Eiichi Fujita

Reactions of vinylsilanes with lewis acid-activated iodosylbenzene: stereospecific syntheses of vinyliodonium tetrafluoroborates and their reactions as highly activated vinyl halides

Abstract Alkenyl(phenyl) iodonium tetrafluoroborates 3 were synthesized from alkenylsilanes 1 by the reaction with iodosylbenzene and boron trifluoride-diethyl ether or triethyloxonium tetrafluoroborate. The reaction proceeds stereospecifically with retention of configuration of 1 . X-ray diffraction analysis of (4-tert-butylcyclohexenyl)phenyliodonium tetrafluoroborate ( 3b ) revealed the highly ionic structure with the distorted T-shape arrangement. Iodonium salts 3 behave like the highly activated species of vinyl iodides due to the high leaving ability of the iodine(III) substituents. Thus, a variety of substituted olefins including α-cyano and α-nitro olefins, vinyl sulfides, vinyl halides, and α,β-unsaturated esters, were synthesized from 3 under mild conditions. A ligand coupling mechanism via the formation of 10-I-3 intermediate 27 containing a copper(III) ligand is proposed for the substitutions of 3 with nucleophiles.

A cytotoxic principle of the brown alga Sargassum tortile and structures of chromenes

Abstract Bioassay-directed fractionation of a methanolic extract of the marine alga Sargassum tortile has led to the isolation and characterization of eight compounds which include the new chromenes sargaol, sargasal-II, and sargadiols-I and -II in addition to sargasal-I, hydroxysargaquinone, kjellmanianone, and fucosterol. Among them, hydroxysargaquinone and sargasals-I and -II demonstrated significant and marginal cytotoxicity against cultured P-388 lymphocytic leukemia cells, respectively.

Iodosylbenzene-trimethylsilyl azide-boron trifluoride etherate: A highly efficient system for direct synthesis of allyl azides from allylsilanes

Abstract Simple method for the synthesis of allyl azides from allyltrimethylsilanes utilizing the combination of iodosylbenzene-trimethylsilyl azide-boron trifluoride etherate in dichloromethane was developed. A reaction mechanism involving the allyliodine(III) species was proposed.

Chiral Induction Using Heterocycles

Publisher Summary The useful physiological activity of pharmaceuticals containing asymmetric center(s) appears usually in only one enantiomer. Hence, an effective synthesis of the desired enantiomer with optical purity is now an important subject in chemistry. The chiral synthon has been obtained by asymmetric chemical synthesis, synthesis of a racemate followed by its optical resolution, chiral induction in a specific prochiral compound with enzymes or micro-organisms, and chemical transformation from easily available sugars, amino acids, terpenoids, and other optically active natural products. An overview of chiral designs, reactions, and applications are discussed in this chapter. Novel chiral designs using functional and chiral heterocycles seem likely in the future, especially when used in combination with organometallic reagents and/or molecular symmetry. Creative investigations employing such chiral heterocycles and related compounds will be extensively pursued.

Effect of oridonin, a Rabdosia diterpenoid, on radiosensitization with misonidazole.

The radiosensitization brought about by oridonin, one of theRabdosia diterpenoids, alone or in combination with misonidazole, was investigated in Chinese hamster V79 cells. The enhancement ratio of 1.92 was obtained when 0.01 mM oridonin and 1 mM misonidazole were administered to hypoxic cells under radiation. The enhancement ratios of oridonin and misonidazole for hypoxic cells were 1.16 and 1.59 respectively. Hence, a supra-additive effect was obtained by the combined treatment with these two drugs. Under aerobic conditions, no effect of 0.01 mM oridonin on the radiosensitization caused by misonidazole was observed.