Shunsaku Ohta

Synthesis and characterization of a practically better DEPMPO-type spin trap, 5-(2,2-dimethyl-1,3-propoxy cyclophosphoryl)-5-methyl-1-pyrroline N-oxide (CYPMPO)

5-(2,2-Dimethyl-1,3-propoxy cyclophosphoryl)-5-methyl-1-pyrroline N-oxide (CYPMPO), a new cyclic DEPMPO-type nitrone was evaluated for spin-trapping capabilities toward hydroxyl and superoxide radicals. CYPMPO is colorless crystalline and freely soluble in water. Both the solid and diluted aqueous solution did not develop electron spin resonance (ESR) signal for at least 1 month at ambient conditions. CYPMPO can spin-trap superoxide and hydroxyl radicals in both chemical and biological systems, and the ESR spectra are readily assignable. Half life for the superoxide adduct of CYPMPO produced in UV-illuminated hydrogen peroxide solution was approximately 15 min, and in biological systems such as hypoxanthine (HX)/xanthine oxidase (XOD) the half-life of the superoxide adduct was approximately 50 min. In UV-illuminated hydrogen peroxide solution, there was no conversion from the superoxide adduct to the hydroxyl adduct. Although overall spin-trapping capabilities of CYPMPO are similar to DEPMPO, its high melting point, low hygroscopic property, and the long shelf-life would be highly advantageous for the practical use.

A recyclable catalyst for asymmetric transfer hydrogenation with a formic acid–triethylamine mixture in ionic liquid

A novel task-specific ionic ligand with an imidazolium salt moiety was synthesized, and its catalytic ability and recyclability for asymmetric transfer hydrogenation of acetophenone derivatives with a formic acid-triethylamine azeotropic mixture in an ionic liquid [bmim][PF6] was examined.

Novel Diels–Alder-type dimerization of 5-ethenyl-2-phenylsulfanyl-1H-imidazoles and its application to biomimetic synthesis of 12,12′-dimethylageliferin

Abstract Diels–Alder-type dimerization of various 5-ethenyl-2-phenylsulfanyl-1 H -imidazoles provided a novel highly regio- and stereoselective route to the preparation of multifunctionalized 4,5,6,7-tetrahydrobenzimidazoles, the basic skeleton of ageliferin, a biologically active pyrrole–imidazole marine alkaloid. The reaction was applied to the synthesis of 12,12′-dimethylageliferin.

Syntheses of 3-acetoacetylaminobenzo[b]furan derivatives having cysteinyl leukotriene 2 receptor antagonistic activity

Novel 3-acetoacetylaminobenzo[b]furan derivatives having a modified triene system at the 3-position were synthesized starting with 3-aminobenzo[b]furans. The enol isomers, 3-[(3-hydroxybut-2-enonyl)amino]benzo[b]furans (), of the 3-acetoacetylaminobenzo[b]furans were obtained as stable isomers owing to formation of a hydrogen bonding between the enol hydroxyl group and the amidocarbonyl group. The planarity of the C-2 substituent through the C-3 side chain suggested the existence of a modified conjugational triene system in the enol compound. Cysteinyl leukotriene 1 and 2 receptor antagonistic activities for these compounds were evaluated. 2-(4-Cyanobenzoyl or ethoxycarbonyl)-3-[(2-cyano-3-hydroxybut-2-enonyl)amino]benzo[b]furans (, ) were moderately active.

Preparation of 3-acetoacetylaminobenzo[b]furan derivatives with cysteinyl leukotriene receptor 2 antagonistic activity

Novel 3-acetoacetylaminobenzo[b]furan derivatives with a modified triene system at the 3-position were prepared through acylation of the 3-aminobenzo[b]furans with 5-methylisoxazole-4-carboxylic acid chloride followed by basic cleavage of the isoxazole ring and several of these compounds showed moderate cysteinyl leukotriene receptor 2 antagonistic activity.

First Total Synthesis of (±)-Linderol A, a Tricyclic Hexahydrodibenzofuran Constituent of Lindera umbellata Bark, with Potent Inhibitory Activity on Melanin Biosynthesis of Cultured B-16 Melanoma Cells

The first total synthesis of (+/-)-Linderol A, a hexahydrodibenzofuran constituent of Lindera umbellata bark, with potent inhibitory activity on the melanin biosynthesis of cultured B-16 melanoma cells, was achieved through 19 steps of reaction in 6.6% overall yield, in which the critical step was a tandem reaction of a 3-ethoxycarbonylcoumarin derivative with dimethylsulfoxonium methylide to yield the 2-ethoxycarbonylcyclopenta[b]benzofuran-3-ol derivative.

Antitumor agents 238. anti-tubulin and in vitro cytotoxic effects of N-substituted allocolchicinoids

(-)-N-Substituted colchinol methyl ethers (6-10) and N-alkyl HCl salts (8a-10a) were synthesized from (-)-colchicine (1). The new compounds were evaluated for in vitro cytotoxic activity against five human tumor cell lines and for inhibition of tubulin polymerization. The new carbamate (6) and amide (7) showed 10-fold stronger activity against human tumor cell line replication than the amines (8-10). The corresponding HCl salts (8a-10a) generally showed decreased activity. Compounds (6) and (7) also exerted strong inhibitory effects on tubulin polymerization. All of the colchinol methyl ethers showed essentially equal cytotoxic effects against MDR-resistant (KB-V) and non-resistant (KB) cells, while the potency of colchicine was decreased 100-fold against KB-V cells.

The first total synthesis of (+/-)-linderol A, a tricyclic hexahydrodibenzofuran constituent of Lindera umbellata bark, with potent inhibitory activity on melanin biosynthesis of cultured B-16 melanoma cells.

[reaction in text] The first total synthesis of (+/-)-linderol A, a hexahydrodibenzofuran isolated from Lindera umbellata bark, with potent inhibitory activity on melanin biosynthesis of cultured B-16 melanoma cells was achieved via a 20-step of reaction in 7.64% overall yield starting from 4,6-dimethoxysalicylaldehyde.

Total synthesis of a marine imidazole alkaloid, clathridine A

Abstract The first total synthesis of clathridine A ( 8 ), a marine imidazole alkaloid, was achieved by using a novel regioselective condensation as a key step, in which preclathridine A ( 2 ) was treated with 1-methylparabanic acid ( 11 ) in the presence of a silylating agent.

Functional masking of carbonyl group by 1-methyl-1H-imidazol-2-YL moiety

Abstract Easily obtained 1-methyl-2-(1′-hydroxyalkyl)-1H-imidazoles (4) were found to be a new type of masked form for carbonyl group which could survive under various severe conditions. The corresponding carbonyl compounds (3) were easily reproduced by quarternization of the imidazole (4) with CH 3 I followed by aqueous basic treatment. 2-Acyl-1H-imidazoles (5) were convertible to aldehydes or ketones (3) by using the present methodology.