Amino alcohol-modified β-cyclodextrin inducing biomimetic asymmetric oxidation of thioanisole in water

Ultrasonication-Assisted Synthesis of a d-Glucosamine-Based β-CD Inclusion Complex and Its Application as an Aqueous Heterogeneous Organocatalytic System

For the first time, an inclusion complex has been crafted between a carbohydrate-based molecule and a β-cyclodextrin (CD) hydrophobic cavity for asymmetric catalytic applications. This novel d-glucosamine-based inclusion compound has been synthesized in high yields using an innovative and proficient acoustic cavitation technology and well characterized using various techniques, such as infrared spectroscopy, nuclear magnetic resonance spectroscopy, ultraviolet-visible spectroscopy, thermogravimetric analysis, scanning electron microscopy, and other spectroscopic techniques. It was observed that the inclusion of a d-glucosamine derivative into the hydrophobic cavity of β-CD increased its surface area and thermal stability. This catalytic system worked well in water for the direct aldol reaction to afford the products in excellent yields with high diastereo- and enantioselectivities.

Remote loading of curcumin-in-modified β-cyclodextrins into liposomes using a transmembrane pH gradient

The current study provides a novel remote loading approach utilizing chemically modified cyclodextrins to incorporate hydrophobic drugs into liposomes.

Chiral sulfoxides: advances in asymmetric synthesis and problems with the accurate determination of the stereochemical outcome

Chiral sulfoxides are in extremely high demand in nearly every sector of the chemical industry concerned with the design and development of new synthetic reagents, drugs, and functional materials. The primary objective of this review is to update readers on the latest developments from the past five years (2011-2016) in the preparation of optically active sulfoxides. Methodologies covered include catalytic asymmetric sulfoxidation using either chemical, enzymatic, or hybrid biocatalytic means; kinetic resolution involving oxidation to sulfones, reduction to sulfides, modification of side chains, and imidation to sulfoximines; as well as various other methods including nucleophilic displacement at the sulfur atom for the desymmetrization of achiral sulfoxides, enantioselective recognition and separation based on either metal-organic frameworks (MOF's) or host-guest chemistry, and the Horner-Wadsworth-Emmons reaction. A second goal of this work concerns a critical discussion of the problem of the accurate determination of the stereochemical outcome of a reaction due to the self-disproportionation of enantiomers (SDE) phenomenon, particularly as it relates to chiral sulfoxides. The SDE is a little-appreciated phenomenon that can readily and spontaneously occur for scalemic samples when subjected to practically any physicochemical process. It has now been unequivocally demonstrated that ignorance in the SDE phenomenon inevitably leads to erroneous interpretation of the stereochemical outcome of catalytic enantioselective reactions, in particular, for the synthesis of chiral sulfoxides. It is hoped that this two-pronged approach to covering the chemistry of chiral sulfoxides will be appealing, engaging, and motivating for current research-active authors to respond to in their future publications in this exciting area of current research.

Cyclodextrin-Catalyzed Organic Synthesis: Reactions, Mechanisms, and Applications

Cyclodextrins are well-known macrocyclic oligosaccharides that consist of α-(1,4) linked glucose units and have been widely used as artificial enzymes, chiral separators, chemical sensors, and drug excipients, owing to their hydrophobic and chiral interiors. Due to their remarkable inclusion capabilities with small organic molecules, more recent interests focus on organic reactions catalyzed by cyclodextrins. This contribution outlines the current progress in cyclodextrin-catalyzed organic reactions. Particular emphases are given to the organic reaction mechanisms and their applications. In the end, the future directions of research in this field are proposed.

Metal-free chemoselective oxidation of sulfides to sulfoxides catalyzed by immobilized l-aspartic acid and l-glutamic acid in an aqueous phase at room temperature

Immobilized l-aspartic and l-glutamic acid were employed in the oxidation of sulfides, and 99% conversion and 97% selectivity were achieved.

Merging supramolecular catalysis and aminocatalysis: amino-appended β-cyclodextrins (ACDs) as efficient and recyclable supramolecular catalysts for the synthesis of tetraketones

Efficient synthesis of tetraketones was established with well-designed amino-appended β-cyclodextrins (ACDs) in water, while possible reaction mechanism merging supramolecular catalysis and aminocatalysis was proposed.

A Click Chemistry Approach towards Flavin-Cyclodextrin Conjugates-Bioinspired Sulfoxidation Catalysts

A click chemistry approach based on the reaction between alkynylflavins and mono(6-azido-6-deoxy)-β-cyclodextrin has proven to be a useful tool for the synthesis of flavin-cyclodextrin conjugates studied as monooxygenase mimics in enantioselective sulfoxidations.

pH-Dependence of the Aqueous Phase Room Temperature Brønsted Acid-Catalyzed Chemoselective Oxidation of Sulfides with H₂O₂

A pH-dependence of the Brønsted acid-catalyzed oxidation of sulfides to the corresponding sulfoxides with H₂O₂ is reported for the first time based on our systematic investigation of the catalytic performance of a series of Brønsted acids. For all of the Brønsted acids investigated, the catalytic performances do not depend on the catalyst loading (mol ratio of Brønsted acid to substrate), but rather depend on the pH value of the aqueous reaction solution. All of them can give more than 98% conversion and selectivity in their aqueous solution at pH 1.30, no matter how much the catalyst loading is and what the Brønsted acid is. This pH-dependence principle is a very novel perspective to understand the Brønsted-acid catalysis system compared with our common understanding of the subject.

One-pot synthesis of tetrahydro-4H-chromenes by supramolecular catalysis in water

Tetrahydro-4H-chromenes were synthesizedviaan efficient one-pot three-component protocol by supramolecular catalysis with β-cyclodextrin in water.

Surface immobilization of β-cyclodextrin on hybrid silica and its fast adsorption performance of p-nitrophenol from the aqueous phase

Fast adsorption of p-nitrophenol was achieved through surface immobilization of β-cyclodextrin onto hybrid silica and maintenance of its hydrophobic cavity.

Supramolecular assemblies obtained by mixing different cyclodextrins and AOT or BHDC reverse micelles

In this contribution we show the effect of the surfactant polar head and the external solvent on the incorporation of different cyclodextrins (CDs) {α-CD, β-CD, γ-CD, decenylsuccinyl-β-CD (Mod-β-CD), and hydroxypropyl-β-CD (hp-β-CD)} in different reverse micelles (RMs) {benzene/sodium 1,4-bis(2-ethylhexyl) sulfosuccinate(AOT)/water, and benzene/benzyl-n-hexadecyldimethylammonium chloride (BHDC)/water} and compare them with previous results obtained in n-heptane/AOT/water RMs. To investigate the different systems, we have used UV-vis spectrophotometry, induced circular dichroism spectroscopy (ICD), and the achiral molecular probe methyl orange (MO). The results show dramatic differences changing the external solvent and the surfactant, which are explained by considering the differences in the RMs interface composition, the water-surfactant interaction, and the CDs' location in the different media investigated. None of the CDs were incorporated into the benzene/AOT/water RMs at any [H2O]/[surfactant] ratio studied (W0) whereas it was previously shown that Mod-β-CD and hp-β-CD could be included in n-heptane/AOT/water RMs. However, all of the CDs are incorporated in benzene/BHDC/water RMs at W0 > 10 and hp-β-CD is dissolved even at W0 = 0. Different from what was found in n-heptane/AOT RMs, in BHDC RMs MO showed ICD signals with two different CDs: Mod-β-CD and hp-β-CD. The results are explained by considering the known difference in the interfacial water structure for AOT and BHDC RMs and the electron-rich region on the secondary hydroxyl (wider side of the CDs), which helps to solubilize all CDs in BHDC. This study shows that chiral cyclodextrin could be available for a guest in an organic medium such as the RMs. Therefore we have created a potentially powerful nanoreactor with two different confined regions in the same aggregate: the polar core of the RMs and the chiral hydrophobic cavity of cyclodextrin.

Three-dimensional graphene oxide: a promising green and sustainable catalyst for oxidation reactions at room temperature

Three-dimensional graphene oxide foam (3DGO) was found to be a highly efficient and recyclable catalyst for the oxidation of thioanisole at room temperature.