Clavulanic acid

P-Lactams. AH 3-lactams are chemically characterized by having a 3-lactam ring. Substmcture groups are the penicillins, cephalosporias, carbapenems, monobactams, nocardicias, and clavulanic acid. Commercially this family is the most important group of antibiotics used to control bacterial infections. The 3-lactams act by inhibition of bacterial cell wall biosynthesis. 

Clavulanic acid has only weak antibacterial activity, but is a potent irreversible inhibitor for many clinically important P-lactamases (10—14,57,58) including penases, and Richmond-Sykes types 11, 111, IV, V, VI ([Bacteroides). Type I Cephases are poorly inhibited. Clavulanic acid synergizes the activity of many penicillins and cephalosporins against resistant strains. The chemistry (59—63), microbiology (64,65), stmcture activity relationships (10,13,60—62,66), biosynthesis (67—69), and mechanism of action (6,26,27,67) have been reviewed. 

Table 2. P-Lactamase Inhibitory Activity for Clavulanic Acid and Analogues ...

Garbapenem P-Lactamase Inhibitors. Carbapenems are another class of natural product P-lactamase inhibitors discovered about the same time as clavulanic acid. Over forty naturally occurring carbapenems have been identified many are potent P-lactamase inhibitors. Garbapenem is the trivial name for the l-a2abicyclo[3.2.0]hept-2-ene ring system (21) shown in Table 3. The synthesis (74), biosynthesis (75), and P-lactamase inhibitory properties (13,14,66) of carbapenems have been reviewed. Carbapenems are often more potent than clavulanic acid and include type I Cephases in the spectmm of inhibition. Table 3 Hsts the available P-lactamase inhibition data. Synergy is frequendy difficult to demonstrate because the compounds are often potent antibacterials. 

R " = CH3) which has activity similar to that of clavulanic acid and inhibits many of the type I Cephases. The synthesis (156), microbiological activity (152,156—162), and stabiUty (152) of ta2obactam have been reported. 

The 6-methoxymethylene penicillanic acid [93040-42-7] (31, R = CH OCH (2)-isomer, R" = R " = 3) designed to mimic the amino acrylate species found usiag clavulanic acid and sulbactam. Upon the reaction of this compound with the enzyme, the potential exists for further Michael addition to inactivate the enzyme. The compound is indeed a -lactamase inhibitor but no synergy data have been reported. The related imine stmcture... 

Although a broad range of P-lactamase inhibitors has been discovered, only clavulanic acid and sulbactam have been commercialized. Clavulanic acid (12, R = CH2OH, R = H), manufactured by SmithKlinp Beecham, is sold as an oral and parenteral product in combination with amoxicillin under the trade name Augmentin. A parenteral product in combination with ticarcillin [34787-01-4], C25H2gN20 S, has the trade name, Timentin. In 1990 worldwide sales of clavulanic acid containing products were about 725 million. 

Antibiotics, P-Lactams, Clavulanic Acid, Thienamycin, and Others," in ECT 3rd ed.. Supplement, pp. 83—131, by Allan Brown, Beecham Research Laboratories. 

In an unusual application of the Wittig reaction, treatment of clavulanic acid derivatives and esters of penicillin V with methoxycarbonylmethylenetriphenylphosphorane afforded the corresponding exo-alkylideneazetidines. Thus penicillin V benzyl ester (104) gave (lOS) as a mixture of E and Z isomers. The /3-lactam could be regenerated by low-temperature ozonolysis (81CC929). 

There are several examples of intramolecular reactions of monocyclic /3-lactams with carbenes or carbenoids most of these involve formation of olivanic acid or clavulanic acid derivatives. Thus treatment of the diazo compound (106) with rhodium(II) acetate in benzene under reflux gives (107), an intermediate in the synthesis of thienamycin (80H(14)1305, 80TL2783). 

Cyclization of the diazo compound (108) with a copper catalyst affords the clavulanic acid derivatives (110) and (111), possibly via rearrangement of the sulfur ylide (109) (80H(14)1999). Similar reactions have been reported in the recent literature (80H(14)1967, 81H(16)1305, 80TL31). 

An intermolecular carbenoid reaction followed by intramolecular displacement of acetate gives the clavulanic acid derivative (112) in one step from 4-acetoxyazetidin-2-one (91) (80CC1257). Carbene-induced reactions of penicillins and cephalosporins have been reviewed (75S547, 78T1731). 

The previously described penem syntheses from 6-APA-derived starting materials have been inefficient in the sense that the C(2) and C(3) atoms of the penam are lost during the sequence. Scheme 71 shows a route in which C(2) and C(3) of the penam become C(2) and C(3) of the penem (79CC665). The major product of this sequence is the (55) enantiomer. A related synthetic approach, starting with the natural product clavulanic acid, has been described (79CC663). 

Sterile air was supplied at 1,200 liters per minute. Antifoam was added in 25 ml amounts as required. (10% Piuronic LSI in soybean oil.) The fermentation was controlled at 26°C until a maximum yield of clevulanic acid wes obtained between 3-5 days when 200-300 /.Ig/ml of clavulanic acid were produced. 

Streptomyces capreolus Capreomycin sulfate Streptomyces davuHgerus Clavulanic acid Streptomyces distallicus Stallimycin HCl Streptomyces erythreus Erythromycin Streptomyces fradiae Neomycin... 

Soybean meal, by fermentation Bacitracin Clavulanic acid Cycloserine Erythromycin Gentamicin sulfate Kanamycin sulfate Micronomicin Novobiocin Oleandomycin Oxamniquine Oxytetracycline Paromomycin Ribostamicin Sisomicin... 

Scheme 10.30 Part of clavulanic acid biosynthesis. Bonds installed byclavaminic acid synthase (CAS) are circled. CAS clavaminic acid synthase. PAH proclavaminic acid amidino hydrolase.

Other examples of a-keto acid-dependent enzymes are mammalian proline hydroxylase and bacterial clavaminate synthase [113]. The latter enzyme is of particular interest as it is responsible for the catalysis of three individual steps in the biosynthesis of the (3-lactamase inhibitor clavulanic acid (Scheme 10.30). 

Metallo-enzymes belonging to group 3 naturally show a very broad substrate spectrum including all (3-lactams excqrt monobactams and are not inhibited by clavulanic acid, but by complexing agents, like EDTA. This can only be exploited for diagnostic purposes. 

Aminopenicillins amoxicillin a-mox-i-sil -in amoxicillin and clavulanate acid a-mox-i-sil -in/ klah-view-lan -ate Amoxil, Trimox, Wymox, generic Augmentin Same as penicillin G Same as penicillin G... 

The cis P-lactams 57 are shown to act as cholesterol absorption inhibitors <96BMCL1947> and 58, an analogue of the dipeptide Phe-Gly methyl ester, is a protease inhibitor <96BMCL983>. A straightforward synthesis of proclavaminic acid 59, a biosynthetic precursor of clavulanic acid, is reported <96TA2277>. 

Fig. 5.5 A, clavulanic acid B, latamoxef C, 1-carbapenems D, olivanic acid (general structure) E, thienamycin F, meropenem G, 1-carbacephems H, loracarbef.

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