Synthesis and Enantioselective Recognition of a Calix[5]arene-based Chiral Receptor

Calix[5]arene-based artificial receptor 1 capped with chiral macrocycle 6 was synthesized and showed strong binding towards ethyltrimethylammonium derivatives via cation/π and/or hydrogen bonding interactions. The calix[5]arene cavity provided the dissymmetric guest-binding environment in which chiral guests 9–19 were encapsulated in an enantioselective fashion. Thermodynamic studies for this chiral recognition gave an insight into the binding manner of the receptor: the enantioselective recognition is enthalpy favoured. Probably, the attractive interactions between the host and the guest gives rise to the enthalpy difference in enantioselection; however, the enthalpy gains of one of the enantiomers are compensated by entropy costs, reducing the enantioselectivity of the receptor.