Abstract

Receptors based on cis- and trans-tetrahydrobenzoxanthene skeletons combined with benzoxazoles and pyridines have shown enantioselective binding to sulfonylamino acids. The keto-enol tautomeric equilibrium of the receptors shifts towards the keto form upon complexation. X-ray analysis of the trans receptor complex with L-leucine triflamide (H) reveals an unexpected structure, in which the basic pyridine nitrogen accepts the strong H-bond of the guest, while the benzoxazole acts as a counterpart for the sulfonamide group. 1-Carbamoyllactic acid (C) is a suitable guest for the resolution of the racemic mixture of the trans receptor, which can be performed by impregnating TLC plates with the guest. Extraction of racemic carbamoyllactic acid (C) and its ammonium salt from a chloroform/water system with the trans receptor 4 provided a procedure for the resolution of the guest. ((C) Wiley-VCH Verlag GmbH Co. KGaA, 69451 Weinheim, Germany, 2004).