Host–guest complexes of cucurbit[6]uril with phenethylamine-type stimulants

Abstract

Host–guest complexes between the cucurbit[6]uril macrocycle and phenethylamine ‘natural’ stimulants (ephedrine, synephrine and octopamine) have been obtained in the presence of magnesium ions. Ephedrine and synephrine form partial inclusion complexes with the macrocycle upon insertion of the methylammonium moieties into the host cavity, stabilizing the ion–dipole and hydrogen bonding interactions. Octopamine, lacking a methyl group attached to the ammonium function, forms perching complexes with the macrocycle. Meanwhile the magnesium ions used to enhance the aqueous solubility of cucurbit[6]uril do not interfere in the crystallization of ephedrine and synephrine host–guest complexes; in the case of octopamine the sequential crystallization of a metastable metal-free host–guest complex and a thermodynamically stable magnesium-captured form of the host–guest complex was observed.