Molecular scaffold for the construction of three-armed and cage-like receptors.
An efficient procedure was developed for the synthesis of the C3-sym. mol. scaffold I (R = H). The latter can easily be converted by a single step into either the three-armed receptors I [R = PhCH2, 4-MeO2CC6H4CH2, 4-MeOC6H4CH2, 4-(2-pyridyl)benzyl, etc.] or the cage-like receptor II [(I)2(2,2'-bipyridin-5,5'-diyldimethyl)3]. X-ray structures were obtained for I (R = H, PhCH2) and I [R = 2-(5-methyl-2-pyridyl)pyridin-5-ylmethyl; (III)], which are discussed in regard to their aptitude as receptor platforms. The interaction of the three-armed receptors I and the cage-like receptor II with phloroglucinol was investigated. In accordance with the conclusions obtained from mol. modeling and X-ray crystallog. studies on the host-guest complexes, the three-armed bipyridine receptor III exhibits, due to its induced fit, a larger assocn. const. toward phloroglucinol than the cage II. This new receptor system shows all of the pos. 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, biol. important mols.
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