Synthesis and characterization of persilylated cyclodextrins

Partially and pertrimethylsilylated α-, β- and γ-cyclodextrins (CDs) were prepared by reacting the native CDs with trimethylsilylimidazole. The selectivity of primary silylation can reach a 9/1 preference for the lower α-CD homologue. This selectivity is lost when α or β CDs are used. The total substitution of hydroxyl groups with bulky trimethylsilyl radicals induces a strong conformational deviation of CD molecules compared to the native precursors. An NMR investigation of persilylated α-CD allowed a complete assignment of all resonance peaks. Persilylated CDs are thermally stable compounds (decomposition temperature around 380 °C), soluble in non-polar solvents (petroleum ether, benzene, toluene) and insoluble in water, dimethylformamide or dimethylsulfoxide. The experimentally determined properties were supported sustained by simulation data.