Penicillins amino acid precursors

A simple example is the tripeptide precursor of the penicillin antibiotics, called ACV, an abbreviation for S-(L-a-aminoadipyl)-L-cysteinyl-D-valine. The amino acid precursors for ACV are L-a-aminoadipic acid (an unusual amino acid derived by modification of L-lysine), L-cysteine, and L-valine (not o-valine). 

T Lendenfeld, D Ghali, M Wolschek, EM Kubicek-Pranz, CP Kubicek. Subcellular compartmentation of penicillin biosynthesis in Penicillium chrysogenum. The amino acid precursors are derived from the vacuole. J Biol Chem 268 665-671, 1993. 

It Is believed that penicillin antibiotics are biosynthesized from amino acid precursors. Identify the two amino acids that are most likely utilized during the biosynthesis of penicillin antibiotics ... 

A systematic study of the incorporation of side-chain precursors into penicillins produced by P. chrysogenum was made in the Lilly Research Laboratories in the 1940s. During the following decade H. R. V. Amstein and others confirmed that the penicillin ring system was formed from amino acid precursors—which were described by Sir Robert Robinson as always sun clear —and took the first step toward the elucidation of the interrelated pathways in penicillin and cephalosporin biosynthesis. 

Certain amino acids and their derivatives, although not found in proteins, nonetheless are biochemically important. A few of the more notable examples are shown in Figure 4.5. y-Aminobutyric acid, or GABA, is produced by the decarboxylation of glutamic acid and is a potent neurotransmitter. Histamine, which is synthesized by decarboxylation of histidine, and serotonin, which is derived from tryptophan, similarly function as neurotransmitters and regulators. /3-Alanine is found in nature in the peptides carnosine and anserine and is a component of pantothenic acid (a vitamin), which is a part of coenzyme A. Epinephrine (also known as adrenaline), derived from tyrosine, is an important hormone. Penicillamine is a constituent of the penicillin antibiotics. Ornithine, betaine, homocysteine, and homoserine are important metabolic intermediates. Citrulline is the immediate precursor of arginine. 

The last comprehensive review of the chemistry of oxazolones covered the literature through 1954. Most of the studies up to that time stemmed from either interest in the role of azlactones as precursors of a-amino acids and peptides or the monumental studies on penicillin, which, for a time, was thought to possess an oxazolone ring, rather than the correct jS-lactam moiety. 

Amino acid separations represent another specific application of the technology. Amino acids are important synthesis precursors - in particular for pharmaceuticals -such as, for example, D-phenylglycine or D-parahydroxyphenylglycine in the preparation of semisynthetic penicillins. They are also used for other chiral fine chemicals and for incorporation into modified biologically active peptides. Since the unnatural amino acids cannot be obtained by fermentation or from natural sources, they must be prepared by conventional synthesis followed by racemate resolution, by asymmetric synthesis, or by biotransformation of chiral or prochiral precursors. Thus, amino acids represent an important class of compounds that can benefit from more efficient separations technology. 

In linear NRPSs a product consisting of amino acids is biosynthesized in an N- to C-terminal manner by the multidomain assembly line with a domain organization of A-PCP-(C-A-PCP) i-TE. The initiation module of a linear NRPS lacks a C domain, while the following modules may include any required additional domains. After formation of the full-length peptide, the product is released from the assembly line by a termination domain. Thus, the number and order of amino acids in the peptide directly coincides with the number and order of synthetase modules. Many NRPs are biosynthesized in this manner, and characterized examples include the penicillin tripeptide precursor -(L-0 -aminoadipyl)-L-cysteinyl-D-valine (ACV, Figure 4 (a)), complestatin, cyclosporin, fengycin, surfactin, and tyrocidine. "... 

The tripeptide precursor is called ACV, an abbreviation for 8-(L-a-aminoadipyl)-L-cysteinyl-D-valine. ACV is an acronym, and does not refer to the systematic abbreviations for amino acids described in Table 13.1. ACV is the linear tripeptide that leads to isopenicillin N, the first intermediate with the fused-ring system found in the penicillins. 

Bacitracin is a mixture of polypeptide antibiotics produced by Bacillus subtilis. As with penicillin, it contains a thiazolidine nucleus attached through L-leucine to a peptide composed of both d- and L-amino acids. However, it does not contain a (3-lactam ring. Bacitracin prevents cell wall synthesis by binding to a lipid pyrophosphate carrier that transports cell wall precursors to the growing cell wall. 

A large number of a, 3-didehydro-a-amino acids have been identified as constituents of relatively low molecular weight cyclic compounds from microbial sources. However, the presence of a,p-didehydroalanine in bacterial as well as in mammalian histidine ammonia lyase and in phenylalanine ammonia lyase shows that the occurrence of a,p-didehydro-a-amino acids is not limited to small molecules alone 8 These residues are incorporated in natural sequences by posttranslation modification. a,p-Didehydro-a-amino acids have also been postulated to be precursors in the biosynthesis of several heterocyclic metabolites including penicillin and cephalosporin 9 Other well-known compounds containing ,( -di-dehydro-a-amino acids are nisin 10,11 (a food preservative112 ), subtilin (a broad spectrum antibiotic) 13 and some of the metabolites isolated from Streptomyces strains such as gri-seoviridin 14 ... 

D-p-Hydroxyphenylglycine and its derivatives are important as side-chain precursors for semisynthetic penicillins and cepharosporines. Yamada and coworkers of our laboratory found that these amino acids can be efficiently prepared from the corresponding 5-monosubstituted hydantoins using the microbial enzyme D-hydantoinase [4]. 

HPLC systems were helpful in monitoring cephalosporin production [174] and p-cresol degradation [392]. Other HPLC systems have been reported to serve for the control of penicillin production, namely via the precursor feed [62, 288],3-chlorobenzoate conversion [375] or naphthalenesulfonic acid reduction [279], as well as amino acids [444,445]. HPLC is also found to be useful when linked to biochemical assays [316]. Mailinger et al. [262] have discussed many important aspects of on-line HPLC systems. 

The cross-linking (transpeptidation) of the peptidoglycan chains is facilitated by transpeptidases known as penicillin-binding proteins. 3-lactam antibiotics are analognes of D-alanyl-D-alanine, the terminal amino acid residnes on the precursor N-acetyhnuramic/N-acetylglucosamine (NAM/NAG)-peptide subunits of the nascent peptidoglycan layer. The structural similarity between /3-lactam antibiotics and D-alanyl-D-alanine facilitates their... 

This reaction is accomplished by three megasynthases consisting of 3491, 3567, and 3172 amino acids. The synthesis of deoxyerythronolide B begins with propionyl CoA linked to a phosphopantetheine chain connected to an acyl carrier protein domain. Similarly, the precursor of penicillin [A-(l-aminoadipyl)-l-cysteinyl-d-valine, or ACV] is generated by the following reaction ... 

Although cephalosporin C is divisable into a-aminoadipic acid, cysteine, and valine, the actual mechanism whereby Cephalosporium sp. incorporates the three amino acids into cephalosporin C has not been established, Arnstein and Morris isolated 8 (a-aminoadipyl) cysteinyl valine from mycelia of Penicillium chrysogenum and suggested that the tripeptide is a precursor in all penicillin biosynthesis.. This same tripeptide also appears to be found in the intracellular pool of Cephalosporium sp.- The final postulated step in the biosynthesis of penicillin is an acyl transfer reaction, or the production of 6-aminopeni-cillanic acid if precursor is not added. Cephalosporium sp. apparently do not produce sidechain amidases or acyl transferases, and no 7-ACA has been reported found in the fermentation. Thus, to obtain clinically useful antibiotics, chemical manipulation of cephalosporin C is necessary. Synthesis of many 7-acyl derivatives was possible once a practical cleavage reaction made available large amounts of 7-ACA from cephalosporin C. of these derivatives, sodium cephalothin was the first... 

Bacitracin contains a cyclic peptide as part of a complex structure of 12 amino acid residues (if one considers the thiazole ring as cysteine derived). Bacitracin-treated bacterial cultures accumulate precursor peptidoglycan chains, as do the penicillins. However, the mechanism is very different. Its prevention of lysine inclusion into the murein structure is probably of lesser significance. Later demonstration show that drug binding to the membrane-bound bactoprene phosphate and the metal ions (Zn2+ are particularly involved) is more likely to be important to the antibacterial mechanism, namely, inhibition of dephosphorylation of the phospholipid carrier. 

Inactivation of certain enzyme systems involved in the oxidative metabolism of sensitive organisms by polymyxin and colistin has also been reported. This, however, might be a secondary effect . Bacitracin has been reported to interfere with cell wall synthesis. It causes Staphylococcus aureus to lyse , to form protoplasts and to accumulate cell wall precursors " . The incorporation of radioactive amino acids into cell wall mucopeptides is inhibited. Bacitracin has further been found to prevent Staphylococcus aureus from synthesizing /3-galactosidase , yet it does not interfere with the incorporation of radioactive lysine into cells . In experiments with Staphylococcus aureus, bacitracin and penicillin were shown to share a common binding site on the membrane , a result which could not be confirmed in similar experiments with B. megateriumP . Recently a direct effect of bacitracin on the cytoplasmic membrane has been demonstrated, and it was suggested that the inhibition of cell wall synthesis could be a secondary effect . ... 

Attention has been turned to the cysteine-derived part of the penicillins. The results closely define (a) the fates of the hydrogen atoms present at C-2 and C-3 of cysteine (201) and (b) the overall stereochemistry involved in the incorporation of the amino-acid. L-[l/- C,2- H]Cystine was found to give penicillin G (199) with only slight loss of tritium. The tritium label was shown (in an experiment with singly labelled precursor) to be located exclusively at C-6, similar results being obtained with L-[2- H]cystine. These results, which confirm those obtained earlier, ... 

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