- Synthesis and characterization of mono- and bi-metallic derivatives of groups 4 and 5 with 2,5-dimethoxy-1,4-benzoquinone
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The ligating properties of 2,5-dimethoxy-1,4-benzoquinone, C8H8O4 1 towards metallic Lewis acids and organometallics in low oxidation states has been investigated. The title compound reacts with Group 4 tetrahalides to giv
- Calderazzo,Englert,Pampaloni,Passarelli
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- Design, synthesis and α-glucosidase inhibition study of novel embelin derivatives
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Embelin is a naturally occurring para-benzoquinone isolated from Embelia ribes (Burm. f.) of the Myrsinaceae family. It was first discovered to have potent inhibitory activity (IC50 = 4.2 μM) against α-glucosidase in this study. Then, four seri
- Chen, Wenhua,Chen, Xiaole,Gao, Min,Hong, Weiqian David,Jian, Rongchao,Li, Yuling,Sheng, Zhaojun,Tang, Xiaowen,Wu, Panpan,Zhang, Kun,Zhao, Denggao,Zheng, Xi
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p. 565 - 573
(2020/02/15)
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- 1-Methyl-1,4-cyclohexadiene as a Traceless Reducing Agent for the Synthesis of Catechols and Hydroquinones
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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
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p. 13655 - 13664
(2019/10/28)
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- A self-immolative spacer that enables tunable controlled release of phenols under neutral conditions
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A current challenge in the area of responsive materials is the design of reagents and polymers that provide controlled release of phenols in environments that are less polar than water. In these contexts, a molecular strategy that enables release of nearl
- Schmid, Kyle M.,Jensen, Lasse,Phillips, Scott T.
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experimental part
p. 4363 - 4374
(2012/06/18)
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- Induction of molecular chirality by circularly polarized light in cyclic azobenzene with a photoswitchable benzene rotor
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New phototriggered molecular machines based on cyclic azobenzene were synthesized in which a 2,5-dimethoxy, 2,5-dimethyl, 2,5-difluorine or unsubstituted-1,4-dioxybenzene rotating unit and a photoisomerizable 3,3′-dioxyazobenzene moiety are bridged together by fixed bismethylene spacers. Depending upon substitution on the benzene moiety and on the E/Z conformation of the azobenzene unit, these molecules suffer various degrees of restriction on the free rotation of the benzene rotor. The rotation of the substituted benzene rotor within the cyclic azobenzene cavity imparts planar chirality to the molecules. Cyclic azobenzene 1, with methoxy groups at both the 2- and 5-positions of the benzene rotor, was so conformationally restricted that free rotation of the rotor was prevented in both the E and Z isomers and the respective planar chiral enantiomers were resolved. In contrast, compound 2, with 2,5-dimethylbenzene as the rotor, demonstrated the property of a light-controlled molecular brake, whereby rotation of the 2,5-dimethylbenzene moiety is completely stopped in the E isomer (brake ON, rotation OFF), while the rotation is allowed in the Z isomer (brake OFF, rotation ON). The cyclic azobenzene 3, with fluorine substitution on the benzene rotor, was in the brake OFF state regardless of E/Z photoisomerization of the azobenzene moiety. More interestingly, for the first time, we demonstrated the induction of molecular chirality in a simple monocyclic azobenzene by circular-polarized light. The key characteristics of cyclic azobenzene 2, that is, stability of the chiral structure in the E isomer, fast racemization in the Z isomer, and the circular dichroism of enantiomers of both E and Z isomers, resulted in a simple reversible enantio-differentiating photoisomerization directly between the E enantiomers. Upon exposure to r- or l-circularly polarized light at 488 nm, partial enrichment of the (S)- or (R)-enantiomers of 2 was observed. Copyright
- Hashim,Thomas, Reji,Tamaoki, Nobuyuki
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supporting information; experimental part
p. 7304 - 7312
(2011/08/05)
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- Accelerated hole transfer across a molecular double barrier
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We report on a dyad in which photoinduced hole transfer through a non-uniform molecular double barrier is more than one order of magnitude more rapid than hole transfer across a comparable uniform (rectangular) tunneling barrier.
- Hanss, David,Walther, Mathieu E.,Wenger, Oliver S.
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supporting information; experimental part
p. 7034 - 7036
(2010/10/19)
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- A synthetic study on bauhinoxepin J: Construction of a dibenzo[bf]oxepin ring system by a DDQ-promoted oxidative dearomatization-cyclization approach
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Efforts to construct a dibenzo[b,f]oxepin ring system for a synthesis of bauhinoxepin J are described. A DDQ-promoted oxidative dearomatization-cyclization of the 2-phenoxyethyl-substituted tetramethoxybenzene was used to construct a tricyclic quinone mon
- Yoshida, Masahiro,Maeyama, Yohei,Shishido, Kozo
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experimental part
p. 623 - 629
(2010/04/27)
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- Reaction of phenols with the 2,2-diphenyl-1-picrylhydrazyl radical. Kinetics and DFT calculations applied to determine ArO-H bond dissociation enthalpies and reaction mechanism
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(Figure Presented) The formal H-atom abstraction by the 2,2-diphenyl-1-picrylhydrazyl (dpph?) radical from 27 phenols and two unsaturated hydrocarbons has been investigated by a combination of kinetic measurements in apolar solvents and density functional theory (DFT). The computed minimum energy structure of dpph? shows that the access to its divalent N is strongly hindered by an ortho H atom on each of the phenyl rings and by the o-NO2 groups of the picryl ring. Remarkably small Arrhenius pre-exponential factors for the phenols [range (1.3-19) × 105 M-1 s-1] are attributed to steric effects. Indeed, the entropy barrier accounts for up to ca. 70% of the free-energy barrier to reaction. Nevertheless, rate differences for different phenols are largely due to differences in the activation energy, Ea,1 (range 2 to 10 kcal/mol). In phenols, electronic effects of the substituents and intramolecular H-bonds have a large influence on the activation energies and on the ArO-H BDEs. There is a linear Evans-Polanyi relationship between E a,1 and the ArO-H BDEs: Ea,1/kcal x mol-1 = 0.918 BDE(ArO-H)/kcal x mol-1 - 70.273. The proportionality constant, 0.918, is large and implies a "late" or "product-like" transition state (TS), a conclusion that is congruent with the small deuterium kinetic isotope effects (range 1.3-3.3). This Evans-Polanyi relationship, though questionable on theoretical grounds, has profitably been used to estimate several ArO-H BDEs. Experimental ArO-H BDEs are generally in good agreement with the DFT calculations. Significant deviations between experimental and DFT calculated ArO-H BDEs were found, however, when an intramolecular H-bond to the O? center was present in the phenoxyl radical, e.g., in ortho semiquinone radicals. In these cases, the coupled cluster with single and double excitations correlated wave function technique with complete basis set extrapolation gave excellent results. The TSs for the reactions of dpph ? with phenol, 3- and 4-methoxyphenol, and 1,4-cyclohexadiene were also computed. Surprisingly, these TS structures for the phenols show that the reactions cannot be described as occurring exclusively by either a HAT or a PCET mechanism, while with 1,4-cyclohexadiene the PCET character in the reaction coordinate is much better defined and shows a strong π-π stacking interaction between the incipient cyclohexadienyl radical and a phenyl ring of the dpph? radical.
- Foti, Mario C.,Daquino, Carmelo,Mackie, Iain D.,DiLabio, Gino A.,Ingold
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experimental part
p. 9270 - 9282
(2009/04/07)
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- Total synthesis and biological evaluation of the nakijiquinones
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The Her-2/Neu receptor tyrosine kinase is vastly overexpressed in about 30% of primary breast, ovary, and gastric carcinomas. The nakijiquinones are the only naturally occurring inhibitors of this important oncogene, and structural analogues of the nakijiquinones may display inhibitory properties toward other receptor tyrosine kinases involved in cell signaling and proliferation. Here, we describe the first enantioselective synthesis of the nakijiquinones. Key elements of the synthesis are (i) the reductive alkylation of a Wieland - Mieschertype enone with a tetramethoxyaryl bromide, (ii) the oxidative conversion of the aryl ring into a p-quinoid system, (iii) the regioselective saponification of one of the two vinylogous esters incorporated therein, and (iv) the selective introduction of different amino acids via nucleophilic conversion of the remaining vinylogous ester into the corresponding vinylogous amide. The correct stereochemistry and substitution patterns are completed by conversion of two keto groups into a methyl group and an endocyclic olefin via olefination/reduction and olefination/isomerization sequences, respectively. This synthesis route also gave access to analogues of nakijiquinone C with inverted configuration at C-2 or with an exocyclic instead of an endocyclic double bond. Investigation of the kinase-inhibiting properties of the synthesized derivatives revealed that the C-2 epimer 30 of nakijiquinone C is a potent and selective inhibitor of the KDR receptor, a receptor tyrosine kinase involved in tumor angiogenesis. Molecular modeling studies based on the crystal structure of KDR and a model of the ATP binding site built from a crystal structure of FGF-R revealed an insight into the structural basis for the difference in activity between the natural product nakijiquinone C and the C-2 epimer 30.
- Stahl,Kissau,Mazitschek,Huwe,Furet,Giannis,Waldmann
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p. 11586 - 11593
(2007/10/03)
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- Asymmetric synthesis of the nakijiquinones - Selective inhibitors of the Her-2/Neu protooncogene
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A Wieland-Miescher type ketone and a tetramethoxyaryl derivative are the key building blocks for the enantioselective total synthesis of nakijiquinone C (1). The nakijiquinones are the only natural products known that selectively inhibit the Her-2/Neu tyr
- Stahl, Petra,Waldmann, Herbert
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p. 3710 - 3713
(2007/10/03)
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- Synthesis of cytotoxic maesaquinone bearing a 2,5-dihydroxy-6-methyl-1,4-benzoquinone nucleus
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A synthesis of maesaquinone [2,5-dihydroxy-3-(Z)-10'-pentadecenyl-6-methyl-1,4-benzoquinone] has been achieved in nine steps starting from 1,4,5-trimethoxymethyloxy-2-methoxybenzene which can be readily obtained by successive deprotection and MOM protection of one methoxyl group of 2,5-dimethoxy-1,4-benzoquinone.
- Fukuyama, Yoshiyasu,Yaso, Hideyuki,Kiriyama, Yuuko,Takahashi, Hironobu,Minami, Hiroyuki,Kamikawa, Tadao
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p. 16969 - 16976
(2007/10/03)
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- PREFERENCE FOR PHOTODISSOCIATION OVER INTERNAL -CYCLOADDITION DURING IRRADIATION OF AN UNSATURATED α,β-ENONE
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Irradiation of 2, its trimethylsilyl ether or acetate ester using ultraviolet light of wavelength > 290 nm results not in internal olefin-α,β-enone cycloaddition, but exclusively in photodissociation either of the intercyclic bond (for 2 or the TMS ether)
- Corey, E. J.,Wu, Laurence I.
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p. 663 - 664
(2007/10/02)
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- ISOLATION, STRUCTURE AND SYNTHESIS OF MAESANIN, A HOST DEFENSE STIMULANT FROM AN AFRICAN MEDICINAL PLANT MAESA LANCEOLATA
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The isolation, characterization and an efficient synthesis of maesanin 1, a host defense stimulant isolated from an African medicinal plant Maesa lanceolata is reported.
- Kubo, Isao,Kamikawa, Tadao,Miura, Iwao
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p. 3825 - 3828
(2007/10/02)
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