Enzymatic methods esterification

Shimada, Y., Maruyama, K., Sugihara, A., Moriyama, S., and Tominaga, Y. 1997a. Purification of docosahexaenoic acid from tuna oil by a two-step enzymatic method hydrolysis and selective esterification. J. Am. Oil Chem. Soc., 74,1441-1446. 

Enzymatic Methods The use of enzymes to produce fatty acids and fatty acid-derived products has been a focus in both academic and industrial circles. Lipases may catalyze esterification, hydrolysis, or exchange of fatty acids in esters (115). These processes can be selected by choosing appropriate substrates and reaction conditions. Lipase-catalyzed processes have attracted attention because of the mild reaction conditions under which they occur and the selectivity displayed by these catalysts. In both respects, they differ from typical chemical reactions. As enzymatic reactions occur under mild temperature and pH conditions and at ambient pressure, they generally require less energy and are conducted in equipment of lower capital cost than many other chemical processes. Another advantage of enzymatic process is related to the selectivity of many lipases, which allows obtaining products that are difficult to produce by more conventional chemical reactions. 

Despite its widespread application [31,32], the kinetic resolution has two major drawbacks (i) the maximum theoretical yield is 50% owing to the consumption of only one enantiomer, (ii) the separation of the product and the remaining starting material may be laborious. The separation is usually carried out by chromatography, which is inefficient on a large scale, and several alternative methods have been developed (Figure 6.2). For example, when a cyclic anhydride is the acyl donor in an esterification reaction, the water-soluble monoester monoacid is separable by extraction with an aqueous alkaline solution [33,34]. Also, fiuorous phase separation techniques have been combined with enzymatic kinetic resolutions [35]. To overcome the 50% yield limitation, one of the enantiomers may, in some cases, be racemized and resubmitted to the resolution procedure. 

Since the imidazolide method proceeds almost quantitatively, it has been used for the synthesis of isotopically labeled esters (see also Section 3.2), and it is always useful for the esterification of sensitive carboxylic acids, alcohols, and phenols under mild conditions. This advantage has been utilized in biochemistry for the study of transacylating enzymes. A number of enzymatic transacylations (e.g., those catalyzed by oc-chymo-trypsin) have been shown to proceed in two steps an acyl group is first transferred from the substrate to the enzyme to form an acyl enzyme, which is then deacylated in a second step. In this context it has been shown[21] that oc-chymotrypsin is rapidly and quantitatively acylated by Af-fraw.s-cinnamoylimidazole to give /ra/w-cinnamoyl-a-chymotrypsin, which can be isolated in preparative quantities and retains its enzymatic activity (see also Chapter 6). 

Myristic acid was purchased from Sigma (St Louis, MO) and ethanol (99.85 %) from Prolabo (France). Ultra pure carbon dioxide (99.995 %) was purchased from Airgaz (France). The lipase (E C. 3.1.1.3.) was a commercial enzyme from Mucor miehei kindly supplied by Novo Nordisk (Denmark). This lipase (Lipozyme TM) is immobilized on Duolite A568 (Rohm and Hass). The resin particles have a size comprised between 300 to 600 pm. In order to see if a phenomenon of internal mass transfer occurs during the enzymatic esterification, we sieved the support into different size series. The average granulometry was determined by Coulzer Sizer method (Table 1). 

Lue, B.M., Guo, Z., and Xu, X. High-performance liquid chromatography analysis methods developed for quantifying enzymatic esterification of flavonoids in ionic liquids. J. Chromatogr. A. 2008, 1198, 107-114. 

This approach has been elegantly demonstrated by Biemann and co-workers [174]. They have adapted one of their earlier methods of modifying peptides [193] by esterification, N-terminal acetylation and then reduction with LiAlH4 (or LiAlD4) to give the polyamino-alcohol. These steps are preceded by chemical or enzymatic hydrolysis of the protein to di, tri- and tetrapeptides and concluded by O-silylation of the alcohol and side chain acid or hydroxyl function (see Scheme 1.1). 

The synthetic strategies for the esters of cephalotaxine follow, for the most part, the partial esterification method, lire ideas that are exploited in the access to the fragments vary, but most use as the last step the anionic attachment of the acetate portion. The one method that remains to be exploited here is the enzymatic esterification of the natural enantiomer of cephalotaxine either with a racemate of the complete side chain (kinetic resolution) or with the appropriate enantiomer of the ester side chain. It is hoped that the solution to this particular problem in either enzymatic catalysis or plant tissue culture preparation will materialize in the near future. 

Diester 275 was prepared according to the method of Ward [111]. Reduction of the diester with lithium aluminium hydride furnished the desired meso diol 276. Diol 276 was subjected to the enzymatic esterification reaction by treatment with Candida antartica lipase (CAL)... 

Non-specific esterification of wood sterols can be performed chemically (www. freshpatents.com/Phytosterol-esterification-product-and-method-of-make-same-dt-20070628ptan20070148311.php) however, enzymatic esterification with lipases has the potential advantages of higher specificity and mild reaction conditions which are desirable, both from process and environmental perspectives. More than 20 lipases were previously screened for their ability to catalyze the transesterification of wood sterols and fatty acid esters (Martinez et al. 2004). The goal was now to screen among them those specific for stanol esterification, so as to obtain a product consisting in mostly esterified stanols and mostly free sterols (see Fig. 6.3.4) amenable for separation through short-path distillation. 

As the native cyclodextrins (CDs) exhibit some limitations in application, they need to be modified to improve the properties. All the modification methods could be divided into two kinds, chemical modification and enzymatic modification. Based on the stable cyclic structure, CDs could be modified via etherification, esterification, oxidation and crosslinking reactions. The chemical modification has a special purpose of introducing novel functional group. CDs modified by chemical means were named as cyclodextrin chemical derivatives (CCDs). 

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