Combined Role of the Asymmetric Counteranion-Directed Catalysis (ACDC) and Ionic Liquid Effect for the Enantioselective Biginelli Multicomponent Reaction.

This work describes new chiral task-specific ionic liquids bearing chiral anions as the catalysts for the enantioselective multicomponent Biginelli reaction. For the first time, the combined role of asymmetric counteranion-directed catalysis (ACDC) and ionic liquid effect (ILE) for the chiral induction in the Biginelli multicomponent reaction is demonstrated. The chiral induction arises from a supramolecular aggregate where the anion and the cation of the catalyst are alongside with a key cationic intermediate of the reaction. Each component of the new catalyst had a vital role for the chiral induction success. The mechanism of an asymmetric version of this multicomponent reaction is in addition demonstrated for the first time using electrospray (tandem) mass spectrometry, ESI-MS(/MS). The analyses indicated the reaction takes place preferentially and exclusively through the iminium mechanism. Unprecedented supramolecular aggregates were detected by ESI-MS and characterized by ESI-MS/MS. No intermediate of the other two possible reactions pathways could be detected. Theoretical calculations shed light on the transition state of the transformation during the key step of the chiral induction and helped to elucidate the roles of the chiral anion (ACDC contribution) and of the imidazolium-containing nonchiral cation derivative (ILE contribution) in the molecular reaction process.

Heteropolyacid-Containing Ionic Liquid-Catalyzed Multicomponent Synthesis of Bridgehead Nitrogen Heterocycles: Mechanisms and Mitochondrial Staining.

The current manuscript describes the use of a heteropolyacid-containing task-specific ionic liquid, supported in imidazolium-based ionic liquids, as the catalyst for an efficient multicomponent synthesis of hexahydroimidazo[1,2-α]pyridine derivatives. The reactions conditions were fully optimized, and the bridgehead nitrogen heterocycle derivatives could be obtained in just 1 h exclusively as a single isomer ( trans). Single crystal X-ray analysis confirmed the trans derivative as the only isomer. The mechanism of the reaction was investigated by ESI(+)-MS(/MS), and the use of the elegant charge-tag strategy allowed a catalytic cycle to be proposed for the current transformation and revealed the possibility of at least two reaction pathways. One derivative bearing a coumarin scaffold was synthesized, and its fluorescent properties allowed it to be tested as a probe for live-cell imaging experiments with a preference for mitochondria.

Facts, presumptions, and myths on the solvent-free and catalyst-free Biginelli reaction. What is catalysis for?

The current manuscript describes the role and importance of catalysis and solvent effects for the Biginelli multicomponent reaction. The overwhelming number of new catalysts and conditions recently published for the Biginelli synthesis, including in some manuscripts entitled "catalyst-free" and/or "solvent-free" have incentivized controversies and hot debates regarding the importance of developing new catalysts and reaction conditions to perform this very important multicomponent reaction. These so-called "catalyst-free" reports have generated much confusion in the field, requiring urgent elucidations. In this manuscript, we exemplify, demystify, and discuss the crucial role of catalysis, solvent effects, mechanisms, kinetics, facts, presumptions, and myths associated with the Biginelli reaction aiming to avoid current and future confusion and to stimulate new approaches.

Probing deep into the interaction of a fluorescent chalcone derivative and bovine serum albumin (BSA): an experimental and computational study.

In the present manuscript, a novel fluorescent chalcone derivative is synthesized and its photophysical properties are fully characterized. The designed fluorophore is applied as a probe to study protein-dye interactions with bovine serum albumin. Circular dichroism gave interesting results on the thermodynamics of the interaction. NMR spectroscopy, especially relaxation measurements, revealed the atoms in the chalcone derivative that interacts with the protein upon binding. Molecular docking calculations indicate that the most favourable binding sites are near the two tryptophan residues. Furthermore, ab initio and DFT calculations offer insights into the reactivity and physicochemical properties of this novel fluorophore.