Engineering a thermostable transketolase for arylated substrates

Abstract

Transketolase variants were engineered to utilize arylalkanals and benzaldehyde as substrates with up to 28-fold rate acceleration for C–C bond formation with good yields (50–73%) and virtually complete (3S)-stereoselectivity (>99% ee).

Separating Thermodynamics from Kinetics—A New Understanding of the Transketolase Reaction

“…If LiHPA was used as ketol donor, fast and complete conversion was observed as expected (Figure A). If this reaction was thermodynamically controlled by the release of CO 2 it should stop at complete conversion.…”

“…With regard to the first point, hydroxypyruvate (HPA) has been utilized as the ketol donor of choice because the liberation of CO 2 results in an equilibrium constant entirely in favor of the product (Scheme ). With this large change in Gibbs free energy, the TK‐catalyzed reaction with lithium hydroxypyruvate (LiHPA) is described as irreversible . The first Saccharomyces cerevisiae TK‐catalyzed synthesis of l ‐erythrulose was performed with LiHPA to ensure it to be irreversible .…”

“…With this large change in Gibbs free energy,t he TK-catalyzedr eactionw ith lithium hydroxypyruvate (LiHPA) is described as irreversible. [2][3][4][5][6][7][8][9][10] The first Saccharomyces cerevisiae TK-catalyzed synthesis of l-erythrulose was performed with LiHPAt oe nsure it to be irreversible. [11][12][13] However,i n2 004, the TK-catalyzed couplingo f two molecules of glycolaldehyde to l-erythrulose was reported.…”

The Catalytic Mechanism of Human Transketolase

“…[8,9] In the case of brain dysfunctions [10] and diabetes mellitus, [11,12] regular hTK's activity has been monitored and related to prevention of these diseases. [29][30][31] For what concerns the CÀ C bond, the general accepted reaction mechanism of a transketolase, including hTK, suggests that after the formation of the reactive ylide form of ThDP (activation step), a nucleophilic attack of the ThDP carbanion to the carbonyl carbon of first substrate (the ketose) results in a substrate-ThDP covalent complex (stage one). [1,13,14] The ThDP, a derivative of vitamin B1, furthermore is fundamental in the mechanisms of many essential metabolic enzymes, [15][16][17] Different studies proposed that, before the catalytic action, the cofactor must be activated to generate the relative ylide that presents an unusual carbanion.…”

Robust Organocatalysts for the Cleavage of Vegetable Oil Derivatives to Aldehydes through Retrobenzoin Condensation

“…However, the synthetic utility of this transformation is limited due to the reversibility of the process. Some strategies have employed hydroxypyruvic acid as the ketol donor to render the transformation irreversible but free aldehydes could not be produced through these methods …”