Tyramine derivatives catalyze the aldol dimerization of butyraldehyde in the presence of E. coli

Biogenic amine organocatalysts have transformed the field of synthetic organic chemistry. Yet despite their use in synthesis and to label biomolecules in vitro, amine organocatalysis in vivo has received comparatively little attention – despite the potential of such reactions to be interfaced with living cells and to modify cellular metabolites. Herein we report that biogenic amines derived from L‐tyrosine catalyze the self‐aldol condensation of butanal to 2‐ethylhexenal – a key intermediate in the production of the bulk chemical 2‐ethylhexanol – in the presence of living Escherichia coli and outperform many amine organocatalysts currently used in synthetic organic chemistry. Furthermore, we demonstrate that cell lysate from E. coli and the prolific amine overproducer Corynebacterium glutamicum ATCC 13032 catalyze this reaction in vitro, demonstrating the potential for microbial metabolism to be used as a source of organocatalysts for biocompatible reactions in cells

Phenylalanine meta‐hydroxylase:A single residue mediates mechanistic control of aromatic amino acid hydroxylation

This work was supported by a project grant from the Biotechnology and Biological Sciences Research Council (BBSRC) U. K to R. J. M. G. (BB/I022910/2), and by the European Research Council under the European Union’s Seventh Framework Programme (FP7-3013/ERC grant agreement no 614779 GenoChemetics).The rare non-proteinogenic amino acid, meta- L-tyrosine is biosynthetically intriguing. Whilst the biogenesis of tyrosine from phenylalanine is well characterised, the mechanistic basis for meta-hydroxylation is unknown. Herein, we report the analysis of 3-hydroxylase (Phe3H) from Streptomyces coeruleorbidus. Insight from kinetic analyses, of both the wild-type enzyme and key mutants, of the biocatalytic conversion of synthetic isotopically labelled substrates and fluorinated substrate analogues advances understanding of the process by which meta-hydroxylation is mediated, revealing T202 to play an important role. In contrast to the established mechanism of tyrosine biogenesis, which proceeds via NIH shift, our data support direct, enzyme catalysed deprotonation following electrophilic aromatic substitution. We demonstrate that T202 is responsible for this shift in mechanism, with mutation to alanine resulting in a switch to the NIH shift mechanism and loss of regiospecificity. Furthermore, our kinetic parameters for Phe3H show efficient regiospecific generation of meta-L-tyrosine from phenylalanine and demonstrate the enzyme's ability to regiospecifically hydroxylate unnatural fluorinated substrates.Publisher PDFPeer reviewe

Imidazolium-tagged glycan probes for non-covalent labeling of live cells

The use imidazolium tagged-mannosamine derivative for the non-covalent, rapid and site-specific labeling of sialic acid containing glycoproteins using commercialN-nitrilotriacetate fluorescent reagents in a range of live cells is reported.</p

Chemoselective sequential click ligations directed by enhanced reactivity of an aromatic ynamine

Aromatic ynamines or N-alkynylheteroarenes are highly reactive alkyne components in Cu-catalyzed Huisgen [3 +2] cycloaddition (“click”) reactions. This enhanced reactivity enables the chemoselective formation of 1,4-triazoles using the representative aromatic ynamine N-ethynylbenzimidazole in the presence of a competing aliphatic alkyne substrate. The unique chemoselectivity profile of N-ethynylbenzimidazole is further demonstrated by the sequential click ligation of a series of highly functionalized azides using a heterobifunctional diyne, dispelling the need for alkyne protecting groups

Structural and functional basis of C-methylation of coumarin scaffolds by NovO

C-methylation of aromatic small molecules by C-methyltransferases (C-MTs) is an important biological transformation that involves C–C bond formation using S-adenosyl-l-methionine (SAM) as the methyl donor. Here, two advances in the mechanistic understanding of C-methylation of the 8-position of coumarin substrates catalyzed by the C-MT NovO from Streptomyces spheroides are described. First, a crystal structure of NovO reveals the Arg116-Asn117 and His120-Arg121 motifs are essential for coumarin substrate binding. Second, the active-site His120 is responsible for deprotonation of the phenolic 7-hydroxyl group on the coumarin substrate, activating the rate-determining methyl transfer step from SAM. This work expands our mechanistic knowledge of C-MTs, which could be used in the downstream development of engineered biocatalysts for small molecule C-alkylations