Masahiko Inouye

Saccharide Recognition-Induced Transformation of Pyridine−Pyridone Alternate Oligomers from Self-Dimer to Helical Complex

Co-oligomers involving (1H)-4-pyridone and 4-alkoxypyridine rings were studied, and it was found that their supramolecular transformation was caused by saccharide recognition. In the co-oligomers, pyridone and pyridine rings are alternately linked at their 2,6-position with an acetylene bond. The pyridine rings behave as a hydrogen bonding acceptor, and the pyridone rings and tautomerized 4-pyridinol work as a donor. Pyridine-pyridone-pyridine 3-mer was found to self-dimerize on the basis of vapor pressure osmometry in CHCl(3), and the association constant was obtained as 2.3 x 10(3) M(-1) by (1)H NMR titration. Longer 5-, 7-, 9-, and 11-mer oligomers showed considerable broadening and anisotropy in the (1)H NMR spectra due to self-association. These longer oligomers recognized octyl beta-D-glucopyranoside and changed their form into a chiral helical complex, showing characteristic circular dichroism.

A Doubly Alkynylpyrene‐Threaded [4]Rotaxane That Exhibits Strong Circularly Polarized Luminescence from the Spatially Restricted Excimer

The Sonogashira coupling of γ-CD-encapsulated alkynylpyrenes with terphenyl-type stopper molecules gave a doubly alkynylpyrene-threaded [4]rotaxane. The rotaxane showed only excimer emission, with a high fluorescence quantum yield of Φf =0.37, arising from the spatially restricted excimer within the cavity of the γ-CD. The excimer emission suffered little from self-quenching up to a concentration of 1.5×10(-5)  M and was circularly polarized with a high glum  value of -1.5×10(-2) . The strong circularly polarized luminescence may result from the two stacked pyrenes existing in the rotaxane in an asymmetrically twisted manner.

Artificial DNA made exclusively of nonnatural C-nucleosides with four types of nonnatural bases.

We describe a new class of DNA-like oligomers made exclusively of nonnatural, stable C-nucleosides. The nucleosides comprise four types of nonnatural bases attached to a deoxyribose through an acetylene bond with the beta-configuration. The artificial DNA forms right-handed duplexes and triplexes with the complementary artificial DNA. The hybridization occurs spontaneously and sequence-selectively, and the resulting duplexes have thermal stabilities very close to those of natural duplexes. The artificial DNA might be applied to a future extracellular genetic system with information storage and amplifiable abilities.

ARTIFICIAL-SIGNALING RECEPTORS FOR BIOLOGICALLY IMPORTANT CHEMICAL SPECIES

Abstract In this article, I describe the performance of artificial-signaling receptors that have been synthesized. The receptors were designed to enable molecular recognition information to be signaled as changes in the optical properties of the receptors. The contents are divided into two parts. The first deals with spiropyran derivatives as artificial-signaling receptors. This new type of artificial receptor is conceptually different from the signaling receptors so far synthesized such as the crown ether dyes and functionally referred to as self-indicating receptors. The second part is concerned with artificial-signaling acetylcholine receptors, in which the presence of acetylcholine induces a large fluorescence enhancement of the receptors in protic media. The artificial acetylcholine receptors may be applied to histochemistry for acetylcholine.

Detection of Mismatched Duplexes by Synchronizing the Pulse Potential Frequency with the Dynamics of Ferrocene/Isoquinoline Conjugate‐Connected DNA Probes Immobilized onto Electrodes

Cyclic voltammetry was performed at various scan rates for the duplexes from ferrocene/isoquinoline conjugate-connected DNA probes on gold electrodes. The relationship between the observed currents and the scan rates disclosed the enhanced bending elasticity of the mismatched duplexes compared with the fully matched duplexes. The difference of the dynamics was easily detected through the currents from the conjugate by adjusting the pulse potential frequency in square-wave voltammetry. By using the present strategy, we succeeded in accurately detecting various naturally occurring single-nucleotide polymorphisms.

Alternating 2,6-/3,5-Substituted Pyridine-Acetylene Macrocycles: π-Stacking Self-Assemblies Enhanced by Intermolecular Dipole–Dipole Interaction

Macrocyclic compounds consisting of three 2,6-pyridylene and three 3,5-pyridylene units linked by acetylene bonds were synthesized by a Sonogashira reaction. The X-ray structures showed π-stacked pairs of two macrocycles, in which a 2,6-pyridylene unit of the one molecule overlaps a 3,5-pyridylene of the other molecule because of dipole-dipole interaction. Atomic force microscope (AFM) measurements revealed fibril structures indicating the stacking of the rigid planar macrocycles. Hydrogen-bonding ability of the macrocyclic inside was demonstrated by the addition of octyl β-D-glucopyranoside.

Photoswitchable, DNA‐Binding Helical Peptides Assembled with Two Independently Designed Sequences for Photoregulation and DNA Recognition

Diarylethene-bridged peptides were developed to photoregulate biomolecular interactions. The peptides are made up of diarylethene-bridged and DNA-binding regions at their N- and C termini, respectively. The two regions could be independently designed and combined as desired. The α-helicities of the peptides were photoregulated in on/off or off/on manners, and the manner depended on the positions of two ornithine (Orn) residues for cross-linking reaction at the diarylethene-bridged region. In the case of the on/off manner, when the diarylethene structure adopted the open form on the peptides, the peptides folded into stable α-helices. Upon UV irradiation, the diarylethene moiety isomerized to its closed form to destabilize the helical structures. Quartz crystal microbalance (QCM) analysis showed that the open isomer strongly associated with a target DNA, as compared with the closed one. When the closed-form peptide existing in the DNA complex was irradiated with a fluorescent lamp in the middle of the QCM monitoring, the frequency change (ΔF) was enhanced by the diarylethene photoisomerization.

A DNA duplex-based, tailor-made fluorescent sensor for porphyrin derivatives.

We synthesized a DNA-based fluorescent sensor, tailored to the recognition and signaling for hydrophobic guest molecules. The sensor molecule is made of three functional moieties, per-O-methylated beta-cyclodextrin (per-Me-beta-CD), DNA, and pyrene as guest-binding, dimerizing, and signaling ones, respectively. Addition of a porphyrin derivative as a hydrophobic guest molecule induced emission switching of the sensor molecule from monomer to excimer due to the DNA hybridization promoted by the host-guest binding.

Selective Binding of D2h-Symmetrical, Acetylene-Linked Pyridine/Pyridone Macrocycles to Maltoside

A macrocyclic host molecule having pyridine-pyridone-pyridine modules for saccharide recognition was prepared by Cu(II)-mediated oxidative homocoupling of a tandem diethynyl precursor. In CH(2)Cl(2), the host molecule associated with dodecyl β-maltoside much more strongly (K(a) = 1.4 × 10(6) M(-1)) than with octyl monohexosides (K(a) = ca. 2 × 10(3) to 1 × 10(4) M(-1)), accompanied with induced CDs. An all-pyridine macrocyclic host was also studied, and its binding strength with saccharides was weaker than that for the pyridine-pyridone-pyridine host.

Preparation of Ethynylpyridine Macrocycles by Oxidative Coupling of an Ethynylpyridine Trimer with Terminal Acetylenes

Macrocycles consisted of pyridine rings and acetylene bonds were prepared by Eglinton coupling from a tandem precursor bearing two terminal alkynyl groups. The composition of molecular size in the cyclized products changed by the reaction solvent. In pyridine, 9-meric and bigger macrocycles were obtained, while that of 6-mer was not. On the other hand, in pyridine/THF mixed solvent, the 6-mer was obtained as a major product.