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The asymmetric Henry reaction catalyzed by hydroxynitrile lyase from Hevea brasiliensis is an example of enzymatic catalytic promiscuity. It could be an attractive method to produce optically active β-nitroalcohols, but unfortunately the enzyme has very low activity in this unnatural reaction. To get an insight into the reaction mechanism, the enzyme kinetics of this promiscuous biotransformation were studied using the cleavage and synthesis of 2-nitro-1-phenylethanol as a model system. The results indicate that the kinetic behavior of the enzyme in the Henry reaction fits the classical Rapid Equilibrium Random Bi Uni/Uni Bi mechanistic model with independent substrate binding. The measured kinetic parameters imply that the bottleneck for this biotransformation is the very low turnover number of the enzyme, not the binding of the substrates. [ABSTRACT FROM AUTHOR]

The application of hydroxynitrile lyases (HNLs) as catalysts for the stereoselective condensation of HCN with carbonyl compounds has been reported as early as 1908. This enzymatic C–C bond coupling reaction furnishes enantiopure cyanohydrins which serve as versatile bifunctional building blocks for chemical synthesis. Screening of natural sources led to the discovery of both ( R)- and ( S)-selective HNLs, and several distinctly different classes of these enzymes with substantial differences concerning sequence, structure, and mechanism have been found. Especially during the last two centuries, HNLs have been developed into valuable biocatalysts, which can be produced in recombinant form by overexpression in microbial hosts, resulting in the implementation of industrial processes utilizing these enzymes. Recently, protein engineering in combination with in silico methods gave rise to the development of a tailor-made HNL for large-scale manufacturing of a specific target cyanohydrin. [ABSTRACT FROM AUTHOR]

The biocatalytic transformation of acrolein into (S)-2-hydroxybut-3-enenitrile using the (S)-hydroxynitrile lyase from Hevea brasiliensis followed by Grignard C-elongation, asymmetric epoxidation and nucleophilic ring-opening afforded 1-deoxy-D-xylulose (1) in 47% overall yield. [ABSTRACT FROM AUTHOR]

Abstract: 3,4-Dihydro-2H-pyran-2-carbaldehyde (1) and 2-methoxycyclohex-3-encarbaldehyde (2) obtained by thermal or chemocatalytic Diels–Alder reactions were converted into the corresponding cyanohydrins by hydroxynitrile lyase catalysis. Modelling investigations give a clear interpretation for the steric course of the biocatalytic cyanohydrin reaction of these α- and β-oxygenated aldehydes. [Copyright &y& Elsevier]

Abstract: Four types of threonine aldolases (TAs) with different stereospecificities were tested on the aldol synthesis of phenylserine (PS) starting from benzaldehyde and glycine under kinetic and thermodynamic control. At short time of reaction the chosen enzymes show different stereoselectivities (l-syn, l-anti, d-syn) compared to the reaction at equilibrium where syn-PS is obtained as the major product (d.e. ∼20%) for all types of TAs. A new aspect of the catalytic mechanism involved and a sight on the relative energy barriers for the possible rate-determining steps were obtained, based on data from the 13C-label distribution between components at the conditions close to equilibrium. [Copyright &y& Elsevier]