Chitosan-supported cinchona urea: Sustainable organocatalyst for asymmetric Michael reaction

Microwave-assisted synthesis of crosslinked ureido chitosan for hemostatic applications

In this study, we present a facile method for introducing hydrophilic ureido groups (NH2-CO-NH-) into chitosan using a microwave-assisted reaction with molten urea, with the aim of enhancing chitosan's interaction with blood components for improved hemostasis. The formation of the ureido groups through nucleophilic addition reaction between the amine groups in chitosan and in situ generated isocyanic acid was confirmed by FTIR, CP/TOSS 13C NMR, and CP/MAS 15N NMR spectroscopic techniques. However, in stark contrast to the glucans, the said modification introduced extensive crosslinking in chitosan. Spectroscopic studies identified these crosslinks as carbamate bridges (-NH-COO-), which were likely formed by the reaction between the ureido groups and hydroxyl groups of adjacent chains through an isocyanate intermediate. These carbamate bridges improved ureido chitosan's environmental stability, making it particularly resistant to changes in pH and temperature. In comparison to chitosan, the crosslinked ureido chitosan synthesized here exhibited good biocompatibility and cell adhesion, rapidly arrested the bleeding in a punctured artery with minimal hemolysis, and induced early activation and aggregation of platelets. These properties render it an invaluable material for applications in hemostasis, particularly in scenarios that necessitate stability against pH variations and degradation.

Synthesis of cinchona urea polymers using Yamamoto coupling and their application to asymmetric reaction

Cinchona urea compounds having 3,5-diiodophenyl moieties were subjected to Yamamoto coupling polymerization to afford the chiral urea polymers. These polymers showed high activities as heterogeneous catalysts in asymmetric Michael reactions comparable with those of the corresponding monomeric catalyst in solution systems. Furthermore, the polymeric catalysts are easily recovered from their reaction mixtures due to their insolubility and can be reused several times without loss of catalytic activity.

Ni -chitosan/carbon nanotube: An efficient biopolymer -inorganic catalyst for selective hydrogenation of acetylene

This work developed an efficient Ni catalyst based on chitosan for selective hydrogenation of acetylene. The Ni catalyst was prepared by the reaction of the chitosan/carbon nanotube composite with NiSO₄ solution. The synthesized Ni-chitosan/carbon nanotube catalyst was characterized by inductively coupled plasma, FTIR, SEM and XRD. The results of FTIR and XRD demonstrated that Ni²⁺ successfully coordinated with chitosan. The addition of chitosan greatly improved the catalytic performances of Ni-chitosan/carbon nanotube catalyst. Over the Ni-chitosan/carbon nanotube catalyst, both the acetylene conversion and the selectivity to ethylene all achieved 100% at 160 °C and 190 °C, respectively. The catalytic performances of 6 mg Ni-chitosan/carbon nanotube catalyst were even better than that of 400 mg Ni single atom catalyst in literature. Extending the crosslinking time of chitosan and increasing the amount of the crosslinking agent were beneficial to enhance the catalytic effect of Ni-chitosan/carbon nanotube catalyst.

Synthesis and Applications of Carbohydrate-Based Organocatalysts

Organocatalysis is a very useful tool for the asymmetric synthesis of biologically or pharmacologically active compounds because it avoids the use of noxious metals, which are difficult to eliminate from the target products. Moreover, in many cases, the organocatalysed reactions can be performed in benign solvents and do not require anhydrous conditions. It is well-known that most of the above-mentioned reactions are promoted by a simple aminoacid, l-proline, or, to a lesser extent, by the more complex cinchona alkaloids. However, during the past three decades, other enantiopure natural compounds, the carbohydrates, have been employed as organocatalysts. In the present exhaustive review, the detailed preparation of all the sugar-based organocatalysts as well as their catalytic properties are described.

Chitosan as a chiral ligand and organocatalyst: preparation conditions–property–catalytic performance relationships

Properties of chitosan prepared by alkaline deacetylation of chitin under various conditions were correlated with their performance as ligands or organocatalysts in asymmetric catalytic reactions.

Simple primary β-amino alcohols as organocatalysts for the asymmetric Michael addition of β-keto esters to nitroalkenes

Simple primary β-amino alcohols act as an efficient organocatalysts in the asymmetric Michael addition of β-keto esters with nitroalkenes affording highly pure chiral Michael adducts. Also, both enantiomers of the adducts were obtained, depending on the specific catalyst used and reaction temperature.