Design, synthesis and application of chiral tetraoxacalix[2]arene[2]triazine‐based organocatalysts in asymmetric Michael addition reactions

Organocatalysis for the Asymmetric Michael Addition of Aldehydes and α,β-Unsaturated Nitroalkenes

Michael addition is an important reaction because it can be used to synthesize a wide range of natural products or complex compounds that exhibit biological activities. In this study, a mirror image of an aldehyde and α,β-unsaturated nitroalkene were reacted in the presence of (R,R)-1,2-diphenylethylenediamine (DPEN). Herein, thiourea was introduced as an organic catalyst, and a selective Michael addition reaction was carried out. The primary amine moiety of DPEN reacts with aldehydes to form enamines, which is activated by the hydrogen bond formation between the nitro groups of α,β-unsaturated nitroalkenes and thiourea. Our aim was to obtain an asymmetric Michael product by adding 1,4-enamine to an alkene to form a new carbon–carbon bond. As a result, the primary amine of the chiral diamine was converted to an enamine. The reaction proceeded with a relatively high degree of enantioselectivity, which was achieved using double activation via hydrogen bonding of the nitro group and thiourea. Michael products with a high degree of enantioselectivity (97–99% synee) and diastereoselectivity (syn/anti = 9/1) were obtained in yields ranging from 94–99% depending on the aldehydes.

Toxicological evaluation of ionic liquid in a biological functional tissue construct model based on nano-hydroxyapatite/chitosan/gelatin hybrid scaffolds

The application of ionic liquid is attracting more attentions as green replacement for volatile organic solvents. However, the toxic effects and risks of ionic liquid in different biological systems for human health and environment are poorly evaluated. Among all ionic liquids, 1-ethyl-3-methylimidazolium diethylphosphate ([Emim]DEP-type) ionic liquid is still at the early phase of development, and its toxicity remains unclear. In this study, we fabricated a 3D biological functional tissue construct model based on nano-hydroxyapatite, chitosan and gelatin hybrid scaffold and evaluated its toxic effects of [Emim]DEP-type ionic liquid. As a control group, the examination of ionic liquid's toxic effects on the pre-osteoblast cell line (MC3T3-E1) was detected in 2D cultures. The MTT assay showed that [Emim]DEP-type ionic liquid inhibited the proliferation of cells on both 2D cultures and 3D tissue constructs. This effect was correlated with culturing time and concentration, while the IC50 on 3D scaffolds (12,566, 9015, 7896 μg/mL, at 24 h, 48 h and 72 h, respectively) was found significantly higher compared to 2D cultures (3959, 2226, 1884 μg/mL). Flow cytometry analysis and scanning electron microscope demonstrated that when [Emim]DEP-type ionic liquid acted on MC3T3-E1 cells for 48 h, the shape of 2D cells shrank, together with decreased surface adhesion.

Effective asymmetric Michael addition of anthrone to nitroalkenes using chiral tetraoxacalix[2]arene[2]triazines as organocatalysts

Novel chiral secondary amines bearing a tetraoxacalix[2]arene[2]triazine scaffold were created and used for catalytic asymmetric Michael reaction of anthrone with nitroalkenes. The relevant adducts were obtained in good to excellent yields (82%-98%) and enantioselectivities (75%-98%).

Enantioselective Michael reaction of anthrone catalyzed by chiral tetraoxacalix[2]arene[2]triazine derivatives

A highly enantioselective Michael addition reaction of anthrone with nitroalkenes by chiral tetraoxacalix[2]arene[2]triazine catalysts was investigated as a novel topic. The stereoselective conversion progressed smoothly by employing 10 mol% of the catalyst and afforded the corresponding Michael adducts with acceptable to high enantioselectivities (up to 97% ee) and very high yields (up to 96%).