- UV cell stress induces oxidative cyclization of a protective reagent for DNA damage reduction in skin explants
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UV irradiation is a major driver of DNA damage and ultimately skin cancer. UV exposure leads to persistent radicals that generate ROS over prolonged periods of time. Toward the goal of developing long-lasting antioxidants that can penetrate skin, we have designed a ROS-initiated protective (RIP) reagent that, upon reaction with ROS (antioxidant activity), self-cyclizes and then releases the natural product apocynin. Apocynin is a known antioxidant and inhibitor of NOX oxidase enzymes. A key phenol on the compound 1 controls ROS-initiated cyclization and makes 1 responsive to ROS with a EC50 comparable to common antioxidants in an ABTS assay. In an in vitro DNA nicking assay, the RIP reagent prevented DNA strand breaks. In cell-based assays, the reagent was not cytotoxic, apocynin was released only in cells treated with UVR, reduced UVR-induced cell death, and lowered DNA lesion formation. Finally, topical treatment of human skin explants with the RIP reagent reduced UV-induced DNA damage as monitored by quantification of cyclobutane dimer formation and DNA repair signaling via TP53. The reagent was more effective than administration of a catalase antioxidant on skin explants. This chemistry platform will expand the types of ROS-activated motifs and enable inhibitor release for potential use as a long-acting sunscreen.
- Liu, Jing,Zhu, Haizhou,Premnauth, Gurdat,Earnest, Kaylin G.,Hahn, Patricia,Gray, George,Queenan, Jack A.,Prevette, Lisa E.,AbdulSalam, Safnas F.,Kadekaro, Ana Luisa,Merino, Edward J.
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Read Online
- Selective Oxidation of Alkylarenes to the Aromatic Ketones or Benzaldehydes with Water
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Here a palladium-catalyzed oxidation method for converting alkylarenes into the aromatic ketones or benzaldehydes with water as the only oxygen donor is reported. This C-H bond oxidation functionalization does not require other oxidants and hydrogen accep
- Du, Jihong,Duan, Baogen,Liu, Kun,Liu, Renhua,Yu, Feifei,Yuan, Yongkun,Zhang, Chenyang,Zhang, Jin
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supporting information
(2022/02/09)
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- Discovery, Biocatalytic Exploration and Structural Analysis of a 4-Ethylphenol Oxidase from Gulosibacter chungangensis
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The vanillyl-alcohol oxidase (VAO) family is a rich source of biocatalysts for the oxidative bioconversion of phenolic compounds. Through genome mining and sequence comparisons, we found that several family members lack a generally conserved catalytic aspartate. This finding led us to study a VAO-homolog featuring a glutamate residue in place of the common aspartate. This 4-ethylphenol oxidase from Gulosibacter chungangensis (Gc4EO) shares 42 % sequence identity with VAO from Penicillium simplicissimum, contains the same 8α-N3-histidyl-bound FAD and uses oxygen as electron acceptor. However, Gc4EO features a distinct substrate scope and product specificity as it is primarily effective in the dehydrogenation of para-substituted phenols with little generation of hydroxylated products. The three-dimensional structure shows that the characteristic glutamate side chain creates a closely packed environment that may limit water accessibility and thereby protect from hydroxylation. With its high thermal stability, well defined structural properties and high expression yields, Gc4EO may become a catalyst of choice for the specific dehydrogenation of phenolic compounds bearing small substituents.
- Alvigini, Laura,Fraaije, Marco W.,Gran-Scheuch, Alejandro,Guo, Yiming,Mattevi, Andrea,Saifuddin, Mohammad,Trajkovic, Milos
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p. 3225 - 3233
(2021/10/04)
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- Room temperature depolymerization of lignin using a protic and metal based ionic liquid system: an efficient method of catalytic conversion and value addition
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Lignin is one of the most abundant biopolymer which can be utilized to synthesize various chemicalsviaits depolymerization. However, depolymerization of lignin generally occurs under very harsh conditions. Herein, we report the efficient depolymerization of ligninviadissolution in a mixed ionic liquid system: ethyl ammonium nitrate (EAN) + prolinium tetrachloromanganate(ii) [Pro]2[MnCl4] at 35 °C and under atmospheric pressure conditions. The high dissolution of lignin in ethyl ammonium nitrate provided a large number of H-bonding sites leading to the cracking of lignin and subsequent oxidative conversion by [Pro]2[MnCl4]viathe formation of metal-oxo bonding between Mn and lignin molecules. The extracted yield of vanillin was found to be 18-20% on lignin weight basisviaGC-MS analysis. The depolymerization of lignin was confirmed by SEM, FT-IR and PXRD analysis. Since lignin contains UV-absorbing functional groups, the regenerated biomass after the recovery of the depolymerized products was further utilized to synthesize a UV-shielding material. The constructed films from such a material exhibited a high SPF value of 22 and were found to be very effective by limiting the UV degradation of rhodamine B thus making the lignin valorization process economically viable and environmentally sustainable.
- Mehta, Mohit J.,Kulshrestha, Akshay,Sharma, Shweta,Kumar, Arvind
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p. 1240 - 1247
(2021/02/26)
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- Thio-assisted reductive electrolytic cleavage of lignin β-O-4 models and authentic lignin
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Avoiding the use of expensive catalysts and harsh conditions such as elevated temperatures and high pressures is a critical goal in lignin depolymerization and valorization. In this study, we present a thio-assisted electrocatalytic reductive approach using inexpensive reticulated vitreous carbon (RVC) as the working cathode to cleave the β-O-4-type linkages in keto aryl ethers. In the presence of a pre-electrolyzed disulfide (2,2′-dithiodiethanol) and a radical inhibitor (BHT) at room temperature at a current density of 2.5 mA cm-2, cathodic reduction of nonphenolic β-O-4 dimers afforded over 90% of the corresponding monomeric C-O cleavage products in only 1.5 h. Extended to DDQ-oxidized poplar lignin, this combination of electric current and disulfide, applied over 6 h, released 36 wt% of ethyl acetate soluble fragments and 26 wt% of aqueous soluble fragments, leaving only 38 wt% of insoluble residue. These findings represent a significant improvement over the current alone values (24 wt% ethyl acetate soluble; 22 wt% aqueous soluble; 54 wt% insoluble residue) and represent an important next step in our efforts to develop a mild electrochemical method for reductive lignin deconstruction.
- Fang, Zhen,Flynn, Michael G.,Jackson, James E.,Hegg, Eric L.
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p. 412 - 421
(2021/01/28)
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- Method for preparing acetovanillone and application of acetovanillone
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The invention provides a method for preparing acetovanillone and an application of acetovanillone. Specifically, guaiacol is used as a raw material to react with acetyl chloride to generate ester, andthen the ester reacts with lewis acid such as AlCl3 under the catalysis of the lewis acid to generate acetovanillone. The method has the advantages of mild reaction conditions, high raw material conversion rate and simple process flow, and is suitable for large-scale industrial production.
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Paragraph 0050-0079
(2020/04/02)
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- Preparation method and application of apocynin and derivatives of apocynin
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The invention belongs to the technical field of chemical biology, and particularly relates to a preparation method of apocynin and derivatives of the apocynin and an application of the apocynin and the derivatives of the apocynin in skin care products. The apocynin and the derivatives of the apocynin provided by the invention can promote collagen synthesis, help skin damage repair, and can be usedin the skin care products.
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Paragraph 0041; 0048-0050; 0053; 0054
(2020/01/12)
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- Structural features and antioxidant activities of Chinese quince (Chaenomeles sinensis) fruits lignin during auto-catalyzed ethanol organosolv pretreatment
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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
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p. 4348 - 4358
(2020/09/22)
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- Rhodium-terpyridine catalyzed redox-neutral depolymerization of lignin in water
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Simple rhodium terpyridine complexes were found to be suitable catalysts for the redox neutral cleavage of lignin in water. Apart from cleaving lignin model compounds into ketones and phenols, the catalytic system could also be applied to depolymerize dioxasolv lignin and lignocellulose, affording aromatic ketones as the major monomer products. The (hemi)cellulose components in the lignocellulose sample remain almost intact during lignin depolymerization, providing an example of a "lignin-first" process under mild conditions. Mechanistic studies suggest that the reaction proceeds via a rhodium catalyzed hydrogen autotransfer process.
- Liu, Yuxuan,Li, Changzhi,Miao, Wang,Tang, Weijun,Xue, Dong,Xiao, Jianliang,Zhang, Tao,Wang, Chao
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supporting information
p. 33 - 38
(2020/01/13)
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- A convenient synthetic approach to dioncoquinone B and related compounds
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A total synthesis of dioncoquinone B and related compounds, including ancistroquinones B, C and malvon A, is presented. The strategy is based on available reagents and can be used as a preparative synthesis of a number of natural and synthetic biologically active (3-alkyl)-2,7,8-di(tri)methoxy(hydroxy)-1,4-naphthoquinones.
- Khmelevskaya, Ekaterina A.,Pelageev, Dmitry N.
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supporting information
p. 1022 - 1024
(2019/03/13)
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- Mild Redox-Neutral Depolymerization of Lignin with a Binuclear Rh Complex in Water
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A mild redox-neutral lignin depolymerization system featuring a water-soluble binuclear Rh complex has been developed. The catalytic system could be successfully applied to the depolymerization of a lignin-like polymer, alkaline lignin, as well as raw lignocellulose samples to produce aromatic ketones, providing a homogeneous catalytic system for "lignin-first" biorefinery in water. Mechanistic studies on the model substrate suggest that the reaction proceeds via a metal-catalyzed dehydrogenation step to afford a carbonyl intermediate, followed by C-O bond cleavage to afford ketone and phenol products. Deuterium labeling study shows that the hydrogen used for cleavage of the C-O bond originates from the alcohol moiety in the substrate.
- Liu, Yuxuan,Li, Changzhi,Miao, Wang,Tang, Weijun,Xue, Dong,Li, Chaoqun,Zhang, Bo,Xiao, Jianliang,Wang, Aiqin,Zhang, Tao,Wang, Chao
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p. 4441 - 4447
(2019/05/14)
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- Synthesis of structurally diverse biflavonoids
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Synthetic biflavonoids are associated with interesting biological activities, yet they remain poorly explored within drug discovery. Recent years have witnessed a growing interest in synthetic approaches that can provide access to structurally novel biflavonoids so that the biological usefulness of this compound class can be more fully investigated. Herein, we report upon the exploration of strategies based around Suzuki-Miyaura cross-coupling and alcohol methylenation for the synthesis of two classes of biflavonoids: (i) rare ‘hybrid’ derivatives containing flavonoid monomers belonging to different subclasses, and (ii) homodimeric compounds in which the two flavonoid monomers are linked by a methylenedioxy group. Application of these strategies enabled the preparation of a structurally diverse collection of novel biflavonoids from readily-available starting materials, thereby facilitating the probing of uncharted regions of biologically interesting chemical space.
- Sum, Tze Jing,Sum, Tze Han,Galloway, Warren R.J.D.,Twigg, David G.,Ciardiello, Joe J.,Spring, David R.
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supporting information
p. 5089 - 5101
(2018/05/23)
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- Electrochemical Lignin Degradation in Ionic Liquids on Ternary Mixed Metal Electrodes
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Lignin is the second most abundant natural polymer and a promissing feedstock for the generation of renewable aromatic chemicals. We present an fundamental approach for the electrocatalytic cleavage of lignin dissolved in a recoverable, inexpensive ionic liquid using mixed metal oxide electrodes of different compositions. The distribution of depolymerization products generated by electrochemical oxidation were analyzed by means of mass spectrometry. The distribution and yield of the cracked species was found to depended strongly on the implemented metal catalyst and therefore offers the potential to tailor the amount and composition of the low molecular weight cleavage products. This approach could help to provide a more sustainable valorization of lignin for the potential production of high value aromatic compounds due to synergistic effects.
- Rauber, Daniel,Dier, Tobias K.F.,Volmer, Dietrich A.,Hempelmann, Rolf
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p. 189 - 208
(2017/12/18)
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- Catalytic conversion of lignin: Studies on oxidation of lignin model phenolic monomer over CoMCM-41 and CoMCM-48 catalysts
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The present study focussed on investigation of the potentiality of cobalt containing mesoporous material (M41S) as a robust heterogeneous catalyst for the oxidation of lignin model phenolic compound. Cobalt containing MCM-41 and MCM-48 were prepared under hydrothermal condition and characterized by various spectroscopic and analytical techniques. Formation of well ordered hexagonal and cubic mesopore structures of MCMs, containing cobalt in the silicate framework was inferred from XRD, TG-DTA and N2 adsorption-desorption studies. DR UV-visible spectral analysis revealed existence of Co(II) and Co(III) in the tetrahedral framework. The oxidative ability of CoMCMs were studied for the lignin model phenolic monomer, 1-(4-hydroxy-3-methoxyphenoxy)-ethanol, under mild conditions using environmentally benign H2O2 as the oxidant. The catalytic results showed that under optimum reaction conditions, apocynol undergoes selective oxidation yielding 2-methoxybenzoquinone and acetovanillone. CoMCM-41 was found to be more selective towards acetovanillone, on the contrary, CoMCM-48 was better catalyst for 2-methoxybenzoquinone yield.
- Sadual,Sahoo,Badamali
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p. 434 - 442
(2018/01/12)
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- Gold-catalyzed conversion of lignin to low molecular weight aromatics
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A heterogeneous catalyst system, employing Au nanoparticles (NPs) and Li-Al (1:2) layered double hydroxide (LDH) as support, showed excellent activity in aerobic oxidation of the benzylic alcohol group in β-O-4 linked lignin model dimers to the corresponding carbonyl products using molecular oxygen under atmospheric pressure. The synergistic effect between Au NPs and the basic Li-Al LDH support induces further reaction of the oxidized model compounds, facilitating facile cleavage of the β-O-4 linkage. Extension to oxidation of γ-valerolactone (GVL) extracted lignin and kraft lignin using Au/Li-Al LDH under similar conditions produced a range of aromatic monomers in high yield. Hydrolysis of the Au/Li-Al LDH oxidized lignin was found to increase the degree of lignin depolymerization, with monomer yields reaching 40% for GVL extracted lignin. Based on these results, the Au/Li-Al LDH + O2 catalyst system shows potential to be an environmentally friendly means of depolymerizing lignin to low molecular weight aromatics under mild conditions.
- Song, Yang,Mobley, Justin K.,Motagamwala, Ali Hussain,Isaacs, Mark,Dumesic, James A.,Ralph, John,Lee, Adam F.,Wilson, Karen,Crocker, Mark
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p. 8127 - 8133
(2018/11/20)
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- Method for synthesizing guaiacyl glycerol-beta-guaiacyl ether from lignin beta-O-4 linkage dimer model compound
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The invention provides a method for synthesizing guaiacyl glycerol-beta-guaiacyl ether from a lignin beta-O-4 linkage dimer model compound. The content of beta-O-4 linkages in all linkages of lignin is highest and about 40-60%, so research of the beta-O-4 linkage lignin model compound plays an important role in research of the structure of lignin and the reaction mechanism of lignin in reaction. The method is simple, reaction conditions are mild, the yield is high, and the production period is short.
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Paragraph 0052; 0055; 0070; 0082; 0085
(2017/08/25)
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- ECO-FRIENDLY MATERIALS AND METHODS FOR RENEWABLE AND SUSTAINABLE APPLICATIONS IN MATERIAL CHEMISTRY
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The invention relates to novel hydrazide-based templates, methods of making the same, and methods of using the hydrazide-based templates as molecular scaffolds for asymmetric light driven transformations, light driven material synthesis, and biological applications. Furthermore, the present invention relates to photoinitiators, monomers, and polymers derived from biomass, together with methods and methods of using the same.
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- Selective Oxidation of Aromatic Olefins Catalyzed by Copper(II) Complex in Micellar Media
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Abstract: The selective oxidation of aromatic olefins 1,2-dimethoxy-4-vinylbenzene (DEVB) and 2-methoxy-4-vinylphenol (MOVP) by H2O2 into 1-(3,4-dime-thoxyphenyl)ethanol (MVA) and 1-(4-hydroxy-3-methoxyphenyl)ethanol (HMOPE) catalyzed by copper(II) complex CuL (L = 6,8,15,17-tetramethyl-7,16-dihydrodibenzo-1,4,8,11-tetraazacyclotetradecine) were achieved in cationic surfactant cetyl trimethylammonium bromide (CTAB), anionic surfactant sodium dodecyl benzene sulfonate (SDBS) and nonionic surfactant Triton X-100 (TX-100) micellar media, respectively. Micelle showed great influence on both reaction rate and selectivity of product. Aromatic olefins could be oxidized into corresponding aromatic ketones in aqueous solution, but into secondary alcohols in micellar media. The combination of TEMPO and CuL/H2O2 resulted in relatively fast reaction rate and S > 96% selectivity of aromatic ketones. The reaction rate constants, k1, k2 and k3 for three oxidation reactions pathways: olefin to ketone, olefin to alcohol and alcohol to ketone were obtained, respectively. The kinetic study indicated that the CuL catalyzed oxidation of olefins by H2O2 to alcohols was a relatively rapid and major reaction and ketone was generated by the direct oxidation of olefins, not by further oxidation of alcohol in micellar media. Graphical Abstract: [Figure not available: see fulltext.].
- Li, Xiao-Hong,Mi, Chun,Liao, Xiao-Hong,Meng, Xiang-Guang
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p. 2508 - 2514
(2017/09/06)
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- Depolymerisation Of Lignin In Biomass
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A method of obtaining depolymerized lignin from biomass using a transition metal catalyst and a solvent mixture of organic solvent and water. The invention further relates to a composition obtainable by the method and the production of fuel.
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Paragraph 0067; 0068
(2017/09/07)
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- Method for degrading lignin
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The invention discloses a method for degrading lignin. Water is used as a solvent. The method includes carrying out reaction on the lignin under the effects of double-rhodium catalysts or terpyridine rhodium trichloride catalysts and alkali under the protection of inert gas at the temperatures of 100-120 DEG C for 10-16 hours to degrade the lignin. Compared with existing methods, the method has the advantages that extra hydrogen sources can be omitted, the water is used as the solvent, reaction conditions are mild, the method is easy to implement, high in reaction yield and low in industrial production cost and is green and environmentally friendly, and environmental pollution can be abated.
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Paragraph 0036; 0037; 0038
(2017/10/28)
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- Fine Tuning the Redox Potentials of Carbazolic Porous Organic Frameworks for Visible-Light Photoredox Catalytic Degradation of Lignin β-O-4 Models
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We report a facile approach to fine tune the redox potentials of π-conjugated porous organic frameworks (POFs) by copolymerizing carbazolic electron donor (D) and electron acceptor (A) based comonomers at different ratios. The resulting carbazolic copolymers (CzCPs) exhibit a wide range of redox potentials that are comparable to common transition-metal complexes and are used in the stepwise photocatalytic degradation of lignin β-O-4 models. With the strongest oxidative capability, CzCP100 (D:A = 0:100) exhibits the highest efficiency for the oxidation of benzylic β-O-4 alcohols, while the highly reductive CzCP33 (D:A = 66:33) gives the highest yield for the reductive cleavage of β-O-4 ketones. CzCPs also exhibit excellent stability and recyclability and represent a class of promising heterogeneous photocatalysts for the production of fine chemicals from sustainable lignocellulosic biomass.
- Luo, Jian,Zhang, Xiang,Lu, Jingzhi,Zhang, Jian
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p. 5062 - 5070
(2017/08/17)
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- Biocatalytic Properties and Structural Analysis of Eugenol Oxidase from Rhodococcus jostii RHA1: A Versatile Oxidative Biocatalyst
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Eugenol oxidase (EUGO) from Rhodococcus jostii RHA1 had previously been shown to convert only a limited set of phenolic compounds. In this study, we have explored the biocatalytic potential of this flavoprotein oxidase, resulting in a broadened substrate scope and a deeper insight into its structural properties. In addition to the oxidation of vanillyl alcohol and the hydroxylation of eugenol, EUGO can efficiently catalyze the dehydrogenation of various phenolic ketones and the selective oxidation of a racemic secondary alcohol—4-(1-hydroxyethyl)-2-methoxyphenol. EUGO was also found to perform the kinetic resolution of a racemic secondary alcohol. Crystal structures of the enzyme in complexes with isoeugenol, coniferyl alcohol, vanillin, and benzoate have been determined. The catalytic center is a remarkable solvent-inaccessible cavity on the si side of the flavin cofactor. Structural comparison with vanillyl alcohol oxidase from Penicillium simplicissimum highlights a few localized changes that correlate with the selectivity of EUGO for phenolic substrates bearing relatively small p-substituents while tolerating o-methoxy substituents.
- Nguyen, Quoc-Thai,de Gonzalo, Gonzalo,Binda, Claudia,Rioz-Martínez, Ana,Mattevi, Andrea,Fraaije, Marco W.
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p. 1359 - 1366
(2016/08/31)
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- Flow Synthesis in Hot Water: Synthesis of the Atypical Antipsychotic Iloperidone
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Inductively heated steel reactors continuously perform organic transformations in water under high temperature conditions, utilizing the unique physiochemical properties of water at subcritical conditions. We demonstrated the power of this set-up in the continuous synthesis of the atypical antipsychotic drug iloperidone, in which we performed four out of five steps under aqueous conditions.
- Hartwig, Jan,Kirschning, Andreas
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supporting information
p. 3044 - 3052
(2016/03/23)
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- Investigate cleavage of β-O-4 linkage in lignin model compounds by aerobic oxidation of Cα and Cγ hydroxyl groups
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The selective cleavage of common linkages in lignin polymers is a promising approach to generate valuable aromatic hydrocarbons. Herein, we found that on oxidation of Cα and Cγ hydroxyl groups in β-O-4 lignin model compounds with TEMPO catalyst resulted in the formation of 1,3-dicarbonyl TEMPO adduct. These oxidized products readily underwent fragmentation at Cα-Cβ bond in the presence of a catalytic amount of acid to generate corresponding carboxylic acid and phenol monomers.
- Patil, Nikhil D.,Yan, Ning
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supporting information
p. 3024 - 3028
(2016/07/06)
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- Lignin Depolymerization with Nitrate-Intercalated Hydrotalcite Catalysts
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Hydrotalcites (HTCs) exhibit multiple adjustable parameters to tune catalytic activity, including interlayer anion composition, metal hydroxide layer composition, and catalyst preparation methods. Here, we report the influence of several of these parameters on β-O-4 bond scission in a lignin model dimer, 2-phenoxy-1-phenethanol (PE), to yield phenol and acetophenone. We find that the presence of both basic and NO3- anions in the interlayer increases the catalyst activity by 2-3-fold. In contrast, other anions or transition metals do not enhance catalytic activity in comparison to blank HTC. The catalyst is not active for C-C bond cleavage on lignin model dimers and has no effect on dimers without an α-OH group. Most importantly, the catalyst is highly active in the depolymerization of two process-relevant lignin substrates, producing a significant amount of low-molecular-weight aromatic species. The catalyst can be recycled until the NO3- anions are depleted, after which the activity can be restored by replenishing the NO3- reservoir and regenerating the hydrated HTC structure. These results demonstrate a route to selective lignin depolymerization in a heterogeneous system with an inexpensive, earth-abundant, commercially relevant, and easily regenerated catalyst.
- Kruger, Jacob S.,Cleveland, Nicholas S.,Zhang, Shuting,Katahira, Rui,Black, Brenna A.,Chupka, Gina M.,Lammens, Tijs,Hamilton, Phillip G.,Biddy, Mary J.,Beckham, Gregg T.
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p. 1316 - 1328
(2016/02/18)
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- Divergent and concise total syntheses of dihydrochalcones and 5-deoxyflavones recently isolated from Tacca species and Mimosa diplotricha
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Dihydrochalcones and 5-deoxyflavones are types of compounds possessing various biologically interesting properties. Herein, we report the concise and divergent total syntheses of several naturally occurring dihydrochalcones and 5-deoxyflavones from readily available starting materials. The divergent strategy is based around manipulation of a common chalcone scaffold and features application of Algar-Flynn-Oyamada oxidation and benzoquinone C-H activation methodologies. These are the first reported total syntheses of these biologically interesting compounds and the concise and flexible route should be readily amenable to future analogue generation. Furthermore, this work provides an illustration of the utility of divergent synthesis for the expedient and step-economical preparation of natural product libraries.
- Sum, Tze Han,Sum, Tze Jing,Stokes, Jamie E.,Galloway, Warren R.J.D.,Spring, David R.
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p. 4557 - 4564
(2015/06/08)
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- Catalytic oxidation of lignin-acetoderivatives: A potential new recovery route for value-added aromatic aldehydes from acetoderivatives
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Catalytic wet air oxidation (CWAO) of lignin and phenolic composition of wastewater is a useful pathway towards the recovery of valuable compounds. In this study, bamboo lignin was catalytically oxidized to aromatic aldehydes and acetoderivatives; similarly acetovanillone and acetosyringone were oxidized to vanillin and syringaldehyde, respectively. A total product yield of 9.5% from bamboo lignin and a vanillin yield of 51% with greater than 90% selectivity from acetovanillone were achieved. The proposed reaction pathways suggest a two-step route towards the formation of value-added aromatic aldehydes from lignin via degradation of acetoderivatives. The kinetics study for the degradation of acetovanillone and formation of vanillin was reported for the first time in the temperature range of 120-150°C, with activation energies of 85.29 kJ mol-1 and 120.7 kJ mol-1, respectively. To date, CWAO breaks down the lignin polymer and toxic phenolic compounds reasonably and effectively, producing value-added aldehydes, which could become a potential new route for the recovery of value-added products.
- Alunga, Kissa R.,Ye, Yue-Yuan,Li, Shui-Rong,Wang, Duo,Liu, Yun-Quan
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p. 3746 - 3753
(2015/06/30)
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- Mild and Robust Redox-Neutral Pd/C-Catalyzed Lignol β-O-4′ Bond Cleavage Through a Low-Energy-Barrier Pathway
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A Pd/C catalyzed redox neutral C - O bond cleavage of 2-aryloxy-1-arylethanols has been developed. The reactions are carried out at 80 °C, in air, using a green solvent system to yield the aryl ketones in near quantitative yields. Addition of catalytic amounts of a hydrogen source to the reaction mixture activates the catalyst to proceed through a low energy barrier pathway. Initial studies support a transfer hydrogenolysis reaction mechanism that proceeds through an initial dehydrogenation followed by an enol adsorption to Pd/C and a reductive C - O bond cleavage.
- Galkin, Maxim V.,Dahlstrand, Christian,Samec, Joseph S. M.
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p. 2187 - 2192
(2015/07/15)
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- Highly chemoselective and versatile method for direct conversion of carboxylic acids to ketones utilizing zinc Ate complexes
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Various carboxylic acids were directly transformed into the corresponding ketones by utilizing organozinc ate complexes, which provide high chemoselectivity without any overreaction to the undesired tertiary carbinol, owing to formation of a stable tetrahedral zincioketal intermediate. This method offers good overall atom/step/pot economy and operational simplicity. No need to overreact: Various carboxylic acids were directly transformed to the corresponding ketones by utilizing organozinc ate complexes, which provide high chemoselectivity without any overreaction to undesired tertiary carbinol, owing to formation of a stable tetrahedral zincioketal intermediate. This method offers good overall atom/step/pot economy and operational simplicity.
- Murata, Ryo,Hirano, Keiichi,Uchiyama, Masanobu
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supporting information
p. 1286 - 1290
(2015/06/08)
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- Synthesis and biological evaluation of phenoxyacetic acid derivatives as novel free fatty acid receptor 1 agonists
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Free fatty acid receptor 1 (FFA1) is a new potential drug target for the treatment of type 2 diabetes because of its role in amplifying glucose-stimulated insulin secretion in pancreatic β-cell. In the present studies, we identified phenoxyacetic acid derivative (18b) as a potent FFA1 agonist (EC50 = 62.3 nM) based on the structure of phenylpropanoic acid derivative 4p. Moreover, compound 18b could significantly improve oral glucose tolerance in ICR mice and dose-dependently reduced glucose levels in type 2 diabetic C57BL/6 mice without observation of hypoglycemic side effect. Additionally, compound 18b exhibited acceptable PK profiles. In summary, compound 18b with ideal PK profiles exhibited good activity in vitro and in vivo, and might be a promising drug candidate for the treatment of diabetes mellitus.
- Wang, Xuekun,Zhao, Tianxiao,Yang, Baowei,Li, Zheng,Cui, Jian,Dai, Yuxuan,Qiu, Qianqian,Qiang, Hao,Huang, Wenlong,Qian, Hai
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p. 132 - 140
(2015/02/18)
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- CHEMOSELECTIVE ENRICHMENT FOR COMPOUND ISOLATION
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Chemoselective isolation of aliphatic hydroxyl group-containing and aromatic hydroxyl group-containing compounds is accomplished via formation of polymeric siloxyl ethers. Chemoselective release of aliphatic hydroxyl group-containing and aromatic hydroxyl group-containing compounds from polymeric siloxyl reagents is described.
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Paragraph 0284; 0289
(2014/05/07)
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- Mild heterogeneous palladium-catalyzed cleavage of β-o-4'-ether linkages of lignin model compounds and native lignin in air
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A mild and robust heterogeneous palladium-catalyzed C - O bond cleavage of 2-aryloxy-1-arylethanols using formic acid as reducing agent in air was developed. The cleaved products were isolated in 92-98 % yield; and by slightly varying the reaction conditions, a ketone, an alcohol, or an alkane can be generated in near-quantitative yield. This reaction is applicable to cleaving the β-O-4'-ether bond found in lignin polymers of different origin. The reaction was performed on a lignin polymer model to generate either the monomeric aryl ketone or alkane in a quantitative yield. Moderate depolymerization was achieved with native lignin at similar reaction conditions. Mechanistic studies under kinetic control indicate that an initial palladium-catalyzed dehydrogenation of the alcohol is followed by insertion of palladium to an enol equivalent. A palladium-formato complex reductively cleaves the palladium-enolate complex to generate the ketone. Copyright
- Galkin, Maxim V.,Sawadjoon, Supaporn,Rohde, Volker,Dawange, Monali,Samec, Joseph S. M.
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p. 179 - 184
(2014/01/23)
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- Triple nanocomposites of CoMn2O4, Co 3O4 and reduced graphene oxide for oxidation of aromatic alcohols
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A composite of reduced graphene oxide (RGO) with oxides of manganese and cobalt together was prepared by a solvothermal method. During synthesis, both the reduction of graphene oxide as well as the growth of nanorod shaped CoMn2O4 and Co3O4 occurred simultaneously having a crystallite size of ~8 nm calculated from X-ray diffraction (XRD). The as-obtained triple nanocomposite material designated as RGO-MnCoO exhibited excellent activity for the liquid phase aerobic oxidation of aromatic alcohols under base-free conditions selectively giving the corresponding aldehydes (>85%). RGO loading was varied in the range of 1-10%, among which 1% RGO-MnCoO showed maximum catalytic activity enhancement of 24% as compared to the bare mixed oxide (MnCo-MO) for the oxidation of vanillyl alcohol. HR-TEM of RGO-MnCoO revealed that it was a composite material having uniform nanotubes of ~25 nm length and 6 nm diameter with a fringe pattern showing the (103) and (004) planes and lattice spaces of 0.26 nm and 0.22 nm, respectively, for the spinel CoMn2O4. The detailed studies on the morphology, size and composition of the as-prepared RGO-MnCoO nanocomposite by XRD, XPS, N2-adsorption/desorption and O 2-TPD techniques were used to understand the role of RGO in the enhancement of catalytic activity for oxidation reaction. This journal is the Partner Organisations 2014.
- Jha, Ajay,Mhamane, Dattakumar,Suryawanshi, Anil,Joshi, Sameer M.,Shaikh, Parvez,Biradar, Narayan,Ogale, Satishchandra,Rode, Chandrashekhar V.
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p. 1771 - 1778
(2014/06/09)
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- Escherichia coli/ADH-A: An all-inclusive catalyst for the selective biooxidation and deracemisation of secondary alcohols
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The nicotinamide adenine dinucleotide regeneration system present in Escherichia coli cells was exploited for the oxidation and deracemisation of secondary alcohols with the overexpressed alcohol dehydrogenase from Rhodococcus ruber DSM 44541 (E. coli/ADH-A). Thus, various racemic alcohols were selectively oxidised with lyophilised or resting E. coli/ADH-A cells without need for an external cofactor or co-substrate. The addition of these substrates to the E. coli/ADH-A cells in buffer afforded the corresponding ketones and the remaining enantioenriched (R)-alcohols. This methodology was used for the desymmetrisation of a meso-diol and for the synthesis of the highly valuable raspberry ketone. Moreover, a biocatalytic concurrent process was developed with the resting cells of E. coli/ADH-A, ADH from Lactobacillus brevis, and glucose dehydrogenase for the deracemisation of various secondary alcohols, which afforded the desired enantiopure alcohols in more than 99 % ee starting from the racemic mixture. The reaction time of deracemisation of 1-phenylethanol was estimated to be less than 30 min. The stereoinversion of (S)-1-phenylethanol to its pure (R)-enantiomer was also achieved, which provided a biocatalytic alternative to the chemical Mitsunobu inversion reaction. An integrated recycling system: A nicotinamide adenine dinucleotide regeneration system present in Escherichia coli cells is exploited for the oxidation of secondary alcohols with E. coli/alcohol dehydrogenase (ADH-A). Racemic alcohols are oxidized selectively without need for an external cofactor or cosubstrate, which affords the remaining enantioenriched (R)-alcohols. Deracemization, desymmetrization, and stereoinversion processes are developed, which leads to optically pure high value-added compounds. Copyright
- Paul, Caroline E.,Lavandera, Ivan,Gotor-Fernandez, Vicente,Kroutil, Wolfgang,Gotor, Vicente
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p. 3875 - 3881
(2014/01/06)
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- Correlating lignin structural features to phase partitioning behavior in a novel aqueous fractionation of softwood Kraft black liquor
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In this work, a set of softwood lignins were recovered from a Kraft black liquor using a novel pH-based fractionation process involving sequential CO 2 acidification and separation of the solvated aqueous lignin fraction. These recovered lignin fractions were characterized with respect to properties that may be responsible for their phase partitioning behavior as well as properties that may render the lignins more suitable for materials applications. Lignin fractions were recovered between a pH range of 12.8 and 9.5 with the bulk of the lignin (90%) recovered between a pH of 11.1 and 10.0. While all the fractions were found to consist primarily of lignin as validated by sample methoxyl content, the first fractions to phase separated were found to be especially enriched in aliphatic extractives and polysaccharides. From the bulk of the lignin that was recovered between a pH of 11.1 and 10.0 a number of noteworthy trends were discernible from the data. Specifically, the phenolic hydroxyl content was found to exhibit a strong negative correlation to the fractionation pH and exhibited a nearly 50% increase with recovery at decreasing pH, while the GPC-estimated molecular weights and 13C NMR-estimated β-O-4 content showed strong positive correlations to the pH at recovery. The aliphatic hydroxyl content exhibited minimal differences between recovery conditions. Overall, these results suggest that this fractionation approach can generate lignin fractions enriched in select physical or structural properties that may be important for their application as feedstocks for renewable chemicals or materials.
- Stoklosa, Ryan J.,Velez, Julian,Kelkar, Shantanu,Saffron, Christopher M.,Thies, Mark C.,Hodge, David B.
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supporting information
p. 2904 - 2912
(2013/10/08)
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- Taming of a superbase for selective phenol desilylation and natural product isolation
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Hydroxyl moieties are highly prevalent in natural products. We previously reported a chemoselective strategy for enrichment of hydroxyl-functionalized molecules by formation of a silyl ether bond to a resin. To generate smaller pools of molecules for analysis, we developed cleavage conditions to promote stepwise release of phenolic silyl ethers followed by aliphatic silyl ethers with a "tamed" version of the superbase 1,1,3,3-tetramethylguanadine. We demonstrate this as a general strategy for selective deprotection of phenolic silyl ethers under neutral conditions at room temperature.
- Trader, Darci J.,Carlson, Erin E.
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p. 7349 - 7355
(2013/08/23)
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- Unprecedented oxidative properties of mesoporous silica materials: Towards microwave-assisted oxidation of lignin model compounds
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The unusual oxidative ability of mesoporous silicas towards oxidation of an important lignin model molecule, 1,2-(4-hydroxy-3methoxy-phenoxy) ethanol, apocynol under microwave irradiation is presented in this work. Mesoporous MCM-41, HMS, SBA-15 and amorphous silica were employed as catalysts in the present study. Different reactivities were obtained for the various silica materials. It was assumed that the substrate conversion and product selectivity were highly influenced by the nature of mesoporous silica materials. Based on the nature of the catalysts and reaction product profile, a plausible mechanism has been proposed.
- Badamali, Sushanta K.,Luque, Rafael,Clark, James H.,Breeden, Simon W.
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- Studies on pyrrolidinones. On the synthesis of 5-aryl-2-pyrrolidones
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The optimization of the synthesis of 5-aryl-2-pyrrolidinones from decarbonylation of pyroglutamic acid in Eaton's reagent in the presence of aromatic derivatives is described. Four synthesized compounds were evaluated for their antiproliferative activity in the NCI-60 cancer cell lines panel.
- Ghinet, Alina,Rigo, Benoit,Gautret, Philippe
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p. 1065 - 1072
(2013/09/23)
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- DEPOLYMERIZATION OF LIGNIN USING SOLID ACID CATALYSTS
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The invention provides for a process for the depolymerization of lignin in an inert atmosphere to result in substituted phenolic monomer compounds. The process is catalysed by heterogeneous solid acid catalysts and is carried out in batch or continuous mode.
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Page/Page column 6; 7
(2012/12/13)
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- Hydrogenolysis of β-O-4 lignin model dimers by a ruthenium-xantphos catalyst
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Hydrogenolysis reactions of so-called lignin model dimers using a Ru-xantphos catalyst are presented (xantphos = 4,5-bis(diphenylphosphino)-9,9- dimethylxanthene). For example, of some nine models studied, the alcohol, 2-(2-methoxyphenoxy)-1-phenylethanol (1), with 5 mol% Ru(H)2(CO) (PPh3)(xantphos) (18) in toluene-d8 at 135 °C for 20 h under N2, gives in ～95% yield the C-O cleavage hydrogenolysis products, acetophenone (14) and guaiacol (17), and a small amount (1H NMR spectroscopy. The in situ Ru(H)2(CO)(PPh 3)3/xantphos system gives similar findings, confirming a recent report (J. M. Nichols et al., J. Am. Chem. Soc., 2010, 132, 12554). The active catalyst is formulated 'for convenience' as 'Ru(CO)(xantphos)'. The hydrogenolysis mechanism proceeds by initial dehydrogenation to give the ketone 4, which then undergoes hydrogenolysis of the C-O bond to give 14 and 17. Hydrogenolysis of 4 to 14 and 17 also occurs using the Ru catalyst under 1 atm H2; in contrast, use of 3-hydroxy-2-(2-methoxyphenoxy)-1-phenyl-1- propanone (7), for example, where the CH2 of 4 has been changed to CHCH2OH, gives a low yield (≤15%) of hydrogenolysis products. Similarly, the diol substrate, 2-(2-methoxyphenoxy)-1-phenyl-1,3-propanediol (9), gives low yields of hydrogenolysis products. These low yields are due to formation of the catalytically inactive complexes Ru(CO)(xantphos)[C(O)C(OC 6H4OMe)C(Ph)O] (20) and/or Ru(CO)(xantphos)[C(O)CHC(Ph)O] (21), where the organic fragments result from dehydrogenation of CH 2OH moieties in 7 and 9. Trace amounts of Ru(CO)(xantphos)(OC 6H4O), a catecholate complex, are isolated from the reaction of 18 with 1. Improved syntheses of 18 and lignin models are also presented.
- Wu, Adam,Patrick, Brian O.,Chung, Enoch,James, Brian R.
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p. 11093 - 11106
(2012/10/30)
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- REDUCTION OF C-0 BONDS BY CATALYTIC TRANSFER HYDROGENOLYSIS
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The present invention relates to a method of reducing a C-O bond to the corresponding C-H bond in a substrate which could be a benzylic alcohol, allylic alcohol, ester,or ether or an ether bond beta to a hydroxyl group or alpha to a carbonyl group.
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Page/Page column 14-15
(2012/09/22)
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- Synthesis and biological evaluation of phenstatin metabolites
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Previous investigations on the incubation of phenstatin with rat and human microsomal fractions revealed the formation of nine main metabolites. The structures of eight of these metabolites have been now confirmed by synthesis and their biological properties have been reported. Eaton's reagent was utilized as a convenient condensing agent, allowing, among others, a simple multigram scale preparation of phenstatin. Synthesized metabolites and related compounds were evaluated for their antiproliferative activity in the NCI-60 cancer cell line panel, and for their effect on microtubule assembly. Metabolite 23 (2′-methoxyphenstatin) exhibited the most potent in vitro cytotoxic activity: inhibition of the growth of K-562, NCI-H322M, NCI-H522, KM12, M14, MDA-MB-435, NCI/ADR-RES, and HS 578T cell lines with GI50 values 50 = 3.2 μM vs 15.0 μM) and induced G2/M arrest in murine leukemia DA1-3b cells. The identification of this active metabolite led to the design and synthesis of analogs with potent in vitro cytotoxicity and inhibition of microtubule assembly.
- Ghinet, Alina,Rigo, Beno?t,Hénichart, Jean-Pierre,Le Broc-Ryckewaert, Delphine,Pommery, Jean,Pommery, Nicole,Thuru, Xavier,Quesnel, Bruno,Gautret, Philippe
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supporting information; experimental part
p. 6042 - 6054
(2011/11/29)
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- Simple synthesis of amides and weinreb amides Using PPh3 or PolymerSupported PPh3 and Iodine
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The combination of PPh3/I2 has been shown to be effective for the conversion of a range of carboxylic acids into secondary, tertiary, and Weinreb amides. Simplification of the procedure was possible with the use of polymer-supported PPh3/ I2. Weinreb amides produced with the use of polymer-supported PPh3 could be filtered through a short silica gel plug and used in further transformations. Thus, the use of polymer-supported PPh3 offers potential applicability to diversityoriented reactions. Formal total syntheses of apocynin and pratosine, as well as syntheses of anhydrolychorinone and hippadine, have been achieved through the use of this amide-forming method. An attempt has been made to gain insight into this reaction.
- Kumar, Amit,Akula, Hari Kiran,Lakshman, Mahesh K.
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body text
p. 2709 - 2715
(2010/08/05)
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- One-pot two-step oxidative cleavage of 1,2-arylalkenes to aryl ketones instead of arylaldehydes in an aqueous medium: A complementary approach to ozonolysis
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A new approach has been developed for a one-pot and selective oxidative cleavage of aryl- and 1,2-diarylalkenes leading to one-carbon shorter aryl ketones; thereby, providing a complementary approach to classical ozonolysis. The methodology was applicable to diverse aromatic and polyaromaticarylalkenes bearing electron-donating or -withdrawing groups on the aromatic ring. The protocol also provided a useful one-pot oxidative cleavage-condensation sequence, which could potentially have important applications in natural product total synthesis. A one-pot, two-step approach has been achieved for the oxidative cleavage of 1,2-disubstituted arylalkenes into the corresponding aryl ketones instead of arylaldehydes (see scheme; NIS = N-iodosuccinimide; CTAB = cetyltrimethylammonium bromide; PDC/TBHP = pyridinium dichromate/tert-butyl hydroperoxide). The methodology also led to a valuable one-pot oxidative cleavage-condensation reaction that has widespread utility in the total synthesis of natural products.
- Sharma, Naina,Sharma, Abhishek,Kumar, Rakesh,Shard, Amit,Sinha, Arun K.
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supporting information; experimental part
p. 6025 - 6032
(2011/02/23)
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- The biosynthesis of acetovanillone in tobacco cell-suspension cultures
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A soluble enzyme, extracted from tobacco cell-suspension cultures 24 h after treatment with 100 μM methyl jasmonate, has been shown to synthesize acetovanillone (apocynin) from feruloyl-CoA in the presence of NAD. The enzyme displayed Michaelis-Menten kinetics with apparent Km values of 5.6 μM for feruloyl-CoA and 260 μM for NAD and exhibited very high specificity for its substrates. The increase in acetovanillone synthase activity was followed by an increase in the concentration of both acetovanillone and acetosyringone in the culture medium. No intermediate could be detected when analysing the reaction medium by HPLC during the formation of acetovanillone in cell-free extracts. The apparent molecular mass estimated by gel permeation on an FPLC column was ca. 79 kDa. To our knowledge, this is the first report of an enzymic system catalysing the synthesis of an acetophenone. This work demonstrates that the biosynthesis of acetophenones in tobacco proceeds from hydroxycinnamic acids through a CoA-dependent β-oxidation pathway. Interestingly in methyl jasmonate-treated cells, which synthesize very large amounts of hydroxycinnamoylputrescines, inhibition of the synthesis of these conjugates increased the concentration of acetovanillone and acetosyringone in the culture medium, suggesting that the two metabolic pathways can compete for their common precursors, i.e. hydroxycinnamoyl-CoA thioesters.
- Negrel, Jonathan,Javelle, Francine
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body text
p. 751 - 759
(2010/07/06)
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- Significant lability of guaiacylglycerol β-phenacyl ether under alkaline conditions
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It was observed that the β-O-4 bond cleavage of a dimeric phenolic lignin model compound with an α-carbonyl group at the B-ring, 2-(2-ethoxy-4-formylphenoxy)-1-(4-hydroxy-3-methoxyphenyl)propane-1,3-diol (I), is extremely fast in a mild anaerobic alkaline treatment (0.45 mol/L NaOH, 95°C, 0.8 MPa of N2). This phenomenon significantly contrasts with the case of a common dimeric phenolic lignin model compound without any specific functional group, 1-(4-hydroxy-3-methoxyphenyl)-2-(2-methoxyphenoxy) propane-1,3-diol (II). The most plausible mechanism is the migration of the B-ring from the β- to the α-position following the SNAr mechanism. Because this migration affords the alkaline labile phenolic α-O-4-type compound (XI), the formation of the quinone methide as well as the cleavage of the originally alkaline very stable alkyl-aryl ether bond is promoted. This promotion of the quinone methide formation explains why a relatively large amount of 4-hydroxy-3-methoxybenzaldehyde (IV) is produced from I in an oxygen-alkali treatment.
- Imai, Alko,Yokoyama, Tomoya,Matsumoto, Yuji,Meshitsuka, Gyosuke
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experimental part
p. 9043 - 9046
(2009/09/29)
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- A NEW PROCESS FOR THE PREPARATION OF PHENOLIC HYDROXY-SUBSTITUTED COMPOUNDS
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The invention relates to a process for the preparation of a phenolic hydroxy-substituted compound of the general formula (I) by desalkylation of an alkyl aryl ether of the general formula (II) by treatment with a thiourea/aluminium chloride reagent pair, in said general formulae R1 stands for straight chain or branched C1-6 alkyl group; R2, R3, R4, R5 , and R6 have the same or different meanings and stand for hydrogen or halogen atom, hydroxy, carboxy, nitro, oxo, C1-6 alkylcarbonyl, straight chain or branched alkyl or - alkoxy, or aryl group, or R2 and R3 together stand for a 5-7 membered ring or fused ring system; said 5-7 membered ring may be a partially saturated ring optionally substituted with an oxo group or can be an unsaturated ring; or said fused ring system may constitute with the first ring a steroid, preferably an estratriene derivative optionally substituted with an oxo or C1-6 alkylcarbonyloxy group in the 17 position -.
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Page/Page column 22-23
(2008/06/13)
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- One-step reaction of friedel-crafts acylation and demethylation of aryl-methyl ethers catalyzed by ytterbium(III) triflate
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Catalytic amount of ytterbium(III) inflate [Yb(OTf)3] has been used to catalyze Friedel-Crafts acylation and demethylation of aryl-methyl ethers in one-step reaction to produce hydroxyacylphenones with moderate yields under mild conditions.
- Su, Weike,Jin, Can
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p. 4199 - 4205
(2007/10/03)
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- The immobilized porphyrin-mediator system Mn(TMePyP)/clay/HBT (clay-PMS): A lignin peroxidase biomimetic catalyst in the oxidation of lignin and lignin model compounds
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A biomimetic system for lignin peroxidase (LiP) was designed by using a cationic porphyrin, [Mn(TMePyP)OAc5], supported on the smectitic clay montmorillonite [Mn(TMe-PyP)/clay]. The natural role of the polypeptidic pocket of LiP was mimicked by the clay. The possibility to use low-molecular-weight redox mediators as active readily diffusible oxidizing species has been investigated. This assembly - a sort of "synthetic enzyme" - can be defined as an immobilized porphyrin-mediator system (clay-PMS). The clay-PMS was found to be a stable, recyclable, and efficient catalyst for the environmentally friendly H2O2-catalyzed oxidation of different lignins and representative lignin model compounds. The clay-PMS showed a higher reactivity than Mn(TMePyP)/clay alone due to an effective role of the redox mediator on the oxidation. Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004.
- Crestini, Claudia,Pastorini, Alessandra,Tagliatesta, Pietro
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p. 4477 - 4483
(2007/10/03)
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- 2-aminopyridine derivatives and combinatorial libraries thereof
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The present invention relates to novel 2-aminopyridine derivative compounds of the following formula: wherein R1to R5have the meanings provided herein. The invention further relates to combinatorial libraries containing two or more such compounds, as well as methods of preparing 2-aminopyridine derivative compounds.
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