Microorganisms excrete low-molecular-weight ligands specific for iron (III) termed. “siderophore” for sequestering iron from the environment and transport it into a cell via the sophisticated iron transport system. More than 200 siderophores, which have been isolated and characterized, fall primarily into two structural classes; hydroxamic acid and catechol. Recently the author has report-ed on synthesis of hydroxyazine heterocycles, which are regarded as cyclic hydroxamic acids and/or catechol derivatives, and characterization of their iron (III) complexes. On the other hand, diabetes mellitus (DM), one of the most widespread disease in the world, is generally classified into insulin-depen-dent DM (IDDM) and non-insulin-dependent DM (NIDDM). Several chemotherapeutic agents for NIDDM have already been developed and clinically used. Patients with IDDM can be only treated by daily hypodemic injection of insulin, because it is easily degradated by the ingestive systems. Recently vanadyl complexes have received much attention because of their insulin-mimetic activities. In this review, the author would like to discuss 1) application of hydroxyazine heterocycles to chemotherapuetic agents for the iron-overload disease, 2) design of functional molecules containing hydroxamic acid, catechol, and hydroxyazine heterocyle, 3) application of siderophore-drug conjugates based upon the iron transport system to new antibiotics, and 4) the insulin-mimetic activity of heterocycle-VO (IV) complexes.

View full abstract

Artificial signal transduction systems as molecular devices can be designed through functional connection of supramolecules self-organized in lipid bilayer membranes. A lipid membrane containing gramicidin ion channels linked to antibodies acted as a biosensor using an ion channel switching based on molecular recognition of the antibodies. An artificial photosynthetic membrane composed of a molecular triad, consisting of an electron donor and acceptor linked to a photosensitive porphyrin group, and ATP synthase effectively converted light energy into ATP chemical potential via a proton-pumping photocycle. Supramolecular bilayer assemblies constituted in combination with an artificial receptor and an effector enzyme exhibited signal transduction behavior in which a receptor transmitted an external signal to an enzyme in collaboration with a signal mediator. The artificial supramolecular systems inspired by the G protein-coupled biological signaling were extended to use as a sensing system for biologically active amines and a logic gate for developing molecular devices in nanotechnology.

View full abstract

Recent development of organic synthetic method has enables us to constract elaborated molecular systems. Therefore, much effort has been devoted to the construction, being due to the requirement of the understanding of biological aspects in microscopic level and the exploration of bio-inspired materials. As for the strategy of the molecular design, information-relay based on host-guest interaction is of particular importance. This critical review mainly focuses on our recent approach in synthetic molecular systems, which are characterized by combined “host-guest interactions” and “optical functions” as following directions. First, a simple fluorescent-active sensor comprising a naphthalene-thiouronium dyad has been described, the design of which is mainly our idea that anion recognition events on the electron-deficient binding site of the thiouronium moiety would be efficiently communicated to the fluorescent property of naphthalene via the change of a photoinduced electron transfer process. Second, a new chromophore-derived calix [4] crown as a potential use of a molecular photonic system possesses an effective "off-on-off' signaling for metal cationic inputs, the controllable signal function may being welcome for new materials. Finally, nonlinear optical (NLO) -active receptors based on a dibenzo-diaza-crown ether system has been developed, the estimation being conducted by using hyper-Rayleigh scattering method so that the hyperpolarizability (β) has been regulated by the guest recognition in the crowned cavity of the system. New trend of chromogenic molecular systems has been discussed from point of view of host-guest chemistry.

View full abstract

Glycosphingolipids present on animal cell surface have several functions such as receptors for toxins and viruses. The research using a monolayer as a biomembrane was found to be useful for the evaluation of receptor function of glycosphingolipid, the selection of a sugar-binding peptide from peptide library and the evaluation of a inhibitor for influenza virus infection, and etc. Furthermore, biocombinatorial syntheses of oligosaccharides using saccharide primers were indicated to be useful for the construction of saccharide library.

View full abstract

In biological systems saccharides play important roles as signallers, triggers and name tags. The saccharide structure can include a large amount of information using the specific configuration of hydroxyl groups. For the purpose of the control of the higher order structure for aggregates and polymers, we used a saccharide as an interaction point and introduced them into a system, which forms a molecular aggregate.
We synthesized a series of gelators, which have both a saccharide moiety and a cholesterol moiety within one molecule. The gelation properties, such as gel stability, superstructure and solvent-depen-dence were remarkably changed by a slight change in the saccharide configuration. Phenylboronic-acid-appended-poly (L-lysine) forms an α-helix structure under basic conditions. Various higher-order conformational changes could be induced in the poly (L-lysine) main chain by adding different saccharides. We found that this method was useful for the control of higher order structures.
The selected saccharide can act as an excellent functional material and the combinatorial approach is very helpful to be applied further, in particular to the design of the molecular assemblies, such as macrocycles, DNA-mimics, monolayers, bilayer membranes, liquid crystals. etc.

View full abstract