Mild Friedel–Crafts Reactions inside a Hexameric Resorcinarene Capsule: C−Cl Bond Activation through Hydrogen Bonding to Bridging Water Molecules

A novel catalytic feature of a hexameric resorcinarene capsule is highlighted. The self‐assembled cage was exploited to promote the Friedel–Crafts benzylation of several arenes and heteroarenes with benzyl chloride under mild conditions. Calculations showed that there are catalytically relevant hydrogen‐bonding interactions between the bridging water molecules of the capsule and benzyl chloride, which is fundamental for the activation of the C?Cl bond. The capsule controls the reaction outcome. Inside the inner cavity of the capsule, N‐methylpyrrole is preferentially benzylated in the unusual β‐position while mesitylene reacts faster than 1,3‐dimethoxybenzene despite the greater π‐nucleophilicity of the latter compound.     

Convenient metal-free direct oxidative amidation of aldehyde using dibromoisocyanuric acid under mild conditions

A facile method for the direct synthesis of amides from aldehydes is described. Amide bonds were synthesized by an oxidative amidation in the presence of dibromoisocyanuric acid (DBI). Treatment of aromatic and aliphatic aldehydes with dibromoisocyanuric acid generated acyl bromide intermediates, which were employed to react with a variety of secondary and primary amines to give amides. Through this reaction method, various amides were synthesized directly from aldehydes under mild conditions in high yields and short times. This facile and efficient procedure provides potential strategy for the direct synthesis of amides from aldehydes.     

Facile synthesis of diphenylmethyl esters from 2-diphenylmethoxypyridine using catalytic boron trifluoride·diethyl etherate

A practical method for the direct preparation of diphenylmethyl (DPM) esters from 2-diphenylmethoxypyridine is described. The reaction was readily performed in the presence of a catalytic amount of boron trifluoride-diethyl etherate at room temperature. Using this reaction protocol, various carboxylic acids were converted to DPM esters with high yields. This method is highly effective for the protection of carboxylic acids and the synthesis of DPM esters, and offers a promising approach for facile esterification of a variety of carboxylic acids.     

Comparative Study of Reversed-Phase High-Performance Liquid Chromatography and Ultraviolet–Visible Spectrophotometry to Determine Doxorubicin in pH-Sensitive Nanoparticles

Analytical methods by reversed-phase high-performance liquid chromatography (HPLC) and ultraviolet–visible spectrophotometry were developed and validated to determine doxorubicin in pH-sensitive chitosan nanoparticles. Chromatographic separation was performed on a reversed-phase C₁₈ column, with ultraviolet detection at 254?nm and a mobile phase composed by 90% (v/v) acetonitrile in water and water pH 3.0 (33:67, v/v). The spectrophotometry method had the wavelength set at 480?nm and pH 3.0 water was used as a diluent. Calibration curves were linear from 1 to 30?µg/?mL (r?>?0.9995) and the specificity was demonstrated by verifying the absence of interferences from nanoparticle components. The values of accuracy and precision were within the acceptable limits, and robustness studies were performed by a two-level full factorial design. The validated methods were further tested to assess doxorubicin content in six different batches of pH-sensitive chitosan nanoparticles. The comparative analyses showed nonsignificant differences (p?>?0.05). Likewise, the HPLC method was successfully applied to determine the drug encapsulation efficiency as well as to measure doxorubicin during in vitro release assays and degradation kinetic studies under ultraviolet light C irradiation. Both methods fulfilled all validation parameters and were shown to be suitable for the characterization of doxorubicin-loaded pH-sensitive chitosan nanoparticles, without interferences from nanoparticle matrix.