736985-90-3Relevant articles and documents
Substituent effects on oxidation-induced formation of quinone methides from arylboronic ester precursors
Cao, Sheng,Christiansen, Robin,Peng, Xiaohua
, p. 9050 - 9058 (2013/07/26)
A series of arylboronic esters containing different aromatic substituents and various benzylic leaving groups (Br or N+Me3Br -) have been synthesized. The substituent effects on their reactivity with H2O2 and formation of quinone methide (QM) have been investigated. NMR spectroscopy and ethyl vinyl ether (EVE) trapping experiments were used to determine the reaction mechanism and QM formation, respectively. QMs were not generated during oxidative cleavage of the boronic esters but by subsequent transformation of the phenol products under physiological conditions. The oxidative deboronation is facilitated by electron-withdrawing substituents, such as aromatic F, NO2, or benzylic N+Me 3Br-, whereas electron-donating substituents or a better leaving group favor QM generation. Compounds containing an aromatic CH 3 or OMe group, or a good leaving group (Br), efficiently generate QMs under physiological conditions. Finally, a quantitative relationship between the structure and activity has been established for the arylboronic esters by using a Hammett plot. The reactivity of the arylboronic acids/esters and the inhibition or facilitation of QM formation can now be predictably adjusted. This adjustment is important as some applications may benefit and others may be limited by QM generation. Tunable quinone methide formation: Aromatic substituents and the benzylic leaving group strongly affect the H 2O2-induced formation of quinone methides (QMs) from arylboronic esters (see scheme). The reactivity of arylboronic esters can be predictably adjusted by varying substituents. Copyright
Dual reactivity of hydroxy- and methoxy- substituted o-Quinone methides in aqueous solutions: Hydration versus tautomerization.
Arumugam, Selvanathan,Popik, Vladimir V.
scheme or table, p. 7338 - 7346 (2011/01/12)
4-Hydroxy-6-methylene-2,4-cyclohexadien-1-one (1) and 4-methoxy-6- methylene-2,4-cyclohexadien-1-one (2) were generated by efficient (Φ = 0.3) photodehydration of 2-(hydroxymethyl)benzene-1,4-diol (3a) and 2-(hydroxymethyl)-4-methoxyphenol (4a), respectively. o-Quinone methides 1 and 2 can be quantitatively trapped as Diels-Alder adducts with ethyl vinyl ether or intercepted by good nucleophiles, such as azide ion (kN3(1) = 3.15 × 104 M-1 s-1 and kN3(2) = 3.30 × 104 M-1 s-1). In aqueous solution, o-quinone methide 2 rapidly adds water to regenerate starting material (τH2O(2) = 7.8 ms at 25 °C). This reaction is catalyzed by specific acid (kH+(2) = 8.37 × 10 3 s-1 M-1) and specific base (k OH-(2) = 1.08 × 104 s-1 M -1) but shows no significant general acid/base catalysis. In sharp contrast, o-quinone methide 1 decays (τH2O(1) = 3.3 ms at 25 °C) via two competing pathways: nucleophilic hydration to form starting material 3a and tautomerization to produce methyl-p-benzoquinone. The disappearance of 1 shows not only specific acid (kH+(1) = 3.30 × 104 s-1 M-1) and specific base catalysis (kOH-(1) = 3.51 × 104 s -1 M-1) but pronounced catalysis by general acids and bases as well. The o-quinone methides 1 and 2 were also generated by the photolysis of 2-(ethoxymethyl)benzene-1,4-diol (3b) and 2-(ethoxymethyl)-4- methoxyphenol (4b), as well as from (2,5-dihydroxy-1-phenyl)methyl- (3c) and (2-hydroxy-5-methoxy-1-phenyl)methyltrimethylammonium iodides (4c). Short-lived (τ25°C ≈ 20 μs) precursors of o-quinone methides 1 and 2 were detected in the laser flash photolysis of 3a,b and 4a,b. On the basis of their reactivity, benzoxete structures have been assigned to these intermediates.
A catalytic antibody against a tocopherol cyclase inhibitor
Manetsch, Roman,Zheng, Lei,Reymond, Martine T.,Woggon, Wolf-Dietrich,Reymond, Jean-Louis
, p. 2487 - 2506 (2007/10/03)
The cyclic ammonium cation 5 and its guanidinium analogue 4 areinhibitors of tocopherol cyclase. Monoclonal antibodies were raised against protein conjugates of the haptens 1-3 and screened for catalytic reactions with alkene 8, a short chain analogue of
