Alcohols enzymatic

Martearena, M. R., Blanco, S. and Ellenrieder, G. (2003). Synthesis of alkyl-alpha-L-rhamnosides by water soluble alcohols enzymatic glycosylation. Bioresource Technology 90 297-303. 

Scheme 7.4 Resolution of racemic alcohol enzymatic acylation.

The conventional electrochemical reduction of carbon dioxide tends to give formic acid as the major product, which can be obtained with a 90% current efficiency using, for example, indium, tin, or mercury cathodes. Being able to convert CO2 initially to formates or formaldehyde is in itself significant. In our direct oxidation liquid feed fuel cell, varied oxygenates such as formaldehyde, formic acid and methyl formate, dimethoxymethane, trimethoxymethane, trioxane, and dimethyl carbonate are all useful fuels. At the same time, they can also be readily reduced further to methyl alcohol by varied chemical or enzymatic processes. 

One approach called enzymatic resolution, involves treating a racemic mixture with an enzyme that catalyzes the reaction of only one of the enantiomers Some of the most commonly used ones are lipases and esterases enzymes that catalyze the hydrol ysis of esters In a typical procedure one enantiomer of the acetate ester of a racemic alcohol undergoes hydrolysis and the other is left unchanged when hydrolyzed m the presence of an esterase from hog liver... 

High yields of the enantiomerically pure alcohol and enantiomerically pure ester are reg ularly achieved The growing interest m chiral drugs (see the boxed essay on this topic p 296) has stimulated the development of large scale enzymatic resolution as a com mercial process... 

In keeping with its biogenetic origin m three molecules of acetic acid mevalonic acid has six carbon atoms The conversion of mevalonate to isopentenyl pyrophosphate involves loss of the extra carbon as carbon dioxide First the alcohol hydroxyl groups of mevalonate are converted to phosphate ester functions—they are enzymatically phosphorylated with introduction of a simple phosphate at the tertiary site and a pyrophosphate at the primary site Decarboxylation m concert with loss of the terti ary phosphate introduces a carbon-carbon double bond and gives isopentenyl pyrophos phate the fundamental building block for formation of isoprenoid natural products... 

According to a widely accepted concept, lignin [8068-00-6] may be defined as an amorphous, polyphenoHc material arising from enzymatic dehydrogenative polymerization of three phenylpropanoid monomers, namely, coniferyl alcohol [485-35-5] (2), sinapyl alcohol [537-35-7] (3), and /)-coumaryl alcohol (1). 

Enzymatic hydrolysis of A/-acylamino acids by amino acylase and amino acid esters by Hpase or carboxy esterase (70) is one kind of kinetic resolution. Kinetic resolution is found in chemical synthesis such as by epoxidation of racemic allyl alcohol and asymmetric hydrogenation (71). New routes for amino acid manufacturing are anticipated. 

A pilot plant ia India has been estabUshed to extract fiber, pulp, and juice from the leaves of sisal plants. The fiber is sold direcdy or used to manufacture rope, the cmshed pulp is used ia paper processiag, and the juice is an excellent source of hecogenin. During a three- to five-day fermentation of the juice, partial enzymatic hydrolysis causes hecogenin to precipitate as the hemisaponin ia the form of a fine sludge. This sediment is hydrolyzed with aqueous hydrochloric acid, neutralized, and filtered. This filter cake is washed with water and extracted with alcohol. The yield of hecogenin varies between 0.05 and 0.1% by the weight of the leaf (126). 

Many products made by fermentation are also based on the conversion of starch. Some examples of the use of enzymatically hydrolyzed starches are the production of alcohol, ascorbic acid, enzymes, lysine, and penicillin. 

A number of examples of monoacylated diols produced by enzymatic hydrolysis of prochiral carboxylates are presented in Table 3. PLE-catalyzed conversions of acycHc diesters strongly depend on the stmcture of the substituent and are usually poor for alkyl derivatives. Lipases are much less sensitive to the stmcture of the side chain the yields and selectivity of the hydrolysis of both alkyl (26) and aryl (24) derivatives are similar. The enzyme selectivity depends not only on the stmcture of the alcohol, but also on the nature of the acyl moiety (48). 

In contrast to the hydrolysis of prochiral esters performed in aqueous solutions, the enzymatic acylation of prochiral diols is usually carried out in an inert organic solvent such as hexane, ether, toluene, or ethyl acetate. In order to increase the reaction rate and the degree of conversion, activated esters such as vinyl carboxylates are often used as acylating agents. The vinyl alcohol formed as a result of transesterification tautomerizes to acetaldehyde, making the reaction practically irreversible. The presence of a bulky substituent in the 2-position helps the enzyme to discriminate between enantiotopic faces as a result the enzymatic acylation of prochiral 2-benzoxy-l,3-propanediol (34) proceeds with excellent selectivity (ee > 96%) (49). In the case of the 2-methyl substituted diol (33) the selectivity is only moderate (50). 

Cychc alcohols are excellent targets for enantioselective enzymatic acylations. For example, acylation of (65) with vinyl acetate catalyzed by Hpase SAM-II gives the (R),(3)-ester with 95% ee (81). Similarly (66), which is a precursor for seratonin uptake inhibitor, is resolved in a high yield and selectivity with Amano Hpase P (82). The prostaglandin synthon (67) is resolved by the same method into the optically pure alcohol in 35% yield (83). 

On the base of alcohol oxidase and flavocytochrome b, the enzymatic kits for selective assay of ethanol, methanol, formaldehyde and L-lactate were developed. 

Mention should also be made here of the extensive use of poly(vinyl alcohol) in potentially biodegradable applications. At appropriate hydroxyl contents these polymers will dissolve in water (see Chapter 14) and can apparently be conveniently washed away after use as a water-soluble packaging. Biodegradation does, however, appear to be slow and first requires an oxidative step involving enzymatic attack to a ketone such as polyenolketone, which then biodegrades more rapidly. 

Fermentation An anaerobic bioprocess. An enzymatic transformation of organic substrates, especially carbohydrates, generally accompanied by the evolution of gas as a byproduct. Fermentation is used in various industrial processes for the manufacture of products (e.g., alcohols, organic acids, solvents, and cheese) by the addition of yeasts, moulds, and bacteria. 

Two new sections on the protection of phosphates and the alkyne-CH are included. All other sections of the book have been expanded, some more than others. The section on the protection of alcohols has increased substantially, reflecting the trend of the nineties to synthesize acetate- and propionate-derived natural products. An effort was made to include many more enzymatic methods of protection and deprotection. Most of these are associated with the protection of alcohols as esters and the protection of carboxylic acids. Here we have not attempted to be exhaustive, but hopefully, a sufficient number of cases are provided that illustrate the true power of this technology, so that the reader will examine some of the excellent monographs and review articles cited in the references. The Reactivity Charts in Chapter 10 are identical to those in the first edition. The chart number appears beside the name of each protective group when it is first introduced. No attempt was made to update these Charts, not only because of the sheer magnitude of the task, but because it is nearly impossible in... 

Much of the chemistry of monosaccharides is the familiar chemistry of alcohols and aldehydes/ketones. Thus, the hydroxyl groups of carbohydrates form esters and ethers. The carbonyl group of a monosaccharide can be reduced with NaBH4 to form an alditol, oxidized with aqueous Br2 to form an aldonic acid, oxidized with HNO3 to form an aldaric acid, oxidized enzymatically to form a uronic acid, or treated with an alcohol in the presence of acid to form a glycoside. Monosaccharides can also be chain-lengthened by the multistep Kiliani-Fischer synthesis and can be chain-shortened by the Wohl degradation. 

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