No abstract

Pyridine-phenol alternating oligomers in which pyridine and phenol moieties are alternatingly linked through acetylene bonds at the 2,6-positions of the aromatic rings were designed and synthesized. The pyridine nitrogen atom and the neighboring phenolic hydroxyl group were oriented so that they do not form an intramolecular hydrogen bond but cooperatively act as hydrogen-bonding acceptor and donor in a push-pull fashion for the hydroxyl group of saccharides. The longer oligomer strongly bound to lipophilic glycosides in 1,2-dichloroethane, and association constants approached 10(8)  M(-1) . Moreover, the oligomer extracted native saccharides from a solid phase to apolar organic solvents up to the extent of an equal amount of the oligomer and showed mannose-dominant extraction among naturally abundant hexoses. The oligomer bound to native saccharides even in 20 % DMSO-containing 1,2-dichloroethane and exhibited association constants of greater than 10 M(-1) for D-mannose and D-glucose.

Hexagonal shape-persistent macrocycles (SPMs) consisting of three pyridine and three phenol rings linked with acetylene bonds were developed as a preorganized host for saccharide recognition by push-pull-type hydrogen bonding. Three tert-butyl or 2,4,6-triisopropylphenyl substituents were introduced on the host to suppress self-aggregation by steric hindrance. In spite of the simple architecture, association constants K of the host with alkyl glycoside guests reached the order of 10 m on the basis of UV/Vis titration experiments. This glycoside recognition was much stronger than that in the cases of acyclic equivalent hosts because of the entropic advantage brought by preorganization of the hydrogen-bonding sites. Solid-liquid extraction and liquid-liquid transport through a liquid membrane were demonstrated by using native saccharides, and much preference to mannose was observed.

A perylene-based [4]rotaxane was synthesized by the Sonogashira coupling of the 2:2 inclusion complex consisting of two alkynylperylenes and two γ-cyclodextrins with terphenyl-type stopper molecules. The [4]rotaxane showed orange emission attributable to the spatially restricted alkynylperylene excimer with a high fluorescence quantum yield of Φ =0.15. The excimer emission was circularly polarized as a result of the asymmetrically twisted perylene pair under the influence of chirality of γ-cyclodextrin. The g value of the excimer emission was determined to be -2.1×10 at 573 nm, as large as those of the corresponding known pyrene-based series. This is the first example, in which circularly polarized luminescence was clearly observed from the excimer of a pair of perylene cores.

Phenol-based oligomers linked with acetylenes at their meta positions, " meta"-ethynylphenol oligomers, were developed as a synthetic helical foldamer. The architecturally simple oligomers spontaneously formed helical higher-order structures by sequential intramolecular hydrogen bonds through the multiple phenolic hydroxy groups inside the cavities. The hydrogen bonds forced C-C≡C-C bond angles to largely bend toward the inside. Addition of chiral amines caused the helices to be chiral by electrostatic interactions between the resulting chiral ammonium cations and the phenolate anions.