This review describes the remarkable transition in the manufacture of β‐lactam antibiotics, which is driven by the desire to reduce or eliminate the production of waste and the dependence on organic solvents. To this effect, traditional chemical procedures are gradually being replaced by biotransformations. The β‐lactam antibiotics industry has led the way in the introduction of biocatalysis in the fine chemicals industry by replacing the chemical multi‐step process for the penicillin nucleus 6‐aminopenicillanic acid (6‐APA) by an enzymatic one in the early 1990's. Recently, bioprocesses have been developed for the synthesis of the cephalosporin nucleus, 7‐aminodeacetoxycephalosporanic acid (7‐ADCA) from a penicillin precursor and will shortly be commercialized. Thirty years of research have now resulted in viable enzymatic procedures for coupling the β‐lactam nuclei with D‐phenylglycine side‐chains. The necessary adaptations in the synthesis of the side‐chain donors have likewise resulted in more efficient procedures. 1 Introduction 2 Semi‐Synthetic β‐Lactam Antibiotics: Industrial Production Prior to 1985 3 Biocatalytic Synthesis of β‐Lactam Nuclei 3.1 6‐Aminopenicillanic Acid 3.2 7‐Aminodeacetoxycephalosporanic Acid 4 Biocatalytic Routes to Side‐Chains 4.1 Synthesis of the Side‐Chain Building Blocks 4.2 Synthesis of Activated Side‐Chain Donors 5 Enzymatic Coupling of the Side‐Chains to the β‐Lactam Nuclei 5.1 Chemical Procedures 5.2 Enzymatic Coupling 5.3 Practical Procedures for Enzymatic Coupling6 Conclusion and Future Outlook

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A truly catalytic procedure is described for the esterification of a-amino acids, thereby circumventing the formation of stoichiometric quantities of salts associated with conventional procedures. The acid form of ultrastable zeolite Y (H-USY), a naphtha cracking catalyst, acted as a solid acid catalyst in the reaction of several a-amino acids with methanol at 100-130 °C (15-20 bar). For example, L-phenylalanine afforded the methyl ester in 83% yield after 20 h at 100 °C. Based on the (unlikely) participation of all the Al atoms of the zeolite this corresponded to a turnover number of 180. The ester product was partially racemised (52% ee). Phenylglycine, p-hydroxyphenylglycine and homophenylalanine were similarly converted to their methyl esters. The H-USY catalyst could be recycled albeit with decreased activity after each cycle owing to the adsorption of water (formed in the reaction). Its activity was completely restored, however, after calcination.