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Glycobiology ◽  
2020 ◽  
Author(s):  
Kazi Zubaida Gulshan Ara ◽  
Javier A Linares-Pastén ◽  
Jonas Jönsson ◽  
Maria Viloria-Cols ◽  
Stefan Ulvenlund ◽  
...  

Abstract Alkyl glycoside surfactants with elongated carbohydrate chains are useful in different applications due to their improved biocompatibility. Cyclodextrin glucanotransferases can catalyze the elongation process through the coupling reaction. However, due to the presence of a hydrophobic tail, the interaction between an alkyl glycoside acceptor and the active site residues is weaker than the interaction with maltooligosaccharides at the corresponding site. Here we report the mutations of F197, G263 and E266 near the acceptor subsites in the CGTase CspCGT13 from Carboxydocella sp. The results showed that substitutions of both F197 and G263 were important for the binding of acceptor substrate dodecyl maltoside during coupling reaction. The double mutant F197Y/G263A showed enhanced coupling activity and displayed a 2-fold increase of the primary coupling product using γ-cyclodextrin as donor when compared to wildtype CspCGT13. Disproportionation activity was also reduced, which was also the case for another double mutant (F197Y/E266A) that however not showed the corresponding increase in coupling. A triple mutant F197Y/G263A/E266A maintained the increase in primary coupling product (1.8-fold increase) using dodecyl maltoside as acceptor, but disproportionation was approximately at the same level as in the double mutants. In addition, hydrolysis of starch was slightly increased by the F197Y and G263A substitutions, indicating that interactions at both positions influenced the selectivity between glycosyl and alkyl moieties.


Molecules ◽  
2020 ◽  
Vol 25 (18) ◽  
pp. 4134
Author(s):  
Daniel Álvarez ◽  
Elena López-Castro ◽  
Arturo Guerrero ◽  
Lucía Riera ◽  
Julio Pérez ◽  
...  

A comparative theoretical study on the reactivity of the complexes [ReY(CO)3(bipy)] (Y = NH2, NHMe, NHpTol, OH, OMe, OPh, PH2, PHMe, PMe2, PHPh, PPh2, PMePh, SH, SMe, SPh; bipy = 2,2′-bipyridine) towards methyl propiolate was carried out to analyze the influence of both the heteroatom (N, O, P, S) and the alkyl and/or aryl substituents of the Y ligand on the nature of the product obtained. The methyl substituent tends to accelerate the reactions. However, an aromatic ring bonded to N and O makes the reaction more difficult, whereas its linkage to P and S favour it. On the whole, ligands with O and S heteroatoms seem to disfavour these processes more than ligands with N and P heteroatoms, respectively. Phosphido and thiolato ligands tend to yield a coupling product with the bipy ligand, which is not the general case for hydroxo, alcoxo or amido ligands. When the Y ligand has an O/N and an H atom the most likely product is the one containing a coupling with the carbonyl ligand, which is not always obtained when Y contains P/S. Only for OMe and OPh, the product resulting from formal insertion into the Re-Y bond is the preferred.


2020 ◽  
Author(s):  
Abolghasem (Gus) Bakhoda ◽  
Otome Okoromoba ◽  
Christine Greene ◽  
Mahdi Raghibi Boroujeni ◽  
Jeffery A. Bertke ◽  
...  

<p>Copper(II) alkynyl species are proposed as key intermediates in numerous Cu−catalysed C−C coupling reactions. Supported by a β−diketiminate ligand, the three coordinate copper(II) alkynyl [Cu<sup>II</sup>]−C≡CAr (Ar = 2,6−Cl<sub>2</sub>C<sub>6</sub>H<sub>3</sub>) forms upon reaction of the alkyne H−C≡CAr with the copper(II) <i>tert</i>−butoxide complex [Cu<sup>II</sup>]−O<i><sup>t</sup></i>Bu. In solution, this [Cu<sup>II</sup>]−C≡CAr species cleanly transforms the to the Glaser coupling product ArC≡C−C≡CAr and [Cu<sup>I</sup>](solvent). Addition of nucleophiles R′C≡CLi (R′ = aryl, silyl) and Ph–Li to [Cu<sup>II</sup>]−C≡CAr affords the corresponding C<sub>sp</sub>−C<sub>sp</sub> and C<sub>sp</sub>−C<sub>sp2</sub>coupled products RC≡C−C≡CAr and Ph–C≡CAr with concomitant generation of [Cu<sup>I</sup>](solvent) and {[Cu<sup>I</sup>]−C≡CAr}<sup>−</sup>. Supported by DFT calculations, redox disproportionation forms [Cu<sup>III</sup>](C≡CAr)(R) species that reductively eliminate R−C≡CAr products. [Cu<sup>II</sup>]−C<a>≡</a>CAr also captures the trityl radical Ph<sub>3</sub>C• to give Ph<sub>3</sub>C−C≡CAr. Radical capture represents the key C<sub>sp</sub>−C<sub>sp3</sub> bond forming step in the copper catalysed C-H functionalization of benzylic substrates R−H with alkynes H−C≡CR′ (R′ = (hetero)aryl, silyl) that provide C<sub>sp</sub>−C<sub>sp3</sub> coupled products R−C≡CR via radical relay with <i><sup>t</sup></i>BuOO<i><sup>t</sup></i>Bu as oxidant.</p>


2020 ◽  
Author(s):  
Abolghasem (Gus) Bakhoda ◽  
Otome Okoromoba ◽  
Christine Greene ◽  
Mahdi Raghibi Boroujeni ◽  
Jeffery A. Bertke ◽  
...  

<p>Copper(II) alkynyl species are proposed as key intermediates in numerous Cu−catalysed C−C coupling reactions. Supported by a β−diketiminate ligand, the three coordinate copper(II) alkynyl [Cu<sup>II</sup>]−C≡CAr (Ar = 2,6−Cl<sub>2</sub>C<sub>6</sub>H<sub>3</sub>) forms upon reaction of the alkyne H−C≡CAr with the copper(II) <i>tert</i>−butoxide complex [Cu<sup>II</sup>]−O<i><sup>t</sup></i>Bu. In solution, this [Cu<sup>II</sup>]−C≡CAr species cleanly transforms the to the Glaser coupling product ArC≡C−C≡CAr and [Cu<sup>I</sup>](solvent). Addition of nucleophiles R′C≡CLi (R′ = aryl, silyl) and Ph–Li to [Cu<sup>II</sup>]−C≡CAr affords the corresponding C<sub>sp</sub>−C<sub>sp</sub> and C<sub>sp</sub>−C<sub>sp2</sub>coupled products RC≡C−C≡CAr and Ph–C≡CAr with concomitant generation of [Cu<sup>I</sup>](solvent) and {[Cu<sup>I</sup>]−C≡CAr}<sup>−</sup>. Supported by DFT calculations, redox disproportionation forms [Cu<sup>III</sup>](C≡CAr)(R) species that reductively eliminate R−C≡CAr products. [Cu<sup>II</sup>]−C<a>≡</a>CAr also captures the trityl radical Ph<sub>3</sub>C• to give Ph<sub>3</sub>C−C≡CAr. Radical capture represents the key C<sub>sp</sub>−C<sub>sp3</sub> bond forming step in the copper catalysed C-H functionalization of benzylic substrates R−H with alkynes H−C≡CR′ (R′ = (hetero)aryl, silyl) that provide C<sub>sp</sub>−C<sub>sp3</sub> coupled products R−C≡CR via radical relay with <i><sup>t</sup></i>BuOO<i><sup>t</sup></i>Bu as oxidant.</p>


Synthesis ◽  
2019 ◽  
Vol 51 (13) ◽  
pp. 2678-2686 ◽  
Author(s):  
Wing In Lai ◽  
Man Pan Leung ◽  
Pui Ying Choy ◽  
Fuk Yee Kwong

A family of 2-(9H-carbazol-9-yl)phenyl-based phosphine ligands were synthesized and their efficacy in promoting the steric hindered Buchwald–Hartwig amination was evaluated. In the presence of Pd(OAc)2 (0.03–1.0 mol%) associated with the newly developed a carbazolyl-derived phosphine ligand, the synthesis of tetra-ortho-substituted diarylamines proceeded smoothly with excellent product yields (up to 99%). A remarkable result was obtained even for the coupling of highly sterically congested 2,6-diisopropylaniline and hindered 2-chloro-1,3,5-triisopropylbenzene (96% isolated yield). A possible decomposition pathway for the anthracenyl C–N coupling product is also reported.


Catalysts ◽  
2019 ◽  
Vol 9 (1) ◽  
pp. 76 ◽  
Author(s):  
Saurabh Shahane ◽  
Bernardo de P. Cardoso ◽  
Michael Chetcuti ◽  
Vincent Ritleng

NiCp†L(NHC)](+) complexes (Cp† = Cp (η5-C5H5), Cp* (η5-C5Me5); NHC = N-heterocyclic carbene; L = Cl− or NCMe) have been tested as pre-catalysts for the direct arylation of benzothiazole in the presence of an alkoxide. Only the pentamethylcyclopentadienyl derivative, [NiCp*Cl(IMes)] (IMes = 1,3-bis(2,4,6-trimethylphenylimidazol-2-ylidene), enabled low conversion to the desired coupling product with phenyl iodide as the electrophilic coupling partner. In contrast, all cyclopentadienyl complexes proved to be inactive. 1H NMR studies of the “catalytic” reaction mixtures demonstrate that they cleanly convert to an unreactive C(2)-benzothiazolyl derivative, whose identity has been confirmed by an independent synthesis and characterization. The latter constitutes a potential energy well that quenches all further reactivity, and provides a rare example of C(2)-metallated azolyl complex.


2019 ◽  
Vol 43 (39) ◽  
pp. 15743-15753
Author(s):  
Eric Brüllingen ◽  
Jörg-Martin Neudörfl ◽  
Bernd Goldfuss

Palladium-catalyzed allylic alkylations of Na(CH(CO2Me)2 with 1,3-diphenylallyl acetate, employing BIFOP-X (X = H, D, Cl, CN, N3) ligands, yield the C–C coupling product (up to 91% yield, 70% ee). A NBO effect reveals a change of stereochemistry.


IUCrData ◽  
2018 ◽  
Vol 3 (4) ◽  
Author(s):  
Lukas Brieger ◽  
Christian Unkelbach ◽  
Carsten Strohmann

The title compound, C18H22, is a coupling product of two metallated mesitylene molecules. The dihedral angle between the aromatic rings is 11.10 (5)° and the Car—Cm—Cm—Car (ar = aromatic and m = methylene) torsion angle is 179.60 (14)°. No directional interactions beyond normal van der Waals contacts could be identified in the crystal. To our best knowledge, it is the first known coupling product of metallated mesitylene.


2018 ◽  
Vol 54 (96) ◽  
pp. 13555-13558 ◽  
Author(s):  
Imtiaz Begum ◽  
Gregor Schnakenburg ◽  
Zsolt Kelemen ◽  
László Nyulászi ◽  
René. T. Boeré ◽  
...  

Synthesis of a novel tricyclic 1,4-diphosphinine I and, subsequently, of a stable anionic 1,4-diphosphinine II is reported; while II can be used as precursor for 1,4-disubstitution products, its oxidation leads to the formation of the P–P coupling product III.


2017 ◽  
Vol 87 ◽  
pp. 292-305 ◽  
Author(s):  
Frezah J. Muhana ◽  
Bassam I. El-Eswed ◽  
Fawwaz I. Khalili

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