Candida catalysis

Lipases are the enzymes for which a number of examples of a promiscuous activity have been reported. Thus, in addition to their original activity comprising hydrolysis of lipids and, generally, catalysis of the hydrolysis or formation of carboxylic esters [107], lipases have been found to catalyze not only the carbon-nitrogen bond hydrolysis/formation (in this case, acting as proteases) but also the carbon-carbon bond-forming reactions. The first example of a lipase-catalyzed Michael addition to 2-(trifluoromethyl)propenoic acid was described as early as in 1986 [108]. Michael addition of secondary amines to acrylonitrile is up to 100-fold faster in the presence of various preparations of the hpase from Candida antariica (CAL-B) than in the absence of a biocatalyst (Scheme 5.20) [109]. 

An interesting example of biocatalysis and chemical catalysis is the synthesis of a derivative of y-aminobutyric acid (GABA) that is an inhibitor for the treatment of neuropathic pain and epilepsy (Scheme 10.4). The key intermediate is a racemic mixture of cis- and trons-diastereoisomer esters obtained by a hydrogenation following a Horner-Emmons reaction. The enzymatic hydrolysis of both diaste-reoisomers, catalyzed by Candida antarctica lipase type B (CALB), yields the corresponding acid intermediate of the GABA derivative. It is of note that both cis- and trans-diastereoisomers of the desired enantiomer of the acid intermediate can be converted into the final product in the downstream chemistry [10]. 

Chemoenzymatic polymerizations have the potential to further increase macro-molecular complexity by overcoming these limitations. Their combination with other polymerization techniques can give access to such structures. Depending on the mutual compatibility, multistep reactions as well as cascade reactions have been reported for the synthesis of polymer architectures and will be reviewed in the first part of this article. A unique feature of enzymes is their selectivity, such as regio-, chemo-, and in particular enantioselectivity. This offers oppormnities to synthesize novel chiral polymers and polymer architectures when combined with chemical catalysis. This will be discussed in the second part of this article. Generally, we will focus on the developments of the last 5-8 years. Unless otherwise noted, the term enzyme or lipase in this chapter refers to Candida antarctica Lipase B (CALB) or Novozym 435 (CALB immobilized on macroporous resin). 

Classic resolntion has been performed by formation of diastereomeiic salts which could be separated. In a series of synthetic steps and when resolution is one step, it is of utmost importance that the correct chirality is introduced at an early stage. When a racemate is subject to enzyme catalysis, one enantiomer reacts faster than the other and this leads to kinetic resolution (Figure 2.2c). Results of hydrolysis using lipase B from Candida antarctica (CALB) and a range of C-3 secondary butanoates are shown in Table 2.1. 

The same concept is applicable to allylic alcohols, ketones, or ketoximes. Enol acetates or ketones were successfully converted in multi-step reactions to chiral acetates in high yields and optical yields through catalysis by Candida antarctica lipase B (CALB, Novozyme 435) and a ruthenium complex. 2,6-Dimethylheptan-4-ol served as a hydrogen donor and 4-chlorophenyl acetate as an acyl donor for the conversion of the ketones (Jung, 2000a). 

Moreno, Jose M. Samoza, A. del Campo, Carmen Liama, Emilio F. Sinisterra, Jose V. Organic reactions catalyzed by immobilized lipases. Part I. Hydrolysis of 2-aryl propionic and 2-aryl butyric esters with immobilized Candida cylindracea lipase. J. Mol. Catalysis A Chemical 1995, 95, 179-92. 

Gotor-Femandez, V., Busto, E., and Gotor, V. 2006. Candida antarctica lipase B An ideal biocatalyst for the preparation of nitrogenated organic componnds. Advanced Synthesis Catalysis, 348 797-812. 

There are many reports of enzymatic catalysis in scC02 performing hydrolysis, oxidations, esterifications, and franr-esterification reactions. For example, the enzymatic kinetic resolution of 1-phenylethanol with vinyl acetate in scC02 using lipase from Candida antarctica B produces (R)-l-phenyethylacetate in >99% ee (i.e., enantiomeric excess, a measure of how much of one enantiomer is present as compared to the other), as shown in Figure 12.20. 

So far, only very little attention has been focussed on the use of zeolites in biocatalysis, i.e., as supports for the immobilization of enzymes. Lie and Molin [116] studied the influence of hydrophobicity (dealuminated mordenite) and hydrophilicity (zeolite NaY) of the support on the adsorption of lipase from Candida cylindracea. The adsorption was achieved by precipitation of the enzyme with acetone. Hydrolysis of triacylglycerols and esterification of fatty acids with glycerol were the reactions studied. It was observed that the nature of the zeolite support has a significant influence on enzyme catalysis. Hydrolysis was blocked on the hydrophobic mordenite, but the esterification reaction was mediated. This reaction was, on the other hand, almost completely suppressed on the hydrophilic faujasite. The adsorption of enzymes on supports was also intensively examined with alkaline phosphatase on bentolite-L clay. The pH of the solution turned out to be very important both for the immobilization and for the activity of the enzyme [117]. Acid phosphatase from potato was immobilized onto zeolite NaX [118]. Also in this study, adsorption conditions were important in causing even multilayer formation of the enzyme on the zeolite. The influence of the cations in the zeolite support was scrutinized as well, and zeolite NaX turned out to be a better adsorbent than LiX orKX. 

On the basis of these three cross coupling reactions, it is probably fair to say that using the OSSOS concept is highly compatible with palladium catalysis but probably not limited to it. For example, a lipase can be used for the kinetic resolution of a racemic ibuprofen ester supported on an imidazolium salt. In a DMSO/phosphate buffer mixture and in the presence of the lipase isolated from Candida antartica, the, V-(+(-supported ibuprofen ester is hydrolyzed selectively (87% ee) in 87% yield. Noticeably, during workup, the support can easily be recovered and reused for another cycle while the other enantiomer can be obtained by hydrolysis using K2CQ3 [137] (Fig. 48). 

Modulating Ejfect of Surf actants on Candida Rugosa Lipase Catalysis... 

Aliphatic polyesters were also synthesized via an enzymatic polymerization of dicarboxyiic acids and glycols in a solvent-free system [69, 70]. The lipase from Candida antarctica (lipase CA) provided an efficient catalysis of the polymerization under mild reaction conditions, despite the presence of a heterogeneous mixture of the monomers and catalyst. The ahphatic chain length of the monomers had a major effect on both the polymer yield and molecular weight typically, a molecular weight in excess of 1 x Da was obtained when the reaction was conducted under reduced pressure. However, the addition of a small amount of adjuvant proved effective for polymer production when both monomers were solid at the reaction temperature [71]. 

Various cychc esters have been subjected to hpase-catalyzed ring-opening polymerization (ROP), notably of four- to 17-membered nonsubstituted lactones. Initially, it was shown that medium-sized lactones, 5-valerolactone (5-VL, six-membered) and e-CL (seven-membered), were each polymerized via the action of a lipase from Candida cylindracea (hpase CC), hpases BC and PF, and a porcine pancreatic hpase (PPL) [83,84]. Later, a variety of cychc esters with different ring sizes and structures were also polymerized via a hpase-mediated catalysis. 

An example of a successful esterification reaction on industrial scale is shown in Scheme 3.1. 6-0-Acyl derivatives of alkyl glucopyranosides, which are used as fully biodegradable nonionic surfactants in cosmetics [142], were synthesized from fatty acids and the corresponding l-O-aUcyl glucopyranosides under catalysis of thermostable Candida antarctica lipase B in the absence of solvents [137]. In order to drive the reaction towards completion, the water produced during the reaction was evaporated at elevated temperature and reduced pressure (70°C, 0.01 bar). 

Dynamic resolution of various sec-alcohols was achieved by coupling a Candida antarctica lipase-catalyzed acyl transfer to in-situ racemization based on a second-generation transition metal complex (Scheme 3.17) [237]. In accordance with the Kazlauskas rule (Scheme 2.49) (/ )-acetate esters were obtained in excellent optical purity and chemical yields were far beyond the 50% limit set for classical kinetic resolution. This strategy is highly flexible and is also applicable to mixtures of functional scc-alcohols [238-241] and rac- and mcso-diols [242, 243]. In order to access products of opposite configuration, the protease subtilisin, which shows opposite enantiopreference to that of lipases (Fig. 2.12), was employed in a dynamic transition-metal-protease combo-catalysis [244, 245]. 

Hen, XL Chen, BQ Tan, TW.Enzymatic synthesis of 2-ethylhexyl esters of fatty acids by immobilized lipase from Candida sp. 99-125. Journal of Molecular Catalysis B Enzymatic, 2002, v. 18, 333-339. 

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