scholarly journals Unlocking Iminium Catalysis in Artificial Enzymes to Create a Friedel-Crafts Alkylase

2021 ◽  
Author(s):  
Reuben B. Leveson-Gower ◽  
Zhi Zhou ◽  
Ivana Drienovská ◽  
Gerard Roelfes
Keyword(s):  
Artificial Enzymes ◽  
Artificial Enzyme ◽  
Triple Mutant ◽  
Protein Scaffold ◽  
Rate Acceleration ◽  
Iminium Ion ◽  
Canonical Amino Acid ◽  
Catalytic Reactivity ◽  
Ion Species ◽  
Kinetics Of

We show that the incorporation of the non-canonical amino acid para-aminophenylalanine (pAF) into the non-enzymatic protein scaffold LmrR creates a proficient and stereoselective artificial enzyme (LmrR_pAF) for the vinylogous Friedel-crafts alkylation between alpha, beta-unsaturated aldehydes and indoles. pAF acts as a catalytic residue, activating enal substrates towards conjugate addition via the formation of intermediate iminium ion species, whilst the protein scaffold provides rate acceleration and enantio-induction. Improved LmrR_pAF varants were identified by direted evolution advised by alanine-scanning to obtain a triple mutant that provided higher yields and enantioselectivities for a range of enals and indoles. Analys of Michaelis-Menten kinetics of LmrR-pAF and tevolved mutants reveals that new activities emerge via evolutionary pathways that diverge from one another and specialise catalytic reactivity.<br>

scholarly journals Unlocking Iminium Catalysis in Artificial Enzymes to Create a Friedel-Crafts Alkylase

2021 ◽  
Author(s):  
Reuben B. Leveson-Gower ◽  
Zhi Zhou ◽  
Ivana Drienovská ◽  
Gerard Roelfes
Keyword(s):  
Artificial Enzymes ◽  
Artificial Enzyme ◽  
Triple Mutant ◽  
Protein Scaffold ◽  
Rate Acceleration ◽  
Iminium Ion ◽  
Canonical Amino Acid ◽  
Catalytic Reactivity ◽  
Ion Species ◽  
Kinetics Of

We show that the incorporation of the non-canonical amino acid para-aminophenylalanine (pAF) into the non-enzymatic protein scaffold LmrR creates a proficient and stereoselective artificial enzyme (LmrR_pAF) for the vinylogous Friedel-crafts alkylation between alpha, beta-unsaturated aldehydes and indoles. pAF acts as a catalytic residue, activating enal substrates towards conjugate addition via the formation of intermediate iminium ion species, whilst the protein scaffold provides rate acceleration and enantio-induction. Improved LmrR_pAF varants were identified by direted evolution advised by alanine-scanning to obtain a triple mutant that provided higher yields and enantioselectivities for a range of enals and indoles. Analys of Michaelis-Menten kinetics of LmrR-pAF and tevolved mutants reveals that new activities emerge via evolutionary pathways that diverge from one another and specialise catalytic reactivity.<br>

scholarly journals Tandem Friedel-Crafts-Alkylation-Enantioselective-Protonation by Artificial Enzyme Iminium Catalysis

2021 ◽  
Author(s):  
Reuben Leveson-Gower ◽  
Ruben de Boer ◽  
Gerard Roelfes
Keyword(s):  
Amino Acid ◽  
Small Molecule ◽  
Bond Formation ◽  
Side Chain ◽  
Artificial Enzymes ◽  
Protein Scaffolds ◽  
Artificial Enzyme ◽  
Protein Scaffold ◽  
Tertiary Carbon ◽  
Canonical Amino Acid

The incorporation of organocatalysts into protein scaffolds, i.e. the production of organocatalytic artificial enzymes, holds the promise of overcoming some of the limitations of this powerful catalytic approach. In particular, transformations for which good reactivity or selectivity is challenging for organocatalysts may find particular benefit from translation into a protein scaffold so that its chiral microenvironment can be utilised in catalysis. Previously, we showed that incorporation of the non-canonical amino acid para-aminophenylalanine into the non-enzymatic protein scaffold LmrR forms a proficient and enantioselective artificial enzyme (LmrR_pAF) for the Friedel-Crafts alkylation of indoles with enals. The unnatural aniline side-chain is directly involved in catalysis, operating via a well-known organocatalytic iminium-based mechanism. In this study, we show that LmrR_pAF can enantioselectively form tertiary carbon centres not only during C-C bond formation, but also by enantioselective protonation. Control over this process is an ongoing challenge for small-molecule catalysts for which general solutions do not exist. LmrR_pAF can selectively deliver a proton to one face of a prochiral enamine intermediate delivering product enantiomeric excesses and yields that rival the best organocatalyst for this transformation. The importance of various side-chains in the pocket of LmrR is distinct from the Friedel-Crafts reaction without enantioselective protonation, and two particularly important residues were probed by exhaustive mutagenesis. This study shows how organocatalytic artificial enzymes can provide solutions to transformations which otherwise require empirical optimisation and design of multifunctional small molecule catalysts.

scholarly journals An In Vivo Biocatalytic Cascade Featuring an Artificial Enzyme Catalyzed New-to-Nature Reaction

2021 ◽  
Author(s):  
Linda Ofori Atta ◽  
Zhi Zhou ◽  
Gerard Roelfes
Keyword(s):  
Carbonyl Compounds ◽  
Artificial Enzymes ◽  
Catalytic Residue ◽  
Artificial Enzyme ◽  
E Coli ◽  
Iminium Ion ◽  
Catalyzed Reactions ◽  
Enzyme Catalyzed Reactions ◽  
Benzaldehyde Derivatives

Artificial enzymes utilizing the genetically encoded non-proteinogenic amino acid p-aminophenylalanine (pAF) as catalytic residue are able to react with carbonyl compounds through an iminium ion mechanism, making reactions possible that have no equivalent in nature. Here, we report an in vivo biocatalytic cascade that is augmented with such an artificial enzyme catalyzed new-to-nature reaction. The artificial enzyme in this study is a pAF containing evolved variant of the Lactococcal multidrug resistance Regulator, designated LmrR_V15pAF_RMH, which efficiently converts in vivo produced benzaldehyde derivatives into the corresponding hydrazone products inside E. coli cells. These in vivo biocatalytic cascades comprising an artificial enzyme catalyzed reactions are an important step towards achieving a hybrid metabolism.

Fe-N-C Artificial Enzyme: Activation of Oxygen for Dehydrogenation and Monoxygenation of Organic Substrates under Mild Condition and Cancer Therapeutic Application

2018 ◽  
Author(s):  
Fei He ◽  
Li Mi ◽  
Yanfei Shen ◽  
Toshiyuki Mori ◽  
Songqin Liu ◽  
...  
Keyword(s):  
Mild Condition ◽  
Enzyme Activation ◽  
Artificial Enzymes ◽  
Organic Substrates ◽  
Artificial Enzyme ◽  
Therapeutic Application ◽  
Highly Efficient ◽  
Activation Of Oxygen

Developing highly efficient artificial enzymes that directly employ O<sub>2</sub> as terminal oxidant has long been pursued but has rarely achieved yet. We report Fe-N-C has unusual enzyme-like activity in both dehydrogenation and monoxygenation of organic substrates with ~100% selectivity by direct using O<sub>2</sub>.

scholarly journals Purification and kinetic mechanism of the major glutathione S-transferase from bovine brain

1989 ◽  
Vol 257 (2) ◽  
pp. 541-548 ◽  
Author(s):  
P R Young ◽  
A V Briedis
Keyword(s):  
Decanoic Acid ◽  
Kinetic Mechanism ◽  
Order Rate Constant ◽  
Bovine Brain ◽  
Glutathione S Transferase ◽  
Rate Acceleration ◽  
Hydrophobic Binding ◽  
Kinetics Of ◽  
Kinetics Of Inhibition

The major glutathione S-transferase isoenzyme from bovine brain was isolated and purified approx. 500-fold. The enzyme has a pI of 7.39 +/- 0.02 and consists of two non-identical subunits having apparent Mr values of 22,000 and 24,000. The enzyme is uniformly distributed in brain, and kinetic data at pH 6.5 with 1-chloro-2,4-dinitrobenzene (CDNB) as substrate suggest a random rapid-equilibrium mechanism. The kinetics of inhibition by product, by GSH analogues and by NADH are consistent with the suggested mechanism and require inhibitor binding to several different enzyme forms. Long-chain fatty acids are excellent inhibitors of the enzyme, and values of 1nKi for hexanoic acid, octanoic acid, decanoic acid and lauric acid form a linear series when plotted as a function of alkyl chain length. A free-energy change of -1900 J/mol (-455 cal/mol) per CH2 unit is calculated for the contribution of hydrophobic binding energy to the inhibition constants. The turnover number of the purified enzyme dimer is approx. 3400/min. When compared with the second-order rate constant for the reaction between CDNB and GSH, the enzyme is providing a rate acceleration of about 1000-fold. The role of entropic contributions to this small rate acceleration is discussed.

Discreteness-of-charge effects in electrode kinetics. III. The electroreduction of aquopentamminochromium(III) cation in the presence of specifically adsorbed iodide anions

1984 ◽  
Vol 62 (8) ◽  
pp. 1497-1501 ◽  
Author(s):  
W. Ronald Fawcett ◽  
Kveta Markušová
Keyword(s):  
Ionic Strength ◽  
Electrode Kinetics ◽  
Reaction Site ◽  
Charge Effects ◽  
Iodide Concentration ◽  
Rate Acceleration ◽  
Rate Of Reaction ◽  
Layer Effect ◽  
Kinetics Of ◽  
Outer Helmholtz Plane

The kinetics of electroreduction of the aquopentamminochromium(III) cation have been studied at a Hg electrode in acidified aqueous solutions of NaI+ NaClO4 with an ionic strength of 0.25 M. The rate of reaction increased with increase in iodide concentration due to the accelerating effect of this anion when it is adsorbed on the electrode. Analysis of the double layer effect indicates that the rate acceleration is greater than that predicted by the Frumkin theory chiefly because the reaction site is closer to the electrode than to the outer Helmholtz plane.

scholarly journals KINETICS OF ION MOVEMENT IN THE SQUID GIANT AXON

1955 ◽  
Vol 39 (2) ◽  
pp. 279-300 ◽  
Author(s):  
Abraham M. Shanes ◽  
Morris D. Berman
Keyword(s):  
Sea Water ◽  
Giant Axon ◽  
Cortical Layer ◽  
Central Segment ◽  
Exponential Decline ◽  
Rate Of Emergence ◽  
The Individual ◽  
Two Stages ◽  
Ion Species ◽  
Kinetics Of

The loss of Na22, K42, and Cl36 from single giant axons of the squid, Loligo pealii, following exposure to an artificial sea water containing these radioisotopes, occurs in two stages, an initial rapid one followed by an exponential decline. The time constants of the latter stage for the 3 ion species are, respectively, 290, 200, and 175 minutes. The outflux of sodium is depressed while that of potassium is accelerated in the absence of oxygen; the emergence of potassium is slowed by cocaine, while that of sodium is unaffected. One cm. ends of the axons take up about twice as much radiosodium as the central segment; this difference in activity is largely preserved during exposure to inactive solution. Such marked differences are not observed with radiopotassium. From the experimental data estimates are given of the influxes and outfluxes of the individual ions. The kinetics of outflux suggests a cortical layer of measureable thickness which contains the ions in different proportions from those in the medium and which governs the rate of emergence of these ions from the axon as though it contained very few but large (relative to ion dimensions) pores.

The application of resonant ion ejection to quadrupole ion storage mass spectrometry: a study of ion/molecule reactions in the QUISTOR

1979 ◽  
Vol 57 (16) ◽  
pp. 2108-2113 ◽  
Author(s):  
Mary Alison Armitage ◽  
John Edward Fulford ◽  
Duong-Nhu- Hoa ◽  
Richard James Hughes ◽  
Raymond Evans March
Keyword(s):  
Quadrupole Mass ◽  
Ion Chemistry ◽  
Mass Filter ◽  
Chemical Systems ◽  
Ion Molecule Reactions ◽  
Resonant Ejection ◽  
Ion Storage ◽  
Product Ions ◽  
Ion Species ◽  
Kinetics Of

Resonant ejection of ion species from the quadrupole ion store (QUISTOR) is shown to reveal the coupling of reactant ions with product ions in ion/molecule reactions studied with the QUISTOR – quadrupole mass filter combination. The technique involves the use of selective ejection of a chosen ionic precursor and the simultaneous observation of the perturbations in the concentration of product ions. The technique is demonstrated in studies of the ion chemistry and reaction kinetics of two known chemical systems.

Kinetics of Schiff base ligand transfer and rate enhancement by metal ions

1973 ◽  
Vol 26 (11) ◽  
pp. 2541 ◽  
Author(s):  
WW Fee ◽  
A Gaetano
Keyword(s):  
Schiff Base ◽  
Metal Ions ◽  
Schiff Base Ligand ◽  
Chain Reaction ◽  
Schiff Base Ligands ◽  
Rate Enhancement ◽  
Rate Acceleration ◽  
Ligand Transfer ◽  
Kinetics Of

The kinetics of the transfer of Schiff base ligands between their nickel(II) and zinc(II) complexes have been examined in dmso. Reactions completed in the presence of added nickel(II) and zinc(II) ions indicate the occurrence of a coordination chain reaction with rate acceleration prompted by one chain initiating and one chain propa- gating step.

scholarly journals Synergistic Catalysis of Tandem Michael Addition/Enantioselective Protonation Reactions by an Artificial Enzyme

2021 ◽  
Author(s):  
Zhi Zhou ◽  
Gerard Roelfes
Keyword(s):  
Lewis Acid ◽  
Michael Addition ◽  
Conjugate Addition ◽  
Chiral Center ◽  
Artificial Enzymes ◽  
Artificial Enzyme ◽  
Synergistic Catalysis ◽  
Protonation Reaction ◽  
Stereochemical Control ◽  
Catalytic Sites

Enantioselective protonation is conceptually one of the most attractive methods to generate an α-chiral center. However, enantioselective protonation presents major challenges, especially in water as a solvent. Herein, we report an artificial enzyme catalyzed tandem Michael addition and enantioselective protonation reaction of α-substituted acroleins with 2-acyl imidazole derivatives in water. The artificial enzyme uses a synergistic combination of two abiological catalytic sites: a genetically encoded non-canonical p-aminophenylalanine residue and a Lewis acid Cu(II) complex. The exquisite stereochemical control achieved in the protonation of the transient enamine intermediate generated by conjugate addition of the Michael donor is illustrated by the >20:1 dr and up to >99% ee obtained for the products. These results illustrate the potential of exploiting synergistic catalysis in artificial enzymes for challenging reactions.<br>

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