We have demonstrated that chemical efficiency of biocatalysts mediated reactions could be improved by several chemical methodologies. Herin, I report the results focus to three topics: (1)Design of building blocks for organic synthesis via yeast-mediated asymmetric reduction of ketones. (2)Synthesis of chiral gem-difluorocyclopropanes using lipase-catalyzed reaction and linker-oriented design of binaphthol derivatives for optical resolution using lipase-catalyzed reaction. (3)Innovation of lipase-catalyzed reactions by the use of ionic liquids solvent system. We have succeeded in showing that activation of lipase-performances has been accomplished by the coating of enzyme with alkyl PEG ionic liquid. Furthermore, a rational design of phosphonium ionic liquid for ionic liquid coated-lipase (IL1-PS)-catalyzed reaction has been investigated, and very rapid transesterification of secondary alcohols accomplished when IL1-PS was used as catalyst in 2-methoxyethoxymethyl(tri-n-butyl)phosphonium bis(trifluoromethanesulfonyl)amide ([P444MEM] [NTf2]) as solvent while perfect enantioselectivity was maintaining. Increased Kcat value was suggested to be the most important factor in IL1-PS working the best in [P444MEM] [NTf2] solvent.
Electronic paper has received much attention as next generation display to contribute energy- and resource-saving, because electronic paper can hold images even after the power is turned off unlike conventional displays such as liquid crystalline one. Electronic books bearing an electrophoretic type of electronic paper are already commercially available, but the colorization is becoming one of significant subjects in electronic paper. Electrochromic type of electronic paper is expected to achieve the colorization, since electrochromic materials can show various colors. Recently, we found organic-metallic hybrid polymers formed by the complexation of metal ions as Fe(II) or Ru(II) with bis(terpyridine) ligands have specific colors based on metal-to-ligand charge transfer (MLCT) absorption and show electrochromic properties, which is caused by electrochemical redox of the metal ions. Interestingly, multicolor electrochromic change is also possible by the introduction of two types of metal ions into the polymer. In addition, solid-state electrochromic displays using the organic-metallic hybrid polymers was fabricated successfully. The new electrochromic materials and the devices have possibility to be applied to color electronic paper in the future.
Rh-catalyzed hydroacylation reaction can be classified into intramolecular reaction (cyclization) and intermolecular reaction. The intramolecular hydroacylation of 4-pentenals by Rh-complex was clarified about 40 years ago. Intramolecular hydroacylation by Rh-complex has been developed into catalytic reaction, enantioselective reaction, and medium-ring formation reaction. At the beginning, however, Rh-catalyzed intermolecular hydroacylation reaction did not proceed because of decarbonylation side reaction, but, the chelation of aldehyde having an additional functional group suppressed the decarbonylation, and the Rh-catalyzed intermolecular hydroacylation reaction using the chelation of aldehyde proceeded. Especially, the double chelation of both salicylaldehyde and diene promoted the intermolecular hydroacylation under mild reaction conditions. The Rh-catalyzed intermolecular hydroacylation has been developed into diastereoselective and enantioselective reactions.
Over the last decade, transition-metal-mediated or -catalyzed reactions involving a C-H bond cleavage have received much attention and grown rapidly because of their possibility for transformation of ubiquitous C-H bonds into the versatile functions in one synthetic operation. These methodologies are now applied to the direct functionalization of heteroarenes, which are prevalent in pharmaceutical and material sciences, and provide a potentially more efficient alternative to the conventional cross-coupling strategies with halogenated or metalated heterocycles. However, most reported procedures rely on the precious metal catalysts such as palladium, rhodium, and ruthenium. Recently, we have focused on the inherent catalytic activity of less expensive first transition elements and succeeded in the copper- and nickel-promoted direct C-H arylation, alkynylation, and amination reactions, which are reported herein.
Several types of host molecules based on a phenolphthalein (one of the most popular pH indicators) and two crown ethers were prepared for use in colorimetric recognition of linear diamines, triamines, sequence of non-protected dipeptides, and chirality of alanine derivatives in methanol or water solution. Especially, host 30 with a dimethylamino group showed excellent selectivity for spermidine and spermine among other biogenic amines and high sensitivity.
The complex issues of stereoselectivity posed by polyketides are most often addressed through the use of chiral auxiliaries, chiral reagents, and premetalated nucleophiles. Prof. Krische’s approach takes advantage of carbonyl allylation and crotylation protocols, wherein primary alcohol dehydrogenation concurrently triggers aldehyde formation and reductive generation of allyliridium nucleophiles, enabling asymmetric carbonyl allylation and crotylation directly from the alcohol oxidation level. His approach circumvents additional manipulations associated with the use of non-native functional groups or substructures to mediate bond construction, as evident in the use of chiral auxiliaries, and minimizes (re)functionalizations, especially redox manipulations.