This article describes our recent achievements in developing synthetic chromogenic receptors which are characterized by combined “recognition” and “optical sensing” functions. The focus is on preparation and some intriguing properties of several kinds of azomethine-derived calixarenes : this work is extended in two related directions, the incorporation of indoaniline-type chromophores as an appropriate optical sensory group into calixarenes bearing a guest-binding site produced new types of receptors for optical sensing against cations. Second, a chiral calix  crown containing an optically active 1, 1' -binaphthyl subunit and two indophenol chromophores was synthesized as a molecular sensor which is capable of translating an enantioselective molecular recognition event into a discernible color change. A simple monitoring system for biologically and/or chemically important species is discussed.
The diastereodifferentiating reactions between a prochiral substrate and a reagent connected with optically active 2, 4-pentanediol were studied. The reactions based on this simple design were found to give products of over 99% diastereomeric excess during carbenoid addition, mata-arene-olefin photocycloaddition, oxidative couplings, and epoxidation, and after removal of the chiral auxiliary from the products, optically pure compounds were obtained in good yields. By using the obtained asymmetric reaction, total synthesis of (+) -africanol was achieved in 16 steps. Newly found highly effective and diastereodifferentiating radical abstraction was applied for total syntheses of (+) -ipomeamarone and (-) -ngaione.
Synthesis, reaction, and metal-chelating property of N-hydroxyamide-containing heterocycles such as 1-hydroxy-2 (1H) -pyrimidinones and -pyrazinones are described. The diazines showed remarkable high water solubility and acidity, which enable them to act as an effective acylating agent for amines, amino acids, and alcohols. The diazines were also found to be an bidentate ligand to a ferric iron in aqueous solution, in particular, under acidic to neutral conditions. The five types of tripodal hexadentate ligands bearing 1-hydroxy-2 (1H) -pyrimidinone or -pyrazinone as bidentate ligands were synthesized, and effects of their structural feature and the chirality on their metal-chelating behavior were also discussed. Among them, a hexadenate ligand bearing 1-hydroxy-2 (1H) -pyrazinone, L-alanine, and tris (2-aminoethyl)amine showed high iron removal ability from human transferrin, and its pseudo-first-order-rate constant was more than five times greater than naturally-occurring siderophore, desferrioxamine B, even in small excess of the ligand concentration to transferrin.
Maitotoxin (MTX, 1) is the most toxic and largest non-biopolymer known to date. The complete structural determination of MTX including the absolute configuration has been achieved recently. The relative configurations of the four acyclic portions (C1-C15, C35-C39, C63-C68, and C134-C142) were elucidated by (1) the extensive configurational analysis mainly using long-range carbon-proton coupling constants (2, 3JC, H), and (2) the stereoselective synthesis of the eight model compounds (2A-2D, 13, 27A, 27B, and 47) which were furnished with thus assigned relative configurations. The comparison of their 1H and 13C-NMR data with those for the corresponding portion of MTX evidently established the relative configuration from C1 to C138. The absolute configuration of the entire molecule was determined by the enantioselective synthesis and chiral gas chromatographic comparison with a degradated fragment (3, 4-dimethy1-6-hepten-1-o1) derived from the natural product, which involved two chiral centers at C138 and C139. The present results have revealed that the preferred conformation of an appropriately designed model compound with the correct configuration closely mimics that of the corresponding portion of MTX. Thus, we could deduce the overall conformation of MTX by assembling the preferred conformation of each model compound based on the NMR data.
Ate complexes have been used for selective carbon-carbon bond forming reactions, however access to ate complexes with electrophilic functional groups has been limited. Main reason for the limitation lies on the preparative method of ate complexes, which includes usage of highly reactive organolithium and organomagnesium reagents. In order to develop a new strategy for the preparation of ate complexes directly from other ate complexes, we investigated halogen-metal exchange reactions of organic halides with ate complexes. The metalation is considered to be potentially chemoselective and wide spectrum of application in organic synthesis is expected. Cuprates and zincates turned out to be excellent metalating reagents of functionalized aryl and alkyl halides. Some chemoselective transformations were achieved using the metalation with ate complexes and modified zincates showed very specific reactivity toward intramolecular epoxide opening reaction.
Electron transfer (ET) reactions play a central role in both photosynthesis and respiratory oxidative phosphorylation. They occur in nature with remarkably high efficiency, but attempts to duplicate them in homogeneous solutions consisting of metalloporphyrins and appropriate donor and acceptor molecules have not been successful. In order to obtain a better understanding of the exact nature of specific partner-to-partner ET processes and to be able to duplicate them in vitro, the research has focussed on the more complicated “supramolecular” model systems. In the light of the previous studies, the roles of electric fields and non-covalent pathways in mediating long-range ET reactions were studied. Multi-component arrays with improved charge separating capabilities were prepared, and these species may find application in new charge separating devices. This review summarizes some recent progress in this rapidly growing field.
A new indolocarbazole anticancer agent, NB-506 (6-N-formylamino-12, 13-dihydro-1, 11-dihydroxy-13-β-D-glucopyranosyl) -5H-indolo [2, 3-a] pyrrolo [3, 4-c] carbazole-5, 7 (6H) -dione) was developed. The total synthesis of NB-506 was successfully achieved with a new glycosylation reaction which was carried out in good yield with high β-selectivity. Moreover the Mitsunobu reaction was newly found to be a convenient method for synthesizing dissymmetric indolocarbazole glycosides at the glycosylation step.