The discovery and development of the β-lactam antibiotics are among the most powerful and successful achievements of modern science and technology. Since Fleming's accidental discovery of the penicillin-producing mold, seventy years of steady progress has followed, and today the β-lactam group of compounds are the most successful example of natural product application and chemotherapy. Following on the heels of penicillin production by Penicillium chrysogenum came the discoveries of cephalosporin formation by Cephalosporium acremonium, cephamycin, clavam and carbapenem production by actinomycetes, and monocyclic β-lactam production by actinomycetes and unicellular bacteria. Each one of these groups has yielded medically-useful products and has contributed to the reduction of pain and suffering of people throughout the world. Research on the microbiology, biochemistry, genetics and chemistry of these compounds have continued up to the present with major contributions being made by both individual and collaborative groups from industry and academia. The discovery of penicillin not only led to the era of the wonder drugs but provided the most important antibiotics available to medicine. Continued efforts have resulted in the improvement of these compounds with respect to potency, breadth of spectrum, activity against resistant pathogens, stability and pharmacokinetic properties. On the research front, major advances are being made on structural and regulatory biosynthetic genes and metabolic engineering of the pathways involved. New semisynthetic compounds especially those designed to combat resistance development are being examined in the clinic, and unusual non-antibiotic activities of these compounds are being pursued. Although seventy years of age, the β-lactams are not yet ready for retirement.

The beta-lactam antibiotics: past, present, and future.

Partial purification and properties of the α-ketoglutarate-linked ring-expansion enzyme of β-lactam biosynthesis of Cephalosporium acremonium

Micrococcus luteus was found to be very sensitive to isopenicillin N and was used as assay organism for purification of the enzyme isopenicillin N synthetase, which cyclizes δ-(L-α-aminoadipyl)-L-c...

Studies on the ring-cyclization and ring-expansion enzymes of β-lactam biosynthesis in Cephalosporium acremonium

The discovery of penicillin by Fleming (1929) and its development by the Oxford group (Florey et al. 1949) began the antibiotic era. The success of this β-lactam antibiotic led the way for the development of all other antibiotics. As will be described later in this chapter, new and more effective β-lactam antibiotics are being discovered now, over 50 years after Fleming’s initial discovery.

Biosynthesis of β-Lactam Antibiotics

Publisher Summary This chapter discusses the biosynthesis of β-lactam antibodies. These compounds can be grouped into three structural classes: (1) nocardicin, (2) clavam, and (3) 1-carbapen-2-em antibiotics. The biosynthesis of nocardicins may involve a tripeptide intermediate, but the synthesis of clavam and l-carbapen-2-em antibiotics appears to involve N-acylamino acid intermediates. The nucleus of the nocardicin antibiotics, 3-aminonocardicinic acid, can be prepared by enzymatic deacylation, but the occurrence of the nucleus has not been reported in the fermentation broth of N. uniformis. The β-lactam ring in nocardicin A is formed by nucleophilic displacement of an activated seryl hydroxyl by acid nitrogen. In a study described in the chapter, the enrichments observed with [l-13C]propionate and [3-13]propionate suggested that the primary route of propionate metabolism was carboxylation of propionylCoA to methylmalonylCoA, isomerization to succinylCoA, and conversion by the TCA cycle to oxalacetate and α-ketoglutarate. Discoveries of new β-lactam antibiotics have been thrust upon investigators interested in unraveling the means by which microorganisms synthesize β-lactam antibiotics. It is interesting to speculate about the isolation of β-lactam synthetases and their use for the conversion of synthetic substrates to new β-lactam antibiotics.

The Biosynthesis of β-Lactam Antibiotics

The rate of microbiological ring-expansion of penicillin N to deacetoxycephalosporin C using protoplast lysates of the antibiotic-negative mutant Cephalosporium acremonium M-0198 has been increased some 70-fold over that of our earlier system. We confirmed the stimulatory effects of FeSO4 and ascorbate described by HOOKet al. (Biochem. Biophys. Res. Commun. 87: 258, 1979); the optimum concentrations found were 0.04 mM FeSO4 and 0.67 mM ascorbate. Adenosine triphosphate concentration was lowered to 0.83 mM; phosphoenolpyruvate and pyruvate kinase were eliminated. The optimum pH and temperature for the reaction were 7.2 and 25°C, respectively. α-Ketoglutarate and MnCl2 showed no marked effect on the reaction, MgSO4 and KCl were mildly stimulatory, and CUSO4 and ZnSO4 were very inhibitory. Penicillin N was optimal at a concentration of 0.07 mM. Specific ring-expansion activity reached its peak 13 hours after growth ceased and then disappeared rapidly.

N. A. Hunt

Papers

Further studies on microbiological ring-expansion of penicillin N.