Cephalosporin antibiotics discovery

The class A P-lactamases are a subset of the active-site serine P-lactamases. TEM-1 P-lactamase is a class A enzyme encoded by the ft/ajEM-l gene that is present on the transposons Tn2 and Tn3 (Datta et al, 1965). Epidemiological studies have shown that TEM-1 is the most common plasmid-mediated P-lactamase and is therefore a major determinant of bacterial resistance to P-lactam antibiotics (Wiedemann et al, 1989). Compounding the problem of resistance is the discovery that TEM-1 mutant variants with altered substrate specificity have been identified in natural isolates (Jacoby and Medieros, 1991). These variant enzymes contain from one to three amino acid substitutions that enable the enzyme to hydrolyze the newer extended-spectrum cephalosporin antibiotics such as cefotaxime and ceftazidime (Jacoby and Medieros, 1991). Thus, the selective pressure of antibiotic therapy le s to die creation of new enzymes with expanded hydrolytic capabilities. 

The novelty of this structure coupled with its interesting spectrum of antibacterial activity were clearly of potential commercial interest, and this time there were no qualms about patenting the discoveries. The strain of Cephalosporium acremonium was made the property of the National Research Development Corporation (NRDC) in Britain, and over the course of the next 15 years or so, this body received (on behalf of the British government) a fortune in royalties for the development of the cephalosporin antibiotics. 

Cephalosporins have a 3,6-dihydro-2//-l,3-thiazine nucleus, and some of their total syntheses start from 6//-l,3-thiazines. Since the discovery of the cephalosporins by Brotzu in 1943 and the enormous developments occuring in the chemistry of these antibiotics since the 1940s, the 1,3-thiazine nucleus has become one of the most important six-membered heterocycles. Cephalosporins now exceed penicillins in importance and presently account for 31% of the world market of all antibiotics. 

Further, the discovery of 7-a-methoxy cephalosporins [5] from Streptomyces in 1971, carbapenems [6], thienamycin [7], clavulanic acid [8], sulbactum [9] as well as the totally synthetic oxapenems [10], oxacephams [11], and other bicyclic (3-lactams stimulated the search for novel antibiotics. More recent dedicated efforts to find new active molecules and modify the penicillin and cephalosporin structure have resulted in the discovery of simple monocyclic (3-lactams such as norcardicins and monobactams [12, 13]. Yet another dimension has been added to the (3-lactam research with the recent discovery of tricyclic (3-lactam antibiotics called trinems [14]. Thus, (3-lactam antibiotics in general can be classified into several groups based on their structures (Fig. 1). 

The development of antibacterial chemotherapy during the past 75 years has spearheaded the successful use of today s drugs to combat bacterial infections. Studies in (3-lactam chemistry were stimulated when (3-lactam ring, the four membered heterocycle, was recognized as a key structural feature as well as a key therapeutic feature of the bicyclic (3-lactam antibiotics such as penicillins, cephalosporins, and other classical antibiotics. The last two decades have registered the discovery of several nonclassical bicyclic (3-lactam antibiotics, e.g., thienamycin and carba-penems of natural origin like olivanic acids, carpetimycin, pluracidomycin, and aspareomycins. 

After the discovery of penicillins and cephalosporins as classical (3-lactam antibiotics and clinically useful active agents, the past few decades have witnessed a remarkable growth in the field of (3-lactam chemistry [1, 2]. The need for potentially effective (3-lactam antibiotics as well as more effective (3-lactamase inhibitors has motivated synthetic organic and medicinal chemists to design new functionalized 2-azetidinones. Besides their clinical use as antibacterial agents, these compounds have also been used as synthons in the preparation of various heterocyclic compounds of biological significance [3-7]. The potential use of some... 

The discovery of penicillin by Sir Alexander Fleming in 1929 has been recognized as one of the most fortunate discoveries in modem times [1], The (3-lactam ring is the key component of commonly used antibiotics such as penicillins, cephalosporins, carbapenems, and monobactams [2], The development of (3-lactam antibiotics... 

The importance of j -lactams in the penicillins , cephalosporins , thienamycin and the recent discovery of antibiotic activity among monocyclic j -lactams such as norcardicins or the )5-lactamase inhibitor clavulanic acid have recently intensified research toward the synthesis of this system . Among the different procedures that have been developed for incorporating a 2-azetidinone unit , the ring expansion of cyclopropanol amines provides a simple and convenient route to these attractive small ring compounds. 

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