- Enantioselective friedel-crafts alkylation of pyrrole with chalcones catalyzed by a dinuclear zinc catalyst
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A highly enantioselective Friedel-Crafts (F-C) alkylation of pyrrole with a wide range of simple nonchelating chalcone derivatives catalyzed by a chiral (Zn2EtL)n (L = (S,S)-1) complex has been developed. The catalyst (Zn2EtL)n complex was prepared in situ by reacting the chiral ligand (S,S)-1 with 2 equiv of diethylzinc. A series of β-pyrrole-substituted dihydrochalcones were usually formed mostly in excellent yields (up to 99%) and excellent enantioselectivity [up to 99% enantiomeric excess (ee)] by using 15 mol % catalyst loading under mild conditions. The absolute stereochemistry of the products was determined to be the S-configuration by X-ray crystallographic analysis of 13g. Meanwhile, a weak negative nonlinear effect was observed. On the basis of the experimental results and previous reports, a possible mechanism was proposed to explain the origin of the asymmetric induction.
- Hua, Yuan-Zhao,Han, Xing-Wang,Yang, Xiao-Chao,Song, Xixi,Wang, Min-Can,Chang, Jun-Biao
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p. 11690 - 11699
(2015/01/16)
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- Using ionic liquid [EMIM][CH3COO] as an enzyme-'friendly' co-solvent for resolution of amino acids
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An ionic liquid (IL), 1-ethyl-3-methylimidazolium acetate [EMIM][CH3COO], was used in 0-4.0 M (~60% IL, v/v), as a nonvolatile organic medium for the enzymatic resolution of amino acids. When dl-phenylalanine methyl ester was studied as a model substrate, high enantiomeric excesses (ee) of l-amino acid were obtained in all ionic concentrations; however, lower yields were observed at high IL concentrations. This IL is more enzyme-'friendly' than the hydrophilic organic solvent acetonitrile and those ILs containing chaotropic anions (such as [EMIM][OTs]). Among three proteases and two lipases investigated, lyophilized Bacillus licheniformis protease exhibited the best enantioselectivity and activity. Highly enantioselective resolutions were also produced for several other amino acids in 2.0 M IL. Interestingly, high ee were also found in deuterium oxide (D2O) rather than in ordinary water, and a further enhancement was achieved with the co-existence of [EMIM][CH3COO]. The heavy water effect was explained in terms of protein stabilization by D2O. The secondary structural changes of enzyme in various media were interpreted by the second derivatives of FT-IR spectra.
- Zhao, Hua,Jackson, Lee,Song, Zhiyan,Olubajo, Olarongbe
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p. 2491 - 2498
(2007/10/03)
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- Crystallographic studies on the reaction of isopenicillin N synthase with an unsaturated substrate analogue
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Isopenicillin N synthase (IPNS) catalyses conversion of the linear tripeptie δ-(L-α-aminoadipoyl)-L-cysteinyl-D-valine (ACV) to isopenicillin N (IPN), the central step in biosynthesis of the β-lactam antibiotics. The unsaturated substrate analogue δ-(L-α-aminoadipoyl)-L-cysteinyl-D-vinylglycine (ACvG) has previously been incubated with IPNS and a single product was isolated, a 2-α-hydroxymethyl isopenicillin N (HMPen), formed via a monooxygenase mode of reactivity. ACvG has now been crystallised with IPNS and the structure of the anaerobic IPNS:Fe(II):ACvG complex determined to 1.15 A resolution. Furthermore, by exposing the anaerobically grown crystals to high-pressure oxygen gas, a structure corresponding to the bicyclic product HMPen has been obtained at 1.60 A resolution. In light of these and other IPNS structures, and recent developments with related dioxygenases, the [2 + 2] cycloaddition mechanism for HMPen formation from ACvG has been revised, and a stepwise radical mechanism is proposed. This revised mechanism remains consistent with the observed stereospecificity of the transformation, but fits better with apparent constraints on the coordination geometry around the active site iron atom.
- Elkins, Jonathan M.,Rutledge, Peter J.,Burzlaff, Nicolai I.,Clifton, Ian J.,Adlington, Robert M.,Roach, Peter L.,Baldwin, Jack E.
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p. 1455 - 1460
(2007/10/03)
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- Picking the S1, S1' and S2' pockets of matrix metalloproteinases. A niche for potent acyclic sulfonamide inhibitors.
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A series of acyclic hydroxamic acids harboring strategically placed alpha-arylsulfonamido and thioether groups was synthesized and found to be potent inhibitors of various MMPs. An unprecedented cleavage of t-butyl hydroxamates to hydroxamic acids was found.
- Hanessian,Bouzbouz,Boudon,Tucker,Peyroulan
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p. 1691 - 1696
(2007/10/03)
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- Potential application of Sulfolobus solfataricus as catalyst in organic synthesis
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Sulfolobus solfataricus, a thermoacidophilic archaeon, has been utilized as catalyst for several enzymatic transformations such as carbonyl-alcohol oxidoreductions, synthesis of glycosides, kinetic resolution of aminoacid esters, etc.All these reactions have been carried out at 75 deg C in accordance with the thermophilic nature of the enzymes present in the organisms.
- Trincone, Antonio,Nicolaus, Barbara,Lama, Licia,Gambacorta, Agata
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