- Regioselectivity of Cobalamin-Dependent Methyltransferase Can Be Tuned by Reaction Conditions and Substrate
-
Regioselective reactions represent a significant challenge for organic chemistry. Here the regioselective methylation of a single hydroxy group of 4-substituted catechols was investigated employing the cobalamin-dependent methyltransferase from Desulfitobacterium hafniense. Catechols substituted in position four were methylated either in meta- or para-position to the substituent depending whether the substituent was polar or apolar. While the biocatalytic cobalamin dependent methylation was meta-selective with 4-substituted catechols bearing hydrophilic groups, it was para-selective for hydrophobic substituents. Furthermore, the presence of water miscible co-solvents had a clear improving influence, whereby THF turned out to enable the formation of a single regioisomer in selected cases. Finally, it was found that also the pH led to an enhancement of regioselectivity for the cases investigated.
- Pompei, Simona,Grimm, Christopher,Farnberger, Judith E.,Schober, Lukas,Kroutil, Wolfgang
-
p. 5977 - 5983
(2020/10/06)
-
- Catalytic activation of unstrained C(aryl)–C(aryl) bonds in 2,2′-biphenols
-
Transition metal catalysis has emerged as an important means for C–C activation that allows mild and selective transformations. However, the current scope of C–C bonds that can be activated is primarily restricted to either highly strained systems or more polarized C–C bonds. In contrast, the catalytic activation of non-polar and unstrained C–C moieties remains an unmet challenge. Here we report a general approach for the catalytic activation of the unstrained C(aryl)–C(aryl) bonds in 2,2′-biphenols. The key is to utilize the phenol moiety as a handle to install phosphinites as a recyclable directing group. Using hydrogen gas as the reductant, monophenols are obtained with a low catalyst loading and high functional group tolerance. This approach is also applied to the synthesis of 2,3,4-trisubstituted phenols. A further mechanistic study suggests that the C–C activation step is mediated by a rhodium(i) monohydride species. Finally, a preliminary study on breaking the inert biphenolic moieties in lignin models is illustrated.
- Zhu, Jun,Wang, Jianchun,Dong, Guangbin
-
-
- ANTI-HIV COMPOUNDS
-
This invention provides, among other things, tetrahydroisoquinolines useful for treating viral infections, pharmaceutical formulations containing such compounds, as well as methods of inhibiting the replication of a virus, such as HIV, or treating a disease, such as AIDS.
- -
-
Paragraph 0232
(2016/07/05)
-
- Facile and regioselective dealkylation of alkyl aryl ethers using niobium(V) pentachloride
-
A simple and facile method for the cleavage of carbon-oxygen bonds promoted by niobium pentachloride(V) is described. Excellent yields and regioselectivities were observed with various alkyl aryl ethers to give the phenols. NMR studies revealed the formation of monoaryloxy niobium salt(V), and a neighboring-group effect may play a significant role in the regioselectivity. Wiley-VCH Verlag GmbH & Co. KGaA, 2006.
- Sudo, Yukinori,Arai, Shigeru,Nishida, Atsushi
-
p. 752 - 758
(2007/10/03)
-
- Galactose oxidase models: Solution chemistry, and phenoxyl radical generation mediated by the copper status
-
Galactose oxidase (GO) is an enzyme that catalyzes two-electron oxidations. Its active site contains a copper atom coordinated to a tyrosyl radical, the biogenesis of which requires copper and dioxygen. We have recently studied the properties of electrochemically generated mononuclear CuII-phenoxyl radical systems as model compounds of GO. We present here the solution chemistry of these ligands under various copper and dioxygen statuses: N3O ligands first chelate CuII, leading, in the presence of base, to [CuII(ligand)(CH3CN)]+ complexes (ortho-tert-butylated ligands) or [(CuII)2(ligand) 2]2+ complexes (orthomethoxylated ligands). Excess copper-(II) then oxidizes the complex to the corresponding mononuclear Cu II-phenoxyl radical species. N2O2 tripodal ligands. in the presence of copper(II), afford directly a copper(II)-phenoxyl radical species. Addition of more than two molar equivalents of copper( II) affords a CuII-bis(phenoxyl) diradical species. The donor set of the ligand directs the reaction towards comproportionation for ligands possessing an N3O donor set, while disproportionation is observed for ligands possessing an N2O2 donor set. These results are discussed in the light of recent results concerning the self-processing of GO. A path involving copper(II) disproportionation is proposed for oxidation of the crosslinked tyrosinate of GO, supporting the fact that both copper(I) and copper(II) activate the enzyme.
- Michel, Fabien,Thomas, Fabrice,Hamman, Sylvain,Saint-Aman, Eric,Bucher, Christophe,Pierre, Jean-Louis
-
p. 4115 - 4125
(2007/10/03)
-
- O-Methylation of tert-Alkylpyrocatecholes. Analytical Method for Determination of the Content of Product Mixtures and Way for Preparation of 4-tert-Alkylveratroles
-
The O-methylation of tert-alkylpyrocatecholes with dimethylsulfate leads to a mixture of substituted guaiacoles 6/7, 9/10 and veratroles 5, 6 which are separated by gas/liquid-chromatography for analytical purposes.It is also possible to prepare 4-tert-alkylsubstituted veratroles 5 with good yields in this way.On the other hand, the alkylation of veratrole was only successful with lower tert-alkanols or alkenes.Long-chained tert-alkanols fail in this reaction.The analytical and spectroscopical data of some new 4-tert-alkylveratroles 5a-g are given.
- Beger, J.,Meerbote, M.
-
p. 119 - 125
(2007/10/02)
-
- Process for preparing alkoxyphenols
-
A process for preparing an alkoxyphenol represented by the formula: STR1 wherein R is hydrogen, alkyl having 1 to 4 carbon atoms, formyl, hydroxymethyl, alkoxymethyl, dialkoxymethyl, acetoxymethyl or diacetoxymethyl, R' is alkyl having 1 to 4 carbon atoms, and n is an integer of 1 to 5, characterized in that a phenol halide represented by the formula: STR2 wherein R and n are as defined above, and X is chlorine or bromine is reacted, in the presence of a copper salt serving as a catalyst and of a solvent, with a product prepared by heating, in the presence of a dehydrating agent, an alkali metal hydroxide and a compound of the formula R'OH wherein R' is as defined above.
- -
-
-