Transesterification synthetic applications

Other phospholipases have properties ancillary to the ones displayed by PLD in synthetic applications. Their utility for the synthesis of specific compounds is limited by their modest transesterification capacities. However, there are some interesting applications besides the one cited in Sect. 2.2.1. Scheme 11 shows the... 

Special attention should be devoted to less conventional applications of the enzymatic transesterification methodology such as resolution of unstable substrates as racemic secondary hydroperoxides [291]. The development of new reactions in the presence of enzymes should pursued, as, for example, the simultaneous formation of a hemithioac-etal and die irreversible transesterification in the presence of a lipase [292]. Also, for synthetic applications, the combination of enzymatic and chemical asymmetrical methods could lead to interesting results, such as the one-pot lipase-catalyzed acylation and the Mitsonobu inversion of the configuration of the unreacted alcohol, which should lead to only one enantiomeric ester [293]. 

In order to enhance the potential of synthetic reactions of lipids and the transesterification in organic solvents, a fungal lipase from Phycomyces nites was chemically modified. The promotion of dispersibility in orgaiuc solvents resulted in a much higher reactivity. Chemically modified lipases showed higher reactivity than unmodified lipase when they were utilized for the transesterification of triglycerides and other lipids. The initial rate of transesterification in organic solvents by modified lipase was 40 times faster than that of unmodified lipase. Chemically modified lipase was also found applicable for the syndesis of other fatty acids esters. 

The application of lipases in synthetic biotransformations encompasses a wide range of solvolytic reactions of the carboxyl group, such as esterification, transesterification (alcoholysis), perhydrolysis, and aminolysis (amide synthesis) [103]. Transesterification and amide synthesis are preferably performed in an anhydrous medium, often in the presence of activated zeolite, to suppress unwanted hydrolytic side reactions. CaLB (which readily tolerates such conditions [104,105]), PsL, and PcL are often used as the biocatalyst [106]. 

Transesterification reactions provide an applicable synthetic route to the preparation of organometallic compounds with unusual structures. Tricyclic organometallic compounds, which have the general formula... 

Lipases (EC 3.1.1.3) are powerful tools that in addition to hydrolysis reactions, also catalyze various synthetic reactions including esterification, transesterification, and aminolysis. Lipases have excellent catalytic activity and stability in nonaqueous media and their specificity, regioselectivity, and enantioselectivity can be successfully used for many applications in organic synthesis, including kinetic resolution and asymmetric synthesis (Gog et al., 2012). 

Recent developments in organocatalytic pathways for the ROP of lactide and several lactones, without adverse transesterification creating polymers that are metal-free and therefore perfect candidates for biomedical and microelectronic applications, have been developed using N-heterocyclic carbenes, thiourea-tertiary amines, and amidine and guanidine bases. Here, the exquisite control, the absence of metal ions, the ready synthetic availability of the catalysts, and the mild reaction conditions are of major importance for tailor-made polyesters, and also have high potential for functional polycarbonates [91, 92]. 

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