Hydroxynitrile lyases applications

J.N. Andexer, J.V. Langermann, U. Kragl, M. Pohl, How to overcome limitations in biotechnological processes - examples from hydroxynitrile lyase applications. Trends Biotechnol. 27 (2009) 599-607. 

Forster, S., Roos, J., Effenberger, F. et al. (1996) The first recombinant hydroxynitrile lyase and its application in the synthesis of (S)-cyanohydrins. Angewandte Chemie (International Edition in English), 35, 457 459. 

The production of optically active cyanohydrins, with nitrile and alcohol functional groups that can each be readily derivatized, is an increasingly significant organic synthesis method. Hydroxynitrile lyase (HNL) enzymes have been shown to be very effective biocatalysts for the formation of these compounds from a variety of aldehyde and aliphatic ketone starting materials.Recent work has also expanded the application of HNLs to the asymmetric production of cyanohydrins from aromatic ketones. In particular, commercially available preparations of these enzymes have been utilized for high ee (5)-cyanohydrin synthesis from phenylacetones with a variety of different aromatic substitutions (Figure 8.1). 

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. ... 

Fechter, M.H. and Griengl, H., Hydroxynitrile lyases biological sources and application as biocatalysts. Food Technol. BiotechnoL, 2004, 42, 287. 

Hydroxynitrile lyases (HNLs) have been found in plants and some insects. In plants their natural function is in the defence against herbivores by release of HCN from hydroxynitriles upon cell damage. The reverse reaction, the formation of (chiral) hydroxynitriles, is interesting for bioorganic chemistry, making FlNLs important biocatalysts for technical applications [14-16]. 

HNLs comprise a heterogenous enzyme family, since hydroxynitrile lyase activity has evolved in different structural frames by convergent evolution [17, 18]. Thus, (S) -specific HNLs based on an a/P-hydrolase fold framework from Manihot esculmta (cassava) [19-21], Hevea hrasilensis (rubber tree) [22-26], and Sorghum hicolor (millet) [27-33] have been described. (R)-specific HNLs based on the structural framework of oxidoreductases were isolated from Linum usitatissimum (flax) [30, 34-37] and Rosaceae (e.g., bitter almonds) [31, 38]. Despite their potential in biocatalysis only few HNLs (from cassava and rubber tree) are available by recombinant gene expression, which is a prerequisite for their technical application [20, 24]. Thus, cloning, recombinant expression, and... 

The first synthesis of mandelonitrile using hydroxynitrile lyases was published by Rosenthaler in 1908 [7], but only fifty years later this research field regained attention for synthetic purposes by Becker et al. [8-10]. However, because of the spontaneous chemical addition of HCN in the aqueous and alcoholic medium used, only low enantiomeric excesses ( ) were achieved. In addition, the low solubility of many substrates in the buffer made this reaction unsuitable for laboratory scale and industrial application. 

The application of crude enzyme preparations also constitutes a convenient method to find new sources for hydroxynitrile lyases [56-58]. 

This section will focus on the development of (R)- and (S)-hydroxynitrile lyases as biocatalysts and their large-scale application. 

The (5)-hydroxynitrile lyase from Hevea brasiliensis has been made available in sufficient quantities by cloning and overexpressirai to allow industrial-scale applications [1563]. It should be noted that also a,p-unsaturated aliphatic aldehydes were transformed into the corresponding cyanohydrins in a clean reaction. No formation of saturated p-cyano aldehydes through Michael-type addition of hydrogen cyanide across the C=C double bond occurred. The latter is a common side reaction using traditional methodology. 

A. (2012) Application of a recombinant Escherichia coli whole-cell catalyst expressing hydroxynitrile lyase and nitrilase activities in ionic liquids for the production of (S)-mandelic acid and (S)-mandeloamide. Adv. Synth. Catal., 354, 113-122. 

Enzymes from plants have been used since andent times, even though their nature remained obscure until the nineteenth century. Malting of cereals and the hydrolysis of complex polysaccharides are two of the oldest uses of enzymes in human history. Like their animal counterparts, most commerdally available plant-derived enzymes are hydrolases, particularly lipases and proteases. Papain, a cysteine protease from papaya, is the best-known plant-derived hydrolytic enzyme. Bromelain from pineapple and ficain from fig latex are similar cysteine proteases that have also found applications in biocatalysis. Horseradish peroxidase is a versatile oxidative enzyme obtained from its namesake that oxidizes many organic compounds, especially phenols. Hydroxynitrile lyase (often called oxynitrilase) from bitter almond is one of the most important plant-derived... 

The application of nitrile-converting enzymes, nitrilases, and hydroxynitrile lyases in the s)mthesis of chiral compounds and cyanohydrins is covered. 

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. 

Figure 33 Application of (i )-hydroxynitrile lyases from plants for the synthesis of (/ )-cyanohydrins.

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