The syntheses of 5,6‐dihydroxyindole and some of its derivatives

Benigni, J. D.; Minnis, Ralph L.

doi:10.1002/jhet.5570020413

Cited by 84 publications

(36 citation statements)

References 19 publications

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“…The broad peak at 463 nm decayed over time as dopachrome underwent further reaction to form 5,6-dihydroxyindole-2-carboxylic acid (λ max ) 320 nm). 30 Similarly, in MT/O 2 oxidation ( Figure 5B), dopachrome peaks (295, 458 nm) was observed initially but decayed with time as dopachrome further transformed to the DOPA indole derivative with λ max ) 324 nm. Dopachrome was initially observed for the HRP/H 2 O 2 -mediated reaction ( Figure 5C), and there was a continuous increase in the intensity of the peak at 320 nm, suggesting the formation of dihydroxyindole derivative of DOPA.…”

Section: Resultsmentioning

confidence: 78%

Synthesis and Gelation of DOPA-Modified Poly(ethylene glycol) Hydrogels

2002

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3,4-Dihydroxyphenylalanine (DOPA) residues are known for their ability to impart adhesive and curing properties to mussel adhesive proteins. In this paper, we report the preparation of linear and branched DOPAmodified poly(ethylene glycol)s (PEG-DOPAs) containing one to four DOPA endgroups. Gel permeation chromatography-multiple-angle laser light scattering analysis of methoxy-PEG-DOPA in the presence of oxidizing reagents (sodium periodate, horseradish peroxidase, and mushroom tyrosinase) revealed the formation of oligomers of methoxy-PEG-DOPA, presumably resulting from oxidative polymerization of DOPA endgroups. In the case of PEG-DOPAs containing two or more DOPA endgroups, oxidative polymerization resulted in polymer network formation and rapid gelation. The amount of time required for gelation of aqueous PEG-DOPA solutions was found to be as little as 1 min and was dependent on the polymer architecture as well as the type and concentration of oxidizing reagent used. Analysis of reaction mixtures by UV-vis spectroscopy allowed the identification of reaction intermediates and the elucidation of reaction pathways. On the basis of the observed reaction intermediates, oxidation of the catechol side chain of DOPA resulted in the formation of highly reactive DOPA-quinone, which further reacted to form cross-linked products via one of several pathways, depending on the presence or absence of N-terminal protecting groups on the PEG-DOPA. N-Boc protected PEG-DOPA cross-linked via phenol coupling and quinone methide tanning pathways, whereas PEG-DOPA containing a free amino group cross-linked via a pathway that resembled melanogenesis. Similar differences were observed for the rate of gel formation as well as the molecular weight between cross-links (M h c ), calculated using equilibrium swelling and the FloryRehner equation.

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Section: Resultsmentioning

confidence: 78%

Synthesis and Gelation of DOPA-Modified Poly(ethylene glycol) Hydrogels

2002

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“…The literature values for the absorption cross sections of DHI and DHICA vary, depending on the solvent, pH, or both; representative values are 1720 (in deaerated water) and 6590 M -1 cm -1 (in NaOH solution), respectively. [40][41][42] Both molecules exhibit larger absorption cross sections in phosphate buffer (4485 and 8205 M -1 cm -1 for DHI and DHICA, respectively). Thus, if the DHI/DHICA ratio were to change for the eumelanin present in the melanosomes from different colored irides, then the data in Table 1 could reflect changes in the eumelanin pigment.…”

Section: Discussionmentioning

confidence: 99%

The Ultraviolet Absorption Coefficient of Melanosomes Decreases with Increasing Pheomelanin Content

Peles

Simon

2010

J. Phys. Chem. B

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Uveal melanosomes from the iridal stroma contain both eumelanin and pheomelanin, the ratio of which varies with iris color. Herein, we report the absorption coefficient at λ ) 244 nm for individual human iridal stroma melanosomes from dark brown and blue-green irides. The melanosomes are nearly identical in size, but differ in the relative concentration composition, ranging from a eumelanin/pheomelanin ratio of 14.8:1 (dark brown) to 1.3:1 (blue-green or hazel). The absorption coefficient of the melanosome decreases as its pheomelanin content increases. The origin of this decrease is attributed to a corresponding decrease in the number of UV-absorbing chromophores, reflecting the different molecular volumes of the monomeric building blocks of the two pigments. In agreement with reported data on synthetic pigments, the absorption coefficient of pheomelanin is found to be slightly larger than that for eumelanin at λ ) 244 nm (by a factor of 1.2). On the basis of the reported optical properties of synthetic models, this result suggests that the absorption of pheomelanin is less than eumelanin at wavelengths of biological relevance (∼315-400 nm).

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“…12 Synthetic DHICA melanins were prepared by enzymatic oxidation of the substrates, according to previously reported procedures. 10,13 In brief, DHICA (1 mmol) in 80 mL of 0.1 M phosphate buffer, pH 6.8, was incubated for 4 h in the presence of tyrosinase (16 000 units) under a stream of oxygen.…”

Section: Methodsmentioning

confidence: 99%

Identification of Partially Degraded Oligomers of 5,6-Dihydroxyindole-2-carboxylic Acid inSepia Melanin by Matrix-assisted Laser Desorption/Ionization Mass Spectrometry

Pezzella

Napolitano

d’Ischia

et al. 1997

Rapid Commun. Mass Spectrom.

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Despite extensive efforts over more than half a century, the direct structural investigation of natural melanins has, so far, been largely unsuccessful, because of the adverse physical and chemical properties of these pigments. In the present study, we applied matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) to the direct analysis of fresh melanin samples from the cuttlefish Sepia officinalis, and succeeded in identifying clearly distinct patterns of low molecular weight ionic species, ranging from 450 to 1200 Da. Detailed analysis of the molecular weights and mass differences between the major species, aided by comparison with MALDI-MS spectra of synthetic melanins, allowed formulation of the major components as oligomers of 5,6-dihydroxyindole-2-carboxylic acid partially degraded by peroxidative fission of the o-diphenol moieties with concomitant decarboxylation and oxygenation reactions. These results provide the first direct insight into the structure of Sepia melanin and confirm the unique value of MALDI-MS techniques for the investigation of highly complex and heterogeneous polymers such as melanins.

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The syntheses of 5,6‐dihydroxyindole and some of its derivatives

Cited by 84 publications

References 19 publications

Synthesis and Gelation of DOPA-Modified Poly(ethylene glycol) Hydrogels

Synthesis and Gelation of DOPA-Modified Poly(ethylene glycol) Hydrogels

The Ultraviolet Absorption Coefficient of Melanosomes Decreases with Increasing Pheomelanin Content

Identification of Partially Degraded Oligomers of 5,6-Dihydroxyindole-2-carboxylic Acid inSepia Melanin by Matrix-assisted Laser Desorption/Ionization Mass Spectrometry

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