Amino-1,4-quinones

Compiex Substances Formed from Breakdown Intermediates, e.g, Phenols + quinones + amino compounds —h Melanins, melanoidin, gelbstoffe... 

In photosynthesis radical-ions and triplet states of the pigments, radical-pairs and biradicals involving various chlorophylls and quinones, amino acid radicals, hemes in cytochromes, metal clusters of low and higher nuclearity and even coupled metallo-radical species have been observed. Thus the field of photosyn-... 

Scheme 42. Reassignment of ellipticine quinone amino acid adduct 258 and proposed mechanism of formation by Potier and co-workers (107).

Whitehead and Tinsley (1963) state that humus represents a quasi-equilibrium stage in the decomposition of plant and microbial constituents, and as such its chemical composition is likely to fluctuate to some extent with variations in these materials. The major components, apart from polysaccharides, are thought to be polymers formed from the recombination of units such as quinones, amino-acids and aldehydes, compounds of... 

Many enzymes use redox centers to store and transfer electrons during catalysis. These redox centers can be composed of metals such as iron or cobalt, or organic cofactors such as quinones, amino acid radicals, or flavins. In order to fully appreciate the catalytic mechanisms of these enzymes, it is often necessary to determine the free energy required to reduce or oxidize their protein redox centers. This is called the redox potential. The measurement of enzyme redox potentials can be performed by either direct or indirect electrochemical methods. The type of electrochemistry suitable for a particular protein system is simply dictated by the accessibility of its redox center to the electrode surface. Because most reactions catalyzed by enzymes occur within hydrophobic pockets of the protein, the redox sites are often far from the surface of the protein. Unless an electron transfer path exists from the protein surface to the redox center, it is not feasible to use direct electrochemistry to measure the redox potential. Since only a few enzymes (most notably certain heme-containing enzymes) have such electron transferring paths and... 

Rifamycin S also undergoes conjugate addition reactions to the quinone ring by a variety of nucleophiles including ammonia, primary and secondary amines, mercaptans, carbanions, and enamines giving the C-3 substituted derivatives (38) of rifamycin SV (117,120,121). Many of the derivatives show excellent antibacterial properties (109,118,122,123). The 3-cycHc amino derivatives of rifamycin SV also inhibit the polymerase of RNA tumor vimses (123,124). 

The close electrochemical relationship of the simple quinones, (2) and (3), with hydroquinone (1,4-benzenediol) (4) and catechol (1,2-benzenediol) (5), respectively, has proven useful in ways extending beyond their offering an attractive synthetic route. Photographic developers and dye syntheses often involve (4) or its derivatives (10). Biochemists have found much interest in the interaction of mercaptans and amino acids with various compounds related to (3). The reversible redox couple formed in many such examples and the frequendy observed quinonoid chemistry make it difficult to avoid a discussion of the aromatic reduction products of quinones (see Hydroquinone, resorcinol, and catechol). 

The kinetics of formation and hydrolysis of /-C H OCl have been investigated (262). The chemistry of alkyl hypochlorites, /-C H OCl in particular, has been extensively explored (247). /-Butyl hypochlorite reacts with a variety of olefins via a photoinduced radical chain process to give good yields of aUyflc chlorides (263). Steroid alcohols can be oxidized and chlorinated with /-C H OCl to give good yields of ketosteroids and chlorosteroids (264) (see Steroids). /-Butyl hypochlorite is a more satisfactory reagent than HOCl for /V-chlorination of amines (265). Sulfides are oxidized in excellent yields to sulfoxides without concomitant formation of sulfones (266). 2-Amino-1, 4-quinones are rapidly chlorinated at room temperature chlorination occurs specifically at the position adjacent to the amino group (267). Anhydropenicillin is converted almost quantitatively to its 6-methoxy derivative by /-C H OCl in methanol (268). Reaction of unsaturated hydroperoxides with /-C H OCl provides monocyclic and bicycHc chloroalkyl 1,2-dioxolanes. 

Cosolvents ana Surfactants Many nonvolatile polar substances cannot be dissolved at moderate temperatures in nonpolar fluids such as CO9. Cosolvents (also called entrainers, modifiers, moderators) such as alcohols and acetone have been added to fluids to raise the solvent strength. The addition of only 2 mol % of the complexing agent tri-/i-butyl phosphate (TBP) to CO9 increases the solubility ofnydro-quinone by a factor of 250 due to Lewis acid-base interactions. Veiy recently, surfac tants have been used to form reverse micelles, microemulsions, and polymeric latexes in SCFs including CO9. These organized molecular assemblies can dissolve hydrophilic solutes and ionic species such as amino acids and even proteins. Examples of surfactant tails which interact favorably with CO9 include fluoroethers, fluoroacrylates, fluoroalkanes, propylene oxides, and siloxanes. 

NENITZESCU Indole Synthesis Indole synthesis trom quinones and amino crotonates... 

This derivative is prepared from an A-protected amino acid and the anthrylmethyl alcohol in the presence of DCC/hydroxybenzotriazole. It can also be prepared from 2-(bromomethyl)-9,10-anthraquinone (Cs2C03). It is stable to moderately acidic conditions (e.g., CF3COOH, 20°, 1 h HBr/HOAc, / 2 = 65 h HCl/ CH2CI2, 20°, 1 h). Cleavage is effected by reduction of the quinone to the hy-droquinone i in the latter, electron release from the —OH group of the hydroqui-none results in facile cleavage of the methylene-carboxylate bond. The related 2-phenyl-2-(9,10-dioxo)anthrylmethyl ester has also been prepared, but is cleaved by electrolysis (—0.9 V, DMF, 0.1 M LiC104, 80% yield). ... 

Aminosalicylic acid (5-amino-2-hydroxybenzoic acid) [89-57-6] M 153.1, m 276-280 , 283 (dec), pK 2.74 (CO2H), pK 5.84 (NH2). Cryst as needles from H2O containing a little NaHS03 to avoid aerial oxidation to the quinone-imine. The Me ester gives needles from C6H6, m 96°, and the hydrazide has m 180-182° (From H2O). [Fallab et al. Helv Chim Acta 34 26 1951, Shavel J Amer Pharm Assoc 42 402 1953.]... 

Orange RO acid orange 8, l,8-[bis(4-n-propyl-3-sulfopbenyl-l-amino)]antbra-9,10-quinone di-Na salt] [5850-86-2] M 364.4, Cl 15575, Xmax 490nm. Salted out three times with sodium acetate, then repeatedly extracted with EtOH. 

Dioxo-2, 4, 5 -trimethylcyclohexa-l, 4 -diene)-3,3-dimetbylpropi-onamide (Q). The application of this well-known acid [3-(3, 6 -dioxo-2, 4, 5 -trimethylcyclohexa-l, 4 -diene)-3,3-dimethylpropionic acid] to protection of the amino function for peptide synthesis has been examined. Reduction of the quinone with sodium dithionite causes rapid trimethyl lock -facilitated ring closure with release of the amine. 

The Nenitzescu reaction generally occurs under relatively mild reaction conditions. Moreover mono-, di-, and tri-substituted quinones react with equal facility. Many enamines including p-aminoacrylonitriles, p-aminoacrylamides, and p-amino-a,p-unsaturated ketones react with quinones to form indole nuclei as well. The mild reaction conditions and the availability of the starting material render it attractive even in those instances where the yield of the product is low. ... 

Oxidations of pyridopyrimidines are rare, but the covalent hydrates of the parent compounds undergo oxidation with hydrogen peroxide to yield the corresponding pyridopyrimidin-4(3 T)-ones. Dehydrogenation of dihydropyrido[2,3-(i]pyrimidines by means of palladized charcoal, rhodium on alumina, or 2,3-diehloro-5,6-dicyano-p-benzo-quinone (DDQ) to yield the aromatic derivatives have been reported. Thus, 7-amino-5,6-dihydro-1,3-diethylpyrido[2,3-d]-pyri-midine-2,4(lif,3f/)-dione (177) is aromatized (178) when treated with palladized charcoal in refluxing toluene for 24 hours. 

Different azanthraquinones 390-392 were prepared from 3-amino-4-imino-4//-pyrido[l,2-a]pyrazines 373 with 1,4-quinones in one pot reactions via [4-1-2] cycloaddition and the subsequent ring transformation (Scheme 9) (97T5455). 

Figure 11.5 3-Amino-5-hydroxybenzoic acid as a precursor to the porfiromycin C quinone. 

The vast majority of azo dyes are azo compounds containing hydroxy or amino groups in the 2- or 4-position with respect to the azo group (e.g., 1.8). They are in equilibrium with their tautomers, the quinone hydrazones (quinone monoimine hydrazones). In spite of the fact that in most hydroxyazo dyes the equilibrium is shifted in favor of the quinone hydrazone, they are still called azo compounds. 

The major problem of these diazotizations is oxidation of the initial aminophenols by nitrous acid to the corresponding quinones. Easily oxidized amines, in particular aminonaphthols, are therefore commonly diazotized in a weakly acidic medium (pH 3, so-called neutral diazotization) or in the presence of zinc or copper salts. This process, which is due to Sandmeyer, is important in the manufacture of diazo components for metal complex dyes, in particular those derived from l-amino-2-naphthol-4-sulfonic acid. Kozlov and Volodarskii (1969) measured the rates of diazotization of l-amino-2-naphthol-4-sulfonic acid in the presence of one equivalent of 13 different sulfates, chlorides, and nitrates of di- and trivalent metal ions (Cu2+, Sn2+, Zn2+, Mg2+, Fe2 +, Fe3+, Al3+, etc.). The rates are first-order with respect to the added salts. The highest rate is that in the presence of Cu2+. The anions also have a catalytic effect (CuCl2 > Cu(N03)2 > CuS04). The mechanistic basis of this metal ion catalysis is not yet clear. 

In conclusion, with regard to the structure of benzenediazonium compounds with electron donor substituents in the 2- or 4-position, the most recent experimental data, mainly X-ray analyses and 13C and 15N NMR data, are consistent with 4.4 as the dominant mesomeric structure of quinone diazides, as proposed by Lowe-Ma et al. (1988). For benzenediazonium salts with a tertiary amino group in the 4-position the data are consistent with the quinonoid structure 4.20 as the dominant mesomeric form. 

The photolysis of o-quinone diazides was carefully investigated by Stis in 1944, many years before the development of photoresists. Scheme 10-102 shows the photolysis sequence for the diazoquinone 10.75 formed in the diazotization of 2-amino-1-naphthol. The product of the photolytic step is a ketocarbene (10.76), which undergoes a Wolff rearrangement to a ketene (10.77). In the presence of water in-dene-3-carboxylic acid (10.78) is formed this compound is highly soluble in water and can be removed in the development step. The mechanism given in Scheme 10-102 was not postulated as such by Stis, because in 1944 ketocarbenes were unknown (for a mechanistic discussion of such Wolff rearrangements see review by Zollinger, 1995, Sec. 8.6, and Andraos et al., 1994). 

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