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Folding and selectivity: The noncyanogenic plant Arabidopsis thaliana contains a new hydroxynitrile lyase, which was cloned and characterized. This enzyme is readily available form a recombinant source, has a broad range of substrates, and enantioselectively transforms aliphatic and aromatic aldehydes as well as ketones into the corresponding R‐cyanohydrins.

Biochemical syntheses O 0035An R-Selective Hydroxynitrile Lyase from Arabidopsis thaliana with an α/β-Hydrolase Fold. -The method tolerates aromatic and aliphatic aldehydes as well as ketones. Cyanohydrin (Vd) represents a precursor of enalapril. An increasing chain length of aliphatic aldehydes reduces the activity but not stereoselectivity. The enzyme is less active towards aromatic and aliphatic ketones. -(ANDEXER*, J.; VON LANGERMANN, J.; MELL, A.; BOCOLA, M.; KRAGL, U.; EGGERT*, T.; POHL, M.; Angew. Chem., Int. Ed. 46 (2007) 45, 8679-8681;

Abstract:The overcoming of thermodynamic limitations in the synthesis of optically active ketone cyanohydrins by using organic solvent-free systems has been investigated. Therefore, substrates with known unfavorable results within hydroxynitrile lyase-catalyzed reactions were selected for the determination of limitations and bottlenecks in ketone cyanohydrin synthesis. The highly (S)-selective hydroxynitrile lyase from Manihot esculenta (MeHNL) has been chosen for the conversion of acetophenone and the corresponding derivatives, which are substrates that exhibit only low grades of conversion also with several other hydroxynitrile lyases. With organic solventfree systems under optimized reaction conditions conversions up to 78 % with > 99.0 ee (S) were obtained. Finally, 5 mL of (S)-acetophenone cyanohydrin with an enantiomeric excess of 98.5 % ee (S) were synthesized.

Faltung und Selektivität: In der nichtcyanogenen Pflanze Arabidopsis thaliana wurde eine neue Hydroxynitril‐Lyase entdeckt, kloniert und charakterisiert. Das Enzym ist aus rekombinanter Quelle leicht verfügbar, hat ein breites Substratspektrum und setzt aliphatische und aromatische Aldehyde ebenso wie Ketone enantioselektiv zu R‐Cyanhydrinen um.

The potential of the hydroxynitrile lyase from Manihot esculenta towards ketone substrates was investigated. It was observed that the length of the aliphatic chain is a key parameter for the conversion of aliphatic, non‐branched ketones. Smaller substrates are readily converted with high enantioselectivites, but the elongation of the chain length causes a significant loss in enzyme activity. For a number of halogenated, herein especially fluorinated, acetophenone derivatives the corresponding cyanohydrins have been synthesized with good to moderate enantioselectivities.

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