Helices in proteins play an important role in a variety of fields such as biology, medicinal chemistry, and organic chemistry. Therefore, stabilized helical peptides have been developed in recent years. As tools for peptide-helix stabilization, non-proteinogenic amino acids such as α,α-disubstituted α-amino acids, cyclic β-amino acids, and cross-linked side chains are often utilized. Herein we report secondary structural control of short peptides using L-amino acids, D-amino acids, α,α-disubstituted α-amino acids, and cross-linked side chains. Furthermore, we applied the stabilized short helical peptides to the catalytic enantioselective epoxidation of α,β-unsaturated ketones, to the inhibitors of vitamin D receptor(VDR)-coactivator interaction, and to the efficient cell-penetrating molecules.
Various types of functionalized fullerenes have been widely developed by considering unique reactivities of the spherical reaction sites; such as not only the enhanced reactivity due to the curved and thus strained C=C double bonds, but also the multiple addition and its electronic control for the selective monoaddition, the regioselectivity controls by spherical π-conjugation and by twisted C=C double bond, the unprecedented substitution mechanism, the highly symmetrical multiple addition via fullerene anion, and the drastic reactivity change by ion encapsulation. The derivatives also proved effective against many potential applications to CMP polishing slurry, antioxidant, anti-inflammatory agent, resist materials, n-type materials for organic photovoltaics, and more.
Four types of synthetic applications of indium(III) salts as characteristic Lewis acids have been discussed. (1) Reductive functionalizations of carbonyl compounds were assisted by a catalytic amount of indium(III) halides, which achieved reductive chlorination and reductive Friedel-Crafts alkylation of aldehydes or ketones, moreover presented reductive allylation and reductive aldol reaction of esters. (2) Direct substitution of hydroxy groups of alcohols and carboxylic acids were also achieved by characteristic interactions between indium trihalide catalyst and silicon moieties. (3) Indium halides catalyzed direct couplings of alcohols with carbon nucleophiles such as enol acetates or 1,3-dicarbonyls were achieved. (4) A novel type of carboindation of alkynes or alkenes was successful, in which direct anti addition of indium tribromide and carbon nucleophiles to alkynes or alkenes takes place.
Although quaternary onium salts-catalyzed phase-transfer reactions are generally believed to require base additives, we discovered even without any base additives conjugate additions of 3-substituted oxindoles to nitroolefins proceeded smoothly in the presence of lipophilic quaternary ammonium bromide under water-organic biphasic conditions. The mechanism of this novel base-free neutral phase-transfer reaction system was investigated, and the assumed catalytic cycle was presented together with interesting effects of water and lipophilicity of the phase-transfer catalyst. The base-free neutral phase-transfer reaction system could be applied to highly enantioselective conjugate addition and aldol reactions under the influence of chiral bifunctional ammonium bromides as key catalysts. The efficient approach for the design of chiral quaternary phosphonium bromides as chiral phase-transfer catalysts was also introduced. A catalyst library with various structures has readily been constructed by the use of commercially available chiral phosphines as catalyst precursors. The optimized catalyst has successfully been applied to highly enantioselective conjugate additions and sulfenylation under base-free neutral phase-transfer conditions with low catalyst loading.
DNA is an attractive chiral source because of its unique helical chirality. Recently, DNA-based hybrid catalysts, self-assembled from DNA and a metal complex with a specific ligand through supramolecular or covalent anchoring strategies, have been developed and applied successfully in a variety of carbon-carbon or carbon-heteroatom bond-forming reactions. Now these enticing biohybid catalysts are expanding their role in asymmetric synthesis. In this review, we summarize the advent and significant progress of DNA-based asymmetric catalysis and discuss remaining challenges for future applications of DNA-based hybrid catalysts.
Polycyclic aromatic compounds possessing heteroatoms are one of the most important materials for organic electronics. Because of the lack of a suitable synthetic methodology, only a few polycyclic aromatic compounds with ring junction heteroatoms, heteroatom-doped nanographenes, have been synthesized to date, even though theoretical investigations have suggested that those molecules are attractive not only as the electronic materials but also as substructures of heteroatom-doped nanocarbons. Herein, we describe development of novel tandem hetero-Friedel-Crafts reactions and their application for the synthesis of heteroatom-fused polycyclic aromatic compounds. These compounds showed strong luminescence or carrier transport ability, thus can be a promissing class of organic materials for optelectronic devices. We have demonstrated their potential utility by fablicating phosphorescent organic light-emitting diodes with a sufficiently high efficiency and a long device lifetime.
Organic macrocycles have been attracted much attention as functional host molecules that selectively recognize and encapsulate small molecules such as ions and organic molecules within its cavity. Usually, artificial organic macrocycles are synthesized by repetitive connection of monomer units and cyclization of linear oligomers formed thereby. In this context, there have been problems in the control of the number of units or in the selectivity of cyclic products over linear ones. This review focuses on recent breakthroughs that achieved the synthesis of novel functional macrocyclic molecules from fresh and original points of view to overcome the synthetic challenges.
An aziridine is a highly strained, triangular molecule that has been recognized as an invaluable synthetic intermediate as well as a structural motif of bioactive molecules. Numerous catalytic/stoichiometric, racemic/asymmetric methods for synthesis of N-protected aziridines have been demonstrated but a practical method for direct N-H aziridine synthesis has been missing for decades despite of its promising utility for drug design. The present review describes recent developments of intermolecular N-H aziridine synthesis as an emerging field of potential application to practical and stereoselective synthesis.
Development of direct catalytic anti-Markovnikov addition reactions of oxygen nucleophiles to simple alkenes is a difficult challenge due to the propensity to form Markovnikov adducts under ordinary reaction conditions. Herein selected recent examples that realize these reactions with high anti-Markovnikov selectivity are summarized.