Synthesis and Selective Molecular Recognition of a Macrotricyclic Receptor Having Crown Ether and Cyclophane Subunits as Binding Sites

The synthesis and selective molecular recognition of a new type of cylindrical, macrotricyclic receptor (1) having crown ether and cyclophane subunits as binding sites and a large hydrophobic cavity are described. Receptor 1 was synthesized by the stepwise construction of three individually prepared subunits: bis(p-toIuenesulfonamido)dibenzo-18-crown-6 (6); diaminocyclophane (7); ethyl 4′-(bromomethyl)biphenyl-4-carboxylate (8). The interaction of 1 and various (ω-phenylalkyl) ammonium picrates 2, for which the number of methylene units varies from 3 to 9, was examined, and they were found to form 1/1 complexes. The selectivity of 1 for 2 was evaluated by comparing the stability constants (K_s′) of these complexes. The K_s′ values were calculated on the basis of the chemical shift changes of the protons in 2 on varying the 1/2 ratio. The K_s′ values of the complexes with (5-phenylpentyl)ammonium (2c) and (6-phenylhexyl)ammonium picrates (2d) were more than 3 times as large as those of the other complexes; i.e., 1 showed selective molecular recognition for 2. The selectivity could result from a cooperative phenomenon involving the electrostatic and hydrophobic interactions between the crown ether subunit and the ammonium group and between the cyclophane subunit and the phenyl group, respectively.