A convenient and economic method for the synthesis of mono-2-tosyl-β-cyclodextrin

Comparison of Various Tosylating Reagents for the Synthesis of Mono-2-O-tosyl-β-cyclodextrin

Mono-2-O-tosyl-β-cyclodextrin is a key compound, as starting material, for the preparation of multifunctional systems in supramolecular chemistry. Although several methods are available in the literature for its synthesis, yields are always moderate (usually less than 42%) and reproducibility can be an issue as a result of the difficulties encountered in its preparation that are related to selectivity, monofunctionalization, solubility and purification, among others. A modification of a literature method was developed giving emphasis to simplicity and reproducibility and, for the first time, was tested with nine easily accessible tosylating reagents that differ significantly in their nature and reactivity. Product isolation was accomplished with precipitation followed by reverse-phase flash chromatography, which is easy to scale up. Interestingly, with the proposed method, all nine reagents can be successfully applied for the synthesis of the product with yields ranging from 33% to 40%. Optimum reaction times and temperatures were found and conclusions for each tosylating reagent are drawn.

Selective Secondary Face Modification of Cyclodextrins by Mechanosynthesis

α-, β-, and γ-cyclodextrins (CDs) were modified on their secondary face by mechanosynthesis at room temperature using a laboratory-scale ball-mill. Mono-2-tosylated α-, β-, and γ-CDs were obtained in good yield from mixtures of native α-, β-, and γ-CDs, respectively, N-tosylimidazole, and an inorganic base, with each of them being in the solid state. The yields appeared to be dependent upon the nature of the base and the reaction time. A kinetic monitoring by (1)H NMR spectroscopy demonstrated that the highest yields in mono-2-tosyl-CDs were measured using KOH as a base in very short reaction times (up to 65% in 80 s). Mono-(2,3-manno-epoxide) α-, β-, and γ-CDs were subsequently synthesized by ball-milling a mixture of monotosylated α-, β-, and γ-CDs, respectively, and KOH. The characterization of the modified CDs was carried out by X-ray diffraction, mass spectrometry, solid-state NMR, and diffuse reflectance UV-vis (DR UV-vis) spectroscopies. Clues to the supramolecular arrangement of the molecules in the solid state provide information on the reaction mechanism.