Chiral recognition by hemicarcerand-like host in aqueous solution

The synthesis and binding properties of a hydrophilic hemicarcerand-like host with three chiral linker groups and one enlarged opening, that is partially blocked by two appending coumarin moieties, are reported. The complexation behavior towards three achiral and eight chiral guests were investigated. For those guests, in which binding was observed, guest exchange was slow on the NMR time scale and allowed the observation of free and complexed guest signals. At 22°C, binding affinities ranged from 1.4 to 370 mol^-1. Guest binding is driven by enthalpy. In binding studies with racemic guests, the highest diastereomeric excess of complexation (de=20%) was observed for racemic 3-methylcyclohex-1-ene. The much lower de for racemic 3-methylpent-1-ene suggests that guest rigidity is important to achieve selectivity.