Synthesis of N,4-diaryl substituted ?-lactams via Kinugasa cycloaddition/rearrangement reaction

Unraveling the synthetic strategy, structure activity relationship of azetidinones: Insights into their multidrug and toxin extrusion protein (MATE transporter) inhibition facilitating drug development against MDR

Heterocyclic chemistry gathered a wide audience due to their presence in potential drug candidates and being attractive synthons initiating several retro-syntheses the organic as well as in medicinal chemistry fields. Among them, azetidinones have been a subject of discussion due to their serendipity, curiosity, versatility by Penicillin and Cephalosporins as β-lactam antibiotics. Despite possessing a large margin of biological activities, azetidinones mainly work as antimicrobial, interfering with bacterial cell-wall synthesis blocking transpeptidase. The structure and synthetic strategy of the azetidinone arouse its research interest in drug discovery pipeline. However, the extensive use of antibiotics in the modern era contributes to drug resistance that could only be counterbalanced involving hybridization approach. To explore the potency of the azetidinones, potent compounds found from literatures, have been screened through molecular docking against MATE transporter, targeting for prevailing multidrug resistance. The present review makes a sincere effort to compile the synthetic information and orientations involving hybridization of azetidinones with biologically active scaffolds emphasizing on antimicrobial and anticancer efficacies along with their MATE inhibition, keeping an eye upon the structure activity relationship in a systematic way. The study could motivate the researchers for developing a wide array of β-lactam derivatives more prominently targeting newer pathways to fight MDR.

Synthesis of β-lactams via diastereoselective, intramolecular Kinugasa reactions

Intramolecular Kinugasa reactions on in situ generated carbohydrate-derived alkynylnitrones are described. The effects of the length of chains, their mutual configuration, influence of experimental conditions on product distribution and feasibility of the β-lactam ring construction were studied. Intramolecular reactions proceed with high stereoselectivity to provide in each case one product only. The cycloadducts from tartaric acid were converted into the corresponding non-racemic 4-acetoxy azetidinones in good yields.

Bypassing the stereoselectivity issue: transformations of Kinugasa adducts from chiral alkynes and non-chiral acyclic nitrones

An approach to β-lactams via a reaction between chiral copper acetylides and acyclic nitrones is reported. Electronic circular dichroism (ECD) in combination with NMR spectroscopy was used to determine the absolute configuration of all components of complex mixtures of azetidinones. Stereochemical preferences observed in the studied reactions are discussed and a model of a new reaction pathway supported by DFT conformational analysis is proposed. Subsequent transformations of the synthesized Kinugasa adducts followed by epimerization at the C-3 carbon atom led to trans-substituted azetidinones with improved stereoselectivity, mimicking a variety of important β-lactam structures. On the other hand, the oxidation of the furyl residue to the carboxylic group followed by oxidative decarboxylation with lead tetraacetate afforded the more thermodynamically stable trans-substituted 4-acetoxy azetidinone. The latter strategy is particularly attractive for the diastereomeric mixture in which isomers with the same configuration at the C-3 carbon atom dominate.

In Depth Analysis of Chiroptical Properties of Enones Derived from Abietic Acid

With the use of inexpensive commercially available abietic acid, a whole series of abietane enones were prepared in high yields. The structures of all the products obtained were determined by comprehensive spectroscopic analysis with particular emphasis on the use of advanced NMR techniques, comparison with previously reported data and, where possible, by single crystal X-ray diffraction. However, in cases where X-ray crystallography was not applicable or compounds tested were unstable, a final stereochemical assignment could be inferred only by electronic circular dichroism (ECD) supported by vibrational circular dichroism to increase credibility. To reveal the relationship between structure and chiroptical properties, we used combined experimental and theoretical analysis of geometries, structural parameters, and chiroptical properties of all enones synthesized. A thorough analysis of their conformational flexibility by examining the effect of solvent and temperature on the ECD spectra was also used to achieve desired objectives. As a result, the impact of substituents adjacent to the enone chromophore on the conformation was determined by demonstrating that even slight changes in the position of hydroxyl and isopropyl groups attached to carbon C13 may substantially affect ECD curves' pattern, leading in some cases to Cotton effects sign reversal.

A theophylline based copper N-heterocyclic carbene complex: synthesis and activity studies in green media

The synthesis of an easily accessible theophylline-derived copper complex with additional ammonium functionalization has been developed.