Comparison of structural and chemical properties of black and red human hair melanosomes

Melanosomes in black and red human hair are isolated and characterized by various chemical and physical techniques. Different yields of 4-amino-hydroxyphenolanaline by HI hydrolysis (a marker for pheomelanin) and pyrrole-2,3,5-tricarboxylic acid by KMnO(4)/H(+) oxidation (a marker for eumelanin) indicate that the melanosomes in black hair are eumelanosomes, whereas those in red hair are mainly pheomelanosomes. Atomic force microscopy reveals that eumelanosomes and pheomelanosomes have ellipsoidal and spherical shapes, respectively. Eumelanosomes maintain structural integrity upon extraction from the keratin matrix, whereas pheomelanosomes tend to fall apart. The black-hair eumelanosomes have an average of 14.6 +/- 0.5% amino acids content, which is attributed to the internal proteins entrapped in the melanosomes granules. The red-hair melanosomes contain more than 44% of amino acid content even after extensive proteolytic digestion. This high content of amino acids and the poorly reserved integrity of red-hair melanosomes suggest that some proteins are possibly covalently bonded with the melanin constituents in addition to those that are entrapped inside the melanin species. Soluene solubilization assay indicates the absorbance of melanin per gram of sample, adjusted for the amino acid content, is a factor of 2.9 greater for the black-hair melanosomes than the red-hair melanosomes. Metal analysis reveals significant amounts of diverse heavy metal ions bound to the two types of melanosomes. The amount of Cu(II) and Zn(II) are similar but Fe(III) content is four times higher in the red-hair melanosomes. (13)C solid-state nuclear magnetic resonance spectra and infrared spectra are presented and are shown to be powerful techniques for discerning differences in the amino acid contents, the 5,6-dihydroxyindole-2-carboxylic acid:5,6-dihydroxyindole ratio, and the degree of cross-linking in the pigment. Excellent agreement is observed between these spectral results and the chemical degradation data.     

Comparisons of the structural and chemical properties of melanosomes isolated from retinal pigment epithelium, iris and choroid of newborn and mature bovine eyes

Melanosomes were isolated from the retinal pigment epithelium (RPE), iris and choroid of mature (age >2 years) and newborn (age <1 week) bovine eyes. Scanning electron microscopy was utilized to analyze the morphology of the melanosomes, which were found to vary among different tissues and different ages. While the total content of amino acids differs slightly (ranging from 9% to 15% by mass), the distributions of the amino acids are similar. The pheomelanin content is low in the choroid and the RPE (0.1-0.5%), and moderate in the iris (<2%); therefore, the major melanin component of bovine eye melanosomes is eumelanin, independent of the shape of the melanosomes. The yields of pyrrole-2,3,5-tricarboxylic acid from melanosomes decrease in the following order: choroid > iris > RPE, and exhibit decreasing yields with age. 13C solid-state nuclear magnetic resonance (NMR) spectroscopic analysis of iris and choroid melanosomes indicates the same trends. These observations suggest that the 5,6-dihydroxyindole-2-carboxylic acid contents decrease in the following order: choroid > iris > RPE, and decrease with age. Moreover, the 13C solid-state NMR spectra show (1) for the same age samples, the CH:Cq ratio for choroid is larger than that for iris melanosomes; and (2) an increase in the concentration of carbonyl groups with age within each type of melanosome.     

Polycondensed heterocycles. I. Synthesis of 11-oxo-5H, 11H-pyrrolo[2,1-c][1,4]benzothiazepine,Derivative of a novel ring system

The synthesis of the title compound 4 by cyclization of 1-(2-ethoxycarbonylthiobenzyl)pyrrole 9 , prepared by treating with ethyl chloroformate the 1-(2-mercaptobenzyl)pyrrole 7 previously obtained by debenzylation of 1-(2-benzylthiobenzyl)pyrrrole 6 , failed. On the other hand 4 was successfully synthesized by intramolecular cyclization of 1-(2-mercaptobenzyl)pyrrole-2-carboxylic acid 15 by DMAP -catalyzed DCC method. The pyrrole 6 and 1-(2-benzylthiobenzyl)pyrrole-2-carboxaldehyde 11 were useful as starting materials to obtain 1-(2-benzylthiobenzyl)pyrrole-2-carbonitrile 13 , which was hydrolyzed to corresponding amide 16 . Debenzylation of 16 afforded 1-(2-mercaptobenzyl)pyrrole-2-carboxyamide 17 , whose hydrolysis led to required acid 15 .     

Photodegradation of Eumelanin and Pheomelanin and Its Pathophysiological Implications

Eumelanin is photoprotective for pigmented tissues while pheomelanin is phototoxic. In this review, we summarize current understanding of how eumelanin and pheomelanin structures are modified by ultraviolet A (UVA ) and also by visible light and how reactive oxygen species participate in those processes. Alkaline hydrogen peroxide oxidation was employed to characterize eumelanin and benzothiazole‐type pheomelanin, giving pyrrole‐2,3,5‐tricarboxylic acid (PTCA ) and thiazole‐2,4,5‐tricarboxylic acid (TTCA ), respectively. Reductive hydrolysis with hydroiodic acid gives 4‐amino‐3‐hydroxyphenylalanine (4‐AHP ) from the benzothiazine moiety of pheomelanin. The results show that the photoaging of eumelanin gives rise to free PTCA (produced by peroxidation in situ ) and pyrrole‐2,3,4,5‐tetracarboxylic acid (PT eCA , produced by cross‐linking). The TTCA /4‐AHP ratio increases with photoaging, indicating the conversion of benzothiazine to the benzothiazole moiety. Analysis of those markers and their ratios show that both eumelanin and pheomelanin in human retinal pigment epithelium melanosomes undergo extensive structural modifications due to their lifelong exposure to blue light. Using synthetic melanins, we also found that singlet oxygen, in addition to superoxide anions, is photogenerated and quenched upon UVA irradiation. The (patho)physiological significance of those findings is discussed in relation to the tanning process, to melanomagenesis in the skin and to age‐related macular degeneration in the eyes.     

The reaction of methyl pyrrole-2-carboxylate with epoxides

Potassium methyl pyrrole-2-carboxylate and styrene oxide are shown to yield trans-1-styrylpyrrole-2-carboxylic acid (dry conditions) and 1-(2-hydroxy-2-phenylethyl)pyrrole-2-carboxylic acid (moist conditions). The hydroxy acid yields 1H-3-phenyl-3,4-dihydropyrrolo[2.1-c]-[1.4]oxazin-1-one, on treatment with polyphosphoric acid. Vinyl acids were also obtained from the potassium pyrrole ester and ethylene oxide, propylene oxide, and cis- and trans-stilbene oxide; the latter two compounds yielded stereospecific products. A pyrrolo[2.1-c]-[1.4]benzoxazinone was obtained from cyclohexene oxide. The photo chemical isomerization of the trans-1-styryl acid and the attempted conversion into lactones is described.     

Regiocontrolled synthesis of pyrrole-2-carboxaldehydes and 3-pyrrolin-2-ones from pyrrole Weinreb amides

A regiocontrolled synthesis of 3,4-disubstituted pyrrole-2-carboxaldehydes was completed in two steps from acyclic starting materials. A Barton-Zard pyrrole synthesis between N-methoxy-N-methyl-2-isocyanoacetamide and alpha-nitroalkenes or beta-nitroacetates provided N-methoxy-N-methyl pyrrole-2-carboxamides (pyrrole Weinreb amides), which were converted into the corresponding pyrrole-2-carboxaldehydes by treatment with lithium aluminum hydride. A regioselective oxidation of the pyrrole-2-carboxaldehydes gave the corresponding 3,4-disubstituted 3-pyrrolin-2-ones.     

Pyrrolo[1,2-d]triazines-1,2,4. I. Dérivés pyrroliques

Pyrrole hydrazides and hydrazones were synthesized from pyrrole-2-carboxylic acid and pyrrole-2-carboxaldehyde, The 2-pyrrolyloxadiazoles and thiadiazoles were obtained by cyclising the pyrrole hydrazides with phosphorus oxychloride and tetraphosphorus decasulphide. These derivatives have been used for the synthesis of pyrrolo[1,2-d]-1,2,4-triazines by cyclisation or rearrangement.     

Synthesis of 1-Substituted Pyrrole-3-carboxaldehydes

The Vilsmeier-Haack formylation is the route most frequently employed for the introduction of a formyl group into the 2 or 3 position of a pyrrole ring.^2,3 Factors affecting the extent of substitution in the 2 and 3 positions in N-substituted pyrroles under Vilsmeier-Haack conditions have been investigated and the product distribution appears mainly to be the result of steric interactions.^4,5 Although it is relatively simple to introduce a formyl residue into the 2-position of a pyrrole nucleus, considerable molecular manipulation must normally be undertaken to prepare pyrrole-3-carboxaldehydes which do not bear substituents in the 2 and 5 positions of the pyrrole ring.⁶ An alternative method is the generation of isomeric mixtures of pyrrole-2-carboxaldehyde and pyrrole-3-carboxaldehyde by the acid mediated rearrangement of t h e corresponding pyrrole-2-carboxaldehydes.     

Indole- and pyrrole-sulfonium ylides

Electrophilic substitution of indole and pyrrole with sulfoxides and acid anhydrides leads to the formation of indole-3-sulfonium salts and pyrrole-2-sulfonium salts. These are deprotonated with potassium carbonate to give indole-3-sulfonium ylides and pyrrole-2-sulfonium ylides. An indole-2-sulfonium ylide was obtained by methylation and subsequent deprotonation of 2-(methylthiol)indole.     

Ground state structures and excited state dynamics of pyrrole-water complexes: ab initio excited state molecular dynamics simulations

Structures of the ground state pyrrole-(H2O)n clusters are investigated using ab initio calculations. The charge-transfer driven femtosecond scale dynamics are studied with excited state ab initio molecular dynamics simulations employing the complete-active-space self-consistent-field method for pyrrole-(H2O)n clusters. Upon the excitation of these clusters, the charge density is located over the farthest water molecule which is repelled by the depleted pi-electron cloud of pyrrole ring, resulting in a highly polarized complex. For pyrrole-(H2O), the charge transfer is maximized (up to 0.34 a.u.) around approximately 100 fs and then oscillates. For pyrrole-(H2O)2, the initial charge transfer occurs through the space between the pyrrole and the pi H-bonded water molecule and then the charge transfer takes place from this water molecule to the sigma H-bonded water molecule. The total charge transfer from the pyrrole to the water molecules is maximized (up to 0.53 a.u.) around approximately 100 fs.     

Polycondensed heterocycles. II. A new preparative route to 11-Oxo-5H,11H-pyrrolo[2,1-c][1,4]benzothiazepine

6-Methylthio-10-oxo-5H,10H-pyrrolo[1,2-b]isoquinoline 11 was isolated in an attempted synthesis of 11-oxo-5H,11H-pyrrolo[2,1-c][1,4]benzothiazepine 1 from 1-(2-methylthiobenzyl)pyrrole-2-carboxylic acid chloride 9 , obtained using as starting material o-methylthiobenzyl bromide 3 and passing through 1-(2-methylthiobenzyl)pyrrole-2-carbonitrile 5 , by cyclization with aluminum chloride. However the successful demethylation with sodium in dimethylacetamide of 1-(2-methylthiobenzyl)pyrrole-2-carboxyamide 12 , formed by hydrolysis of nitrile 5 , allowed us to prepare by another way the corresponding thiol 13 and consequently the 1-(2-mercaptobenzyl)pyrrole-2-carboxylic acid 14 , which when subjected to intramolecular ring closure by CDI in place of DCC gave 1 in higher yield, 69% instead of 43%. Finally, the direct cyanation of 1-(2-ethoxycarbonylthiobenzyl)pyrrole 16 , prepared utilizing the 1-(2-mercaptobenzyl)pyrrole 15 obtained by demethylation of the corresponding thioanisol 4 which was carried out as above, afforded the unexpected 1-(2-ethylthio-benzyl)pyrrole-2-carbonitrile 17 .     

聚{吡咯-2,5-二[(对二甲氨基)苯甲烯]}的电化学和原位拉曼光谱

采用电化学循环伏安法（CV）和原位拉曼光谱（in situ Raman）对窄能隙共轭高分子聚{吡咯 2,5 二[(对二甲氨基)苯甲烯]}（PPDMABE）的电化学行为进行了研究.结果表明,在不同pH值NaNO3溶液中, PPDMABE的电化学氧化还原过程中存在吡咯环的氧化态结构与芳式和醌式结构之间的转变.聚合物在氧化态时吡咯环主要以氧化态存在,而还原态以芳式和醌式结构吡咯环为主.PPDMABE在酸性和中性介质中氧化态吡咯环以质子化的状态存在,而在碱性溶液中氧化态吡咯环既有质子化态,又有去质子化态的.在酸性条件下,PPDMABE较易发生氧化还原反应,而在碱性条件还原反应则较难发生.     

Pyoluteorin derivatives. II. Synthetic approaches to pyrrole ring substituted pyoluteorins

A method for the regiospecific synthesis of 3-substituted 2-aroylpyrroles is described. These pyrroles, which are structurally related to the naturally occurring antibiotic pyoluteorin, are prepared by a Friedel-Crafts aroylation of 4-substituted pyrrole-3-carboxylic acid esters with 2,6-dimethoxybenzoyl chloride. The carboalkoxy group is then removed by hydrolysis and decarboxylation to produce isomerically pure 3-substituted-2-(2′,6′-dimethoxybenzoyl)pyrroles ( 5 and 13 ). Conversion of these pyrroles into pyoluteorin-like compounds led to some unexpected products which arise from facile cleavage of the dihydroxybenzoyl portion of the molecules during chlorination.     

Determination of the absolute configuration of sialic acids in gangliosides from the sea cucumber Cucumaria echinata

Enantiomeric pairs of sialic acid, D- and L-NeuAc (N-acetylneuraminic acid), were converted to D- and L-arabinose, respectively, by chemical degradation. Using this method, the absolute configuration of the sialic acid residues, NeuAc and NeuGc (N-glycolylneuraminic acid), in the gangliosides from the sea cucumber Cucumaria echinata was determined to be the D-form. Although naturally occurring sialic acids have been believed to be the D-form on the basis of biosynthetic evidence, this is the first report of the determination of the absolute configuration of the sialic acid residues in gangliosides using chemical methods.     

A likely biogenetic gateway linking 2-aminoimidazolinone metabolites of sponges to proline: spontaneous oxidative conversion of the pyrrole-proline-guanidine pseudo-peptide to dispacamide A

A new spontaneous oxidative transformation of the associated pyrrole-proline-guanidine to the natural marine pyrrole 2-aminoimidazolinone derivative has been achieved. The sensitive reaction requires air oxygen and the N-acylation of proline by pyrrole-2-carboxylic acid. Proline metabolism and pyrrole 2-aminoimidazole secondary metabolites formation seem to be related and are utilized by sponges under stress conditions for their defense against predators. A plausible stress-induced oxidative chemical pathway that establishes dispacamide derivatives as the forerunners in the biogenetic synthesis of the key pyrrole 2-aminoimidazole oroidin is proposed. The mechanism of the reaction seems to be another development of the known luciferins' chemiluminescent reactions in bioluminescent marine organisms.     

Syntheses of two cytotoxic polyunsaturated pyrrole metabolites of the marine sponge Mycale micracanthoxea

Starting from eicosapentaenoic acid (EPA) the marine, naturally occurring, pyrrole derivatives, mycalazol 5 and mycalazal 2 have been synthesized. The Stille coupling reaction is a key step in the syntheses.     

Analytical characterization of poly(pyrrole-3-carboxylic acid) films electrosynthesised on Pt, Ti and Ti/Al/V substrates

With the aim of developing a polymeric multilayer film for application in advanced biomaterials, as a first step poly(pyrrole-3-carboxylic acid) films (abbreviated as PPy-3-carbox) were electropolymerised from pyrrole-3-carboxylic acid solutions by cyclic voltammetry and chronoamperometry on platinum, titanium and Ti90Al6V4 substrates and characterised both electrochemically (cyclic voltammetry) and spectroscopically (X-Ray Photoelectron Spectroscopy, XPS). Electrochemical experiments showed that the potential range adopted for electropolymerization affects the polymer electroactivity, by analogy with unsubstituted polypyrrole. The combination of conventional and chemical derivation-XPS provided information on PPy-3-carbox surface structure, showing no significant difference between films grown on different substrates and an increase of the COOH groups amount (one group over three pyrrole rings, as an average) with respect to unsubstituted polypyrrole (PPy), as expected. Finally, a preliminary Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) investigation was performed in order to get further information on the polymer structure and electroactivity.     

Proposed Mechanism for Microbial Degradation of Polyacrylate

Abstract

A possible aerobic degradation mechanism for polyacrylate (PA) was examined with acrylic oligomer-utilizing bacteria (Microbacterium sp., Xanthomonas maltophilia, and Acinetobacter sp.), using a model compound (1,3,5-pentane tricarboxylic acid, PTCA). Acyl-coenzyme A synthetase activities were detected with dialyzed cell-free extracts of PTCA-utilizing bacteria toward PTCA, PA 500, and PA 1000. This result suggested that PA is activated by coenzyme A and metabolized via PA-coenzyme A. Metabolic products formed from PTCA were detected in culture filtrates and reaction mixtures of washed cells. Fraction A was detected as a main metabolite by high-performance liquid chromatography. A small amount of fraction B was concomitant with fraction A. Also, another fraction, C, was detected. These intermediate metabolites were characterized by LC-MS as 1,3,5-(1- or 2-pentene)tricarboxylic acid for fractions A and B and as 1,3,5-(2-oxopentane)tricarboxylic acid for fraction C. Fraction A was metabolized far faster than fraction B. Fraction B was thought to be an artifact formed from fraction A under alkaline conditions. Thus PTCA and also PA seemed to be metabolized by the mechanism similar to β-oxidation of fatty acids. The degradation of PTCA by washed cells was slower than that by growing cells and was inhibited by 5 mM NaN₃. This suggests that the metabolism is linked to a respiratory chain of bacteria.     

Synthesis of unsymmetrical 3,4-diaryl-3-pyrrolin-2-ones utilizing pyrrole Weinreb amides

A regiocontrolled synthesis of unsymmetrical 3,4-diaryl-3-pyrrolin-2-ones has been achieved in three steps from 1,2-diaryl-1-nitroethenes with pyrrole-2-carboxamides (pyrrole Weinreb amides) serving as the key linchpin intermediates. Two different methods for the preparation of the requisite nitroalkenes were investigated: (1) modified Henry reaction between arylnitromethanes and arylimines; and (2) Suzuki-Miyaura cross-coupling reaction of 2-aryl-1-bromo-1-nitroethenes with arylboronic acids. Some difficulty was encountered in the preparation of arylnitromethanes, thus leading to the exploration of a cross-coupling strategy that proved more useful. A Barton-Zard pyrrole cyclocondensation reaction between 1,2-diaryl-1-nitroethenes and N-methoxy-N-methyl-2-isocyanoacetamide gave the corresponding pyrrole Weinreb amides, which were then converted into the desired 3-pyrrolin-2-ones in two steps. Overall, this method allowed for the construction of 3,4-diaryl-3-pyrrolin-2-ones with complete regiocontrol of the substituents with respect to the lactam carbonyl. The utility of this synthetic methodology was demonstrated by the preparation of eight unsymmetrical and symmetrical 3,4-diaryl-3-pyrrolin-2-ones including the N-H lactam analogue of the selective COX-II inhibitor, rofecoxib.     

Remarkable solvent effect in Barton-Zard pyrrole synthesis: application in an efficient one-step synthesis of pyrrole derivatives

A unique solvent effect encountered in the Barton-Zard pyrrole synthesis was exploited to develop an efficient synthesis of pyrrole-2-esters. The chemistry was extended to a one-pot synthesis of pyrrole-2,4-dicarboxylates.