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Epoxidation of styrenes with the peroxidase from the cultured cells of Nicotiana tabacum
An enzyme concerned with the epoxidation of styrenes was isolated from cultured cells of Nicotiana tabacum. The enzyme had peroxidase activity as well as epoxidation activity, and its amino acid sequence showed 89% homology in their 9 amino acid overlap with horseradish peroxidase. In the enzymatic reaction, hydrogen peroxide and p-cresol were necessary and molecular oxygen was the source of the oxygen atom of the epoxide. The enzymatic reaction using a spin trap reagent and monitoring of the reaction with ESR indicated that the epoxidation reaction of styrenes proceeded by a radical mechanism with peroxidase.
Hirata, Toshifumi,Izumi, Shunsuke,Ogura, Masayuki,Yawata, Takayuki
p. 15993 - 16003
(1998)
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Hydroxylation of chlorotoluenes and cresols: a pulse radiolysis, laser flash photolysis, and product analysis study
The reactions of ·OH, O·- and SO4·- with 2-, 3-, and 4-cresols were studied by pulse radiolysis, laser flash photolysis, and product analysis techniques. The rates of OH reaction with cresols are very high (k ≈ 1 × 1010 M-1 s-1), whereas O·- was found to be less reactive (k ≈ 2.4 × 109 M-1 s-1). The second-order rate constants for SO4·- reaction with cresols are in the range (3-6) × 109 M-1 s-1. The transient absorption spectra measured in OH reaction exhibited peaks in the range 295-325 nm with a red shift for the meta isomer. The absorption spectra obtained for O·- reaction with 2-cresol has a peak at 360 nm. The absorption spectra of the transient species in SO4·- reaction obtained by pulse radiolysis and flash photolysis techniques are similar, with absorption maxima centered around 290 and 390 nm in all three isomers. The intermediates formed in ·OH, O·-, and SO4·- reactions are assigned to OH adducts, substituted benzyl radicals, and radical cations, respectively.
Choure,Bamatraf,Rao,Das,Mohan,Mittal
p. 9837 - 9845
(1997)
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Selective C-C Bond Cleavage of Methylene-Linked Lignin Models and Kraft Lignin
Biorefinery and paper pulping lignins, referred hereto as technical lignins, contain condensed C-C interunit linkages. These robust C-C linkages with higher bond dissociation energies are difficult to disrupt under hydrogenolysis conditions, which are gen
Shuai, Li,Sitison, Jake,Sadula, Sunitha,Ding, Junhuan,Thies, Mark C.,Saha, Basudeb
p. 6507 - 6512
(2018)
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Efficient demethylation of aromatic methyl ethers with HCl in water
A green, efficient and cheap demethylation reaction of aromatic methyl ethers with mineral acid (HCl or H2SO4) as a catalyst in high temperature pressurized water provided the corresponding aromatic alcohols (phenols, catechols, pyrogallols) in high yield. 4-Propylguaiacol was chosen as a model, given the various applications of the 4-propylcatechol reaction product. This demethylation reaction could be easily scaled and biorenewable 4-propylguaiacol from wood and clove oil could also be applied as a feedstock. Greenness of the developed methodversusstate-of-the-art demethylation reactions was assessed by performing a quantitative and qualitative Green Metrics analysis. Versatility of the method was shown on a variety of aromatic methyl ethers containing (biorenewable) substrates, yielding up to 99% of the corresponding aromatic alcohols, in most cases just requiring simple extraction as work-up.
Bomon, Jeroen,Bal, Mathias,Achar, Tapas Kumar,Sergeyev, Sergey,Wu, Xian,Wambacq, Ben,Lemière, Filip,Sels, Bert F.,Maes, Bert U. W.
supporting information
p. 1995 - 2009
(2021/03/26)

Thiols Act as Methyl Traps in the Biocatalytic Demethylation of Guaiacol Derivatives
Demethylating methyl phenyl ethers is challenging, especially when the products are catechol derivatives prone to follow-up reactions. For biocatalytic demethylation, monooxygenases have previously been described requiring molecular oxygen which may cause oxidative side reactions. Here we show that such compounds can be demethylated anaerobically by using cobalamin-dependent methyltransferases exploiting thiols like ethyl 3-mercaptopropionate as a methyl trap. Using just two equivalents of this reagent, a broad spectrum of substituted guaiacol derivatives were demethylated, with conversions mostly above 90 %. This strategy was used to prepare the highly valuable antioxidant hydroxytyrosol on a one-gram scale in 97 % isolated yield.
Grimm, Christopher,Kroutil, Wolfgang,Pompei, Simona,Schiller, Christine,Schober, Lukas
supporting information
p. 16906 - 16910
(2021/07/02)

Anchimerically Assisted Selective Cleavage of Acid-Labile Aryl Alkyl Ethers by Aluminum Triiodide and N, N-Dimethylformamide Dimethyl Acetal
Aluminum triiodide is harnessed by N,N-dimethylformamide dimethyl acetal (DMF-DMA) for the selective cleavage of ethers via neighboring group participation. Various acid-labile functional groups, including carboxylate, allyl, tert-butyldimethylsilyl (TBS), and tert-butoxycarbonyl (Boc), suffer the conditions intact. The method offers an efficient approach to cleaving catechol monoalkyl ethers and to uncovering phenols from acetal-type protecting groups such as methoxymethyl (MOM), methoxyethoxymethyl (MEM), and tetrahydropyranyl (THP) chemoselectively.
Sang, Dayong,Yue, Huaxin,Zhao, Zhengdong,Yang, Pengtao,Tian, Juan
p. 6429 - 6440
(2020/07/14)

Selective ether bond breaking method of aryl alkyl ether
The invention discloses a selective aryl alkyl ether cracking method, which comprises that aryl alkyl ether, aluminum iodide and an additive are subjected to a selective ether bond cleavage reaction in an organic solvent at a temperature of -20 DEG C to a reflux temperature to generate phenol and derivatives thereof. The method is mild in condition and simple and convenient to operate, is suitablefor cracking aryl alkyl ether containing o-hydroxyl and o-carbonyl and acetal ether, and can also be used for removing tertiary carbon hydroxyl protecting groups with higher steric hindrance, such astriphenylmethyl, tertiary butyl and the like.
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Paragraph 0109-0113

(2020/09/16)

METHOD OF ENHANCED AROMATIC SELECTIVITY FOR GAS PHASE DEOXYGENATION OF BIO-OILS
Methods for gas-phase deoxygenation of a bio-oil are provided. In embodiments, such a method comprises exposing a bio-oil vapor comprising hydrocarbon compounds having oxygenated aromatic groups, to hydrogen gas in the presence of catalyst under conditions to induce deoxygenation of the oxygenated aromatic groups to provide a deoxygenated aromatic species, wherein the catalyst is a transition metal-incorporated mesoporous silicate having platinum deposited thereon and the transition metal is selected from Nb, W, Zr, and combinations thereof. The transition metal-incorporated mesoporous silicate catalysts are also provided.
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Paragraph 0010; 0013; 0040-0042

(2021/01/23)

Oxygen-Free Regioselective Biocatalytic Demethylation of Methyl-phenyl Ethers via Methyltransfer Employing Veratrol- O-demethylase
The cleavage of aryl methyl ethers is a common reaction in chemistry requiring rather harsh conditions; consequently, it is prone to undesired reactions and lacks regioselectivity. Nevertheless, O-demethylation of aryl methyl ethers is a tool to valorize natural and pharmaceutical compounds by deprotecting reactive hydroxyl moieties. Various oxidative enzymes are known to catalyze this reaction at the expense of molecular oxygen, which may lead in the case of phenols/catechols to undesired side reactions (e.g., oxidation, polymerization). Here an oxygen-independent demethylation via methyl transfer is presented employing a cobalamin-dependent veratrol-O-demethylase (vdmB). The biocatalytic demethylation transforms a variety of aryl methyl ethers with two functional methoxy moieties either in 1,2-position or in 1,3-position. Biocatalytic reactions enabled, for instance, the regioselective monodemethylation of substituted 3,4-dimethoxy phenol as well as the monodemethylation of 1,3,5-trimethoxybenzene. The methyltransferase vdmB was also successfully applied for the regioselective demethylation of natural compounds such as papaverine and rac-yatein. The approach presented here represents an alternative to chemical and enzymatic demethylation concepts and allows performing regioselective demethylation in the absence of oxygen under mild conditions, representing a valuable extension of the synthetic repertoire to modify pharmaceuticals and diversify natural products.
Grimm, Christopher,Lazzarotto, Mattia,Pompei, Simona,Schichler, Johanna,Richter, Nina,Farnberger, Judith E.,Fuchs, Michael,Kroutil, Wolfgang
p. 10375 - 10380
(2020/10/02)

Structural features and antioxidant activities of Chinese quince (Chaenomeles sinensis) fruits lignin during auto-catalyzed ethanol organosolv pretreatment
Chinese quince fruits (Chaenomeles sinensis) have an abundance of lignins with antioxidant activities. To facilitate the utilization of Chinese quince fruits, lignin was isolated from it by auto-catalyzed ethanol organosolv pretreatment. The effects of three processing conditions (temperature, time, and ethanol concentration) on yield, structural features and antioxidant activities of the auto-catalyzed ethanol organosolv lignin samples were assessed individually. Results showed the pretreatment temperature was the most significant factor; it affected the molecular weight, S/G ratio, number of β-O-4′ linkages, thermal stability, and antioxidant activities of lignin samples. According to the GPC analyses, the molecular weight of lignin samples had a negative correlation with pretreatment temperature. 2D-HSQC NMR and Py-GC/MS results revealed that the S/G ratios of lignin samples increased with temperature, while total phenolic hydroxyl content of lignin samples decreased. The structural characterization clearly indicated that the various pretreatment conditions affected the structures of organosolv lignin, which further resulted in differences in the antioxidant activities of the lignin samples. These results can be helpful for controlling and optimizing delignification during auto-catalyzed ethanol organosolv pretreatment, and they provide theoretical support for the potential applications of Chinese quince fruits lignin as a natural antioxidant in the food industry.
Cheng, Xi-Chuang,Guo, Xin-Ran,Liu, Hua-Min,Liu, Yu-Lan,Qin, Zhao,Wang, Xue-De
p. 4348 - 4358
(2020/09/22)

1-Methyl-1,4-cyclohexadiene as a Traceless Reducing Agent for the Synthesis of Catechols and Hydroquinones
Pro-aromatic and volatile 1-methyl-1,4-cyclohexadiene (MeCHD) was used for the first time as a valid H-atom source in an innovative method to reduce ortho or para quinones to obtain the corresponding catechols and hydroquinones in good to excellent yields. Notably, the excess of MeCHD and the toluene formed as the oxidation product can be easily removed by evaporation. In some cases, trifluoroacetic acid as a catalyst was added to obtain the desired products. The reaction proceeds in air and under mild conditions, without metal catalysts and sulfur derivatives, resulting in an excellent and competitive method to reduce quinones. The mechanism is attributed to a radical reaction triggered by a hydrogen atom transfer from MeCHD to quinones, or, in the presence of trifluoroacetic acid, to a hydride transfer process.
Baschieri, Andrea,Amorati, Riccardo,Valgimigli, Luca,Sambri, Letizia
p. 13655 - 13664
(2019/10/28)

Cleavage of Catechol Monoalkyl Ethers by Aluminum Triiodide-Dimethyl Sulfoxide
Using eugenol and vanillin as model substrates, a practical method is developed for the cleavage o -hydroxyphenyl alkyl ethers. Aluminum oxide iodide (O=AlI), generated in situ from aluminum triiodide and dimethyl sulfoxide, is the reactive ether cleaving species. The method is applicable to catechol monoalkyl ethers as well as normal phenyl alkyl ethers for the removal of methyl, ethyl, isopropyl, and benzyl groups. A variety of functional groups such as alkenyl, allyl, amide, cyano, formyl, keto, nitro, and halogen are well tolerated under the optimum conditions. Partial hydrodebromination was observed during the demethylation of 4-bromoguaiacol, and was resolved using excess DMSO as an acid scavenger. This convenient and efficient procedure would be a practical tool for the preparation of catechols.
Sang, Dayong,Tian, Juan,Tu, Xiaodong,He, Zhoujun,Yao, Ming
p. 704 - 712
(2019/01/23)

The multifunctional globin dehaloperoxidase strikes again: Simultaneous peroxidase and peroxygenase mechanisms in the oxidation of EPA pollutants
The multifunctional catalytic hemoglobin dehaloperoxidase (DHP) from the terebellid polychaete Amphitrite ornata was found to catalyze the H2O2-dependent oxidation of EPA Priority Pollutants (4-Me-o-cresol, 4-Cl-m-cresol and pentachlorophenol) and EPA Toxic Substances Control Act compounds (o-, m-, p-cresol and 4-Cl-o-cresol). Biochemical assays (HPLC/LC-MS) indicated formation of multiple oxidation products, including the corresponding catechol, 2-methylbenzoquinone (2-MeBq), and oligomers with varying degrees of oxidation and/or dehalogenation. Using 4-Br-o-cresol as a representative substrate, labeling studies with 18O confirmed that the O-atom incorporated into the catechol was derived exclusively from H2O2, whereas the O-atom incorporated into 2-MeBq was from H2O, consistent with this single substrate being oxidized by both peroxygenase and peroxidase mechanisms, respectively. Stopped-flow UV–visible spectroscopic studies strongly implicate a role for Compound I in the peroxygenase mechanism leading to catechol formation, and for Compounds I and ES in the peroxidase mechanism that yields the 2-MeBq product. The X-ray crystal structures of DHP bound with 4-F-o-cresol (1.42 ?; PDB 6ONG), 4-Cl-o-cresol (1.50 ?; PDB 6ONK), 4-Br-o-cresol (1.70 ?; PDB 6ONX), 4-NO2-o-cresol (1.80 ?; PDB 6ONZ), o-cresol (1.60 ?; PDB 6OO1), p-cresol (2.10 ?; PDB 6OO6), 4-Me-o-cresol (1.35 ?; PDB 6ONR) and pentachlorophenol (1.80 ?; PDB 6OO8) revealed substrate binding sites in the distal pocket in close proximity to the heme cofactor, consistent with both oxidation mechanisms. The findings establish cresols as a new class of substrate for DHP, demonstrate that multiple oxidation mechanisms may exist for a given substrate, and provide further evidence that different substituents can serve as functional switches between the different activities performed by dehaloperoxidase. More broadly, the results demonstrate the complexities of marine pollution where both microbial and non-microbial systems may play significant roles in the biotransformations of EPA-classified pollutants, and further reinforces that heterocyclic compounds of anthropogenic origin should be considered as environmental stressors of infaunal organisms.
Ghiladi, Reza A.,Malewschik, Talita,McGuire, Ashlyn H.,de Serrano, Vesna
(2019/08/30)

Heterogeneous Nitrogen-doped Graphene Catalysed HOO? Generation via a Non-radical Mechanism for Base-free Dakin Reaction
A heterogeneous nitrogen-doped graphene catalytic pathway for H2O2 activation to generate alkaline hydrogen peroxide (HOO?) through a non-radical mechanism was reported. Remarkably, the heterogeneous catalytic procedure has been used for the evergreen and environmentally Dakin reaction without using any transition metals, homogeneous bases, ligands, additives or promoters, completely. The study of catalyst structure and catalytic activities indicate that the most active sites are created by the graphitic N atoms at zig-zag edges of the sheets. In addition, N as dopant element changes the reactivity of the neighbour C atoms, and leads to the formation of carbon-hydroperoxide (C?(HOOH)) and C?O* (C?O?) transition state species on the graphene surface in catalytic the reaction. (Figure presented.).
Sun, Wei,Gao, Lingfeng,Sun, Xu,Yang, Hua,Zheng, Gengxiu
supporting information
p. 5210 - 5216
(2019/11/03)

Ether bond cracking method of phenylalkyl ether
The invention discloses an ether bond cracking method of phenylalkyl ether. The method comprises the following steps: performing ether bond breaking reaction on phenylalkyl ether at -20 to reflux temperature in the presence of aluminium triiodide and dimethyl sulfoxide, thereby generating phenol and derivatives thereof. The method disclosed by the invention is mild in condition, simple and convenient for operation, high in yield, and extensive in applicable phenylalkyl ether range.
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Paragraph 0078-0080

(2018/11/26)

A two-step process for the synthesis of hydroxytyrosol
A new process for the synthesis of hydroxytyrosol (3,4-dihy-droxyphenylethanol), the most powerful natural antioxidant currently known, by means of a two-step approach is reported. Catechol is first reacted with 2,2-dimethoxyacetaldehyde in basic aqueous medium to produce the corresponding mandelic derivative with > 90 % conversion of the limiting reactant and about 70 % selectivity to the desired para-hydroxyalkylat-ed compound. Thereafter, the intermediate is hydrogenated to hydroxytyrosol by using a Pd/C catalyst, with total conversion of the mandelic derivative and 68 % selectivity. This two-step process is the first example of a synthetic pathway for hydroxytyrosol that does not involve the use of halogenated components or reduction methodologies that produce stoichiometric waste. It also avoids the complex procedure currently used for hydroxytyrosol purification when it is extracted from wastewa-ter of olive oil production.
Ziosi, Paolo,Paolucci, Claudio,Santarelli, Francesco,Tabanelli, Tommaso,Passeri, Sauro,Cavani, Fabrizio,Righi, Paolo
p. 2202 - 2210
(2018/10/20)

Mechanistic Aspects of Hydrodeoxygenation of p-Methylguaiacol over Rh/Silica and Pt/Silica
The mechanism of p-methylguaiacol (PMG) hydrodeoxygenation (HDO) has been examined over two Rh/silica catalysts and a Pt/silica catalyst at 300 °C and 4 barg hydrogen. Sequential conversion of PMG to 4-methylcatechol is followed by m- and p-cresol formation and finally toluene production, although direct conversion of PMG to p-cresol is favored over a commercial Rh/silica catalyst. Dehydroxylation and hydrogenation are shown to occur over metal functions, while demethylation and demethoxylation are favored over the fumed silica support. A mechanistic pathway for HDO of PMG is proposed.
Bouxin, Florent P.,Zhang, Xingguang,Kings, Iain N.,Lee, Adam F.,Simmons, Mark J. H.,Wilson, Karen,Jackson, S. David
p. 1586 - 1589
(2018/09/25)

Method for preparing 4-methylcatechol by using methanol and magnesium
The invention relates to a method for preparing 4-methylcatechol by using methanol and magnesium. 4-methylcatechol is an important basic chemical raw material, many document reports on the synthesis processes of 4-methylcatechol exist, but the processes can not easily implement industrialization. The method comprises the following steps: carrying out a reaction on the raw material paracresol with methanol and magnesium to synthesize magnesium p-cresylate, synthesizing 3-methylsalicylaldehyde from the magnesium p-cresylate, and carrying out oxidation by using oxydol to synthesize the 4-methylcatechol. In terms of the paracresol, the total reaction yield can reach 80%. Compared with the existing documents, the method has the advantages of simple process route, mild reaction conditions, high reaction yield and the like, and is suitable for industrialization.
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Paragraph 0004

(2017/10/13)

A process for preparing 5 - substituted benzyl - 2, 4 - diamino pyrimidine and its derivatives (by machine translation)
The invention discloses a process for preparing 5 - substituted benzyl - 2, 4 - diamino pyrimidine and derivatives thereof, in particular can be used for preparing omay pullin, b a oxygen animal pen amine pyrimidine, such as palestinian kuikui purin. The invention relates to 5 - hydroxymethyl uracil as raw materials, through the electrophilic substitution reaction, chlorinated, amino and hydrolysis step preparation 5 - substituted benzyl - 2, 4 - diamino pyrimidine and its derivatives. The method can be used for preparing various 5 - substituted benzyl - 2, 4 - diaminopyrimidines of the molecule, thereby avoiding the high-pressure reaction step, the safety is high, and is suitable for industrial production. (by machine translation)
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Paragraph 0049; 0055; 0059

(2018/01/11)

Synthesis of α-oxygenated ketones and substituted catechols via the rearrangement of N-enoxy- and N-aryloxyphthalimides
A common approach to the synthesis of α-oxygenated carbonyl compounds and catechols is the treatment of a carbonyl compound or a phenol with an electrophilic oxygen source. As an alternative approach to these important structures, formal [3,3]-rearrangements of N-enoxyphthalimides, N-enoxyisoindolinones, and N-aryloxyphthalimides have been explored. When used in combination with an initial Chan-Lam coupling, these transformations facilitate the dioxygenation of alkenylboronic acids for the synthesis of α-oxygenated ketones and the dioxygenation of arylboronic acids for the synthesis of catechols. The rearrangements of N-enoxyisoindolinones have also been shown to be diastereoselective.
Kroc, Michelle A.,Patil, Aditi,Carlos, Anthony,Ballantine, Josiah,Aguilar, Stephanie,Mo, Dong-Liang,Wang, Heng-Yen,Mueller, Daniel S.,Wink, Donald J.,Anderson, Laura L.
p. 4125 - 4137
(2017/06/29)

Deactivation study of the hydrodeoxygenation of p-methylguaiacol over silica supported rhodium and platinum catalysts
Hydrodeoxygenation of para-methylguaiacol using silica supported Rh or Pt catalysts was investigated using a fixed-bed reactor at 300?°C, under 4 barg hydrogen and a WHSV of 2.5?h?1. The activity, selectivity and deactivation of the catalysts were examined in relation to time on stream. Three catalysts were tested: 2.5% Rh/silica supplied by Johnson Matthey (JM), 2.5% Rh/silica and 1.55% Pt/silica both prepared in-house. The Rh/silica (JM) showed the best stability with steady-state reached after 6?h on stream and a constant activity over 3?days of reaction. In contrast the other two catalysts did not reach steady state within the timeframe of the tests, with continuous deactivation over the time on stream. Nevertheless higher coking was observed on the Rh/silica (JM) catalyst, while all three catalysts showed evidence of sintering. The Pt catalyst (A) showed higher selectivity for the production of 4-methylcatechol while the Rh catalysts were more selective toward the cresols. In all cases, complete hydrodeoxygenation of the methylguaiacol to methylcyclohexane was not observed.
Bouxin,Zhang,Kings,Lee,Simmons,Wilson,Jackson
p. 29 - 37
(2017/04/13)

Renewable Thermoplastics Based on Lignin-Derived Polyphenols
A series of renewable triphenylmethane-type polyphenols (TPs) were synthesized from lignin-derived guaiacols (methylguaiacol and propylguaiacol) and aldehydes (4-hydroxybenzaldehyde, vanillin, and syringaldehyde). By converting guaiacols to catechols through ortho-demethylation, the newly formed phenolic para site remarkably improved the reactivity as reflected by conversion of TPs. Optimized reagent molar ratios were aldehyde/catechol (1:4) and aldehyde/H2SO4 (1:3). A typical TP (VAN-M-CAT) was converted to glycidyl ether (GE-VAN-M-CAT) to examine its feasibility as precursor to epoxy thermosets. The resulting network exhibited excellent glassy modulus (12.3 GPa), glass transition temperature (167 °C), and thermal stability, which were attributed to the rigid triphenylmethane framework, high functionality (n = 5), and high cross-link density. A fully biobased epoxy comonomer (VAN-LIN-EPO), which was prepared by esterification of VAN-M-CAT with linoleic acid followed by epoxidation, could tune the material properties. This study widens the synthesis route of fully biobased polyphenols, which can yield polymers with excellent properties.
Zhao, Shou,Abu-Omar, Mahdi M.
p. 3573 - 3581
(2017/05/16)

Quinone-induced protein modifications: Kinetic preference for reaction of 1,2-benzoquinones with thiol groups in proteins
Oxidation of polyphenols to quinones serves as an antioxidative mechanism, but the resulting quinones may induce damage to proteins as they react through a Michael addition with nucleophilic groups, such as thiols and amines to give protein adducts. In this study, rate constants for the reaction of 4-methylbenzoquinone (4MBQ) with proteins, thiol and amine compounds were determined under pseudo first-order conditions by UV-vis stopped-flow spectrophotometry. The chemical structures of the adducts were identified by LC-ESI-MS/MS. Proteins with free thiols were rapidly modified by 4MBQ with apparent second order rate constants, k2 of (3.1±0.2)×104 M-1 s-1 for bovine serum albumin (BSA) and (4.8±0.2)×103 M-1 s-1 for human serum albumin at pH 7.0. These values are at least 12-fold greater than that for α-lactalbumin (4.0±0.2)×102 M-1 s-1, which does not contain any free thiols. Reaction of Cys-34 of BSA with N-ethylmaleimide reduced the thiol concentration by ~59%, which resulted in a decrease in k2 by a similar percentage, consistent with rapid adduction at Cys-34. Reaction of 4MBQ with amines (Gly, Nα-acetyl-l-Lys, N?-acetyl-l-Lys and l-Lys) and the guanidine group of Nα-acetyl-l-Arg was at least 5×105 slower than with low-molecular-mass thiols (l-Cys, Nα-acetyl-l-Cys, glutathione). The thiol-quinone interactions formed colorless thiol-phenol products via an intermediate adduct, while the amine-quinone interactions generated colored amine-quinone products that require oxygen involvement. These data provide strong evidence for rapid modification of protein thiols by quinone species which may be of considerable significance for biological and food systems.
Li, Yuting,Jongberg, Sisse,Andersen, Mogens L.,Davies, Michael J.,Lund, Marianne N.
p. 148 - 157
(2016/06/14)

Conversion of Simple Cyclohexanones into Catechols
A novel I2-catalyzed direct conversion of cyclohexanones to substituted catechols under mild and simple conditions has been described. This novel transformation is remarkable with the multiple oxygenation and dehydrogenative aromatization processes enabled just by using DMSO as the solvent, oxidant, and oxygen source. This metal-free and simple system demonstrates a versatile protocol for the synthesis of highly valuable substituted catechols and therefore streamlines the synthesis and modification of biologically important molecules for drug discovery.
Liang, Yu-Feng,Li, Xinyao,Wang, Xiaoyang,Zou, Miancheng,Tang, Conghui,Liang, Yujie,Song, Song,Jiao, Ning
supporting information
p. 12271 - 12277
(2016/09/28)

ZnCl2 induced catalytic conversion of softwood lignin to aromatics and hydrocarbons
Selective cleavage of C-O-C bonds in lignin without disrupting the C-C linkages can result in releasing aromatic monomers and dimers that can be subsequently converted into chemicals and fuels. Results from this study showed that both biomass-derived lignin and lignin model compounds were depolymerized in a highly concentrated ZnCl2 solution under relatively mild conditions (120 °C-200 °C, 4-6 h). Zn2+ ions in highly concentrated ZnCl2 aqueous solutions appeared to selectively coordinate with C-O-C bonds to cause the key linkages of lignin to be much easier to cleave under mild conditions. In a 63 wt% ZnCl2 solution at 200 °C for 6 h, nearly half of the softwood technical lignin was converted to oil products, of which the majority were alkylphenols. Results indicated that most of the β-O-4 and Cmethyl-OAr bonds of the lignin model compounds were cleaved under the above reaction conditions, providing a foundation towards understanding lignin depolymerization in a concentrated ZnCl2 solution. Furthermore, by adding Ru/C as a co-catalyst, the phenolic products were further converted into more stable cyclic hydrocarbons via hydrodeoxygenation and coupling reactions.
Wang, Hongliang,Zhang, Libing,Deng, Tiansheng,Ruan, Hao,Hou, Xianglin,Cort, John R.,Yang, Bin
p. 2802 - 2810
(2016/05/24)

H2O2 in WEB: a highly efficient catalyst system for the Dakin reaction
Without using any transition metal catalyst, ligand, base, toxic or hazardous reagent, additives/promoters and organic solvent, green Dakin reactions have been successfully carried out by using H2O2 in a natural feedstock extract. The reaction proceeds in neat 'Water Extract of Banana' (WEB) at room temperature under aerobic conditions in very short reaction times and, therefore, it is an evergreen and environmentally sound alternative to the existing protocols for the Dakin reaction. In our system, the reaction was found to afford excellent yield for the desired product with different electron-withdrawing and electron-donating hydroxylated benzaldehydes.
Saikia, Bishwajit,Borah, Parinita,Barua, Nabin Chandra
supporting information
p. 4533 - 4536
(2015/09/15)

A new avenue to the Dakin reaction in H2O2-WERSA
We have developed a novel protocol to realize the Dakin reaction in a more greener way. In fact, by the use of H2O2-WERSA, we can oxidize aromatic arylaldehydes to phenols at room temperature. It is remarkable that the catalytic system does not require activation or any toxic ligand, additive/promoter, transition metal catalyst, base, organic solvent and so on. A range of substituted hydroxylated benzaldehydes were screened to investigate the scope of this protocol.
Saikia, Bishwajit,Borah, Parinita
p. 105583 - 105586
(2015/12/30)

Efficient Biomimetic Hydroxylation Catalysis with a Bis(pyrazolyl)imidazolylmethane Copper Peroxide Complex
Bis(pyrazolyl)methane ligands are excellent components of model complexes used to investigate the activity of the enzyme tyrosinase. Combining the N donors 3-tert-butylpyrazole and 1-methylimidazole results in a ligand that is capable of stabilising a (μ-η2:η2)-dicopper(II) core that resembles the active centre of tyrosinase. UV/Vis spectroscopy shows blueshifted UV bands in comparison to other known peroxo complexes, due to donor competition from different ligand substituents. This effect was investigated with the help of theoretical calculations, including DFT and natural transition orbital analysis. The peroxo complex acts as a catalyst capable of hydroxylating a variety of phenols by using oxygen. Catalytic conversion with the non-biological phenolic substrate 8-hydroxyquinoline resulted in remarkable turnover numbers. In stoichiometric reactions, substrate-binding kinetics was observed and the intrinsic hydroxylation constant, kox, was determined for five phenolates. It was found to be the fastest hydroxylation model system determined so far, reaching almost biological activity. Furthermore, Hammett analysis proved the electrophilic character of the reaction. This sheds light on the subtle role of donor strength and its influence on hydroxylation activity.
Wilfer, Claudia,Liebh?user, Patricia,Hoffmann, Alexander,Erdmann, Hannes,Grossmann, Oleg,Runtsch, Leander,Paffenholz, Eva,Schepper, Rahel,Dick, Regina,Bauer, Matthias,Dürr, Maximilian,Ivanovic-Burmazovic, Ivana,Herres-Pawlis, Sonja
supporting information
p. 17639 - 17649
(2015/12/08)

Carbon nanotubes as activating tyrosinase supports for the selective synthesis of catechols
A series of redox catalysts based on the immobilization of tyrosinase on multiwalled carbon nanotubes has been prepared by applying the layer-by-layer principle. The oxidized nanotubes (ox-MWCNTs) were treated with poly(diallyl dimethylammonium chloride) (PDDA) and tyrosinase to yield ox-MWCNTs/PDDA/ tyrosinase I. Catalysts II and III have been prepared by increasing the number of layers of PDDA and enzyme, while IV was obtained by co-immobilization of tyrosinase with bovine serum albumin (ox-MWCNTs/PDDA/BSA-tyrosinase). Attempts to covalently bind tyrosinase provided weakly active systems. The coating of the enzyme based on the simple layer-by-layer principle has afforded catalysts I-III, with a range of activity from 21 units/mg (multilayer, II) to 66 units/mg (monolayer, I), the best system being catalyst IV (80 units/mg). The novel catalysts were fully characterized by scanning electron microscopy and atomic force microscopy, showing increased activity with respect to that of the native enzyme. These catalysts were used in the selective synthesis of catechols by oxidation of meta- and para-substituted phenols in an organic solvent (CH 2Cl2) as the reaction medium. It is worth noting that immobilized tyrosinase was able to catalyze the oxidation of very hindered phenol derivatives that are slightly reactive with the native enzyme. The increased reactivity can be ascribed to a stabilization of the immobilized tyrosinase. The novel catalysts I and IV retained their activity for five subsequent reactions, showing a higher stability in organic solvent than under traditional buffer conditions.
Subrizi, Fabiana,Crucianelli, Marcello,Grossi, Valentina,Passacantando, Maurizio,Pesci, Lorenzo,Saladino, Raffaele
p. 810 - 822
(2014/04/03)

A general approach towards catechol and pyrogallol through ruthenium- and palladium-catalyzed C-H hydroxylation by weak coordination
An efficient ruthenium(II)- and palladium(II)-catalyzed C-H hydroxylation of aryl carbamates has been developed for the facile synthesis of catechols and pyrogallols. The reaction demonstrates excellent reactivity, regio- and chemoselectivity, good functional group compatibility and high yields. The practicality of this method has been proved by a gram-scale synthesis.
Yang, Xinglin,Sun, Yonghui,Chen, Zhang,Rao, Yu
p. 1625 - 1630
(2014/06/09)

Selective ortho-hydroxylation-defluorination of 2-fluorophenolates with a Bis(μ-oxo)dicopper(III) species
The bis(μ-oxo)dicopper(III) species [CuIII 2(μ-O)2(m-XYLMeAN)]2+ (1) promotes the electrophilic ortho-hydroxylation-defluorination of 2-fluorophenolates to give the corresponding catechols, a reaction that is not accomplishable with a (η2:η2-O2) dicopper(II) complex. Isotopic labeling studies show that the incoming oxygen atom originates from the bis(μ-oxo) unit. Ortho-hydroxylation-defluorination occurs selectively in intramolecular competition with other ortho-substituents such as chlorine or bromine. O in, F out: [CuIII2(μ-O) 2(m-XYLMeAN)]2+ is a bis(μ-oxo)dicopper(III) species and promotes the electrophilic ortho-hydroxylation-defluorination of 2-fluorophenolates to give the corresponding catechols. Isotopic labeling shows that the incoming oxygen atom originates from the bis(μ-oxo) unit. Ortho-hydroxylation-defluorination occurs selectively in intramolecular competition with other ortho-substituents such as chlorine or bromine.
Serrano-Plana, Joan,Garcia-Bosch, Isaac,Miyake, Ryosuke,Costas, Miquel,Company, Anna
supporting information
p. 9608 - 9612
(2014/10/15)

Catalytic phenol hydroxylation with dioxygen: Extension of the tyrosinase mechanism beyond the protein matrix
A new catalyst (see structure) hydroxylates phenols with O2 via a stable side-on peroxide complex, which is similar to the active site of tyrosinase in terms of the ligand environment and its spectroscopic properties. The catalytic oxidation of phenols to quinones proceeds at room temperature in the presence of NEt3 and even non-native substrates can be oxidized catalytically. The reaction mechanism is analogous to that of the enzyme-catalyzed reaction. Copyright
Hoffmann, Alexander,Citek, Cooper,Binder, Stephan,Goos, Arne,Ruebhausen, Michael,Troeppner, Oliver,Ivanovic-Burmazovic, Ivana,Wasinger, Erik C.,Stack, T. Daniel P.,Herres-Pawlis, Sonja
supporting information
p. 5398 - 5401
(2013/06/27)

An efficient strategy for protecting dihydroxyl groups of catechols
A novel strategy for protecting dihydroxyl groups of catechols has been developed. Base-mediated cyclizations of catechols with 1,3-dibromopropane provided the corresponding benzo[b]1,4-dioxepans, and herefrom the protecting group was easily cleaved by aluminum chloride. The preparation of the antibacterial and antifungal agent 4-(2-aminothiazol-4-yl)benzene-1,2-diol from catechol reliably verified its availability amenable to various harsh reaction conditions. Georg Thieme Verlag Stuttgart - New York.
Huang, Wei-Bin,Guo, Ying,Jiang, Jian-An,Pan, Xian-Dao,Liao, Dao-Hua,Ji, Ya-Fei
supporting information
p. 741 - 746
(2013/05/09)

PROCESS FOR THE CONVERSION OF LIGNIN TO LIQUID HYDROCARBONS
Process for the conversion of lignin to liquid hydro-carbons comprising: subjecting the lignin to hydrogenolysis in the presence of at least one hydrogenolysis catalyst, at a temperature ranging from 250° C. to 350° C., preferably ranging from 290° C. to 320 ° C., so as to obtain depolymerized lignin; subjecting said depolymerized lignin to hydrotreating so as to obtain a mixture of liquid hydrocarbons. Said liquid hydrocarbons can be used as such (biofuels) for the production of reformulated gasolines, or they can be used for the production of gasolines or of gas oils through conventional refining processes.
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Paragraph 0153-0168

(2013/03/26)

Layer-by-Layer coated tyrosinase: An efficient and selective synthesis of catechols
Agaricus bisporous tyrosinase was immobilized on commercial available epoxy-resin EupergitC250L and then coated by the Layer-by-Layer method (LbL). The two novel heterogeneous biocatalysts were characterized for their morphology, pH and storage stability, kinetic properties (Km, V max, Vmax/Km) and reusability. These biocatalysts were used for the efficient and selective synthesis of bioactive catechols under mild and environmental friendly experimental conditions. Ascorbic acid was added in the reaction medium to inhibit the formation of ortho-quinones, thus avoiding the known enzyme suicide inactivation process. Catechols were obtained mostly in quantitative yields and conversion of substrate. Tyrosinase immobilized on EupergitC250L and coated by the LbL method showed better catalytic activities, higher pH and storage stability, and reusability with respect to immobilized uncoated tyrosinase. Since chemical procedures to synthesize catechols are often expensive and with high environmental impact, the use of immobilized tyrosinase represents an efficient alternative for the preparation of this family of bioactive compounds.
Guazzaroni, Melissa,Crestini, Claudia,Saladino, Raffaele
experimental part
p. 157 - 166
(2012/02/13)

Hydroxylation of p-substituted phenols by tyrosinase: Further insight into the mechanism of tyrosinase activity
A study of the monophenolase activity of tyrosinase by measuring the steady state rate with a group of p-substituted monophenols provides the following kinetic information: kcatm and the Michaelis constant, KMm. Analysis of these data taking into account chemical shifts of the carbon atom supporting the hydroxyl group (δ) and σp+, enables a mechanism to be proposed for the transformation of monophenols into o-diphenols, in which the first step is a nucleophilic attack on the copper atom on the form Eox (attack of the oxygen of the hydroxyl group of C-1 on the copper atom) followed by an electrophilic attack (attack of the hydroperoxide group on the ortho position with respect to the hydroxyl group of the benzene ring, electrophilic aromatic substitution with a reaction constant ρ of -1.75). These steps show the same dependency on the electronic effect of the substituent groups in C-4. Furthermore, a study of a solvent deuterium isotope effect on the oxidation of monophenols by tyrosinase points to an appreciable isotopic effect. In a proton inventory study with a series of p-substituted phenols, the representation of kcatfn/kcatf0 against n (atom fractions of deuterium), where kcatfn is the catalytic constant for a molar fraction of deuterium (n) and kcatf0 is the corresponding kinetic parameter in a water solution, was linear for all substrates. These results indicate that only one of the proton transfer processes from the hydroxyl groups involved the catalytic cycle is responsible for the isotope effects. We suggest that this step is the proton transfer from the hydroxyl group of C-1 to the peroxide of the oxytyrosinase form (Eox). After the nucleophilic attack, the incorporation of the oxygen in the benzene ring occurs by means of an electrophilic aromatic substitution mechanism in which there is no isotopic effect.
Munoz-Munoz, Jose Luis,Berna, Jose,Garcia-Molina, Maria del Mar,Garcia-Molina, Francisco,Garcia-Ruiz, Pedro Antonio,Varon, Ramon,Rodriguez-Lopez, Jose N.,Garcia-Canovas, Francisco
scheme or table
p. 228 - 233
(2012/10/18)

Electrophilic arene hydroxylation and phenol O-H oxidations performed by an unsymmetric μ-I·1:I·1-O 2-peroxo dicopper(II) complex
Reactions of the unsymmetric dicopper(II) peroxide complex [Cu II2(μ-I·1: I·1-O2)(m-XYLN3N4)]2+ (1O2, where m-XYL is a heptadentate N-based ligand), with phenolates and phenols are described. Complex 1O2 reacts with p-X-PhONa (X=MeO, Cl, H, or Me) at -90°C performing tyrosinase-like ortho-hydroxylation of the aromatic ring to afford the corresponding catechol products. Mechanistic studies demonstrate that reactions occur through initial reversible formation of metastable association complexes [CuII2(μ- I·1:I·1-O2)(p-X-PhO) (m-XYLN3N4)]+ (1O2·X-PhO) that then undergo ortho-hydroxylation of the aromatic ring by the peroxide moiety. Complex 1O2 also reacts with 4-X-substituted phenols p-X-PhOH (X=MeO, Me, F, H, or Cl) and with 2,4-di-tert-butylphenol at -90°C causing rapid decay of 1O2 and affording biphenol coupling products, which is indicative that reactions occur through formation of phenoxyl radicals that then undergo radical C-C coupling. Spectroscopic UV/Vis monitoring and kinetic analysis show that reactions take place through reversible formation of ground-state association complexes [CuII2(μ- I·1:I·1-O2)(X-PhOH) (m-XYLN3N4)]2+ (1O2·X-PhOH) that then evolve through an irreversible rate-determining step. Mechanistic studies indicate that 1O2 reacts with phenols through initial phenol binding to the Cu2O2 core, followed by a proton-coupled electron transfer (PCET) at the rate-determining step. Results disclosed in this work provide experimental evidence that the unsymmetric 1O2 complex can mediate electrophilic arene hydroxylation and PCET reactions commonly associated with electrophilic Cu2O2 cores, and strongly suggest that the ability to form substrate·Cu2O2 association complexes may provide paths to overcome the inherent reactivity of the O 2-binding mode. This work provides experimental evidence that the presence of a H+ completely determines the fate of the association complex [CuII2(μ-I·1: I·1-O2)(X-PhO(H))(m-XYLN3N4)] n+ between a PCET and an arene hydroxylation reaction, and may provide clues to help understand enzymatic reactions at dicopper sites.
Garcia-Bosch, Isaac,Ribas, Xavi,Costas, Miquel
supporting information; body text
p. 2113 - 2122
(2012/04/10)

CoMo sulfide-catalyzed hydrodeoxygenation of lignin model compounds: An extended reaction network for the conversion of monomeric and dimeric substrates
In the present work, extensive hydrodeoxygenation (HDO) studies with a commercial sulfided CoMo/Al2O3 catalyst were performed on a library of lignin model compounds at 50 bar hydrogen pressure and 300 °C in dodecane, using a batch autoclave system. The catalyst was activated under hydrogen atmosphere prior to the reaction, and the spent catalyst was analyzed using thermogravimetric analysis. An extended reaction network is proposed, showing that HDO, demethylation, and hydrogenation reactions take place simultaneously. HDO of mono-oxygenated substrates proved to be difficult at the applied conditions. Starting from most positions in the network, phenol, and cresols are therefore the main final products, suggesting the possibility of convergence on a limited number of products from a mixture of substrates. HDO of dimeric model compounds mimicking typical lignin linkages revealed that coumaran alkyl ethers and β-O-4 bonds can be broken, but 5-5′ linkages not.
Jongerius, Anna L.,Jastrzebski, Robin,Bruijnincx, Pieter C.A.,Weckhuysen, Bert M.
scheme or table
p. 315 - 323
(2012/03/10)

Synthesis of catechols from phenols via Pd-catalyzed silanol-directed C-H oxygenation
A silanol-directed, Pd-catalyzed C-H oxygenation of phenols into catechols is presented. This method is highly site selective and general, as it allows for oxygenation of not only electron-neutral but also electron-poor phenols. This method operates via a silanol-directed acetoxylation, followed by a subsequent acid-catalyzed cyclization reaction into a cyclic silicon-protected catechol. A routine desilylation of the silacyle with TBAF uncovers the catechol product.
Huang, Chunhui,Ghavtadze, Nugzar,Chattopadhyay, Buddhadeb,Gevorgyan, Vladimir
p. 17630 - 17633
(2011/12/16)

The pyridyldiisopropylsilyl group: A masked functionality and directing group for monoselective ortho-Acyloxylation and ortho-Halogenation reactions of arenes
A novel, easily removable and modifiable silicon-tethered pyridyldiisopropylsilyl directing group for C-H functionalizations of arenes has been developed. The installation of the pyridyldiisopropylsilyl group can efficiently be achieved via two complementary routes using easily available 2-(diisopropylsilyl)pyridine (5). The first strategy features a nucleophilic hydride substitution at the silicon atom in 5 with aryllithium reagents generated in situ from the corresponding aryl bromides or iodides. The second milder route exploits a highly efficient room-temperature rhodium(I)-catalyzed cross-coupling reaction between 5 and aryl iodides. The latter approach can be applied to the preparation of a wide range of pyridyldiisopropylsilyl- substituted arenes possessing a variety of functional groups, including those incompatible with organometallic reagents. The pyridyldiisopropylsilyl directing group allows for a highly efficient, regioselective palladium(II)-catalyzed mono-ortho-acyloxylation and ortho-halogenation of various aromatic compounds. Most importantly, the silicon-tethered directing group in both acyloxylated and halogenated products can easily be removed or efficiently converted into an array of other valuable functionalities. These transformations include protio-, deuterio-, halo-, boro-, and alkynyldesilylations, as well as a conversion of the directing group into the hydroxy functionality. In addition, the construction of aryl-aryl bonds via the Hiyama-Denmark cross-coupling reaction is feasible for the acetoxylated products. Moreover, the ortho-halogenated pyridyldiisopropylsilylarenes, bearing both nucleophilic pyridyldiisopropylsilyl and electrophilic aryl halide moieties, represent synthetically attractive 1,2-ambiphiles. A unique reactivity of these ambiphiles has been demonstrated in efficient syntheses of arylenediyne and benzosilole derivatives, as well as in a facile generation of benzyne. In addition, preliminary mechanistic studies of the acyloxylation and halogenation reactions have been performed. A trinuclear palladacycle intermediate has been isolated from a stoichiometric reaction between diisopropyl(phenyl)pyrid-2-ylsilane (3a) and palladium acetate. Furthermore, both C-H functionalization reactions exhibited equally high values of the intramolecular primary kinetic isotope effect (kH/k D=6.7). Based on these observations, a general mechanism involving the formation of a palladacycle via a C-H activation process as the rate-determining step has been proposed.
Huang, Chunhui,Chernyak, Natalia,Dudnik, Alexander S.,Gevorgyan, Vladimir
supporting information; experimental part
p. 1285 - 1305
(2011/07/07)

Anodic oxidation of catechols in the presence of α-oxoketene N,N-acetals with a tetrahydropyrimidine ring: Selective α-arylation reaction
The electrochemical oxidation of catechols leads to the formation of o-benzoquinones. This property has been applied to effectively synthesize α-arylated products of α-oxoketene N,N-acetals with a tetrahydropyrimidine ring.
Zeng, Cheng-Chu,Ping, Da-Wei,Hu, Li-Ming,Song, Xiu-Qing,Zhong, Ru-Gang
scheme or table
p. 2465 - 2472
(2010/07/06)

PyDipSi: A general and easily modifiable/traceless Si-tethered directing group for C-H acyloxylation of arenes
A new general and easily installable silicon-tethered pyridyl-containing directing group (PyDipSi) that allows for highly efficient and regioselective Pd-catalyzed ortho C-H acyloxylation of arenes has been developed. It has also been demonstrated that this directing group can efficiently be removed as well as converted into a variety of other valuable functional groups. In addition, the installation of the PyDipSi directing group along with pivaloxylation and quantitative conversion of the PyDipSi group into a halogen functionality represents a formal three-step ortho oxygenation of haloarenes.
Chernyak, Natalia,Dudnik, Alexander S.,Huang, Chunhui,Gevorgyan, Vladimir
supporting information; experimental part
p. 8270 - 8272
(2010/08/04)

Efficient ortho-oxidation of phenols with diacyl peroxides
A stable symmetric diacyl peroxide, m-chlorobenzoyl peroxide (mCBPO), and an asymmetric diacyl peroxide, chloroacetyl m-chlorobenzoyl peroxide (CAMCBPO), were synthesized from m-chloroperbenzoic acid. Both peroxides oxidized phenols selectively at the ortho position predoninantly. CAMCBPO gave para-oxidized compounds as minor products from some phenols. The improvement of the yield of ortho-oxidation of phenols with mCBPO was also reported.
Tada, Masahiro,Ishiguro, Risa,Izumi, Ryohei
p. 239 - 242
(2008/09/21)

Significant enhancement of monooxygenase activity of oxygen carrier protein hemocyanin by urea
Oxygenation of a series of p-substituted phenols to the corresponding catechols (phenolase activity) by the (μ-η2:η2-peroxo)dicopper(II) species of Octopus hemocyanin has been directly examined for the first time by using a UV-vis spectroscopic method in a 0.5 M borate buffer solution containing 8 M urea under anaerobic conditions. Preliminary kinetic studies have indicated that the reaction involves an electrophilic aromatic substitution mechanism as in the case of phenolase reaction of tyrosinase. The oxygenation of phenols by hemocyanin also proceeded catalytically when the reaction was carried out under aerobic conditions. Copyright
Morioka, Chiyuki,Tachi, Yoshimitsu,Suzuki, Shinnichiro,Itoh, Shinobu
p. 6788 - 6789
(2007/10/03)

Involvement of semiquinone radicals in the in vitro cytotoxicity of cigarette mainstream smoke
Free radicals in cigarette smoke have attracted a great deal of attention because they are hypothesized to be responsible in part for several of the pathologies related to smoking. Hydroquinone, catechol, and their methyl-substituted derivatives are abundant in the particulate phase of cigarette smoke, and they are known precursors of semiquinone radicals. In this study, the in vitro cytotoxicity of these dihydroxybenzenes was determined using the neutral red uptake (NRU) assay, and their radical-forming capacity was determined by electron paramagnetic resonance (EPR). All of the dihydroxybenzenes studied were found to generate appreciable amounts of semiquinone radicals when dissolved in the cell culture medium employed in the NRU assay. Hydroquinone exhibited by far the highest capacity to form semiquinone radicals at physiological pH, even though it is not the most cytotoxic dihydroxybenzene. Methyl-substituted dihydroxybenzenes were found to be more cytotoxic than either hydroquinone or catechol. The formation of semiquinone radicals via auto-oxidation of the dihydroxybenzenes was found to be dependent on the reduction potential of the corresponding quinone/semiquinone radical redox couple. The capacity to generate semiquinone radicals was found to be insufficient to explain the variance in the cytotoxicity among the dihydroxybenzenes in our study; consequently, other mechanisms of toxicity must also be involved. The observed interactions between 2,6-dimethylhydroquinone and hydroquinone in the cytotoxicity assay and EPR analysis suggest that care needs to be taken when the bioactivity of cigarette smoke constituents is evaluated, i.e., the effect of the cigarette smoke complex matrix on the activity of the single constituent studied must be taken into consideration.
Chouchane, Salem,Wooten, Jan B.,Tewes, Franz J.,Wittig, Arno,Mueller, Boris P.,Veltel, Detlef,Diekmann, Joerg
p. 1602 - 1610
(2008/12/22)

One-pot synthesis of substituted catechols from the corresponding phenols
Phenols are converted to salicylaldehydes with paraformaldehyde, MgCl 2-Et3N in THF, and when subsequently treated with aqueous NaOH and H2O2 afford the corresponding catechols. The sequence is conveniently carried out as a one-pot procedure.
Hansen, Trond Vidar,Skatteb?l, Lars
p. 3357 - 3358
(2007/10/03)

Kinetic Evaluation of Phenolase Activity of Tyrosinase Using Simplified Catalytic Reaction System
A very simple tyrosinase reaction system has been developed using borate anion as a trapping agent of catechols and hydroxylamine as an external reductant to evaluate the phenolase activity without the interference of catecholase activity. Reactivities of variously para-substituted phenols in this system were compared directly to those of the phenols in the model reactions, demonstrating that the enzymatic oxygenation reaction of phenols proceeds via the same mechanism as the model reaction, that is, electrophilic aromatic substitution mechanism. Copyright
Yamazaki, Shin-Ichi,Itoh, Shinobu
p. 13034 - 13035
(2007/10/03)

Iodine(V) reagents in organic synthesis. Part 4. o-Iodoxybenzoic acid as a chemospecific tool for single electron transfer-based oxidation processes
o-Iodoxybenzoic acid (IBX), a readily available hypervalent iodine(V) reagent, was found to be highly effective in carrying out oxidations adjacent to carbonyl functionalities (to form α, β-unsaturated carbonyl compounds) and at benzylic and related carbon centers (to form conjugated aromatic carbonyl systems). Mechanistic investigations led to the conclusion that these new reactions are initiated by single electron transfer (SET) from the substrate to IBX to form a radical cation which reacts further to give the final products. Fine-tuning of the reaction conditions allowed remarkably selective transformations within multifunctional substrates, elevating the status of this reagent to that of a highly useful and chemoselective oxidant.
Nicolaou,Montagnon,Baran,Zhong
p. 2245 - 2258
(2007/10/03)

Synthesis of water-soluble polymeric prodrugs possessing 4-methylcatechol derivatives by mechanochemical solid-state copolymerization and nature of drug release.
In this study we synthesized the water-soluble polymeric prodrugs possessing a 4-methylcatechol (4MC) derivative as a side chain by mechanochemical solid-state copolymerization. 1-benzoyl-4-methylcatechol (Bz4MC) was selected as a model compound of 4MC, and its methacryloyl derivative (1) was synthesized. 6-O-methacryloyl-D-galactose (2) was also prepared as a water-soluble monomer. The mechanochemical solid-state copolymerization of 1 and 2 was carried out to obtain the water-soluble polymeric prodrug possessing the Bz4MC as a side chain. The mechanochemical copolymerization of 1 and 2 proceeded to completion, and the polymeric prodrug produced possessed a narrow molecular weight distribution. Three kinds of polymeric prodrugs, whose compositions were different from one another, were hydrolyzed in vitro. The hydrolysis of these polymeric prodrugs proceeded to completion. The rate constants of hydrolysis decreased with increasing the mole fraction of 1 in polymeric prodrug. It was suggested that the rate constant of hydrolysis could be controlled by the composition, the mole fraction of 1 in the polymeric prodrug.
Kondo, Shin-ichi,Sasai, Yasushi,Kuzuya, Masayuki,Furukawa, Shoei
p. 1434 - 1438
(2007/10/03)

Oxygenation of phenols to catechols by a (μ-η2:η2-peroxo)dicopper(II) complex: Mechanistic insight into the phenolase activity of tyrosinase [1]
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Itoh,Kumei,Taki,Nagatomo,Kitagawa,Fukuzumi
p. 6708 - 6709
(2007/10/03)

Nitration and hydroxylation of substituted phenols by peroxynitrite. Kinetic feature and an alternative mechanistic view
The reaction of peroxynitrite (ONOO-) with a series of para-substituted phenols has been examined in aqueous phosphate buffer and acetonitrile solutions. Major products were the corresponding 2-nitro derivative and the 4-substituted catechol. Kinetic study showed good correlation with Hammett σ(p)+ parameters and reduction potentials, suggesting the possible one-electron transfer process involving the nitrosoniun ion (NO+) as initial electrophile generated from peroxynitrous acid.
Nonoyama, Nobuaki,Chiba, Kazuhiko,Hisatome, Kaori,Suzuki, Hitomi,Shintani, Futoshi
p. 6933 - 6937
(2007/10/03)