Identification and characterisation of shunt metabolites from isopenicillin N synthase

γ-Lactam formation from tripeptides with isopenicillin N synthase

“…We have rationalised these results in terms of an enzyme-bound monocyclic intermediate, involving an oxoiron moiety (3) which subsequently forms the second ring.1 Evidence for such a monocyclic intermediate also follows from kinetic isotope studies4 and the isolation of a 'shunt' metabolite. 5 In contrast to the aminocarboxypentanoyl and valinyl residues, informative substrate analogues of the cysteinyl residues have been few. No products were detected when tripeptide (4) or (5), containing L-serine or L-aminobutyrate, was incubated with IPNS.6 Recent work has involved more subtle changes;7 thus, for example ~,~,~-A-[(3R)-methylcysteinyll-V (6) gave the penam (7), but the corresponding (3s)-methylcysteinyl peptide (8) was not a substrate for IPNS.…”

The reaction cycle of isopenicillin N synthase observed by X-ray diffraction

“…4). This type of fragmentation has been found in penicillins and monocyclic lactams in reactions that cause positive polarization of the sulphur atom 13,14 . On the other hand, such reduction of electron density on the nitrogen in ACV would inhibit the reaction that forms the ␤-lactam C-N bond.…”

The biosynthesis of plant alkaloids and nitrogenous microbial metabolites

“…Jluorescens and it is also biosynthesized via L-p-aminophenylalanine (96). 75 The way in which [U-13C]glucose labelled C-1 and C-2 of ( 91) is consistent with glycine being a precursor for these atoms plus the C-2 amino group.…”

“…~~ The labelling pattern for C-3 through to (2-10 of obafluorin, see (94), was that expected for biosynthesis via an aromatic amino acid like phenylalanine (77). Whilst tritiated samples of L-phenylalanine and L-p-nitro-phenylalanine (95) were very poor precursors, L-[2,6-3H,]-p-aminophenylalanine [as (96)] was an excellent precursor. This amino acid (96) was thus identified75 as an intermediate in the biosynthesis of obafluorin (91), as it is in that of chloramphenicol (93).…”

“…Whilst tritiated samples of L-phenylalanine and L-p-nitro-phenylalanine (95) were very poor precursors, L-[2,6-3H,]-p-aminophenylalanine [as (96)] was an excellent precursor. This amino acid (96) was thus identified75 as an intermediate in the biosynthesis of obafluorin (91), as it is in that of chloramphenicol (93). 'v8 Since phenylalanine is not a precursor for obafluorin, amination must occur at a prearomatic stage, probably on chorismic acid (86), just as found for chloramphenicol.…”