A possible mechanism for penicillin biosynthesis involves the rearrangement of a 5- isothiazolidinonyl radical (6) to a β-lactam. However, generation of the model radicals (13 and 20) did not lead to β-lactams. The analogous reaction of a 5-isoxazolidinonyl radical is the basis for a potential synthesis of clavulanic acid, but again the rearrangement was not observed in the model radical (24).
