Kwang-Hyun Ahn

Highly fluorescent photochromic diarylethene with an excellent fatigue property

A series of diarylethenes and their disulfonyl derivatives such as 1,2-bis(2-heptyl-1-benzothiophene-3-yl)perfluorocyclopentene (HBTF6), 1,2-bis(6-acetyl-2-heptyl-1-benzothiophene-3-yl)perfluorocyclopentene (DAHBTF6), 1,2-bis(2-heptyl-1-benzothiophene-1,1-dioxide-3-yl)perfluorocyclopentene (HBTFO4), and 1,2-bis(6-acetyl-2-heptyl-1-benzothiophene-1,1-dioxide-3-yl)perfluorocyclopentene (DAHBTFO4), have been prepared for the examination of a substituent and an oxidation effect on photochromic and photophysical properties. Steady state fluorescence studies indicated that the disulfonyl diarylethenes were highly fluorescent only in the closed form. The introduction of acetyl groups at the 6,6′ positions and heptyl groups at the 2,2′ positions in disulfonyl diarylethene gave rise to an increase in the fluorescence quantum yield and fluorescence lifetime. Fatigue properties of oxidized diarylethenes were improved by the introduction of acetyl groups, indicating that the photochromic properties of diarylethene are strongly affected by substituents. We also demonstrated the recording to and erasing of information from the materials by an alternating illumination with UV and visible light, and the accompanying strong fluorescence intensity changes provided a highly efficient information readout system, which may be applicable to erasable optical data-storage elements.

Highly fluorescent photochromic diarylethene in the closed-ring form

A highly fluorescent diarylethene in the closed-ring form was synthesized by the oxidation of 1,2-bis(2-methyl-1-benzothiophene-3-yl)perfluorocyclopentene (BTF6).

Preparation of diarylethene copolymers and their photoinduced refractive index change

Diarylethene copolymers were synthesized from 1-(6 0 -vinyl-2 0 -methylbenzo[b]thiophene-3 0 -yl)-2-(2 00 -methylbenzo[b]thiophene-3 00 -yl)hexafluorocyclopentene (VMBTF6) and 1-[6 0 -(4 000 -vinylbenzoyl)-2 0 -methylbenzo[b]thiophene-3 0 -yl]-2(2 00 -methylbenzo[b]thiophene-3 00 -yl)hexafluorocyclopentene (VBMBTF6) via living free radical techniques using stable TEMPO derivatives. The diarylethene content was controlled by the feed ratio of diarylethene derivatives and styrene. Transparent photochromic polymer films were prepared from the diarylethene copolymers with narrow molecular weight dispersion (PD � 1:3) by spin coating method. Photoinduced refractive index changes (DnTE) of the polymer films, with 25 mol% of diaryethene content, accompanied by the photochromic change were determined as 0.0009 and 0.0030 for poly(styrene-ran-VMBTF6) and poly(styrene-ran-VBMBTF6), respectively. 2002 Published by Elsevier Science B.V.

Anti-neuroinflammatory activity of 1,5-benzodiazepine derivatives.

A series of 2,3-dihydro-1,5-benzodiazepines were synthesized and evaluated for anti-inflammatory effects in microglia cells. Among the 1,5-benzodiazepines tested, compound 3e strongly inhibited LPS-induced nitric oxide (NO) production, with an IC(50) value of 7.0microM in the microglia cells. Also, compound 3e significantly inhibited the enzymatic activity of inducible NO synthase (iNOS) without changes in iNOS protein expression or NO scavenging activity. This result suggests that compound 3e showed anti-neuroinflammatory effects by suppressing iNOS enzyme activity.

Enantioselective epoxidation of olefins catalyzed by new sterically hindered salen–Mn(III) complexes

Abstract New, sterically hindered chiral salen–Mn(III) complexes, 5 and 6 , were prepared from an aldehyde derived from BINOL. These substances catalyze efficient, enantioselective NaOCl-promoted epoxidations of olefins and enantioselectivities as high as 96–99% ee are observed in epoxidations of cis -β-methylstyrene and 2,2-dimethylchromene.

THE REACTION OF N-(P-TOLUENESULFONYL)IMINO-PHENYLIODINANE WITH ENOL SILANES

Abstract [N-(p-Toluenesulfonyl)imino]phenyliodinane reacts with enol silanes to provide α-tosylamino carbonyl compounds.

STEREOSELECTIVE HOMOCOUPLING OF ENOLATE ANION PROMOTED BY HYPERVALENT IODINE COMPOUND

Abstract (Diacetoxyiodo)benzene reacts with enolates derived from oxazolidinones to produce 1, 4-dicarboxylic acid derivatives.

Chiral 2,2-disubstituted cyclopropanecarboxylic acids: Effective derivatizing agents for analysis of enantiomeric purity of alcohols and for resolution of 1,1′-bi-2-naphthol

The enantiomeric purities of secondary alcohols can be easily analyzed by GC and HPLC through derivatization to the esters of 2,2-disubstituted cyclopropanecarboxylic acids 1, and by 1H NMR analysis of the esters of 2,2-diphenylcyclopropanecarboxylic acid (1b). In addition racemic 1,1′-bi-2-naphthol is easily resolved through derivatization to monoesters of 2,2-dimethylcyclopropanecarboxylic acid (1a), which are crystallized selectively and sequentially in high yields with high optical purities.

Oxidation of Enolate Anion by Hypervalent Iodine Compounds: Synthesis of α-Tempo Carbonyl Compound, A New Living Radical Polymerization Initiator

Abstract Oxyfunctionalization of esters, 1, by (diacetoxyiodo)benzene and 2,2,6,6-tetramethylpiperidinyl-l-oxy radical produced α-TEMPO esters, 2, which are an efficient unimolecular initiator for the living radical polymerization.

A substituted 3,4-dihydropyrimidinone derivative (compound D22) prevents inflammation mediated neurotoxicity; role in microglial activation in BV-2 cells

A novel synthetic 3,4-dihydropyrimidinone derivative, compound D22 (ethyl 6-methyl-4-(3-phenoxyphenyl)-2-thioxo-3,4-dihydropyrimidine-5-carboxylate), was found to exert anti-inflammatory properties in lipopolysaccharide-stimulated microglial BV-2 cells. Compound D22 reduced the pro-inflammatory factors such as nitric oxide, prostaglandin E(2), tumor necrosis factor-α and interleukin-1β. Moreover, it suppressed the expressions of inducible NO synthase and cyclooxygenase-2. Compound D22 inhibited the activation of mitogen-activated protein kinases. When compound D22-conditioned media from BV-2 cells were applied to N2a cells, neuronal cell death was inhibited via suppression of caspase-3 activation and regulation of Bcl-2 and Bax proteins expression. These results suggest that compound D22 may be useful for treating neurodegenerative diseases related with neuroinflammation.