Serine β-lactamase enzyme inhibition: design, stereoselective synthesis, and in vitro antibacterial evaluation

The aim of this contribution is to design, synthesize, characterize, and evaluate stereoselective ligands as inhibitors of the β-lactamase enzyme. Organic synthesis was performed via the Staudinger pericyclic cycloaddition [2 + 2]. Spectroscopic characterization of one of the compounds was carried out using 1 H, 13 C, and HSQC NMR, X-ray diffraction, infrared spectrophotometry, and mass spectrometry. In vitro activity was also assessed using the combined disk method. A chemical library of novel lactams, based on a ligand (clavulanic acid), was designed and evaluated by molecular docking. This evaluation yielded valuable information, concluding that the recognition of the control ligands anchoring occur at serines 70 and 130, which are associated with the catalytic binding site, where the serines act as hydrogen bond donors and the sp 2 oxygens of the ligands act as acceptors. Compound 5c SS showed a ΔG = −7.32 kcal/mol, indicating a higher affinity than clavulanic acid (ΔG = −6.27 kcal/mol) for the catalytic binding site. Interestingly, the conformations of compounds 5a , 5b , and 5c in the three rings are not coplanar, except for compound 5a RR , which showed low affinity. The organic synthesis was stereoselective for 5a and 5b , whose transition state suggests cis stereochemistry, as it exhibited a 3 J H-H of 5.5 Hz. In contrast, compound 5c , whose suggested transition state is trans, showed a 3 J H-H of 2.4 Hz, demonstrating the stereoselectivity of the cycloaddition dependent on the electronic effect of the substituents. Regarding the in vitro biological evaluation, amoxicillin with compound 5c inhibited the serine β-lactamase of Staphylococcus aureus (ATCC 29213) to a level comparable to amoxicillin with clavulanic acid. Curiously, the substitution in the aromatic ring from an aniline with an electron-withdrawing group (EWG) is more potent (compound 5c ), and with an electron-donating group (EDG) it is more effective (compound 5b ). This was obtained by the concentration-response curve (CRC). This is of utmost importance, as it enables mechanistic understanding and the development of new inhibitors of resistance in the medium term. • The anchoring and recognition portion corresponds to a sp 2 carbon‑carbonyl or thionyl oxygen. • The organic synthesis was stereoselective. • The in vitro test of amoxicillin with compound 5c and amoxicillin with clavulanic acid is comparable.