Lena Decuyper

Antibacterial and β-Lactamase Inhibitory Activity of Monocyclic β-Lactams

Due to the widespread emergence of resistant bacterial strains, an urgent need for the development of new antibacterial agents with novel modes of action has emerged. The discovery of naturally occurring monocyclic β‐lactams in the late 1970s, mainly active against aerobic Gram‐negative bacteria, has introduced a new approach in the design and development of novel antibacterial β‐lactam agents. The main goal was the derivatization of the azetidin‐2‐one core in order to improve their antibacterial potency, broaden their spectrum of activity, and enhance their β‐lactamase stability. In that respect, our review covers the updates in the field of monocyclic β‐lactam antibiotics during the last three decades, taking into account an extensive collection of references. An overview of the relationships between the structural features of these monocyclic β‐lactams, classified according to their N‐substituent, and the associated antibacterial or β‐lactamase inhibitory activities is provided. The different paragraphs disclose a number of well‐established classes of compounds, such as monobactams, monosulfactams, monocarbams, monophosphams, nocardicins, as well as other known representative classes. Moreover, this review draws attention to some less common but, nevertheless, possibly important types of monocyclic β‐lactams and concludes by highlighting the recent developments on siderophore‐conjugated classes of monocyclic β‐lactams.

A nitrilase-mediated entry to 4-carboxymethyl-β-lactams from chemically prepared 4-(cyanomethyl)azetidin-2-ones

(3R,4S)-3-Alkoxy/aryloxy-4-(cyanomethyl)azetidin-2-ones were efficiently prepared from readily available 1,2:5,6-di-O-isopropylidene-D-mannitol by means of a classical organic synthesis approach via 4-hydroxymethyl-β-lactams as key intermediates. The corresponding 4-carboxymethyl-β-lactams were subsequently obtained after selective hydrolysis of the nitrile functionality by means of a nitrilase enzyme without affecting the sensitive four-membered ring system, hence overcoming the difficulties associated with the chemical hydrolysis approach. Thus, the implementation of a biocatalytic step allows a convenient synthetic route to new 4-carboxymethyl-β-lactams as versatile building blocks for further elaboration.

In Silico Design and Enantioselective Synthesis of Functionalized Monocyclic 3-Amino-1-carboxymethyl-β-lactams as Inhibitors of Penicillin-Binding Proteins of Resistant Bacteria

As a complement to the renowned bicyclic β-lactam antibiotics, monocyclic analogues provide a breath of fresh air in the battle against resistant bacteria. In that framework, the present study discloses the in silico design and unprecedented ten-step synthesis of eleven nocardicin-like enantiomerically pure 2-{3-[2-(2-aminothiazol-4-yl)-2-(methoxyimino)acetamido]-2-oxoazetidin-1-yl}acetic acids starting from serine as a readily accessible precursor. The capability of this novel class of monocyclic 3-amino-β-lactams to inhibit penicillin-binding proteins (PBPs) of various (resistant) bacteria was assessed, revealing the potential of α-benzylidenecarboxylates as interesting leads in the pursuit of novel PBP inhibitors. No deactivation by representative enzymes belonging to the four β-lactamase classes was observed, while weak inhibition of class C β-lactamase P99 was demonstrated.

Exploring the sequence diversity in glycoside hydrolase family 13_18 reveals a novel glucosylglycerol phosphorylase

In the carbohydrate-active enzyme database, GH13_18 is a family of retaining glycoside phosphorylases that act on α-glucosides. In this work, we explored the functional diversity of this family by comparing distinctive sequence motifs in different branches of its phylogenetic tree. A glycoside phosphorylase from Marinobacter adhaerens HP15 that was predicted to have a novel function was expressed and characterised. The enzyme was found to catalyse the reversible phosphorolysis of 2-O-α-d-glucosylglycerol with retention of the anomeric configuration, a specificity that has never been described before. Homology modelling, docking and mutagenesis were performed to pinpoint particular acceptor site residues (Tyr194, Ala333, Gln336) involved in the binding of glycerol. The new enzyme specificity provides additional insights into bacterial metabolic routes, being the first report of a phosphorolytic route for glucosylglycerol in a glucosylglycerol-producing organism. Furthermore, glucosylglycerol phosphorylase might be an attractive biocatalyst for the production of the osmolyte glucosylglycerol, which is currently produced on industrial scale by exploiting a side activity of the closely related sucrose phosphorylase. Family GH13_18 has clearly proven to be more diverse than was initially assumed, and the analysis of specificity-determining sequence motifs has shown to be a straightforward and fruitful tool for enzyme discovery.