The Metabolic Fate of ortho-Quinones Derived from Catecholamine Metabolites

ortho-Quinones are produced in vivo through the oxidation of catecholic substrates by enzymes such as tyrosinase or by transition metal ions. Neuromelanin, a dark pigment present in the substantia nigra and locus coeruleus of the brain, is produced from dopamine (DA) and norepinephrine (NE) via an interaction with cysteine, but it also incorporates their alcoholic and acidic metabolites. In this study we examined the metabolic fate of ortho-quinones derived from the catecholamine metabolites, 3,4-dihydroxyphenylethanol (DOPE), 3,4-dihydroxyphenylethylene glycol (DOPEG), 3,4-dihydroxyphenylacetic acid (DOPAC) and 3,4-dihydroxyphenylmandelic acid (DOMA). The oxidation of catecholic substrates by mushroom tyrosinase was followed by UV-visible spectrophotometry. HPLC analysis after reduction with NaBH₄ or ascorbic acid enabled measurement of the half-lives of ortho-quinones and the identification of their reaction products. Spectrophotometric examination showed that the ortho-quinones initially formed underwent extensive degradation at pH 6.8. HPLC analysis showed that DOPE-quinone and DOPEG-quinone degraded with half-lives of 15 and 30 min at pH 6.8, respectively, and >100 min at pH 5.3. The major product from DOPE-quinone was DOPEG which was produced through the addition of a water molecule to the quinone methide intermediate. DOPEG-quinone yielded a ketone, 2-oxo-DOPE, through the quinone methide intermediate. DOPAC-quinone and DOMA-quinone degraded immediately with decarboxylation of the ortho-quinone intermediates to form 3,4-dihydroxybenzylalcohol (DHBAlc) and 3,4-dihydroxybenzaldehyde (DHBAld), respectively. DHBAlc-quinone was converted to DHBAld with a half-life of 9 min, while DHBAld-quinone degraded rapidly with a half-life of 3 min. This study confirmed the fact that ortho-quinones from DOPE, DOPEG, DOPAC and DOMA are converted to quinone methide tautomers as common intermediates, through proton rearrangement or decarboxylation. The unstable quinone methides afford stable alcoholic or carbonyl products.     

Asymmetric Diels–Alder and Cascade Reaction of Quinone Imine Ketals and 2,4‐Dienals: Construction of Chiral Benzo[de]quinolone Derivatives

An asymmetric Diels–Alder cycloaddition reaction of quinone imine ketals and 2,4‐dienals has been investigated via trienamine catalysis of a secondary chiral amine. A series of chiral tricyclic benzo[de]quinolone derivatives were efficiently constructed in moderate to good yields and with high to excellent enantioselectivity after a cascade aromatization/intramolecular hemiaminal formation sequence (up to 98% ee, >19:1 dr). The methodology and the useful product scaffolds could be further utilized in both synthetic and medicinal fields.

     

生育酚氧化产物生育酚醌的研究进展

植物油脂中生育酚含量较为丰富。加热是油脂食用的主要方式（微波、烘箱和煎炸等过程）之一,在此过程中油脂会发生氧化,而生育酚作为抗氧化剂参与氧化进程,生成生育酚醌（TQ）,TQ是一类潜在的食品安全危害因子。为食品科研人员科学认识、评价TQ,归纳总结了TQ的检测方法、在食品加工中的生成规律影响因素、细胞毒性及抗氧化活性方面的研究,提出了目前TQ研究存在的问题,并对今后的研究重点作了展望。关于TQ的后续研究应集中于TQ单体的定量检测技术、TQ在食品加工中的迁移规律及其毒性研究等方面。     

直接氧化法合成2,3,5-三甲基氢醌

以MnO2-H2SO4混合物作为氧化剂，通过直接氧化法合成得到2，3，5－三甲基氢醌（TMHQ）。比较理想的工艺条件是：H2SO4的含量控制在30％－40％，2，3，6－三甲基苯酚：二氧化锰＝1：2（摩尔比），在约65℃反应3h，TMHQ的产率为60．8％。     

Understanding Defect‐Stabilized Noncovalent Functionalization of Graphene

The noncovalent functionalization of graphene by small molecule aromatic adsorbates, phenanthrenequinone (PQ), is investigated systematically by combining electrochemical characterization, high‐resolution interfacial X‐ray scattering, and ab initio density functional theory calculations. The findings in this study reveal that while PQ deposited on pristine graphene is unstable to electrochemical cycling, the prior introduction of defects and oxygen functionality (hydroxyl and epoxide groups) to the basal plane by exposure to atomic radicals (i.e., oxygen plasma) effectively stabilizes its noncovalent functionalization by PQ adsorption. The structure of adsorbed PQ molecules resembles the graphene layer stacking and is further stabilized by hydrogen bonding with terminal hydroxyl groups that form at defect sites within the graphene basal plane. The stabilized PQ/graphene interface demonstrates persistent redox activity associated with proton‐coupled‐electron‐transfer reactions. The resultant PQ adsorbed structure is essentially independent of electrochemical potentials. These results highlight a facile approach to enhance functionalities of the otherwise chemically inert graphene using noncovalent interactions.     

Efficient aerobic oxidation of hydrocarbons with O2 catalyzed by DDQ/NHPI

BACKGROUND: Organocatalysis, a promising strategy for the oxidation of organic compounds, does not involve the use of a catalytic metal. In this work, an efficient organocatalyst system consisting of 2,3‐dichloro‐5,6‐dicyano‐benzoquinone (DDQ) and N‐hydroxyphthalimide (NHPI) was studied. RESULTS: 72.2% conversion with 92.3% selectivity for acetophenone was obtained in ethylbenzene oxygenation catalyzed by DDQ/NHPI under 0.3 MPa of molecular oxygen at 80 °C for 10 h. In addition, other hydrocarbons were also oxidized with high efficiency using this catalyst system. UV/Vis spectroscopy of the catalytic system indicated that DDQ accelerated the generation of free radical phthalimido‐N‐oxyl (PINO) by abstracting a hydrogen atom from NHPI. CONCLUSION: An efficient organocatalyst system consisting of DDQ and NHPI for selective oxidation of hydrocarbons to corresponding ketones with molecular oxygen as oxidant is reported. DDQ promoted the generation of PINO from NHPI, and the oxidation reaction was accelerated via PINO. This organocatalyst system should be useful for the design of highly selective catalysts for hydrocarbon oxidation. Copyright © 2010 Society of Chemical Industry     

Role of Quinone Metabolites in PAH Carcinogenesis

Evidence concerning the role of dihydrodiol dehydrogenase-catalyzed formation of quinone metabolites in the mechanism in PAH carcinogenesis is reviewed and methods for the synthesis of the adducts formed by reaction of PAH quinone metabolites with DNA are reported.     

红麻KP法、A-SQ法蒸煮试验

在这篇文章里,红麻采用KP法蒸煮,在硫化度25％左右得到最好的收获率。采用AS—AQ法能比较容易制得红麻化学浆,用试验方法确定了红麻AS—AQ法制浆适宜的蒸煮条件。     

Characterization of the biosynthesis gene cluster for alkyl-O-dihydrogeranyl-methoxyhydroquinones in Actinoplanes missouriensis

A polyketide biosynthesis gene cluster (agq) was found on the genome of a rare actinomycete, Actinoplanes missouriensis. Streptomyces lividans expressing agqA encoding a type III polyketide synthase produced alkylresorcinols mainly from C(16-17) fatty acids. Heterologous expression of the agq genes in S. lividans indicated the function of cognate polyketide modification enzymes; a monooxygenase AgqB hydroxylates the alkylresorcinols to yield 6-alkyl-2-hydroxyhydroquinones, a methyltransferase AgqC catalyzes O-methylation of the alkyl-hydroxyhydroquinones to yield 6-alkyl-2-methoxyhydroquinones, and a UbiA-like prenyltransferase AgqD attaches a prenyl group to the C-4 hydroxy group of the alkyl-methoxyhydroquinones to yield 6-alkyl-4-O-geranyl-2-methoxyhydroquinones and 6-alkyl-4-O-dihydrofarnesyl-2-methoxyhydroquinones derived from C(16-17) fatty acids. In contrast, A. missouriensis was found to produce 6-alkyl-4-O-dihydrogeranyl-2-methoxyhydroquinones derived from C(16-18) fatty acids by the function of the agq gene cluster. All of these prenylated phenolic lipids were novel compounds.     

Insecticidal activity of hypericin towardsManduca sexta larvae

The toxic effect of hypericin (HYP), a photodynamic quinone that occurs in certain species of the genusHypericum, towardsManduca sexta third-instar larvae was investigated. The LD₅₀ of purified hypericin was 16 g/g larval initial fresh weight in constant light (22 W/m²). Reduced irradiance resulted in decreased mortality. Sublethal applications retarded larval growth (body fresh weight) in a dose-dependent manner. Toxicity had an absolute light dependence at the dose levels used, the active wavelengths being >500 nm. The phototoxic effect was rapidly lost when larvae were maintained in darkness (>8 hr) prior to irradiation. However, the potential for light-dependent mortality was retained if larvae were starved prior to irradiation.