Enzymatic approach to syntheses of unnatural beta-lactams.

Four enzymes associated with the transformation of the peptide delta-(L-alpha-aminoadipyl)-L-cysteinyl-D-valine (ACV) into the beta-lactam antibiotic desacetylcephalosporin C have been isolated from the prokaryotic organism Streptomyces clavuligerus and immobilized. Appropriate choice of the cofactors allows continuous and quantitative conversion of the peptide into either penicillins or cephalosporins at room temperature. The overall process includes four oxidations, two ring closures, and one epimerization. In contrast, cell-free transformations with the eukaryotic organism Cephalosporium acremonium do not proceed beyond the oxidation level of penicillin. The amino acids of the natural peptide ACV can be altered by chemical means; several of the resulting peptides are converted into novel antibiotics by the enzymes of Streptomyces clavuligerus.