Penicillin examples

Whole cells are grown for a variety of reasons. The cells may perform a desired transformation of the substrate, e.g., wastewater treatment the cells themselves may be the desired produce, e.g., yeast production or the cells may produce a desired product, e.g., penicillin. In the later case, the desired product may be excreted, as for the penicillin example, and recovered in relatively simple fashion. If the desired product is retained within the cell walls, it is necessary to lyse (rupture) the cells and recover the product from a complex mixture of cellular proteins. This approach is often needed for therapeutic proteins that are created by recombinant DNA technology. The resulting separation problem is one of the more challenging aspects of biochemical engineering. However, culture of the cells can be quite difficult experimentally and is even more demanding theoretically. 

Penicillin (example of a drug with a large therapeutic index) For... 

Antibiotics. Solvent extraction is an important step in the recovery of many antibiotics (qv) such as penicillin [1406-05-9] streptomycin [57-92-17, novobiocin [303-81-1J, bacitracin [1405-87-4] erythromycin, and the cephalosporins. A good example is in the manufacture of penicillin (242) by a batchwise fermentation. Amyl acetate [628-63-7] or -butyl acetate [123-86-4] is used as the extraction solvent for the filtered fermentation broth. The penicillin is first extracted into the solvent from the broth at pH 2.0 to 2.5 and the extract treated with a buffet solution (pH 6) to obtain a penicillin-rich solution. Then the pH is again lowered and the penicillin is re-extracted into the solvent to yield a pure concentrated solution. Because penicillin degrades rapidly at low pH, it is necessary to perform the initial extraction as rapidly as possible for this reason centrifugal extractors are generally used. 

Certain factors and product precursors are occasionally added to various fermentation media to iacrease product formation rates, the amount of product formed, or the type of product formed. Examples iaclude the addition of cobalt salts ia the vitamin fermentation, and phenylacetic acid and phenoxyacetic acid for the penicillin G (hen ylpenicillin) and penicillin V (phenoxymethylpenicillin) fermentations, respectively. Biotin is often added to the citric acid fermentation to enhance productivity and the addition of P-ionone vastly iacreases beta-carotene fermentation yields. Also, iaducers play an important role ia some enzyme production fermentations, and specific metaboHc inhibitors often block certain enzymatic steps that result in product accumulation. 

Pharmaceuticals. -Hydroxybenzaldehyde is often a convenient intermediate in the manufacture of pharmaceuticals (qv). For example, 2-(p-hydroxyphenyl)glycine can be prepared in a two-step synthesis starting with -hydroxybenzaldehyde (86). This amino acid is an important commercial intermediate in the preparation of the semisynthetic penicillin, amoxicillin (see ANTIBIOTICS, P-LACTAMs). Many cephalosporin-type antibiotics can be made by this route as well (87). The antiemetic trimethobenzamide [138-56-7] is convenientiy prepared from -hydroxybenzaldehyde (88) (see Gastrointestinal agents). 

Most of the new commercial antibiotics have resulted from semisynthetic studies. New cephalosporkis, a number of which are synthesized by acylation of fermentation-derived 7-amkiocephalosporanic acid, are an example. Two orally active cephalosporkis called cefroxadine and cephalexin are produced by a synthetic ring-expansion of penicillin V. 

Fermentation Processes. The efficient production of penicillin, yeasts, and single-ceUed protein by fermentation requires defoamers to control gas evolution during the reaction. Animal fats such as lard [61789-99-9] were formerly used as a combined defoamer and nutrient, but now more effective proprietary products are usually employed. Defoamer appHcation technology has also improved. For example, in modem yeast production faciHties, the defoamers are introduced by means of automatic electrode-activated devices. One concern in the use of defoamers in fermentation processes is the potential fouHng of membranes during downstream ultrafiltration (qv). SiHcone antifoams (43,44) seem less troubled by this problem than other materials. 

The second most important group of immobilized enzymes is stiU the penicillin G and V acylases. These are used in the pharmaceutical industry to make the intermediate 6-aminopenici11anic acid [551-16-6] (6-APA), which in turn is used to manufacture semisynthetic penicillins, in particular ampicilHn [69-53-4] and amoxicillin [26787-78-0]. This is a remarkable example of how a complex chemical synthesis can be replaced with a simple enzymatic one ... 

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. 

Following the discovery of penicillins, an extensive program for the screening of culture fluids and residual mycelial material commenced which resulted in the discovery of a large number of pyrazinones and related 1-hydroxy-2-pyrazinones with pronounced antibiotic character. Some examples are shown in Table 4. One of the earliest substances to be isolated, aspergillic acid (110 = OH, = Me, R = Et, R = R = H, R = Pr ), was found... 

As many natural and synthetic /3-lactams bear 3-acylamino substituents, the corresponding free amines or protected forms thereof are versatile synthetic intermediates. They may be prepared in several ways, for example by deacylation of the 7-amido group in naturally occurring penicillins by enzymic or chemical means. Chemical degradation usually involves conversion of the amide to a chloroimidate followed by cleavage with aqueous alcohols (75S547 p. 560, 78T1731 p. 1753). 

The early investigations of the reactions of the penicillin class of compounds were largely of a degradative nature, and were primarily associated with structure elucidation. These have been discussed in detail (B-49MI51102) and some of the principal transformations are outlined in Schemes 2, 3 and 4 using benzylpenicillin as an example. Some of these reactions will be discussed in greater detail later in this section. 

Scheme 6 depicts a typical penicillin sulfoxide rearrangement (69JA1401). The mechanism probably involves an initial thermal formation of a sulfenic acid which is trapped by the acetic anhydride as the mixed sulfenic-acetic anhydride. Nucleophilic attack by the double bond on the sulfur leads to an episulfonium ion which, depending on the site of acetate attack, can afford either the penam (19) or the cepham (20). Product ratios are dependent on reaction conditions. For example, in another related study acetic anhydride gave predominantly the penam product, while chloroacetic anhydride gave the cepham product (7lJCS(O3540). The rearrangement can also be effected by acid in this case the principal products are the cepham (21) and the cephem (22 Scheme 7). Since these early studies a wide variety of reagents have been found to catalyze the conversion of a penicillin sulfoxide to the cepham/cephem ring system (e.g. 77JOC2887).

The intermediate sulfenic acid derived from a penicillin sulfoxide has been trapped by a large assortment of reagents and, in one case, the sulfenic acid itself has been isolated (74JA1609). Only some of these products will be discussed here, and the reader is referred to the cited reviews (especially B-80MI51102) for additional examples. 

Aerobic Fermentation The classic example of large-scale aerobic fermentation is the production of penicillin by the growth of a specific mold. Commercial vessel sizes are 40,000 to 200,000 L (1,400 to 7,000 ft ). The operation is semibatch in that the lactose or glucose nutrient and air are charged at controlled rates to a precharged batch of liquid nutrients and cell mass. Reaction time is 5 to 6 days. 

The o-nitrobenzyl ester, used in this example to protect penicillin precursors, can be cleaved by irradiation (H20/dioxane, pH 7). Reductive cleavage of benzyl or p-nitrobenzyl esters occurred in lower yields. 

The manufacture of penicillin, for example, involves batch fermentation using... 

Norfloxacin (1, R = C2H5, R = H), a typical example, exhibits broad-spectrum activity and is useful in the treatment of upper respiratory tract and urinary infections [7] Lomefloxacin (2), a very recent introduction, is a third-generation product that, given once daily, is especially useful against pathogens resistant to cephalosponns, penicillins, and aminoglycosides [4] Floxacillin (J) is a stable, orally active antibacterial with improved activity over thenonfluonnated product (cloxacillin) [5]... 

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