Cross lipases

Williams and coworkers have reported a DKR of ot-bromo [56a] and a-chloro esters [56b]. In the latter case, the KR is catalyzed by commerdally available cross-linked enzyme crystals derived from Candida cylindracea lipase. The racemization takes place through halide 5 2 displacement. The DKR is possible because the racemization of the substrate is faster than that of the produd (carboxylate). For the ester, the empty ii (C=0) orbital is able to stabilize the Sn2 transition state by accepting... 

The packaging of triacylglycerol into chylomicrons or VLDL provides an effective mass-transport system for fat. On a normal Western diet, approximately 400 g of triacylglycerol is transported through the blood each day. Since these two particles cannot cross the capillaries, their triacylglycerol is hydrolysed by lipoprotein lipase on the luminal surface of the capillaries (see above). Most of the fatty acids released by the lipase are taken up by the cells in which the lipase is catalytically active. Thus the fate of the fatty acid in the triacylglycerol in the blood depends upon which tissue possesses a catalytically active lipoprotein lipase. Three conditions are described (Figure 7.23) ... 

The final intriguing use of CLAs is in the immobilization of enzymes in the soapy shell in order to carry out an enzymatic reaction. Thus the hydrolysis of -nitrophenyl acetate to / -nitrophenol has been demonstrated by immobilizing a lipase into the shell of a CLA. The CLAs were then pumped through a cross-fiow membrane, where they were separated and recycled, with the product appearing in the permeate [70]. 

This quite remarkable process is based on simultaneous use of an insoluble lipase (ChiroCLEC, 10, Scheme 12.3) and vinyl pivaloate for conversion of one enantiomer (R) of the substrate alcohol and of the solid-phase-bound anhydride 11 in combination with the phosphine 5a for the conversion of the other enantiomer (S). This system meets the requirement that the soluble acyl donor (vinyl pivaloate) does not cross-react with the soluble catalyst (phosphine 5a). After completion of the reaction the solid-phase-bound (S) enantiomer can easily be separated from the (R) product which remains in solution. As summarized in Scheme 12.3, this three-phase system affords remarkable yields and enantiomeric purity of the acy-lated alcohols [13]. 

F. J., Janssen, M.H.A., Schoevaart, R., van Rantwijk, F. and Sheldon, R.A. (2007) Cross-linked Candida antarctica lipase B is active in denaturing ionic liquids. Enz. Microb. Technol., 40, 1095. 

Wang polymer-CH2P+Ph3Br r Cross-linked lipase (CRL)... 

JJ Lalonde, C Govardhan, N Khalaf, AG Martinez, K Visuri, AL Margolin. Cross-linked crystals of Candida rugosa lipase highly efficient catalysts for the resolution of chiral esters. J Am Chem Soc 117 6845-6852, 1995. 

Another class of /3-lactone enzyme inhibitors that have attracted attention recently is the ebelactones <20020L2043, 20040BC1051>. These compounds are known to be potent inhibitors of esterases, lipases, and aminopeptidases located on cellular membranes. In recent years, synthetic studies have focused on (-)-ebelactone A 141 as the target compound. A total synthesis was reported by Mandal, with key steps being hydroboration of an alkene, a Suzuki-Miyaura cross-coupling, silylcupration of an acetylene, and iodosilylation <20020L2043>. 

The asymmetric intramolecular crossed benzoin reaction catalysed by a chiral triazolium salt has been used to synthesise 3-hydroxychroman-4-ones 34 in good to high yields and ee. The absolute configuration at the quaternary stereocentre C-3 has been shown to be S by X-ray analysis of the camphanyl ester <06SL2431>. Both enantiomers of 2-(2-phenylethyl)chroman-4-one, flindersiachromanone, have been obtained from racemic l-phenylhex-5-en-3-ol after resolution via lipase-catalysed acetylation <06H(68)483>. 

Williams et al.[13] used a combination of a polymer-bound phosphonium bromide and a cross-linked lipase from Candida rugosa for a resolution process of an -bromo ester (Scheme 5). 

The photopolymer solution used for the immobilization of lipase on a FET contained 10% PVP and 0.3% BASC (7, 13). A lipase-immobilizing soludon was prepared by dissolving 150 mg of lipase and 100 mg of bovine serum albumin in 1 mL of the photopolymer soludon. A photolithographic lipase membrane was formed on one of two FET elements, similar to the glucose oxidase and urease membranes, except that the development was done in water. After the development, the lipase-immobilized membrane was immersed in a 3% glutaraldehyde soludon for the addidonal chemical cross-linking of the protein molecules. 

The application of enzymes as catalysts in organic chemistry is closely linked to their immobilization. Indeed, many enzymes are only available in an immobilized form. The immobilized enzymes can be used as received, greatly easing their application. Numerous of these readily available immobilized enzymes are now the working horses of biocatalysis. This has even led to the incorrect use of the abbreviation of an enzyme name for a specific enzyme preparation, that is CALB for the immobilized form of Candida antarctica lipase B on cross-linked polymethacrylate (also known as Novozym 435). Vice versa the commercial name of an enzyme preparation-Amano PS-has taken the place of the enzyme (Burkhdderia cepacia lipase on dextrin or diatomaceous earth). Surprisingly, often no attention is paid to the fact that the enzyme is immobilized [1]. 

The non-aqueous lipase system for flavor esters developed by our group used components and preparative techniques for enzyme immobilization, that would not only be cost effective and simple but also meet regulatory requirements. The enzyme could have been immobilized by a number of methods however for the Intended application only (i) adsorption (11) ionic bonding or (lii) glutaraldehyde cross-linking would be... 

Fig. 16. Electrophoretic separation of the lipase and esterase activities of porcine pancreas (146, 147). Starch columns equilibrated with 0.025 M acetate buffer, pH 5.25. The activities of the fractions have been determined (o) on emulsions of triolein and tributyrin (black circles), methyl oleate, methyl laurate, and p-nitro-phenyllaurate (black triangles), (b) On solutions of methyl butyrate and p-nitro-phenylacetate (crosses). White circles and dotted line, protein background. Figures along the first peak give the specific activity (lipase) of some fractions, determined against triolein emulsion. Ordinates and abscissas are the same as in Fig. 14.

Lipases liberated from the testa and the cross cells promote rapid hydrolysis of the oil, and therefore, it should be extracted within hours of milling. Attempts have been made to upgrade oil with 30% free acid by reaction with glycerol and the enzyme Lipozyme Mucor miehei lipase) followed by neutralization. The major acids in rice bran oil are palmitic (12-18%, typically 16%) oleic (40-50%, typically 42%), and linoleic acid (29 2%, typically 37%). The oil contains phospholipids ( 5%), a wax that may be removed and finds industrial use, and unsaponifiable matter including sterols, 4-methylsterols, triterpene alcohols, tocopherols, and squalene among others. 

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