Molecular scaffold for the construction of three-armed and cage-like receptors.

An efficient procedure was developed for the synthesis of the C3-symmetric molecular scaffold 2. The latter can easily be converted by a single step into either the three-armed receptors 11-16 or the cage-like receptor 17. X-ray structures were obtained for 2, 11, and 16, which are discussed in regard to their aptitude as receptor platforms. The interaction of the three-armed receptors 12-16 and the cage-like receptor 17 with phloroglucinol was investigated. In accordance with the conclusions obtained from molecular modeling and X-ray crystallographic studies on the host-guest complexes, the three-armed bipyridine receptor 16 exhibits, due to its induced fit, a larger association constant toward phloroglucinol than the cage 17. This new receptor system shows all of the positive features characteristic of 2,4,6-trialkylbenzene receptor systems, such as conformational control by steric gearing, ready availability, and versatility in derivatization. These attributes, combined with the advantageous size of the components, allows this system to be readily tailored to provide receptors for larger, biologically important molecules.