Cephamycin nucleus

There has also been extensive activity towards the replacement of the entire chemical route to 7-ADCA (Scheme 1.14) with a biocatalytic one. This is somewhat more complex than the above example, as the penicillin fermentation product requires ring expansion as well as side-chain hydrolysis in order to arrive at the desired nucleus. The penicillin nucleus can be converted to the cephalosporin nucleus using expandase enzymes, a process that occurs naturally during the biosynthesis of cephalosporin C by Acremonium chryso-genum and cephamycin C by Streptomyces clavuligems from isopenicUhn N (6-APA containing a 6-L-a-aminoadipoyl side chain). ... 

More interesting, the presence of the thiophene ring in position 7 of the cephem nucleus (Figure 2) has been associated with nephrotoxic effects in the case of cephaloridine and cephalothin and to a lesser extent in the case of the cephamycin cefoxitin [26, 66]. When compared to cephalothin, small alterations of the cefoxitin molecule in positions 3 and 7 of the cephem nucleus, such as replacement of the methyl group with... 

Cephalosporins are produced from 7-aminocephalosporanic acid by the addition of different side chains (Table 44-2). Modifications at position 7 of the fflactam ring alter antibacterial activity, while substitutions at position 3 of the dihydrothiazine ring alter the metabolism and pharmacokinetic properties. The cephamycins are similar to the cephalosporins but have a methoxy group at position 7 of the /3-lactam ring of the 7-aminocephalosporanic acid nucleus. 

Cefoxitin, a cephamycin, has a —OCHg group at position 7 of cephem nucleus. 

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