Recent Advances in the Industrial Enzymatic Synthesis of Semi-Synthetic βLactam Antibiotics

The production, under environmentally benign conditions, of efficient and more cost-effective anti-infective agents (available to the whole mankind) is one of most ambitious dreams of the industrial medicinal chemistry. Semi-synthetic βlactam antibiotics are very effective anti-infective agents. They are very stable and can be used via oral delivery. They exhibit a very wide spectrum of anti-bacterial activity and minimal side effects after being massively used for a very long time. In this way, we can assume that semi-synthetic β-lactam antibiotics are going to be one of the key anti-infective agents in the next years. The condensation of natural or modified antibiotic nuclei with different acyl donor chains is one of the key steps for the industrial synthesis of these anti-infective agents. Up to now, these condensations are mainly carried out through classical chemical methods and this implies a number of economical, ecological and technological drawbacks (high energy requirements, many protection and deprotection steps, utilization of toxic methylene chloride as solvent, etc). Enzyme biocatalysts may be very useful to catalyse these selective condensations under very mild experimental and environmental conditions. In fact, the possibility of using enzymes to carry out such biotransformations, at laboratory scale, has been discussed and demonstrated a long time ago. However, industrial synthesis of βlactamic antibiotics is still carried out via unfavorable chemical routes. In fact, enzymes have not been produced in the nature to act in industrial reactors; so they are usually very unstable, inhibited by substrates and products and they may not have ideal catalytic properties for industrial uses (high reaction rates, required selectivity, ability to reach quantitative synthetic yields, stable enough to run a number of reaction cycles, etc). These limitations of enzyme biocatalysis become even more significant mainly when the enzyme is going to be used with non-natural substrates, catalysing non-natural processes and working under non-conventional conditions. However, in the last ten years, a great number of papers have reported substantial improvement of these enzymatic synthetic approaches (new enzymes, better enzyme derivatives, improved reaction designs and so on) and it seems that a massive industrial implementation of enzymes in antibiotic synthesis is approaching. In this review, we would like to make a critical discussion of these very interesting advances in the application of enzyme biocatalysts for the industrial synthesis of semi-synthetic antibiotics.