Beáta Vilhanová

Practical Aspects and Mechanism of Asymmetric Hydrogenation with Chiral Half-Sandwich Complexes

This review is oriented toward the asymmetric transfer hydrogenation (ATH) of imines regarding mostly fundamental, yet important topics from the practical point of view. Development of analytical methods for the monitoring of ATH (i.e., kinetics and stereoselectivity) belongs to those topics, as well as studies on the influence of reaction conditions and structural variations on the reaction performance. The second part is devoted to the reaction mechanism with the emphasis on imine ATH and catalyst behaviour under acidic conditions. The review also addresses the asymmetric hydrogenation (AH) of ketones and imines using molecular hydrogen and the application of ATH in pharmaceutical projects. The contributions of our group to each area are included.

New insight into the role of a base in the mechanism of imine transfer hydrogenation on a Ru(II) half-sandwich complex

Asymmetric transfer hydrogenation (ATH) of cyclic imines using [RuCl(η(6)-p-cymene)TsDPEN] (TsDPEN = N-tosyl-1,2-diphenylethylenediamine) was tested with various aliphatic (secondary, tertiary) and aromatic amines employed in the HCOOH-base hydrogen donor mixture. Significant differences in reaction rates and stereoselectivity were observed, which pointed to the fact that the role of the base in the overall mechanism could be more significant than generally accepted. The hydrogenation mixture was studied by nuclear magnetic resonance (NMR), Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) and vibrational circular dichroism (VCD) with infrared spectroscopy. The results suggested that the protonated base formed an associate with the active ruthenium-hydride species, most probably via a hydrogen bond with the sulfonyl group of the complex. It is assumed that the steric and electronic differences among the bases were responsible for the results of the initial ATH experiments.

Determination of cysteinyl leukotrienes in exhaled breath condensate: method combining immunoseparation with LC-ESI-MS/MS.

A rapid and precise method for the identification and quantification of cysteinyl leukotrienes (leukotriene C(4), leukotriene D(4) and leukotriene E(4)), essential markers of bronchial asthma, in exhaled breath condensate was developed. The protocol consists of immunoaffinity separation and a detection step, liquid chromatography combined with electrospray ionization tandem mass spectrometry (LC-ESI-MS/MS). In particular, the selected reaction monitoring mode was used for its extremely high degree of selectivity and the stable-isotope-dilution assay for its high precision of quantification. The developed method was characterized with a high precision (≤ 7.7%, determined as RSD), an acceptable accuracy (90.4-93.7%, determined as recovery), a low limit of detection (≤ 2 pg/ml EBC) and a low limit of quantification (≤ 10 pg/ml EBC). It was compared to other simple, clinically appropriate combinations of pre-treatment methods (solid phase extraction and lyophilization) with LC/MS. Finally, the method (a combination of immunoaffinity separation with LC-MS) was successfully tested in a clinical study where a significant difference was found in the concentration levels of cysteinyl leukotrienes between patients with occupational bronchial asthma and healthy subjects.

Experimental and Theoretical Perspectives of the Noyori-Ikariya Asymmetric Transfer Hydrogenation of Imines

The asymmetric transfer hydrogenation (ATH) of imines catalyzed by the Noyori-Ikariya [RuCl(η6-arene)(N-arylsulfonyl-DPEN)] (DPEN = 1,2-diphenylethylene-1,2-diamine) half-sandwich complexes is a research topic that is still being intensively developed. This article focuses on selected aspects of this catalytic system. First, a great deal of attention is devoted to the N-arylsulfonyl moiety of the catalysts in terms of its interaction with protonated imines (substrates) and amines (components of the hydrogen-donor mixture). The second part is oriented toward the role of the η6-coordinated arene. The final part concerns the imine substrate structural modifications and their importance in connection with ATH. Throughout the text, the summary of known findings is complemented with newly-presented ones, which have been approached both experimentally and computationally.

Molecular Structure Effects in the Asymmetric Transfer Hydrogenation of Functionalized Dihydroisoquinolines on ( S , S )-[RuCl( η 6 - p -cymene)TsDPEN]

The asymmetric transfer hydrogenation of five dihydroisoquinolines (DHIQs) was studied by NMR spectroscopy. The DHIQs differed by substitution with methoxy groups, which had a significant effect upon the reaction performance in terms of reaction rate and enantioselectivity. The differences are most probably related to the basicity of DHIQs.Graphical Abstract

Synthesis and characterization of two new chiral Kemp’s acid derivatives: structures fixed by a peculiar system of N–H···O, C–H···O and C–H···N hydrogen bonds

Abstract New chiral imide-oxazoline derivatives of Kemp’s acid were synthesized with the aim to produce new ligands suitable for catalytic asymmetric reactions. Compound 1 is C18H28N2O3, systematic name (1R, 5S, 7R)-7-[(S)-4-tert-butyl-4,5-dihydrooxazole-2-yl]-1,5,7-trimethyl-3-azabicyclo-[3.3.1]-nonane-2,4-dione. Compound 2 is C21H26N2O3, systematic name (1R,5S,7R)-7-[(S)-4-benzyl-4,5-dihydrooxazole-2-yl]-1,5,7-trimethyl-3-azabicyclo-[3.3.1]-nonane-2,4-dione. Both compounds contain two molecules with very similar conformations in the asymmetric unit. The two structures were characterized by single crystal X-ray diffraction. DFT calculations of two possible distinct conformations were performed to elucidate the differences between the preferred conformation in vacuo and the one observed in the single crystal. Also, charges on the key atoms of the compounds were compared with a common ligand used for asymmetric transfer hydrogenation.