Cephalosporin biosynthesis: A branched pathway sensitive to an isotope effect

Roles of 2-oxoglutarate oxygenases and isopenicillin N synthase in β-lactam biosynthesis

“…Work with deuterium labelled penicillin N has shown that during the DAOCS reaction, a hydrogen is removed from the (pro- S ) β-methyl group prior to loss of the C-3 hydrogen. 104 , 105 Further, incubation with (3- 2 H)penicillin N resulted in a substantial increase in the observed amount of 3β-hydroxy-3α-methylcepham ( Fig. 7C ), which is only otherwise observed as a minor by-product.…”

Shape‐Selective Interception by Hydrocarbons of the O2‐Derived Oxidant of a Biomimetic Nonheme Iron Complex

“…[15,17] In various metalloenzymes, substrate hydroxylation and dehydrogenation are in fact related transformations that are controlled by the interactions of the substrate with the active-site pocket. [18] DFT calculations indicate that the outcome of the C À H bond oxidation depends on what happens after the rate-determining C À H bond cleavage step. [19] Oxygen rebound from the iron center to the incipient alkyl radical generates the alcohol, while oxidation of the alkyl radical to a carbocation leads to dehydrogenation.…”

Studies on the active site of deacetoxycephalosporin C synthase

“…Binding of penicillin N (1) (and 2-oxoglutarate) probably occurs to an open form of the enzyme. Binding of penicillin N (1) may also assist dioxygen binding via displacement of the water molecule ligated to Isotopic labelling experiments have demonstrated that cleavage of a C-H bond of the penicillin pro-S methyl group occurs before cleavage of the C-3 C-H bond (Baldwin et al, 1991): Binding of penicillin N (1) in the proposed manner projects this methyl group directly towards the iron centre whilst the C-3 C-H bond is further away. The isolated nature of the active site in the closed form, the distance of the thiazolidine sulphur from the iron and the requirement for (at least) one of the iron ligands to be decomplexed renders mechanisms involving complexing of the penam sulphur to the iron unlikely.…”

“…The hydroxylation of (2) to give (3) may be regarded as a typical type of reaction catalysed by 2-oxoglutarate utilising dioxygenases, but the oxidative ring expansion of (1) to give (2) is unique. Labelling studies on the mechanism of ring expansion indicate that cleavage of the C-H bond of the b-methyl group precedes that of the C-2 C-H bond (Baldwin et al, 1991) and have provided evidence for a methylene radical intermediate (Pang et al, 1984;Townsend et al, 1985).…”