The utility of wild-type and variant carboxymethylproline synthases for biocatalysis was demonstrated by preparing functionalised 5-, 6- and 7-membered N-heterocycles from amino acid aldehydes and (alkylated) malonyl-coenzyme A derivatives; the N-heterocycles produced were converted to the corresponding bicyclic β-lactams by a carbapenem synthetase.

Formaldetected: Application of 1H- and 1D 13C HSQC NMR spectroscopy methods for monitoring the activity of a 2-oxoglutarate dependent histone Nε-methyllysine demethylase (JMJD2E) enabled the in situ quantitative analysis of the different components of the reaction, including the direct observation of hydrated formaldehyde resulting from enzyme-catalysed demethylation.

L-Glutamate semialdehyde (L-GSA) is an intermediate in biosynthetic pathways including those leading to the carbapenem antibiotics. We describe studies on asymmetric deuteration or hydrogenation of appropriate didehydro-amino acid precursors for the stereoselective synthesis of C-2- and/or C-3-[2H]-labelled L-GSA suitable for use in mechanistic studies. Regioselective deuterium incorporation into the 5-position of L-GSA was achieved using a labelled form of the Schwartz reagent (Cp2Zr2HCl). 4,4-Dideuterated and fully backbone deuterated L-GSAs were prepared. The application of the labelled L-GSA derivatives to biosynthetic studies was exemplified by the chemo-enzymatic preparation of selectively deuterated trans-carboxymethylprolines using two different carboxymethylproline synthases (CarB and ThnE), enzymes that catalyse early steps in the biosynthesis of two carbapenems: (5R)-carbapenem-3-carboxylate and thienamycin, respectively.

Unusual antibiotic biosynthesis enzymes: The observation that formation of trans-carboxymethylproline (t-CMP) and 6-methyl-t-CMP is catalyzed by ThnE from Streptomyces cattleya using glutamate semi-aldehyde and malonyl- or methylmalonyl-CoA implies the need for a C-5 epimerization step in the biosynthesis of thienamycin and reveals the possibility that a methyl group at C-6 might be introduced at an early stage.

Three of a kind: Vicinal tricarbonyl compounds undergo C-C cleavage mediated by ferric ions (see scheme). The observed cleavage of ninhydrin and dehydroascorbic acid has relevance for amino acid detection and the metabolism of vitamin C.

Enzyme in action: Labeling studies and the finding that carboxymethylproline synthase catalyzes production of deuterated (2S,5S)-6,6′-dimethyl-trans-carboxymethylproline (3) from dimethylmalonyl-CoA (1) and labeled l-pyrroline-5-carboxylate (2) limit possible mechanisms of C-C bond formation and thioester hydrolysis. A key feature in the catalysis is that intermediates are stabilized by hydrogen bonds in the “oxy-anion hole” of the enzyme (dark curve in scheme).

Structural and mechanistic studies on the crotonase superfamily (CS) are reviewed with the aim of illustrating how a conserved structural platform can enable catalysis of a very wide range of reactions. Many CS reactions have precedent in the ‘carbonyl’ chemistry of organic synthesis; they include alkene hydration/isomerization, aryl-halide dehalogenation, (de)carboxylation, CoA ester and peptide hydrolysis, fragmentation of β-diketones and C-C bond formation, cleavage and oxidation. CS enzymes possess a canonical fold formed from repeated ββα units that assemble into two approximately perpendicular β-sheets surrounded by α-helices. CS enzymes often, although not exclusively, oligomerize as trimers or dimers of trimers. Two conserved backbone NH groups in CS active sites form an oxyanion ‘hole’ that can stabilize enolate/oxyanion intermediates. The range and efficiency of known CS-catalyzed reactions coupled to their common structural platforms suggest that CS variants may have widespread utility in biocatalysis.