Enzymatic Desymmetrization of Diol

In the improved synthesis (20), shown in Fig. 6, a diol olefin 13 could be quickly assembled from bromodifluorobenzene. This underwent an iodocyclization reaction to form a 2,2,4-trisubstituted tetrahydrofuran in which the desired ds-isomer 14 predominated (85 15 cis-.trans) (21,22). Introduction of the triazole followed by formation of the chlorosulfonate provided the key intermediate 5, which could be condensed with the side chain to form SCH56592. Like the (KJ-triol 8 in the previous route,...

Organosilicon Compounds as Novel Substrates

Comparative studies were made by the use of organosilicon compounds having a different chain length between hydroxyl group and the silicon atom Me3Si(CH2)nOH, n 0, 1, 2, and 3 and the corresponding carbon compounds Me3C(CH2)nOH, n 0, 1, and 2) as another substrate (acyl acceptor) in the enantioselective esterification of 2-(4-chlorophenoxy)propanoic acid, whose ( )-enantiomer is useful as a herbicide, with lipase OF 360 of Candida cylindracea (Fig. 1) in benzene. The effects of the silicon atom...

Water Exchange with Atmosphere Sealing of Vessels

Any reaction mixture will tend to exchange water with the gas headspace above it. When the total water content is low, this can cause significant changes. Therefore, it is usually sensible to seal reaction vessels to prevent unwanted exchange. In some cases, even water exchange when the vessel is opened for sampling may be significant. Leaks resulting from imperfect sealing may also be important, especially over long reaction times. It might be thought that sealing that was sufficient to...

The Principle of Water Transport

The function of the tubing is to transport water to or from the reaction mixture so that the water activity in the reactor is kept constant or at least within certain limits. The rate of water transport is determined by the reaction catalyzed. Relatively large amounts of water must be transported when water is formed or consumed in the reaction and or when the reaction causes a large change in solubility of water in the reaction medium. The amount of tubing needed can be determined using...

Salt Hydrates for Water Activity Control in Reaction Mixtures

Many salts can form solid hydrates with water molecules present in the crystal lattice. Such salt hydrates can give up water, transforming to a lower hydrate or the anhydrous form. If both forms show ideal crystalline behavior, all the water is given up at a fixed value of water activity. The process is reversible if water is supplied, it being taken up at the same water activity. In practice, many salt pairs come quite close to this ideal behavior. Hence, if a system is prepared so that both...

Notes Organic Solvent

Tetrahydrofuran is the solvent of choice because in other suitable solvents the diol 1 is insoluble. 2. The addition of triethylamine is essential to achieve a high rate of conversion (15,16). However this effect is not understood. 3. This is a crude preparation of porcine pancreatic enzymes with lipase, amylase, and protease activity. Pancreatin can be replaced by a more purified porcine pancreatic lipase. However, there are no advantages compared with the crude preparation. 4. Pancreatin can...

Hydration Properties of Celite R640 in Vapor Phase

A general method for performing biotransformations at known water activity consists of exposing each component of the reaction mixture to a vapor phase characterized by a constant known relative humidity (33,34). In principle, the phases, once mixed, reach the equilibrium water activity. Figures 5 and 6 show the rate of equilibration of dry Celite R-640 (batch 3, Fig. 1) exposed to atmospheres generated by saturated salt solutions or pure water Fig. 3. Adsorption isotherms (equilibration time...

A

Fig. 28. (A) Empirical rule which predicts the faster reacting enantiomer of secondary alcohols with hydrolases, e.g., C. rugosa (adapted from ref. 57). (B) The faster-reacting (2S,3R)-29 obeys the model. Fig. 28. (A) Empirical rule which predicts the faster reacting enantiomer of secondary alcohols with hydrolases, e.g., C. rugosa (adapted from ref. 57). (B) The faster-reacting (2S,3R)-29 obeys the model. shown by this group of enzymes agrees with the model proposed by Kazlauskas (57,58),...

Notes

Na2so4 H2o Nacl

Trimethylsilylmethanol is a better substrate not only for lipase OF 360 but also for other lipases from different sources such as lipase Saiken 100 (Rhizopus japonicus, Osaka Saikin Kenkyusho Co., Osaka, Japan) and lipase (Steapsin) (hog pancreas, Tokyo Kasei Kogyo, Tokyo, Japan). 2. Trimethylsilylmethanol is also a very useful substrate for the enantioselective esterification of racemic naproxen 2-(6-methoxy-2-naphthyl)propionic acid , a nonsteroidal anti-inflammatory drug, by C. cylindracea...

Salt Induced Activation of Enzymes in Organic Solvents

Optimizing the Lyophilization Time and Water Content Michael T. Ru, Jonathan S. Dordick, Jeffrey A. Reimer, and Douglas S. Clark Past studies of enzymatic catalysis in nearly anhydrous organic solvents have shown that the amount of water adsorbed to an enzyme in organic solvents is a critical determinant of enzyme activity, more important than the water content of the solvent itself (1,2). The exact amount of water associated with the enzyme, however, varies depending on the hydrophobicity of...

Enzymatic Approaches to the Chiral Tetrahydrofuran Sulfonate 5 21 Enzymatic Desymmetrization of RTriol

The initial synthesis of the key 2,2,4-trisubstituted tetrahydrofuran 5 was somewhat lengthy (Fig. 3) (12). The (RJ-tertiary hydroxyl chiral center was introduced Fig. 2. Two chiral key intermediates Fig. 2. Two chiral key intermediates 9 R Ts 10a Cis 40 60 10b Trans Fig. 3. Differentiating between primary alcohols. 9 R Ts 10a Cis 40 60 10b Trans Fig. 3. Differentiating between primary alcohols. via a Sharpless-Katsuki epoxidation of the allylic alcohol 7, followed by introduction of the...

Organic Solvent References

Schoffers, E., Golebiowski, A., Johnson C. R. (1996) Enantioselective synthesis through enzymatic asymmetrization. Tetrahedron 52, 3769-3826. 2. Wong, C.-H. and Whitesides, G. M. (1994) Enzymes in Synthetic Organic Chemistry, Tetrahedron Organic Chemistry Series vol. 12, Elsevier Science, Oxford. 3. Faber, K. (1995) Biotransformations in Preparative Organic Chemistry, SpringerVerlag, Berlin. 4. Drauz, K. and Waldmann, H. (eds.) (1995) Enzyme Catalysis in Organic Synthesis, Vols. 1 and 2, VCH,...

Synthesis of Glycosides

In a typical example, glucose 100 mg , ethylene glycol 100 mg , and 50 mM sodium citrate buffer, pH 5.2 see Table 1 for details were mixed in a capped vial and heated up to approx 95 C to dissolve the reactants. The vials were then Almond '.-Glucosidase-Catalyzed Synthesis of Glucosides in Supersaturated Solutions Alcohol Glucose Initial rate Yield Yield Time Almond '.-Glucosidase-Catalyzed Synthesis of Glucosides in Supersaturated Solutions Alcohol Glucose Initial rate Yield Yield Time Note...

Benzyloxy3Pentanol 29 as a Precursor to

The required 2S,3S -formylhydrazine 6 was initially prepared from ethyl lactate, which provided the C2 chiral center Fig. 24 . Subsequent chain elongation Fig. 24. Preparation of 2S,3S -formylhydrazine fom ethyl lactate. Fig. 24. Preparation of 2S,3S -formylhydrazine fom ethyl lactate. via the pyrrolidine amide 27 provided ketone 28. However, under all conditions tried, reduction of 28 resulted in a mixture 90 10 of the 2S,3R - and 2S,3S - 2-benzyloxy-3-pentanol 29 , with separation of the...

Synthesis of Monosaccharide Fatty Acid Esters see Note

General Preparation of 1b-f and 5-O-Acyl-D-Xylofuranoses 2b-f The general approach is exemplified by the enzymatic esterification of 1,2-O-isopropylidene-a-D-xylofuranose 1a with tetradecanoic acid to form Fig. 1. The principle of sugar modification followed by enzymatic esterification and removal of modifying groups in synthesis of sugar esters exemplified by xylose . Fig. 1. The principle of sugar modification followed by enzymatic esterification and removal of modifying groups in...

Imprinting Enzymes for Use in Organic Media

Dordick 1. Introduction Enzymes suspended in nonaqueous media are more rigid than in aqueous media 1,2 . This increased rigidity is thought to be the result of increased electrostatic and hydrogen-bonding interactions among the surface residues of the protein in organic solvents 3 . Despite this rigidity, enzymes remain active and selective in organic solvents, and this has led to a large number of applications that have impacted the chemical, pharmaceutical, and...

Introduction

In nature, the vast majority of enzyme-catalyzed reactions are carried out in water. Traditionally, enzymic catalysis in organic synthesis is carried out in aqueous solution. In some cases, water-miscible organic cosolvents are added to improve the solubility of the hydrophobic substrate in the reaction solution. With the addition of an organic cosolvent, the equilibrium constant of the hydrolytic enzyme-catalyzed reaction can change and subsequently affect the yields of the product 1 . Recent...

Regioselective Carbohydrate Acylation

In one of our research programs aimed at preparing new trimodular nonionic surfactants made of a sugar with a lipophilic tail linked by an aminoacid residue 30 , several esterifications of suitable sugar derivatives have been attempted using different lipases. The potential of lipases as catalysts for the acylation of carbohydrates is currently of considerable interest, as the reaction occurs selectively at the primary hydroxyl group of the sugar. The need for protection and deprotection steps...

Conversion and Enantiomeric Excess Determination

Ten microliters of reactants were withdrawn at scheduled times see Note 3 , diluted in a 1-mL tube with 100 L of acetone and centrifuged for a few seconds to clear the solution from enzyme powder and molecular sieves. 2. Ten microliters of the acetone solution were analyzed by gas chromatography GC under the following conditions oven temperature 130 C for 10 min, then to 160 C with a heating rate of 0.5 C min. The running time was approx 30 min see Note 4 . 3. The enantiomeric ratio was...

Proteases

Proteases have been intensively studied in water-poor organic solvents using transesterification reactions of N-protected amino acid esters 1 . Also, peptide bond formation reactions have been catalyzed by proteases in nonaqueous media, which are obviously of greater practical importance. In order to minimize hydrolysis, both types of enzymatic reactions have to be performed under water-poor conditions. This has the drawback that the protease activity is generally low and, therefore,...

What to Pre Equilibrate

Thought must be given to the initial hydration state of every component of the reaction mixture. If only some are pre-equilibrated, then water redistribution after they are combined will give a final water activity perhaps quite different from the intention. For example, if a biocatalyst brought to a desired water activity is suspended in a dried solvent, it will probably rapidly lose water. The equilibrium water activity eventually reached may be significantly reduced. Such combination of a...

Nocardia rhodocrous Cells

Rhodocrous

Thawed cells of N. rhodocrous 1 g wet cells , suspended in 2.0 mL of a water-saturated mixture of benzene and n-heptane 1 1, v v under mild soni- Fig. 3. Schematic model of lipid-coated lipase entrapped in hydrophobic photo-crosslinked resin gel matrix. Fig. 3. Schematic model of lipid-coated lipase entrapped in hydrophobic photo-crosslinked resin gel matrix. cation 10 kHz for several seconds , were mixed with 1.0 mL of the same solvent containing 1.0 g of ENTP or ENTB and 10 mg of benzoin...

General Comments on Producing Propanol Rinsed Enzyme Preparations

Figure 1 illustrates the process involved in the production of propanol-rinsed enzyme preparations PREPs . The initial step is to immobilize the enzyme on a support material in aqueous buffered solution. This could be via covalent attachment or by an adsorption process. With subtilisin Carlsberg and a-chymotrypsin, we have adopted a very simple method of adsorbing the protein onto chromatog-raphy-grade silica gel. For other enzymes, this may not be the best support and materials such as...

Control of Water Activity by Means of Celite R640 Adsorption Isotherms in Toluene

The following diagrams show how aw varies as different amounts of water are added to Celite rods in dry toluene. The adsorption isotherms are obtained by mixing 1 mL of dry toluene, three Celite rods 95 mg , and water into 5 mL vials with screw caps and Teflon-lined septa, after which the system is equilibrated for at least 24 h in an air-bath-type thermostatted orbital shaker. After equilibration, water activity is measured by sealing the humidity sensor into the open end of the thermostatted...

References

G. 1991 Biodegradation of 3,4-dichloroaniline in a fluidized bed bioreactor and a steady-state biofilm kinetic model. Biotechnol. Bioeng. 38,260-272. 2. Ebert, C., Gardossi, L., and Linda, P. 1998 Activity of immobilised penicillin ami-dase in toluene at controlled water activity. J. Mol. Catal. B Enzymatic 5, 241-244. 3. De Martin, L., Ebert, C., Garau, G., Gardossi, L., and Linda, P. 1999 Penicillin G amidase in low-water media immobilisation and control of water activity by...

Activity Determination of Subtilisin

One of the following organic solvents 1,4-dioxane, carbon tetrachloride, benzene, toluene. Transesterification, Hydrolytic, and Total Transesterification Plus Hydrolytic Activity of Subtilisin and Subtilisin PEG in 1,4-Dioxane, and of Lipase PC and Lipase PC PEG in 1,4-Dioxane and Carbon Tetrachloride Transesterification, Hydrolytic, and Total Transesterification Plus Hydrolytic Activity of Subtilisin and Subtilisin PEG in 1,4-Dioxane, and of Lipase PC and Lipase PC PEG in 1,4-Dioxane and...

Immobilization of Lipases on Hydrogels

Esa, Mahiran Basri, Che Nyonya A. Razak, Wan Md Zin W. Yunus, and Mansor Ahmad Immobilization of enzymes can be achieved by methods of varied complexity and efficiency 1 on a variety of supports. For example, enzymes can be adsorbed onto insoluble materials, copolymerized with a reactive monomer, encapsulated in gels, crosslinked with a bifunctional reagent, covalently bound to an insoluble carrier 2 or entrapped within an insoluble gel matrix of natural or...

Microencapsulation of Enzymes and Cells for Nonaqueous Biotransformations

Vulfson 1. Introduction The use of biocatalysts in nonaqueous organic solvents is now a well-established method for the preparation of pharmaceutical products 1-2 , food ingredients 3-5 , and intermediates used in the fine chemicals industry 6-10 . One of the advantages of this approach is that it enables the bioprocess operation at much higher concentrations of poorly water-soluble substrates, thus making both the synthesis and product recovery more attractive...

Endress Hauser Aluminum Oxide Humidity Sensor

We used this sensor extensively in the past, as it is the only one we know of that can be immersed directly in organic liquids although only the more nonpolar ones . It is also unaffected by most organic vapors when used in the gas phase, but its lower sensitivity and tendency to drift make it no longer our choice for this, compared with the LiCl sensor. The sensor and corresponding hygrometer are manufactured by the German division of Endress amp Hauser Maulburg . In our studies, we have used...

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