Cephalosporin biosynthesis: A branched pathway sensitive to an isotope effect

Article abstract of DOI:10.1016/S0040-4020(01)80725-0

Incubation of penicillin N (3a) with partially purified deacetoxy/deacetylcephalosporin C synthase (DAOC/DAC synthase) from Cephalosporium acremonium CO 728 gave in addition to the expected products, deacetoxycephalosporin C and deacetylcephalosporin C, a third β-lactam metabolite as a 3β-hydroxy-3α-methylcepham (9a). Production of the 3β-hydroxycepham was promoted from [3-²H]penicillin N (3b) which was rationalised by the operation of a kinetic isotope effect on a branched pathway in the enzymic process. The oxygen of the 3β-hydroxy group was shown to be derived in part from molecular oxygen. In addition, the 2β-methyl group of penicillin N was shown to be incorporated into C2 of the 3β-hydroxy-3α-methylcepham, a result in stereochemical accord with the equivalent transformation of the 2β-methyl group of penicillin N into C2 of deacetoxycephalosporin C¹. A mechanistic interpretation, consistent with these observations, is offered.