• Bulletin of the Korean Chemical Society
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• v.13 no.4
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• pp.395-398
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• 1992

Rate of solvolysis of dansyl chloride in aqueous binary mixtures of acetone, methanol and ethanol are reported. Kinetic solvent isotope effects in methanol and product selectivities in alcohol-water mixtures are also reported. Kinetic data are interpreted with the Grunwald-Winstein and Kivinen equations. The value of $k_{CH3OH}/k_{CH3OD}=1.76$ suggests that a general have catalyzed and/or an $S_AN$ pathway is operative in methanol, a less polar solvent. Rate-rate profiles for solvolysis of dansyl chloride in the aqueous binary media indicate a change in reaction channel from $S_AN$ (in less polar media) to $S_N2$ (in more polar media) mechanism.

• Bulletin of the Korean Chemical Society
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• v.33 no.12
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• pp.4117-4121
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• 2012

The solvolysis rate constants of allyl chloroformate ($CH_2=CHCH_2OCOCl$, 3) in 30 different solvents are well correlated with the extended Grunwald-Winstein equation, using the $N_T$ solvent nucleophilicity scale and $Y_{Cl}$ solvent ionizing scale, with the sensitivity values of $0.93{\pm}0.05$ and $0.41{\pm}0.02$ for l and m, respectively. These l and m values can be considered to support a $S_N2$ reaction pathway. The activation enthalpies (${\Delta}H^{\neq}$) were 12.5 to 13.4 $kcal{\cdot}mol^{-1}$ and the activation entropies (${\Delta}S^{\neq}$) were -34.4 to -37.3 $cal{\cdot}mol^{-1}{\cdot}K^{-1}$, which is also consistent with the proposed bimolecular reaction mechanism. The solvent kinetic isotope effect (SKIE, $k_{MeOH}/k_{MeOD}$) of 2.16 was also in accord with the $S_N2$ mechanism. The values of product selectivity (S) for the solvolyses of 3 in alcohol/water mixtures was 1.3 to 3.9, which is also consistent with the proposed bimolecular reaction mechanism.

• Journal of Korean Neurosurgical Society
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• v.66 no.6
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• pp.642-651
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• 2023

Objective : Endothelial colony-forming cells (ECFCs) have been reported to play an important role in the pathogenesis of moyamoya disease (MMD). We have previously observed stagnant growth in MMD ECFCs with functional impairment of tubule formation. We aimed to verify the key regulators and related signaling pathways involved in the functional defects of MMD ECFCs. Methods : ECFCs were cultured from peripheral blood mononuclear cells of healthy volunteers (normal) and MMD patients. Low-density lipoproteins uptake, flow cytometry, high content screening, senescence-associated β-galactosidase, immunofluorescence, cell cycle, tubule formation, microarray, real-time quantitative polymerase chain reaction, small interfering RNA transfection, and western blot analyses were performed. Results : The acquisition of cells that can be cultured for a long time with the characteristics of late ECFCs was significantly lower in the MMD patients than the normal. Importantly, the MMD ECFCs showed decreased cellular proliferation with G1 cell cycle arrest and cellular senescence compared to the normal ECFCs. A pathway enrichment analysis demonstrated that the cell cycle pathway was the major enriched pathway, which is consistent with the results of the functional analysis of ECFCs. Among the genes associated with the cell cycle, cyclin-dependent kinase inhibitor 2A (CDKN2A) showed the highest expression in MMD ECFCs. Knockdown of CDKN2A in MMD ECFCs enhanced proliferation by reducing G1 cell cycle arrest and inhibiting senescence through the regulation of CDK4 and phospho retinoblastoma protein. Conclusion : Our study suggests that CDKN2A plays an important role in the growth retardation of MMD ECFCs by inducing cell cycle arrest and senescence.

• The Korean Journal of Physiology and Pharmacology
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• v.28 no.3
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• pp.265-273
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• 2024

This study aims to explore possible effect of RNA polymerase I subunit D (POLR1D) on proliferation and angiogenesis ability of colorectal cancer (CRC) cells and mechanism herein. The correlation of POLR1D and Yin Yang 1 (YY1) expressions with prognosis of CRC patients in TCGA database was analyzed. Quantitative realtime polymerase chain reaction (qRT-PCR) and Western blot were applied to detect expression levels of POLR1D and YY1 in CRC cell lines and CRC tissues. SW480 and HT-29 cells were transfected with si-POLR1D or pcDNA3.1-POLR1D to achieve POLR1D suppression or overexpression before cell migration, angiogenesis of human umbilical vein endothelial cells were assessed. Western blot was used to detect expressions of p38 MAPK signal pathway related proteins and interaction of YY1 with POLR1D was confirmed by dual luciferase reporter gene assay and chromatin immunoprecipitation (ChIP). TCGA data showed that both POLR1D and YY1 expressions were up-regulated in CRC patients. High expression of POLR1D was associated with poor prognosis of CRC patients. The results showed that POLR1D and YY1 were highly expressed in CRC cell lines. Inhibition or overexpression of POLR1D can respectively suppress or enhance proliferation and angiogenesis of CRC cells. YY1 inhibition can suppress CRC progression and deactivate p38 MAPK signal pathway, which can be counteracted by POLR1D overexpression. JASPAR predicted YY1 can bind with POLR1D promoter, which was confirmed by dual luciferase reporter gene assay and ChIP. YY1 transcription can up-regulate POLR1D expression to activate p38 MAPK signal pathway, thus promoting proliferation and angiogenesis ability of CRC cells.

• Bulletin of the Korean Chemical Society
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• v.15 no.2
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• pp.154-161
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• 1994

Studies have been conducted to explore single electron transfer (SET) induced photocyclization reactions of N-(trimethylsilylmethylthioalkyl)phthalimides (alkyl=ethyl, n-propyl, n-butyl, n-pentyl, and n-hexyl). Photocyclizations occur in methanol in modest to high yields to produce cyclized products in which phthalimide carbonyl carbon is bonded to the carbon of side chain in place of the trimethylsilyl group. Mechanism for these photocyclizations involving intramolecular SET from sulfur in the ${\alpha}$-silylmethylthioalkyl groups to the singlet excited state phthalimide moieties followed by desilylation of the intermediate ${\alpha}$ -silylmethylthio cation radicals and cyclization by radical coupling is proposed. In contrast, photoreactions of N-(trimethylsilylmethylthioalkyl)phthalimides in acetone follow different reaction routes to produce another cyclized products in which carbon-carbon bond formation takes place between the phthalimide carbonyl carbon and the carbon ${\alpha}$ to silicon and sulfur atoms via triplet carbonyl hydrogen abstraction pathway. The normal singlet SET pathway dominates this triplet process for photoreactions of these substances in methanol while the triplet process dominates the singlet SET pathway for those in acetone. The efficient and regioselective cyclization reactions observed for photolyses in methanol represent synthetically useful processes for construction of medium and large ring heterocyclic compounds.

• Bulletin of the Korean Chemical Society
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• v.35 no.7
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• pp.2135-2138
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• 2014

A kinetic study is reported for the SNAr reaction of 1-Y-substituted-phenoxy-2,4-dinitrobenzenes (1a-1h) with OH- in 80 mol % $H_2O$/20 mol % DMSO at $25.0{\pm}0.1^{\circ}C$. The second-order rate constant ($k_{OH^-}$) increases as the substituent Y in the leaving group changes from an electron-donating group (EDG) to an electronwithdrawing group (EWG). The Br${\o}$nsted-type plot for the reactions of 1a-1h is linear with ${\beta}_{lg}$ = -0.16, indicating that the reactivity of substrates 1a-1h is little affected by the leaving-group basicity. A linear Br${\o}$nsted-type plot with ${\beta}_{lg}=-0.3{\pm}0.1$ is typical for reactions reported previously to proceed through a stepwise mechanism in which formation of a Meisenheimer complex is the rate-determining step (RDS). The Hammett plot correlated with ${\sigma}_Y{^{\circ}}$ constants results in a much better correlation than that correlated with ${\sigma}_Y{^-}$constants, implyng that no negative charge is developing on the O atom of the leaving group (or expulsion of the leaving group is not advanced at all in the TS). This excludes a possibility that the $S_NAr$ reaction of 1a-1h with $OH^-$ proceeds through a concerted mechanism or via a stepwise pathway with expulsion of the leaving group being the RDS. Thus, the current reactions have been concluded to proceed through a stepwise mechanism in which expulsion of the leaving group occurs rapidly after the RDS.

• Korean Journal of Plant Tissue Culture
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• v.25 no.5
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• pp.323-327
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• 1998

The flavonoid biosynthetic pathway has been studied as a genetic model system, particularly in Petunia hybrida. In order to study the flavonoid biosynthetic pathway, we constructed a fusion gene system between Cauliflower Mosaic Virus (CaMV) 35S promoter and eggplant flavonoid 3', 5'-hydroxylase in pBI 121 plasmid. An optimal condition for plant regeneration was observed when internode explants were cultured on MS medium supplemented with IAA 0.2 mg/L plus BA 3 mg/L. For plant transformation internode explants of Petunia hybrida were precultured on BM medium supplemented with IAA 0.2 mg/L plus BA 3 mg/L. Putative transgenic plants were selected on medium containing kanamycin 50 mg/L plus cefotaxim 300 mg/L. Putative selected transformants were confirmed by amplification of selectable marker gene (nptII) by polymerase chain reaction (PCR) and Southern hybridization of flavonoid 3',5'-hydroxylase gene.

• Journal of Microbiology and Biotechnology
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• v.27 no.10
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• pp.1867-1876
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• 2017

Most of the biosynthetic pathways for secondary metabolites are influenced by carbon metabolism and supply of cytosolic NADPH. We engineered carbon distribution to the pentose phosphate pathway (PPP) and redesigned the host to produce high levels of NADPH and primary intermediates from the PPP. The main enzymes producing NADPH in the PPP, glucose 6-phosphate dehydrogenase (encoded by zwf1 and zwf2) and 6-phosphogluconate dehydrogenase (encoded by zwf3), were overexpressed with opc encoding a positive allosteric effector essential for Zwf activity in various combinations in Streptomyces lividans TK24. Most S. lividans transformants showed better cell growth and higher concentration of cytosolic NADPH than those of the control, and S. lividans TK24/pWHM3-Z23O2 containing zwf2+zwf3+opc2 showed the highest NADPH concentration but poor sporulation in R2YE medium. S. lividans TK24/pWHM3-Z23O2 in minimal medium showed the maximum growth (6.2 mg/ml) at day 4. Thereafter, a gradual decrease of biomass and a sharp increase of cytosolic NADPH and sedoheptulose 7-phosphate between days 2 and 4 and between days 1 and 3, respectively, were observed. Moreover, S. lividans TK24/pWHM3-Z23O2 produced 0.9 times less actinorhodin but 1.8 times more undecylprodigiosin than the control. These results suggested that the increased NADPH concentration and various intermediates from the PPP specifically triggered undecylprodigiosin biosynthesis that required many precursors and NADPH-dependent reduction reaction. This study is the first report on bespoke metabolic engineering of PPP routes especially suitable for producing secondary metabolites that need diverse primary precursors and NADPH, which is useful information for metabolic engineering in Streptomyces.

• Journal of Microbiology and Biotechnology
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• v.29 no.4
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• pp.577-586
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• 2019

The engineered Aspergillus oryzae has a high NADPH demand for xylose utilization and overproduction of target metabolites. Glucose-6-phosphate dehydrogenase (G6PDH, E.C. 1.1.1.49) is one of two key enzymes in the oxidative part of the pentose phosphate pathway, and is also the main enzyme involved in NADPH regeneration. The open reading frame and cDNA of the putative A. oryzae G6PDH (AoG6PDH) were obtained, followed by heterogeneous expression in Escherichia coli and purification as a his6-tagged protein. The purified protein was characterized to be in possession of G6PDH activity with a molecular mass of 118.0 kDa. The enzyme displayed maximal activity at pH 7.5 and the optimal temperature was $50^{\circ}C$. This enzyme also had a half-life of 33.3 min at $40^{\circ}C$. Kinetics assay showed that AoG6PDH was strictly dependent on $NADP^+$ ($K_m=6.3{\mu}M$, $k_{cat}=1000.0s^{-1}$, $k_{cat}/K_m=158.7s^{-1}{\cdot}{\mu}M^{-1}$) as cofactor. The $K_m$ and $k_{cat}/K_m$ values of glucose-6-phosphate were $109.7s^{-1}{\cdot}{\mu}M^{-1}$ and $9.1s^{-1}{\cdot}{\mu}M^{-1}$ respectively. Initial velocity and product inhibition analyses indicated the catalytic reaction followed a two-substrate, steady-state, ordered BiBi mechanism, where $NADP^+$ was the first substrate bound to the enzyme and NADPH was the second product released from the catalytic complex. The established kinetic model could be applied in further regulation of the pentose phosphate pathway and NADPH regeneration of A. oryzae to improve its xylose utilization and yields of valued metabolites.

• Archives of Pharmacal Research
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• v.28 no.11
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• pp.1205-1212
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• 2005

2-Thiouracil-5-sulphonic acid N-(4-acetylphenyl) Amide (1) was reacted with a series of aromatic aldehydes giving chalcones 2 (Claisen-Schemidt reaction), some of these chalcones were reacted with urea and thiourea giving pyrimidine-2-one and pyrimidine-2 thione derivatives respectively of the type 3a,b and 4a,b. In addition many chalcones were reacted with hydroxylamine hydrochloride giving isoxazoline derivatives 5a,b. They could also reacted with phenylhydrazine to give pyrazoline derivatives 5a,b, chalcones also were reacted withethylcyano acetate and/or malononitryl in pyridine giving pyran derivatives 7a,c and 8a,c. In another pathway chalcones were epoxidised by $H_{2}O_{2}$ giving epoxides 9a,c which in turn were reacted with phenylhydrazine giving 4-hydroxypyrazoline derivatives 10a,c. In another reaction chalcones were reacted with ethylcyanoacetate in presence of amm.acetate giving pyridone derivatives 11a,d which could be prepared also in exellent yield from compound 1 by its reaction with certain aromatic aldehydes and ethylcyanoacetate in presence of ammonium acetate. Finally, compound 1 was reacted with semicarbazide giving semicarbazone intermediate 12 which in turn was reacted with thionyl chloride giving thiadiazole derivative 13. The biological effects of some of the new synthesized compounds were also investigated.