabilities of cycloDOPA and cycloDOPA methyl ester at various pH levels were studied. Both compounds were stable under acidic conditions. By contrast, both compounds were unstable when the pH was shifted from neutral to basic to form indole derivatives as major products. Based on the pH stability, cycloDOPA and its derivatives were subjected to the DPPH radical scavenging assay for the first time.
- Nakagawa, Shiori,Tachrim, Zetryana Puteri,Kurokawa, Natsumi,Ohashi, Fumina,Sakihama, Yasuko,Suzuki, Takeyuki,Hashidoko, Yasuyuki,Hashimoto, Makoto
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supporting information
(2018/09/06)
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- HAIR DYE COMPOSITION
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An air-oxidative type hair dye composition containing a melanin precursor prepared by a process including (A) an oxidation step for converting, into the melanin precursor, a tyrosine or derivative thereof used as a starting substance with an enzyme or cell that is derived from a fungus selected from the group consisting of fungi belonging to the genera Aspergillus, Neurospora, Rhizomucor, Trichoderma, and Penicillium and that exhibits a catechol oxidase activity.
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Page/Page column 12
(2008/06/13)
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- Oxidative Degradation of Melanins to Pyrrole Acids: a Model Study.
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The origin of pyrrole-2,3,5-tricarboxylic acid (PTCA), the most characteristic degradation product of melanins, was investigated by use of synthetic pigments prepared from the major biosynthetic precursors, 5,6-dihydroxyindole (DHI) and 5,6-dihydroxyindole-2-carboxylic acid (DHICA).Under the reported conditions, i.e. acidic permanganate, oxidative degradation of DHI- and DHICA-melanins afforded PTCA in 0.15 and 3.0percent w/w yield, respectively.A significant improvement of PTCA yields up to 7percent was obtained using alkaline hydrogen peroxide as the oxidising agent.Under these conditions pyrrole-2,3-dicarboxylic acid (PDCA) was also obtained in significant yields.Investigations of the oxidative degradation of some model indole obligomers (1-4) provided unambiguous evidence that PTCA may originate from 2-linked DHI-units in the pigment polymer as well as from DHICA-derived units, whereas PDCA arises from DHI-units not substituted at 2-position.Monitoring of the oxidation of dimer 1 to PTCA showed the intermediate formation of DHICA.Accordingly, a mechanistic route is proposed for the degradation of 2-substituted DHI-units in melanin polymer to PTCA, which also accounts for the observed yields of formation of the pyrrole acid from the model oligomers.
- Napolitano, Alessandra,Pezzella, Alessandro,Vincensi, M. Rosaria,Prota, Giuseppe
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p. 5913 - 5920
(2007/10/02)
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- A RE-EXAMINATION OF THE ZINC-CATALYSED REARRANGEMENT OF DOPACHROME USING IMMOBILISED TYROSINASE
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The effect of zinc ions on the rearrangement of dopachrome, 1, has been reinvestigated using an improved technique to obtain the aminochrome which involves aereal oxidation of dopa with mushroom tyrosinase immobilesed on activated sepharose.Zinc-catalysed rearragement of dopachrome thus obtained was found to give 5,6-dihydroxyindole-2-carboxylic acid, 3, mainly, rather than 5,6-dihydroxyindole, 2, as previously reported.Interestingly, the rate of rearrangement and the formation ratio 3/2 are strongly dependent on the amount of metal added, decreasing as zinc concentration is lowered from 10percent to 0.1percent.The relevance of these in vitro experiments is discussed in relation to the role of metallic cations in the biosynthesis of eumelanins.
- Napolitano, Alessandra,Chioccara, Francesco,Prota, Giuseppe
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p. 357 - 360
(2007/10/02)
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