P-lactamase, production

A disadvantage of ampicillin and amoxicillin is that they are inactivated by penicillinase, and more strains of H. influenzae are becoming resistant through penicillinase (p-lactamase) production. The addition of a p-lactamase inhibitor such as clavulanate (clavulanic acid) or sulbactam to a penicillin preparation can protect the penicillin component because these chemicals irreversibly inactivate bacterial P-lactamases. 

Staph, aureus is responsible for a variety of skin infections which require therapeutic approaches different from those of streptococcal infections. Staphylococcal cellulitis is indistinguishable clinically from streptococcal cellulitis and responds to flucloxacillin, but generally fails to respond to penicillin owing to penicillinase (P-lactamase) production. Staph, aureus is an important cause of superficial, localized skin sepsis which varies from small pustules to boils and occasionally to a more deeply invasive, suppurative skin abscess known as a carbuncle. Antibiotics are generally not indicated for these conditions. Pustules and boils settle with antiseptic soaps or creams and often discharge spontaneously, whereas carbuncles frequently require surgical drainage. Staph, aureus may also... 

Further observations were published concerning the mechanism of action of the penicillins.Data support the concept that the P-lactam antibiotics inhibit a transpeptidase essential for a cross-linking reaction in bacterial cell-wall synthesis. Transpeptidase derived from cell-free systems of E. coli, like that from aureus, is inactivated by penicillins. Thus, the possession of cellular permeability barriers in addition to P-lactamase productive capacity apparently tends to protect greun-negative bacteria from lethal attack by P-lactam antibiotics.33... 

Intravenous ciprofloxacin or doxycycline is recommended for treatment of anthrax, usually as part of a cocktail of antibiotics (CDC, 2001a,b). Multiple antibiotics are usually indicated in anthrax cases with signs of septicemia, extensive edema, or for cases with cutaneous lesions in the head and neck (Brook, 2002). Penicillin may be included in the antibiotic cocktail but is not recommended as a stand-alone therapy due to B. anthracis p-lactamase production. B. anthracis can express p-lactamase variants, penicillinases and cepha-losporinases, which would undermine a lone-penicillin therapy (Lightfoot et al., 1990). B. anthracis has shown in vitro resistance to cephaloporins and trimethoprim-sulfamethoxazole (Inglesby et al., 2002). Corticosteroid therapy may help treat edema from head and neck lesions or prevent airway obstruction. Table 29.3 contains... 

Beecham P-lactamase iiihibitoi BRL 42715 [102209-75-6] (89, R = Na), C IlgN O SNa (105). Lithium diphenylamide, a weaker base, was used to generate the anion of (88) which on sequential treatment with l-methyl-l,2,3-ttia2ole-4-carbaldehyde and acetic anhydride gives a mixture of diastereomers of the bromoacetate (90). Reductive elimination then provided the (Z)-penem (89, R = d5 Q [ OC15 -p) as major product which on Lewis acid mediated deprotection gave BRL 42715 (89, R = Na). 

Resistance. Resistance to the cephalosporins may result from the alteration of target pencillin-binding sites (PBPs), decreased permeabdity of the bacterial ced wad and outer membrane, or by inactivation via enzyme mediated hydrolysis of the lactam ring (80,81,138—140). This resistance can be either natural or acquired. Although resistance is often attributed speciftcady to one of these factors, in reaUty it reflects the interplay of several factors. In most instances, however, resistance results from the production of a P-lactamase enzyme, which opens the P-lactam ring as depicted in Figure 2. 

The antibacterial effectiveness of penicillins cephalospotins and other P-lactam antibiotics depends upon selective acylation and consequentiy, iaactivation, of transpeptidases involved ia bacterial ceU wall synthesis. This acylating ability is a result of the reactivity of the P-lactam ring (1). Bacteria that are resistant to P-lactam antibiotics often produce enzymes called P-lactamases that inactivate the antibiotics by cataly2ing the hydrolytic opening of the P-lactam ring to give products (2) devoid of antibacterial activity. 

Active site directed P-lactam-derived inhibitors have a competitive component of inhibition, but once in the active site they form an acyl en2yme species which follows one or more of the pathways outlined in Figure 1. Compounds that foUow Route C and form a transiendy inhibited en2yme species and are subsequendy hydroly2ed to products have been termed inhibitory substrates or competitive substrates. Inhibitors that give irreversibly inactivated P-lactamase (Route A) are called suicide inactivators or irreversible inhibitors. The term progressive inhibitor has also been used. An excellent review has appeared on inhibitor interactions with P-lactamases (28). 

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. 

Penam Sulfone B-Lactamase Inhibitors. Natural product discoveries stimulated the rational design of p-lactamase inhibitors based on the readily accessible penicillin nucleus. An early success was penicillanic acid sulfone, (2(5)-cis)-3,3-dimethyl-7-oxo-4,4-dioxide-4-thia-l-a2abicyclo [3.2.0]heptane-2-carboxylic acid [68373-14-8] (sulbactam) (25, R = = H, R" = R" = CH ), CgH NO S. The synthesis (118), microbiology (119—121),... 

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. 

While screening for p-lactam antibiotics stable to p-lactamases, a strain of Streptomyces lactamdurans was found to contain several such agents which have a 6-a-methoxy group whose electronic and steric properties protect the antibiotic from enzymatic attack. Cephamycin C (29a), one of these substances, is not of commercial value, but side chain exchange has led to much more potent materials. Of the various ways of effecting this transformation, one of the more direct is to react cephamycin C with nitrous acid so that the aliphatic diazo product (29b) decomposes by secondary amide participation giving cyclic iminoether 30. The imino ether moiety solvolyzes more readily than the p-lactam to produce 7-aminocephamycinic... 

The bacterium Staphylococcus aureus, which is a major cause of infection in the developed countries, is now resistant to most antibiotics. It is usually present on the skin, where it causes no problems, but it can invade the body through cuts and wounds, including those caused by surgery. These bacteria are now prevalent in many hospitals, so that infection is a major problem for the medical staff in hospitals. The resistant bacterium is known as methicillin-resistant Staphylococcus aureus (MRSA). It is also known in the mass media as the super bug . Penicillin kiUs bacteria because the P-lactam group in the antibiotic inhibits a reaction that is essential for bacterial ceU wall production. Consequently, the bacteria cannot proliferate. Resistance to penicillin in many bacteria is due to production of an enzyme, p-lactamase, that degrades P-lactams. The antibiotic methicillin is one of a group of semisynthetic penicillins in which the P-lactam group is not... 

Production of enzymes to degrade the antibiotic, e.g. novel (3-lactamases, extended-spectrum p-lactamases, or aminoglycoside-modifying enzymes. 

It would be valuable to develop compounds affording a stable acyl-P-lactamase. Clavulanic acid (40) is a natural product discovered in a Streptomyces strain and acts as a specific inhibitor of p-lactamase. Fisher and Knowles indicated the possibility of the formation of a long-living acyl-enzyme in the catalytic pathway of p-lactamase... 

If both components have one substituent, these will end up trans on the four-membered ring just to keep out of each other s way. This example has more functionality and the product could be used to make p-lactams with antibiotic activity, such as analogues of the P-lactamase inhibitor, clavulanic acid (Chapter 32). 

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