Click Chemistry in Lead Optimization of Boronic Acids as β-Lactamase Inhibitors

Abstract

Boronic acid transition state inhibitors (BATSIs) represent one of the most promising class of β-lactamase inhibitors. Here we describe a new class of BATSIs, namely 1-amido-2-triazolylethaneboronic acids, which were synthesized combining the asymmetric homologation of boronates with Copper-Catalyzed Azide-Alkyne Cycloaddition (CuAAC) for the stereoselective insertion of the amido group and the regioselective formation of the 1,4-disubstituted triazole, respectively. This synthetic pathway, which avoids intermediate purifications, proved to be flexible and efficient, affording in good yields a panel of fourteen BATSIs bearing three different R1 amide side chains (acetamido, benzylamido and 2-thienylacetamido) and several R substituents on the triazole. This small library was tested against two clinically relevant class C β-lactamases from Enterobacter spp. and Pseudomonas aeruginosa. The Ki value of the best compound (13a) was as low as 4 nM with significant reduction of bacterial resistance to the combination of cefotaxime/13a.

Boronic Acid Transition State Inhibitors Active against KPC and Other Class A β-Lactamases: Structure-Activity Relationships as a Guide to Inhibitor Design

“…In addition, at position R2, a substituted phenyl or triazole resulted in lower IC 50 s. Finally, the change of amide into sulfonamide or urea was beneficial (26), while the thiourea was not active. We also discovered that against SHV-1 ␤-lactamase, and more strikingly against KPC-2, compound 2b exhibited a time-dependent inactivation, a behavior that was previously observed for other ␤-lactamases when inactivated with BATSIs (19,24). By identifying common features of these new BATSIs, novel SAR studies to target KPC-2 and other clinically important ␤-lactamases can be performed with the aim of determining key amino acid residues in the catalytic pocket that contribute to molecular recognition.…”

“…For the triazole-containing BATSIs, a Cu-catalyzed azide-alkyne cycloaddition was performed on the suitable ␤-azido-boronate (19,20). A complete description of the organic synthesis of compound 3c is provided in the supplemental material.…”

“…The IC 50 s were determined after a 5-min preincubation of the ␤-lactamase (7 nM KPC-2 or 2.5 nM SHV-1) and the BATSI used at increasing concentrations as previously described (19). The initial velocities (v 0 ) of hydrolysis of the indicator substrate, nitrocefin (⌬ε 482 ϭ 17,400 M Ϫ1 cm Ϫ1 ), were measured, and the data were fit to equation 1.…”

“…Mechanistically, the boronic inhibitors act by binding to the active site of the enzyme, where they sterically resemble the quaternary transition state of the ␤-lactam hydrolysis reaction and occupy the active site with high affinity, leading to inhibition in a reversible competitive manner (9). Recently, rational inhibitor design efforts were directed toward the inclusion of an R1 side chain on BATSIs that resembles the side groups of known ␤-lactams (19). This feature is necessary for specific interactions with the ␤-lactamases.…”

Inhibition of Acinetobacter-Derived Cephalosporinase: Exploring the Carboxylate Recognition Site Using Novel β-Lactamase Inhibitors

“…Specific localized modifications were easily introduced using the flexible and efficient synthesis previously described which relies on “click chemistry”, specifically, the well-known copper-catalyzed azide–alkyne cycloaddition (CuAAC). 12 According to this procedure, the substituted triazole moiety is formed by reaction of the chiral boronic scaffold 1 , bearing both the R1 thienylacetamido side chain and an azido group, with the proper mono-substituted alkyne (Scheme 2). These alkynes are specifically chosen to introduce rational variation of the carboxylate.…”