Kenichiro Yamamoto

Catalytic Asymmetric Synthesis of 3,3′‐Diaryloxindoles as Triarylmethanes with a Chiral All‐Carbon Quaternary Center: Phase‐Transfer‐Catalyzed SNAr Reaction

Catalytic asymmetric synthesis of unsymmetrical triarylmethanes with a chiral all-carbon quaternary center was achieved by using a chiral bifunctional quaternary phosphonium bromide catalyst in the S(N)Ar reaction of 3-aryloxindoles under phase-transfer conditions. The presence of a urea moiety in the chiral phase-transfer catalyst was important for obtaining high enantioselectivity in this reaction.

Organoclays in Water Cause Expansion That Facilitates Caffeine Adsorption

This study investigates the adsorption of caffeine in water on organically modified clays (a natural montmorillonite and synthetic saponite, which are smectite group of layered clay minerals). The organoclays were prepared by cation-exchange reactions of benzylammonium and neostigmine with interlayer exchangeable cations in the clay minerals. Although less caffeine was uptaken on neostigmine-modified clays than on raw clay minerals, uptake was increased by adding benzylammonium to the clays. The adsorption equilibrium constant was considerably higher on benzylammonium-modified saponite (containing small quantities of intercalated benzylammonium) than on its montmorillonite counterpart. These observations suggest that decreasing the size and number of intercalated cations enlarges the siloxane surface area available for caffeine adsorption. When the benzylammonium-smectite powders were immersed in water, the intercalated water molecules expanded the interlayer space. Addition of caffeine to the aqueous dispersion further expanded the benzylammonium-montmorillonite system but showed no effect on benzylammonium-saponite. We assume that intercalated water molecules were exchanged with caffeine molecules. By intercalating benzylammonium into smectites, we have potentially created an adaptable two-dimensional nanospace that sequesters caffeine from aqueous media.

Phase-Transfer-Catalyzed Asymmetric SNAr Reaction of α-Amino Acid Derivatives with Arene Chromium Complexes

Although phase-transfer-catalyzed asymmetric S(N)Ar reactions provide unique contribution to the catalytic asymmetric α-arylations of carbonyl compounds to produce biologically active α-aryl carbonyl compounds, the electrophiles were limited to arenes bearing strong electron-withdrawing groups, such as a nitro group. To overcome this limitation, we examined the asymmetric S(N)Ar reactions of α-amino acid derivatives with arene chromium complexes derived from fluoroarenes, including those containing electron-donating substituents. The arylation was efficiently promoted by binaphthyl-modified chiral phase-transfer catalysts to give the corresponding α,α-disubstituted α-amino acids containing various aromatic substituents with high enantioselectivities.

Caffeine adsorption of montmorillonite in coffee extracts

The growth in health-conscious consumers continues to drive the demand for a wide variety of decaffeinated beverages. We previously developed a new technology using montmorillonite (MMT) in selective decaffeination of tea extract. This study evaluated and compared decaffeination of coffee extract using MMT and activated carbon (AC). MMT adsorbed caffeine without significant adsorption of caffeoylquinic acids (CQAs), feruloylquinic acids (FQAs), dicaffeoylquinic acids (di-CQAs), or caffeoylquinic lactones (CQLs). AC adsorbed caffeine, chlorogenic acids (CGAs) and CQLs simultaneously. The results suggested that the adsorption selectivity for caffeine in coffee extract is higher in MMT than AC. The caffeine adsorption isotherms of MMT in coffee extract fitted well to the Langmuir adsorption model. The adsorption properties in coffee extracts from the same species were comparable, regardless of roasting level and locality of growth. Our findings suggest that MMT is a useful adsorbent in the decaffeination of a wide range of coffee extracts. Montmorillonite (MMT) adsorbed caffeine in various coffee extracts with no significant binding of chlorogenic acids (CGAs).

Influence of hydrophilicity on adsorption of caffeine onto montmorillonite

Some types of montmorillonite containing different interlayer ions were prepared and the changes in the interlayer spacings, the hydrophilicity, and the characteristics of adsorption of caffeine in solution were observed. Ion exchange treatments were performed using Li, Na, K, Rb, Cs, Mg, Ca, Sr, or Ba. As a result, Li- and Na-type montmorillonite showed larger interlayer distance (1.31–1.53 nm), than K, Rb, and Cs-type montmorillonite (1.23–1.26 nm). In the measurement of hydrophilicity using a pulse NMR-based particle interface analyzer, Li- and Na-type montmorillonite showed higher hydrophilicity. In addition, KLang, which indicates the interaction with caffeine, was 0.25–0.32 l/mmol, which is lower than K-, Rb-, and Cs-type montmorillonite (1.14–1.60 l/mmol). It is possible that adsorption of water molecules inhibits caffeine from adsorbing. Because of the difficulty of exchange between caffeine and water molecules in interlayer of the Li- and Na-type montmorillonite, the interaction with caffeine decreased. Alternatively, another possibility is that when highly hydrophilic montmorillonite retains many water molecules, the caffeine adsorption sites are blocked by water molecules. In either case, hydrophilicity has a large influence on the adsorption of caffeine onto montmorillonite.