Vinyl acetate, immobilization

It should be noted that by immobilizing the metal complex catalysts on carbochain polymers it is possible to prepare polymer-polymer compositions using PVC, PMMA, poly(vinyl acetate), etc., as the polymeric fillers [286-287]. 

Immobilized PLE was applied to promote stereoselective acetylation of prochiral bis(hydroxymethyl)methyl-phenylgermane 106 (R = Me) with vinyl acetate as a solvent and acyl donor. Later on, the same group reported that each enantiomer of hydridogermane monoacetates 107 (R = H) was obtained either via acetylation of the bis-hydroxy derivative 106 (R = H) or hydrolysis of the corresponding diacetate 108 (R = H). In both methods, porcine pancreatic lipase was used and, obviously, each reaction led to a different enantiomer of 107 (Equation 51). ... 

A novel continuous-flow SCCO2 process for the kinetic resolution of 1-phenyethanol enantiomers (Figure 30) using Novozym 435 immobilized enzyme from Candida antarctica was described by Matsuda et al. [51], The lipase enzyme, selectively acetylated the R)-alcohol component. A mixture of starting material and vinyl acetate was passed through the enzyme with supercritical carbon-dioxide (Figure 31). The reaction zone was pressurized and heated, so the reaction could be performed imder supercritical conditions, synthesizing the desired (i )-acetate with 99.7% ee. and 47% yield. 

In a similar investigation, transesterification reactions of vinyl acetate with alcohols in [BMIM]BF4 and [BMIM]PF6 in the presence of immobilized lipases CALB and PS-C were found to proceed with higher enantioselectivities than in THF or toluene, with the best result again being observed with [BMIM]PF6 (280). 

Catalytic tests were performed in a glass vessel equipped with a stirrer motor. Two monoliths (diameter 4.3 cm, length 4 cm) were mounted in plane on the stirrer axis. The total reaction volume was 2.5 1. Lipase was assayed in the acylation of vinyl acetate with butanol in toluene. Initial reaction rate was followed by GC analysis. Immobilized trypsin was used in the hydrolysis of N-benzoyl-l-arginine ethyl ester (BAEE) in a 0.01 M phosphate buffer pH 8 at 308 K. The reaction was followed by UV-VIS at 253 nm, and reaction rate was calculated in the mass transfer limited situation. 

Finally, Sanfilippo and coworkers describe the enzymatic kinetic resolution of atropisomeric ( )-3,3 -bis(hydroxymethyl)-2,2 -bipyridine N,N-dioxide by enantioselective esterifcation in an unusual medium of 2-propanol/vinyl acetate (20 80) [139]. Lipase from Mucor miehei (immobilized lipase preparation, Lipozyme ) was found to give good enantioselectivity with an (aS)-enantiopreference in the axial recognition and allowed efficient preparation of both enantioforms with > 98%. Despite the fact that the propanol reacts with the acyl donor, this did not diminish its positive effects on the solubility of the bipyridyl substrate. 

Chiral enantiopure 2,2 -dihydroxybiaryls are important as chiral ligands and are also structural motifs occurring in some natural products. Hydrolase-catalyzed resolution by acylation in organic solvents of some dihydroxybiaryls has been successfully achieved. Thus, the racemic binaphthols 111-113 have been resolved by mono acylation with vinyl acetate in t-butylmethyl ether ( ME) at 45 °C catalyzed by Pseudomonas sp. lipase (Scheme 4.35) [106]. In a similar way the 2,2 -dihydroxybiphenyl 114 can be acylated with vinyl acetate catalyzed by PSL immobilized on celite in TBME at 45 °C (Scheme 4.35) [107]. Butanolysis of the racemic monobutyrate of binaphthol rac-115 catalyzed by CALB in toluene at 80 °C for 72 h gives (R)-binaphthol (93% ) at ca. 50% conversion [108]. 

The enantiorecognition of methyl mandelate (Figure 10.14) in enantioselective acylation with vinyl acetate is often modest Itoh et al. studied this latter reaction with immobilized PcL in [BMIm][PF,s] and found that the E-ratio varied from 10 to >250, depending on the carrier [128]. The best rate and enantioselectivity were obtained with PcL immobilized on a methacryloxypropyl-modified macroporous S BA-15 silica. 

Alterations in pH also can be responsible for the increase in solubility of loaded active agents. Glucose oxidase immobilized on sepharose beads were incorporated into ethyl vinyl acetate matrices along with insulin in the solid form. Glucose from blood enters these matrices, gets oxidized to glucuronic acid, and the decrease in pH increases the solubility of insulin, which diffuses out. The insulin in this case was modified by the addition of three extra lysine residues that ensured an isoelectric point of pH 7.4 for the molecule.33... 

On reaction with vinyl acetate in THF in the presence of immobilized lipase (lipase AK), ( )-8 afforded the optically enriched acetate (+)-9 (46% 70% ee), leaving the optically enriched alcohol (-)-8 (46% 70% ee). On stirring in a phosphate buffer in the presence of lipase PS, ( )-9 afforded enantiocomplementarily the acetate (-)-9 (31% 96% ee) and the alcohol (+)-8 (62% 74% ee). Optically enriched levoglucosenone 1 was obtained from the resolved products under standard conditions (Scheme 2). 

Alternative Polymers for Immobilizing Bizymes. Vinyl acetate (after hydrolysis with bicarbonate) and polycarbonate have also been chemically modified to accommodate glucose oxidase (Donlan,A.M. Mcxx3y,G.J. Thomas,J.D.R., Uiiversity of Wales (Allege of Cardiff, unpublished data). 

Catalase can be easily immobilized on a hydrolysed vinyl acetate-cyanuric chloride membrane ... 

Wu, S. Y., Lin, C. N., Chang, J. S., and Chang, J. S. 2005. Biohydrogen production with anaerobic sludge immobilized by ethylene-vinyl acetate copolymer. Int. I. Hydrogen Energy, 30.1375-1381. 

Compound 25 (Fig. 18.9), a prodrug of 9-P-D-arabinofuranosyl guanine (26), was developed for the potential treatment of leukemia. Compound 24 is poorly soluble in water and its synthesis by conventional techniques is difficult. An enzymatic demethoxylation process was developed using adenosine deaminase (Mahmoudian et al., 1999, 2001). Compound 25 was enzymatically prepared from 6-methoxyguanine (27) and ara-uracil (28) using uridine phosphorylase and purine nucleotide phosphorylase. Each protein was cloned and overexpressed in independent Escherichia coli strains. Fermentation conditions were optimized for production of both enzymes and a co-immobilized enzyme preparation was used in the biotransformation process at 200 g/L substrate input. Enzyme was recovered at the end of the reaction by filtration and reused in several cycles. A more water soluble 5 -acetate ester of compound 26 was subsequently prepared by an enzymatic acylation process using immobilized Candida antarctica lipase in 1,4-dioxane (100 g/L substrate) with vinyl acetate as the acyl donor (Krenitsky et al., 1992). 

Higher hydrolytic stability is exhibited by capillaries based on vinyl coatings as primary anchor group, where, in the second step, vinyl acetate is polymerized and subsequently hydrolyzed with sodium methylate in methanol [6]. Such capillaries are stable up to a pH value of 10. Polyvinyl alcohol has also been thermally immobilized onto the capillary surface [7]. With such stable layers in the acidic and neutral region no measurable EOF is present and the stability of the capillaries is very good. 

FIGURE 32 Initial rates of reaction in catalysis by free lipase and immobilized lipase (Novozyme, and catalyst supported on 200 cpsi carbon monolith) in the acylation of butanol with vinyl acetate in an organic medium at 300 K. 

When Candida rugosa lipase (formerly named Candida cylindracea lipase) was immobilized on an epoxy-activated resin it became resistant against acetaldehyde. Due to this immunization it could be repeatedly employed for the enantioselective acylation of secondary alcohols with vinyl acetate in dry organic solvents (Scheme 2.7) [78]. 

Regioselective acylations of polyhydroxylated compounds such as carbohydrates, glycerols, steroids, or alkaloids have been carried out with lipases, esterases, and proteases [13, 20]. One example is the Candida antartica lipase (immobilized on acrylic resin) catalyzed monoacylation of the signalling steroid ectysone (1) giving selectively the 2-C)-acetate 2 (eq. (1)). Using vinyl acetate for this transesterification the reaction was irreversibly pushed to the product side, since the liberated enol instantaneously isomerizes to acetaldehyde [21]. The sometimes unfavorable aldehyde is avoided when 1-ethoxyvinyl acetates [22], trichloro- or -fluoroethyl esters [23 a, b], oxime esters [23 c] or thioesters [23 d] are employed for the quasi-irreversible reaction courses. 

In addition, immobilized ionic liquids have been employed for the 0-acylation and A-acylation. Kara et al. have investigated the reactions that supported ionic liquids in Upase-catalyzed asymmetric acylation of 7-phenylethanol with vinyl acetate in the reaction temperature range of 25-60°C and found that the immobilized [EMlM][NTfJ can stabilize the lipase against inactivation and maintain good enantioselectivity [152]. Furthermore, Paun s group via grafting 7,5-dimethyl-5-(5-triethoxysilylpropyl)-imidazolium tetrafluoroborate or bis (trifluoromethyl)... 

Such ILCE showed remarkably high enantioselectivity for transesterification reaction of several secondary alcohols in the presence of vinyl acetate in toluene, and there was no significant deterioration in activity even after multiple (five times) use. Horseradish peroxidase (HRP) is another example to be coated with both hydrophobic and hydrophilic ILs such as [BMIMJITf N] and [BMIM][PEg] toward enzymatic synthesis of polyaniline [23]. An attractive point of the ILCE-based immobilization method is easy recovery of enzyme/IL phase by liquid-liquid phase separation and effective reusability of the enzyme (Eigs. 10.8, 10.9) [23, 59]. 

An interesting electrochemical method for the determination of bound sialic acid has been developed, making use of a potentiometric four-channel thick-film sensor [236]. The sialidase sensor consists of a bilayer of a membrane containing Clostridium perfringens sialidase immobilized in a poly(vinyl acetate)-polyethylene copolymer, which is placed on top of an fT -selective poly(vinyl chloride)-poly(vinyl acetate) indicator membrane. The enzyme-induced release of bound sialic acid leads to a concomitant decrease in pA a of the carboxyl function of sialic acid. This decrease affords a local pH change inside the sialidase-containing sensor membrane, which is monitored by the H -selective indicator membrane. The pH optimum of the sialidase sensor was pH 4 for sialyllactose, mucin and colominic acid. 

Catalytic tests with the lipase-monolithic catalysts were performed in a monolithic stirrer reactor consisting of a glass vessel equipped with a stirrer motor (V = 2.5 dm ). 1-Butanol and vinyl acetate concentrations were 0.6 M and 1 M, respectively. Activity tests with immobilized lipase Candida antarctica) were performed at varying stirrer rates and temperatures. Carbon monoliths (Westvaco integral carbon monoliths, with a loading of 30 wt% of microporous activated carbon, wall thickness 0.3 mm) were used as a reference material. 

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