87-87-6Relevant articles and documents
Singh,Rangaswami
, p. 1229 (1966)
Synthetic Photochemistry. XXX. The Addition Reactions of Cycloheptatriene with Some Aromatic p-Quinones
Mori, Akira,Takeshita, Hitoshi
, p. 1581 - 1584 (1985)
The photochemical reactions of cycloheptatriene with p-benzoquinone and 1,4-naphthoquinone yielded the spirocyclic ethers, which had 7-oxabicyclonona-2,4-diene structures, by the characteristic (6+2)? cycloaddition process.The latter quinone further produced the carboxylic (2+2)? and (6+2)? cycloadducts.
Pentachlorophenol hydroxylase, a poorly functioning enzyme required for degradation of pentachlorophenol by sphingobium chlorophenolicum
Hlouchova, Klara,Rudolph, Johannes,Pietari, Jaana M. H.,Behlen, Linda S.,Copley, Shelley D.
, p. 3848 - 3860 (2012)
Several strains of Sphingobium chlorophenolicum have been isolated from soil that was heavily contaminated with pentachlorophenol (PCP), a toxic pesticide introduced in the 1930s. S. chlorophenolicum appears to have assembled a poorly functioning pathway for degradation of PCP by patching enzymes recruited via two independent horizontal gene transfer events into an existing metabolic pathway. Flux through the pathway is limited by PCP hydroxylase. PCP hydroxylase is a dimeric protein that belongs to the family of flavin-dependent phenol hydroxylases. In the presence of NADPH, PCP hydroxylase converts PCP to tetrachlorobenzoquinone (TCBQ). The kcat for PCP (0.024 s -1) is very low, suggesting that the enzyme is not well evolved for turnover of this substrate. Structure-activity studies reveal that substrate binding and activity are enhanced by a low pKa for the phenolic proton, increased hydrophobicity, and the presence of a substituent ortho to the hydroxyl group of the phenol. PCP hydroxylase exhibits substantial uncoupling; the C4a-hydroxyflavin intermediate, instead of hydroxylating the substrate, can decompose to produce H2O2 in a futile cycle that consumes NADPH. The extent of uncoupling varies from 0 to 100% with different substrates. The extent of uncoupling is increased by the presence of bulky substituents at position 3, 4, or 5 and decreased by the presence of a chlorine in the ortho position. The effectiveness of PCP hydroxylase is additionally hindered by its promiscuous activity with tetrachlorohydroquinone (TCHQ), a downstream metabolite in the degradation pathway. The conversion of TCHQ to TCBQ reverses flux through the pathway. Substantial uncoupling also occurs during the reaction with TCHQ.
1-Methyl-1,4-cyclohexadiene as a Traceless Reducing Agent for the Synthesis of Catechols and Hydroquinones
Baschieri, Andrea,Amorati, Riccardo,Valgimigli, Luca,Sambri, Letizia
, p. 13655 - 13664 (2019/10/28)
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.
Calix[4]pyrrole Hydridosilicate: The Elusive Planar Tetracoordinate Silicon Imparts Striking Stability to Its Anionic Silicon Hydride
Ebner, Fabian,Greb, Lutz
supporting information, p. 17409 - 17412 (2019/01/04)
Anionic hydridosilicates are highly reactive and strong hydride donors. In contrast, calix[4]pyrrole hydridosilicate is an entirely water-stable, anionic silicon hydride, which does not show hydridic reactivity. However, it still acts as an electron donor and enables the detection of a single electron transfer process in the reduction chemistry with hydridosilicates. Most important, these unusual properties are imparted by the unique planar structure of its elusive parent neutral silane-substantiating the effect of planar tetracoordinate silicon for the first time.
