Hydroxynitrile lyases enantioselectivity

Persson, M., Costes, D., Wehtje, E. and Adlercreutz, P. (2002) Effects of solvent, water activity and temperature on lipase and hydroxynitrile lyase enantioselectivity. Enzyme and Microbial Technology, 30, 916-923. 

Hydroxynitrile lyase can be used for the decomposition of cyanohydrins with some level of enantioselectivity. " ... 

Figure 19 Enantioselective cyanohydrin formation using hydroxynitrile lyase in...

Starting from enantiomerically pure 4-methylsulfanyl-mandelonitrile, thiamphenicol and florfenicol have been enantioselectively synthesized (Figure 5.14). The enantiomerically pure 4-methylsulfanyl-mandelonitrile was obtained by hydrocyanation reaction of 4-methy lsulfany 1-benzaldehyde catalyzed by (M)-hydroxynitrile lyase of Badamu (almond from Xinjiang, China) (Prunus communis L. var. dulcis Borkh), which, after an extensive screening, was found to be a highly effective bio-catalyst for this reaction [85]. 

Chiral cyanohydrins are versatile intermediates in the synthesis of a-hydroxy acids, /3-amino alcohols, amino nitriles, a-hydroxy ketones and aziridines. For the synthesis of enantiopure cyanohydrins, the use of hydroxynitrile lyases is currently the most effective approach.Application of an organic-solvent-free system allows thermodynamically hindered substrates to be converted with moderate to excellent yields. With the use of the highly selective hydroxynitrile lyase from Manihot esculenta, the syntheses of several acetophenone cyanohydrins with excellent enantioselectivities were developed (Figure 8.2). (5)-Acetophenone cyanohydrin was synthesized on a preparative scale. ... 

A new hydroxynitrile lyase (HNL) was isolated from the seed of Japanese apricot Prunus mume). It accepts benzaldehyde and a large number of unnatural substrates for the addition of HCN to produce the corresponding (7 )-cyanohydrins in excellent optical and chemical yields. A new high-performance liquid chromatography (HPLC)-based enantioselective assay technique was developed for the enzyme, which promotes the addition of KCN to benzaldehyde in a buffered solution (pH 4.0). Asymmetric synthesis of (7 )-cyanohydrins by a new HNL is described (Figure 8.4). ... 

We have found a new (/ )-hydroxynitrile lyase from Japanese apricot (P. mume). The new enzyme accepts a broad array of substrates, ranging from aromatic, heteroaromatic, bicyclic to aliphatic carbonyl compounds, and yields the corresponding cyanohydrins with excellent enantioselection. 

Enantioselective C-C bond formation is gaining more and more importance in bioorganic synthesis. This reaction is efficiently catalyzed by 2-ketoacid decarboxylases (E.C. 4.1.l.X) as well as by hydroxynitrile lyases (E.C. 4.1.2.X). 

In the last decades, cyanohydrins have become versatile chiral building blocks, not only for laboratory synthesis, but also for a range of pharmaceuticals and agrochemicals. Several methods for the enantioselective preparation of these compounds have been published [1, 2]. The most important synthetic approaches are catalysis by oxynitrilases, also termed hydroxynitrile lyases (HNLs), wording used in this chapter, [3] and by transition metal complexes [4], whereas the relevance of cyclic dipeptides as catalysts is decreasing [2]. 

Aliphatic aldehydes have been converted to their (R)-cyanohydrins using a bipha-sic system to accommodate hydroxynitrile lyase enzyme (from the Japanese apricot, Prunus mume) as the enantioselective catalyst.251... 

F. Effenberger, and K. Pfizenmaier, Enantioselective synthesis of aliphatic (S)-cyanohydrins in organic solvents using hydroxynitrile lyase from Manihot esculenta, Ann. N. Y. Acad. Sci. 1996, 799, 771-776. 

In particular, the use of hydroxynitrile lyase has proved to be a general and reliable method for obtaining a-hydroxy nitriles of both configurations [22]. An interesting approach is the Upase- and baseacyl-cyanohydrin for a synthetic DKR [23]. This is a combination of two reaction systems the dynamic, base-catalyzed equiUbrium between acetone cyanohydrin, acetone, HCN, aldehyde and a racemic cyanohydrin and the lipase-catalyzed enantioselective and irreversible acylation of the hydroxyl group. The combination yields the... 

Interest in the synthesis of enantiopure 2-hydroxycarboxylic acids via asymmetric enzymatic transformations is still increasing and two pathways have risen into prominence recently. The first is based on enantioselective hydrocyanation of the appropriate aldehyde in the presence of an oxynitrilase (hydroxynitrile lyase, EC 4.1.2.10), which gives rise to the corresponding enantiomerically pure cyanohydrin, followed by chemical hydrolysis in the presence of strong acid (Figure 16.1, route a). This latter step generates copious quantities of salt and is not compatible with sensitive functional groups, which is a serious limitation. 

Figure 16.1 Synthetic routes to enantiomerically pure 2-hydroxycarboxylic acids, via oxynitrilase (hydroxynitrile lyase) catalysed enantioselective hydrocyanation (route A) and (R)-nitrilase (nitrilase) mediated dynamic kinetic resolution (route B).

The bienzymatic approach described above could also be advantageously applied to the synthesis of (R)-2-hydroxycarboxylic acids in cases where no satisfactorily enantioselective nitrilase is available (Figure 16.5). The best enantioselectivity in the hydrolysis of lb, for example, was 92% ee. The enantioselectivity of the hydroxynitrile lyase from ahnonds (PaHnL) in the synthesis of lb is also less then perfect [13], but we found that a combiCLEA of PaHnL and NIT-106 quantitatively converted 2b (O.IM starting concentration) into 3b with ee>99% R (reaction in 90 10 DlPE-buffer pH 5.5, as before) with very little (>3%) amide formation. 

A more recent example of enzyme-catalyzed synthesis performed in micro reactors was reported by Rutjes and co-workers [81], who demonstrated the use of crude enzyme lysates, containing hydroxynitrile lyase, for the enantioselective synthesis of cyanohydrins. Employing a wet-etched borosilicate glass micro reaction channel, containing pillars to promote biphasic laminar flow, the authors evaluated the... 

Promising results using hydroxynitrile lyases were achieved by Gaisberger et al. and Lou et al. in tetrafluoroborate-based ionic liquids, especially when using the enzyme from Prunus amygdalus. Gaisberger et al. used the lyases for reactions with long chain aldehydes. Lou et al. discovered increased thermal enzyme stability, improved enantioselectivity and enzymatic activity for a transcyanation reaction at low ionic liquid contents in buffer solution [52,53]... 

By studying the ring opening of (rac)-2-phenyl-4-benzyl-5(4H)-oxazolone with butanol catalysed by CALB in organic media, it has been possible to correlate the protonation state of the enzyme with the enantioselectivity of the reaction [36]. The protonation state was controlled by the use of either organo-soluble bases or solid-state buffers of known pfC. Both triethylamine and the buffer pair CAPSO/CAPSO.Na [CAPSO = 3-(cyclohexylamino)-2-hydroxy-l-propanesulfonic acid] were found to increase the enantioselectivity of reactions catalysed by CALB and also the lipase from Mucor miehei. The effect of solvent, water activity and temperature on the enantioselectivity of reactions catalysed by lipases and hydroxynitrile lyases (enzymes that catalyse the addition of cyanide to aldehydes) has been reported [37]. 

Enantioselective A. thaliana hydroxynitrile lyase (>1Henry reaction of benzaldehyde and MeNO, [23]. 

F.L. Cabirol, U. Hanefeld, Immobilized Hydroxynitrile Lyases for Enantioselective Synthesis of Cyanohydrins Sol-Gels and Cross-Linked Enzyme Aggregates, Adv. Synth. Catal. (2006)... 

One important class of enzymes, which are nowadays commercially available and used at industrial scale, comprises hydroxynitrile lyases (HNLs) (EC 4.1.2.10, EC 4.1.2.11, EC 4.1.2.46, and EC 4.1.2.47). In nature, hydroxynitrile lyases catalyze the enantioselective cleavage of a-cyanohydrins (hydrox3mitriles Scheme 25.1). 

Hydroxynitrile lyases (also known as oxynitrilases) are used for the synthesis of chiral cyanohydrins. Because the hydroxynitrile moiety can be easily converted into a wide range of functional groups (Scheme 28.1), the cyanohydrins represent a versatile building block in total synthesis of natural products. Moreover, both R- and S-selective enzymes are available. They are also straightforward to handle and therefore represent catalysts of choice for syntheses on an industrial scale. Already as early as 1908, they had been used in enantioselective synthesis indeed, the first enantio-selective reaction was performed with an HNL. Consequently, many applications for these enzymes have been developed in natural products synthesis. 

Paravidino M, Sorgedrager Ml, Orru RVA, Hanefeld U. Activity and enantioselectivity of the hydroxynitrile lyase MeHNL in dry organic solvents. Chem. Ear. J. 2010 16 7596-7604. 

I. ENANTIOSELECTIVE SYNTHESIS OF R- AND S-CYANOHYDRINS USING HYDROXYNITRILE LYASE... 

On the other hand, various ( l-cyanohydrins have been prepared using (5)-hydroxy-nitrile lyases from plants (Fig. 34). The (5)-cyanohydrins can be further converted to a-hydroxy acids by acid hydrolysis without racemization [107]. A recent example is the hydroxynitrile lyase from Manihot esculenta, which was cloned in E. coli and used as chiral catalyst for the synthesis of a broad range of optically active a-hydroxynitriles including keto-(5)-cyanohydrins using diisopropyl ether as organic solvent and HCN as cyanide source [112]. Compared to the enzymes from leaves, the overexpressed enzyme in E. coli showed higher enantioselectivity. 

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