- Biomimetic Oxidative Bromination by cis-Dioxidotungsten(VI) Complexes of Salan Type N,N’-Capped Linear Tetradentate Amino Bisphenol
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Reaction of [WVIO2(acac)2] (Hacac=acetylacetone) with salan-type dibasic tetradentate ONNO donor Mannich bases derived from ethylenediamine, formaldehyde and 2,4-di-tert-butylphenol (H2L1), 2-tert-butyl-4-methylphenol (H2L2), 2,4-dimethylphenol (H2L3) and 2,4-dichlorophenol (H2L4) in a 1 : 1 ([WVIO2(acac)2] : H2L) molar ratio in refluxing MeOH gave the corresponding cis-dioxidotungsten(VI) complexes [WVIO2L1] (1), [WVIO2L2] (2), [WVIO2L3] (3) and [WVIO2L4] (4), respectively. Characterization by elemental analysis, various spectroscopic (FT-IR, UV-vis, 1H and 13C NMR) studies, DFT calculations and single-crystal X-ray analysis of 2 and 3 suggest six-coordinated octahedral α-cis (symmetric) isomeric form of the complexes where ligands coordinate through the two phenolate oxygen and two amine nitrogen atoms (in a cis-α type symmetric binding mode) with one of the N atoms of the ligand and one of the terminal O atoms of the cis-WO2 group in the axial position. These complexes are potential catalyst precursors for the oxidative bromination of thymol and styrene. Thymol upon bromination gave three products, namely, 2-bromothymol, 4-bromothymol, and 2,4-dibromothymol; later one being the major product. Oxidative bromination of styrene resulted in 2-bromo-1-phenylethanol and 1-phenylethane-1,2-diol; the later one is the result of nucleophilic attack of water on the α as well as β carbons both of the initially formed 1,2-dibromo-1-phenylethane.
- Maurya, Mannar R.,Maurya, Shailendra K.,Kumar, Naveen,Gupta, Puneet
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p. 2724 - 2738
(2021/06/18)
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- Selective Bromination of β-Positions of Porphyrin by Self-Catalytic Behaviour of VOTPP: Facile Synthesis, Electrochemical Redox Properties and Catalytic Application
-
Oxidovanadium(IV) complex of β-octabromo-meso-tetraphenylporphyrin, {[VIVO(TPPBr8)], 2} was synthesized by self-catalytic oxidative bromination of meso-tetraphenylporphyrinatooxidovanadium(IV) {[VIVO(TPP), 1} in excellent yield under mild conditions at 25 °C and its structure was confirmed by single crystal X-ray study. UV-Vis and 1H NMR spectra further confirmed that the meso-phenyl rings are not brominated and thus emphasizes on the selectivity as well as synthetic importance of this catalytic method. In the presence of substrates e. g. phenol derivatives, 1 biomimics the vanadium bromoperoxidase (VBPO) enzyme and catalyses the oxidative bromination of substrates in water at 25 °C. Remarkably, 2 also catalyses the oxidative bromination of phenol derivatives under similar reaction conditions with very high turnover frequency (TOF) values (ca. 29 s?1) along with its recyclability. It was found that 2 showed superior catalytic performance as compared to 1 because of its electron deficient nature due to electron withdrawing bromo substituents and robust saddle shaped nonplanar structure (further supported by DFT studies).
- Maurya, Mannar R.,Prakash, Ved,Avecilla, Fernando,Sankar, Muniappan
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p. 1685 - 1694
(2021/05/03)
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- Lignosulfonate microcapsules for delivery and controlled release of thymol and derivatives
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Thymol and the corresponding brominated derivatives constitute important biological active molecules as antibacterial, antioxidant, antifungal, and antiparasitic agents. However, their application is often limited, because their pronounced fragrance, their poor solubility in water, and their high volatility. The encapsulation of different thymol derivatives into biocompatible lignin-microcapsules is presented as a synergy-delivering remedy. The adoption of lignosulfonate as an encapsulating material possessing relevant antioxidant activity, as well as general biocompatibility allows for the development of new materials that are suitable for the application in various fields, especially cosmesis. To this purpose, lignin microcapsules containing thymol, 4-bromothymol, 2,4-dibromothymol, and the corresponding O-methylated derivatives have been efficiently prepared through a sustainable ultrasonication procedure. Actives could be efficiently encapsulated with efficiencies of up to 50%. To evaluate the applicability of such systems for topical purposes, controlled release experiments have been performed in acetate buffer at pH 5.4, to simulate skin pH: all of the capsules show a slow release of actives, which is strongly determined by their inherent lipophilicity.
- Piombino, Claudio,Lange, Heiko,Sabuzi, Federica,Galloni, Pierluca,Conte, Valeria,Crestini, Claudia
-
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- A shan tiefen derivative and its synthetic method and application in pesticide
-
The invention relates to a shan tiefen derivative and its synthetic method and in pesticide application, especially in the application of the pesticide in the fungicide, which belongs to the technical field of agricultural chemicals. The invention solves the technical problem is to provide a new shan tiefen derivative and its synthetic method and in pesticide application, the structure of this compound is shown as formula I. This compound the structure is simple, novel, easy to synthesize, at the same time having fungicidal activity, the tomato alteso, zones all of tomato, cucumber wilt disease, magnaporthe grisea, galenical such important plant pathogenic fungi, have better bacteriostatic or bactericidal effect.
- -
-
Paragraph 0050-0053
(2019/07/08)
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- Synthesis and antifungal activity of carvacrol and thymol esters with heteroaromatic carboxylic acids
-
Aiming to obtain the more effective pathogen inhibitive ingredients and explore the influence of introducing different heterocyclic units to carvacrol and thymol esters, twenty ester derivatives with different heterocyclic units were synthesized. And the
- Fan, Liming,Jiang, Shanshan,Su, Fawu,Wang, Kaibo,Yang, Yunhai,Ye, Min
-
p. 1924 - 1930
(2018/06/11)
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- Synthesis, characterization and catalytic activity of dioxidouranium(VI) complexes of ONNO tetradentate Mannich bases
-
The reaction of dibasic tetradentate ONNO donor Mannich bases, derived from ethylenediamine and 2,4–di–tert–butylphenol (H2L1) (I), 2,4–di–methylphenol (H2L2) (II), 2–tert–butyl–4–methylphenol (H2L3) (III) and 2,4–di–chlorophenol (H2L4) (IV), with UVIO2(MeCOO)2·2H2O in a 1:1 M ratio in refluxing MeOH gave the corresponding mononuclear trans-dioxidouranium(VI) complexes of the type trans-[UVIO2L(MeOH)] (H2L = H2L1 to H2L4) (1–4). The synthesized complexes are stable in air, reddish-brown in color and soluble in most solvents. These complexes are characterized by elemental analysis, various spectroscopic (FT-IR, UV/Vis, 1H and 13C NMR) techniques and single-crystal X-ray analysis of 3 and 4. The complexes adopt distorted pentagonal bipyramidal geometry around the metal centre. The ligand acts as tetradentate, coordinating through two phenolato oxygen and two imino nitrogen atoms; two oxido groups are trans to each other. These complexes are used as catalysts to study the oxidative bromination of thymol and styrene. The catalytic oxidative bromination of thymol resulted in the formation of three products namely, 2-bromothymol, 4-bromothymol and 2,4-dibromothymol while oxidative bromination of styrene gave two products, 2-bromo-1-phenylethane-1-ol and 1-phenylethane-1,2-diol. In order to find out the optimized reaction conditions for the fixed concentration (10 mmol) of substrate, effects of different amounts of catalyst, KBr, HClO4, and oxidant (H2O2) have been investigated. Under the optimized reaction conditions, all the complexes have shown good catalytic potentials for the oxidative bromination of substrates, establishing the functional similarity to vanadium dependent haloperoxidases. Changes in the UV–visible absorption spectra of dioxidouranium(VI) complexes upon addition of H2O2 suggest the formation of the corresponding oxidoperoxidouranium(VI) complexes.
- Avecilla, Fernando,Maurya, Mannar R.,Maurya, Shailendra K.,Mengesha, Bekele
-
supporting information
p. 118 - 126
(2019/06/28)
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- 4,6-Diacetyl Resorcinol Based Vanadium(V) Complexes: Reactivity and Catalytic Applications
-
Four ONO donor ligands are isolated from the condensation of 4,6-diacetyl resorcinol with isonicotinoyl hydrazide (H2dar-inh, I), nicotinoyl hydrazide (H2dar-nah, II), benzoyl hydrazide (H2dar-bhz, III), and 2-furoyl hydrazide (H2dar-fah, IV) on refluxing in MeOH. The reaction of in situ generated aqueous K[H2VVO4] with ligands I–IV at neutral pH gives complexes [K(H2O)2][VO2(dar-inh)] (1), [K(H2O)2][VO2(dar-nah)] (2), [K(H2O)2][VO2(dar-bhz)] (3), and [K(H2O)2][VO2(dar-fah)] (4), respectively. The reaction of [VIVO(acac)2] (acac = acetylacetonato) with these ligands (I–IV) under aerobic conditions in methanol yields oxidomethoxidovanadium(V) complexes [VO(OMe)(MeOH)(dar-inh)] (5), [VO(OMe)(MeOH)(dar-nah)] (6), [VO(OMe)(MeOH)(dar-bhz)] (7), and [VO(OMe)(MeOH)(dar-fah)] (8). All the isolated complexes are characterized by elemental, thermal, electrochemical, and spectroscopic techniques [FTIR, UV/Vis, NMR (1H, 13C and 51V NMR)], and single-crystal X-ray diffraction analysis (for 1, 6, 7, and 8). X-ray analysis confirms the coordination of the ligands through Ophenolate, Nazomethine, and Oenolate to the metal center. In the molecular structure of [K(H2O)(EtOH)][VVO2(dar-inh)] (abbreviated as 1a where one molecule of water is replaced by EtOH), water molecules act as bridges between two K+ ions and the complex shows a dimeric structure due to the presence of electrostatic interactions between V=O oxygen atoms with K+ ions. These complexes are active catalysts for the oxidative bromination of thymol in the presence of KBr, HClO4, and H2O2 and give 2-bromothymol, 4-bromothymol, and 2,4-dibromothymol as major products. Complexes 1–4 were also tested as catalysts for the epoxidation of various alkenes (namely styrene, cyclohexene, cis-cyclooctene, 1-hexene, 1-octene, cyclohexenone, and trans-stilbene) with H2O2 in the presence of NaHCO3 as promoter, giving the corresponding epoxides selectively.
- Maurya, Mannar R.,Jangra, Nancy,Avecilla, Fernando,Correia, Isabel
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p. 314 - 329
(2019/01/24)
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- Robust and electron deficient oxidovanadium(iv) porphyrin catalysts for selective epoxidation and oxidative bromination reactions in aqueous media
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meso-Tetrakis(3,5-dimethoxyphenyl)porphyrinatooxidovanadium (1) and β-octabromo-meso-tetrakis(2,6-dibromo-3,5-dimethoxyphenyl)porphyrinatooxidovanadium (2) were synthesized in excellent yields. The synthesized oxidovanadium(iv) porphyrin complexes were characterized by various spectroscopic methods such as UV-Vis, FT-IR, EPR and MALDI-TOF mass spectrometry, as well as by single crystal X-ray crystallography. The acetonitrile coordinated porphyrin 1 is relatively planar whereas 2 is highly nonplanar as shown by their crystal structures and also by electrochemical studies. Selective epoxidation studies of alkenes were successfully carried out in CH3CN/H2O as the solvent mixture at ambient temperature resulting in very high TOF numbers (12227-14347 h-1 for 2) even with low catalyst loadings. Remarkably, 2 biomimics the vanadium bromoperoxidase (VBrPO) enzyme with extremely high TOF values (83333-87719 h-1) for the oxidative bromination of thymol and some other phenols. Both the catalysts were successfully recovered at the end of the reactions, indicating their viability and industrial applicability.
- Dar, Tawseef Ahmad,Uprety, Bhawna,Sankar, Muniappan,Maurya, Mannar R.
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p. 1757 - 1768
(2019/04/08)
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- Dioxidomolybdenum(VI) and dioxidouranium(VI) complexes as functional mimic of haloperoxidases catalytic activity in presence of H2O2–KBr–HClO4
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The stable dibasic tetradentate ligand 1,4-bis-(2-hydroxy-3,5-dimethylbenzyl)piperazine (H2pip-2,4-dmp, I) prepared by reacting 2,4-dimethylphenol with piperazine in the presence of formaldehyde reacts with [MoVIO2(acac)s
- Maurya, Mannar R.,Mengesha, Bekele,Maurya, Shailendra K.,Sehrawat, Nidhi,Avecilla, Fernando
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p. 757 - 765
(2018/12/13)
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- In vitro cytotoxicity and catalytic evaluation of dioxidovanadium(v) complexes in an azohydrazone ligand environment
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Three new anionic dioxidovanadium(v) complexes (HNEt3)[VO2(L)1-3] (1-3) of tridentate binegative aroylhydrazone ligands containing the azobenzene moiety were synthesized and structurally characterized. The aroylhydrazone ligands (H2L1-3) were derived from the condensation of 5-(arylazo) salicylaldehyde derivatives with the corresponding aroyl hydrazides. All the synthesized ligands and metal complexes were successfully characterized by several physicochemical techniques, namely, elemental analysis, electrospray ionization mass spectrometry, spectroscopic methods (IR, UV-vis and NMR), and cyclic voltammetry. Single-crystal X-ray diffraction crystallography of 1-3 revealed five-coordinate geometry, where the ligand coordinates to the metal centre in a binegative tridentate O, N, O coordinating anion and two oxido-O atoms, resulting in distortion towards the square pyramidal structure. The complexes were further evaluated for their in vitro cytotoxicity against HeLa and HT-29 cancer cell lines. All the complexes manifested a cytotoxic potential that was found to be comparable with that of clinically referred drugs, while complex 3 proved to be the most cytotoxic among the three complexes for both cell lines, which may be due to the synergistic effect of the naphthyl substituent in the azohydrazone ligand environment coordinated to the vanadium metal. The synthesized complexes 1-3 were probed as catalysts for the oxidative bromination of thymol and styrene as a functional mimic of vanadium haloperoxidases (VHPOs). All the reactions provided high percentages of conversion (>90%) with a high turnover frequency (TOF) in the presence of the catalysts 1-3. In particular, for the oxidative bromination of thymol, the percentage of conversion and TOF were in the ranges of 98-99% and 5380-7173 (h-1), respectively. Besides, 3 bearing the naphthyl substituent showed the highest TOF among all the complexes for the oxidative bromination of both thymol and styrene.
- Mohanty, Monalisa,Maurya, Shailendra K.,Banerjee, Atanu,Patra, Sushree Aradhana,Maurya, Mannar R.,Crochet, Aurélien,Brzezinski, Krzysztof,Dinda, Rupam
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p. 17680 - 17695
(2019/11/26)
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- SUSTAINABLE PROCESS FOR THE PREPARATION OF HIGHLY PURE 4-BROMOTHYMOL AND ITS APPLICATION AS ANTIMICROBIAL AGENT
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The invention is related to a cheap, efficient and low-environmental impact method for the preparation of highly pure 4-bromothymol, that can be obtained by the catalytic oxidative bromination of thymol. The oil obtained as product from the known catalyti
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-
Page/Page column 13
(2018/03/28)
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- Atom-Economic Electron Donors for Photobiocatalytic Halogenations
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In vitro cofactor supply and regeneration have been a major obstacle for biocatalytic processes, in particular on a large scale. Peroxidases often suffer from inactivation by their oxidative co-factor. Combining photocatalysis and biocatalysis offers an innovative solution to this problem, but lacks atom economy due to the sacrificial electron donors needed. Herein, we show that redox-active buffers or even water alone can serve as efficient, biocompatible electron sources, when combined with photocatalysis. Mechanistic investigations revealed first insights into the possibilities and limitations of this approach and allowed adjusting the reaction conditions to the specific needs of biocatalytic transformations. Proof-of-concept for the applicability of this photobiocatalytic reaction setup was given by enzymatic halogenations.
- Seel, Catharina Julia,Králík, Antonín,Hacker, Melanie,Frank, Annika,K?nig, Burkhard,Gulder, Tanja
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p. 3960 - 3963
(2018/09/25)
-
- Characterization of a Cyanobacterial Haloperoxidase and Evaluation of its Biocatalytic Halogenation Potential
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Vanadium-dependent haloperoxidases (VHPOs) are a class of halogenating enzymes found in fungi, lichen, algae, and bacteria. We report the cloning, purification, and characterization of a functional VHPO from the cyanobacterium Acaryochloris marina (AmVHPO), including its structure determination by X-ray crystallography. Compared to other VHPOs, the AmVHPO features a unique set of disulfide bonds that stabilize the dodecameric assembly of the protein. Easy access by high-yield recombinant expression, as well as resistance towards organic solvents and temperature, together with a distinct halogenation reactivity, make this enzyme a promising starting point for the development of biocatalytic transformations.
- Frank, Annika,Seel, Catharina Julia,Groll, Michael,Gulder, Tanja
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p. 2028 - 2032
(2016/11/09)
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- Oxidoperoxidotungsten(VI) and dioxidotungsten(VI) complexes catalyzed oxidative bromination of thymol in presence of H2O2-KBr-HClO4
-
Two oxidoperoxidotungsten(VI) complexes and the corresponding dioxidotungsten(VI) complexes of tridentate ONO donor Schiff base ligands, H2hap-nah (I) and H2hap-bhz (II) (Hhap = 2-hydroxyacetophenone, nah = nicotinoylhydrazide and bh
- Maurya, Mannar R.,Rana, Lata,Avecilla, Fernando
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p. 172 - 180
(2015/12/01)
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- Synthesis, Characterization, Reactivity, Catalytic Activity, and Antiamoebic Activity of Vanadium(V) Complexes of ICL670 (Deferasirox) and a Related Ligand
-
The reactions of [VIVO(acac)2] (acac = acetylacetonato) with two ONO tridentate ligands, 4-[3,5-bis(2-hydroxyphenyl)-1,2,4-triazol-1-yl]benzoic acid (H2L1, I) and 3,5-bis(2-hydroxyphenyl)-1-phenyl-1,2,4-triazole
- Maurya, Mannar R.,Sarkar, Bithika,Avecilla, Fernando,Tariq, Saba,Azam, Amir,Correia, Isabel
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p. 1430 - 1441
(2016/04/05)
-
- 2,5-DIALKYL-4-H/HALO/ETHER-PHENOL COMPOUNDS
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The present disclosure provides phenolic compounds useful in the treatment of neurological conditions such as convulsions and tremors, having the structure of Formula (I): wherein R2, R4, R5, and R6, are as defined in the detailed description; pharmaceutical compositions comprising at least one of the compounds; and methods for treating neurological conditions.
- -
-
Paragraph 0146; 0147
(2016/12/22)
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- Vanadium(v) complexes of a tripodal ligand, their characterisation and biological implications
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The reaction of the tripodal tetradentate dibasic ligand 6,6′-(2-(pyridin-2-yl)ethylazanediyl)bis(methylene)bis(2,4-di-tert-butylphenol), H2L1I, with [VIVO(acac)2] in CH3CN gives the VVO-complex, [VVO(acac)(L1)] 1. Crystallisation of 1 in CH3CN at ~0 °C gives dark blue crystals of 1, while at room temperature it affords dark green crystals of [{VVO(L1)}2μ-O] 3. Upon prolonged treatment of 1 in MeOH, [VVO(OMe)(MeOH)(L1)] 2 is obtained. All three complexes were analysed by single-crystal X-ray diffraction, depicting a distorted octahedral geometry around vanadium. In the reaction of H2L1 with VIVOSO4 partial hydrolysis of the tripodal ligand results in the elimination of the pyridyl fragment of L1 and the formation of H[VVO2(L2)] 4 containing the ONO tridentate ligand 6,6′-azanediylbis(methylene)bis(2,4-di-tert-butylphenol), H2L2II. Compound 4, which was not fully characterised, undergoes dimerization in acetone yielding the hydroxido-bridged [{VVO(L2)}2μ-(OH)2] 5 having a distorted octahedral geometry around each vanadium. In contrast, from a solution of 4 in acetonitrile, the dinuclear compound [{VVO(L2)}2μ-O] 6 is obtained, with a trigonal bipyramidal geometry around each vanadium. The methoxido complex 2 is successfully employed as a functional catechol-oxidase mimic in the oxidation of catechol to o-quinone under air. The process was confirmed to follow a Michaelis-Menten type kinetics with respect to catechol, the Vmax and KM values obtained being 7.66 × 10-6 M min-1 and 0.0557 M, respectively, and the turnover frequency is 0.0541 min-1. A similar reaction with the bulkier 3,5-di-tert-butylcatechol proceeded at a much slower rate. Complex 2 was also used as a catalyst precursor for the oxidative bromination of thymol in aqueous medium. The selectivity shows quite interesting trends, namely when not using excess of the primary oxidizing agent, H2O2, the para mono-brominated product corresponds to ~93% of the products and no dibromo derivative is formed.
- Maurya, Mannar R.,Uprety, Bhawna,Avecilla, Fernando,Ad?o, Pedro,Costa Pessoa
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p. 17736 - 17755
(2015/10/19)
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- Thymol Bromination - A Comparison between Enzymatic and Chemical Catalysis
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The catalytic activity of the vanadium-dependent bromoperoxidase isolated from the brown alga Ascophyllum nodosum is compared with the activity of a cheap, commercially available V-catalyst precursor in the bromination of thymol. Organic solvents have been avoided to make the system appealing from a sustainable chemistry point of view. It is noteworthy that, notwithstanding the low solubility of the substrate, the thymol bromination reactions were performed in water, with a safe brominating source, under mild conditions, and with relatively inexpensive reagents. In this regard, the greenness of the systems was evaluated by the estimation of the E-factor value; the result is that the chemical reaction has a lower environmental impact than the enzymatic process, with an E-factor in the range of eco-friendly processes. Catalysis of thymol bromination by vanadium derivatives is directly compared to catalysis by a V-dependent bromoperoxidase. All reactions were performed under mild and sustainable conditions with relatively inexpensive reagents. Appealing results were obtained in terms of selectivity and sustainability.
- Sabuzi, Federica,Churakova, Ekaterina,Galloni, Pierluca,Wever, Ron,Hollmann, Frank,Floris, Barbara,Conte, Valeria
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p. 3519 - 3525
(2015/03/30)
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- Oxidative bromination of monoterpene (thymol) using dioxidomolybdenum(VI) complexes of hydrazones of 8-formyl-7-hydroxy-4-methylcoumarin
-
Condensation of equimolar amount of 8-formyl-7-hydroxy-4-methylcoumarin (fhmc) and hydrazides [benzoylhydrazide (bhz), isonicotinoylhydrazide (inh), nicotinoylhydrazide (nah) and furoylhydrazide (fah)] in methanol results in the formation of potential ONO
- Maurya, Mannar R.,Dhaka, Sarita,Avecilla, Fernando
-
-
- Chemoenzymatic Halogenation of Phenols by using the Haloperoxidase from Curvularia inaequalis
-
The vanadium-dependent chloroperoxidase from Curvularia inaequalis is an efficient biocatalyst for the in situ generation of hypohalous acids and subsequent electrophilic oxidation/halogenation reactions. Especially, its superb activity and stability unde
- Fernández-Fueyo, Elena,Van Wingerden, Marco,Renirie, Rokus,Wever, Ron,Ni, Yan,Holtmann, Dirk,Hollmann, Frank
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p. 4035 - 4038
(2015/12/26)
-
- 2,5-DIALKYL-4-H/HALO/ETHER-PHENOL COMPOUNDS
-
The present disclosure provides phenolic compounds useful in the treatment of neurological conditions such as convulsions and tremors, having the structure of Formula (I): wherein R2, R4, and R5, are as defined in the detailed description; pharmaceutical compositions comprising at least one of the compounds; and methods for treating neurological conditions.
- -
-
Paragraph 0184-0185
(2015/06/03)
-
- Identification and structure-activity relationship study of carvacrol derivatives as Mycobacterium tuberculosis chorismate mutase inhibitors
-
In the present study, we identified carvacrol, a major phenolic component of oregano oil as a novel small molecule inhibitor of Mycobacterium tuberculosis (MTB) chorismate mutase (CM) enzyme with IC50 of 1.06±0.4μM. Virtual screening of the BITS-Pilani in-house database using the crystal structure of the MTB CM bound transition state intermediate (PDB: 2FP2) as framework identified carvacrol as a potential lead. Further various carvacrol derivatives were evaluated in vitro for their ability to inhibit MTB CM enzyme, whole cell MTB and cytotoxicity as steps toward the derivation of structure-activity relationships (SAR) and lead optimization.
- Alokam, Reshma,Jeankumar, Variam Ullas,Sridevi, Jonnalagadda Padma,Matikonda, Siddharth Sai,Peddi, Santosh,Alvala, Mallika,Yogeeswari, Perumal,Sriram, Dharmarajan
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p. 547 - 554
(2014/08/05)
-
- A practical highly selective oxybromination of phenols with dioxygen
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A simple, low cost and highly selective method for the synthesis of mono-bromophenols from phenol and electron-rich phenolic compounds has been developed. Bromide ions are used as halogenating agents, dioxygen as a final oxidant, and Cu(OAc)2 as a catalyst.
- Menini, Luciano,Parreira, Luciana A.,Gusevskaya, Elena V.
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p. 6401 - 6404
(2008/02/12)
-
- The (Schiff base)vanadium(v) complex catalyzed oxidation of bromide - A new method for the in situ generation of bromine and its application in the synthesis of functionalized cyclic ethers
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(Schiff base)vanadium(v) complexes 5 with tridentate imine auxiliaries served as catalysts for the oxidation of Br with tert-butyl hydroperoxide (TBHP) in nonaqueous solvents. This reaction has been applied for the conversion of substituted 4-penten-1-ols into 5-exo-bromo-cyclized products, including a diastereomerically pure heterocyclic precursor used in a synthesis of the all-trans-configured 2,3,4,5-substituted tetrahydrofuran 2-epi-magnosalicin. Treatment of co-substituted bis(homoallylic) alcohols with the reagent combination of pyHBr, TBHP, and a vanadium(v) catalyst 5 afforded 6-endo-cyclized products, i.e. brominated tetrahydropyrans, as major compounds. The results from 51V NMR, ESI-MS, and supporting reactivity- selectivity studies indicated that the mechanism of the new bromination reaction consists of vanadium-dependent and vanadium-independent steps. A (Schiff base)vanadium(v) compound 5 is required for activation of TBHP via in situ formation of the corresponding tert-butylperoxy complex. This reagent oxidizes Br-, which under the reaction conditions provides Br2 as the active brominating reagent. The molecular bromine generated thus is released into the solution at a steady rate and serves as a reagent for the synthesis of β-brominated cyclic ethers from bis(homoallylic) alcohols in a second, vanadium-independent step. Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004.
- Greb, Marco,Hartung, Jens,Koehler, Franz,Spehar, Kristina,Kluge, Ralph,Csuk, Rene
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p. 3799 - 3812
(2007/10/03)
-
- THE ABSOLUTE CONFIGURATION OF THE DICIPIENE DITERPENES
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The absolute configuration of the dicipiene diterpenes has been determined by degradation to 4R-4-(2-methoxy-4-methylphenyl)-pentanoic acid.Photolysis of 1,18-diacetoxy-13-oxodecipi-14-ene proceeds through a novel photochemical reaction, formally a cycloreversion, to generate a key intermediate for the degradation.
- Croft, K. D.,Ghisalberti, E. L.,Jefferies, P. R.,Stuart, A. D.
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p. 383 - 387
(2007/10/02)
-