Highly diastereo- and enantioselective direct aldol reaction under solvent-free conditions

N-(Sulfamoylbenzoyl)-L-proline Derivatives as Potential Non-β-lactam ESBL Inhibitors: Structure-Based Lead Identification, Medicinal Chemistry and Synergistic Antibacterial Activities

Background:

There is an urgent need to develop novel inhibitors against clinically widespread extended-spectrum β-lactamases (ESBLs) to meet the challenges of the ever-evolving threat of antibiotic resistances. Most existing ESBL inhibitors sharing a common chemical feature of β-lactam ring in their molecule, this structural characteristic makes them intrinsically susceptible to enzymatic breakdown by the resistance mechanisms employed by the bacteria.

Objective:

The aim of this study was to screen and discover novel lead compounds by using Lproline as initial scaffold to create a “non-sulfur, non-β-lactam” new chemotypes for potential ESBL inhibitors.

Methods:

Structure-based molecular docking and virtual screening were employed in the novel inhibitor generation process for lead compound screening and SAR analysis. Evaluation of the ESBL inhibitory activity of the lead compounds was performed in combination with three of the most susceptible antibiotics: ceftazidime, meropenem and ampicillin, against thirteen ESBL enzymes including four new CTX-M harboring strains and four KPC-2 producing species.

Results:

L-proline derived (S)-1-(2-sulfamoylbenzoyl)pyrrolidine-2-carboxylic acid (compound 6) as a “non-sulfur, non-β-lactam” and the most potential ESBL inhibitor was identified. Compound 6 possesses ideal anti-resistance activities by reducing MICs of ceftazidime, meropenem and ampicillin by 16-133, 32-133 and 67-267 fold respectiveily. The inhibitory mechanism of 6 with CTX-M, KPC-2 and penicillinase were proposed and probed with molecular docking analysis.

Conclusion:

Given that the simple proline derivative but promising synergistic antibacterial properties of compound 6 augers well for further investigations into its in vivo efficacy.

Development of C2-Symmetric Chiral Bifunctional Triamines: Synthesis and Application in Asymmetric Organocatalysis

The synthesis and application of a newly designed C₂-symmetric chiral bifunctional triamine family ( C₂-CBT) is reported. These enantiopure chiral triamine scaffolds can be accessed in multigram amounts from simple amino acids while avoiding chromatographic purification. As a proof of principle, C₂-CBT has been studied in the aldol reaction of cyclic ketones with isatins, with the target tertiary alcohols being formed in a highly efficient manner. Catalyst recovery by simple extraction techniques and subsequent reuse has been performed.

Enantioselective solvent-free synthesis of 3-alkyl-3-hydroxy-2-oxoindoles catalyzed by binam-prolinamides

BINAM-prolinamides are very efficient catalyst for the synthesis of non-protected and N-benzyl isatin derivatives by using an aldol reaction between ketones and isatins under solvent-free conditions. The results in terms of diastereo- and enantioselectivities are good, up to 99% de and 97% ee, and higher to those previously reported in the literature under similar reaction conditions. A high variation of the results is observed depending on the structure of the isatin and the ketone used in the process. While 90% of ee and 97% ee, respectively, is obtained by using (Ra)-BINAM-l-(bis)prolinamide as catalyst in the addition of cyclohexanone and α-methoxyacetone to free isatin, 90% ee is achieved for the reaction between N-benzyl isatin and acetone using N-tosyl BINAM-l-prolinamide as catalyst. This reaction is also carried out using a silica BINAM-l-prolinamide supported catalyst under solvent-free conditions, which can be reused up to five times giving similar results.

Hydrogen-bonding in aminocatalysis: from proline and beyond

This Concept article summarizes recent progress in the field of hydrogen-bonding aminocatalysis using proline-derived systems. The aminocatalysts available in the literature are categorized by the incorporated hydrogen-bonding scaffold and its mode of recognition. Both mono- and double-hydrogen-bonding motifs are discussed and examples of their application in asymmetric synthesis are given.