- Palladium-Catalyzed Formation of Substituted Tetrahydropyrans: Mechanistic Insights and Structural Revision of Natural Products
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A comprehensive study on the stereochemical outcome of palladium-catalyzed formation of 2,4,6-trisubstituted tetrahydropyrans through cyclization of the corresponding allylic acetates using both Pd(0) and Pd(II) catalysts is presented. We have found that
- Della-Felice, Franco,De Assis, Francisco F.,Sarotti, Ariel M.,Pilli, Ronaldo A.
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- Pseudomonas sp. Lipase Immobilized on Magnetic Porous Polymer Microspheres as an Effective and Recyclable Biocatalyst for Resolution of Allylic Alcohols
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Magnetic porous polymeric microspheres containing epoxy groups were prepared by suspension polymerization (denoted as magnetic Fe3O4@GEM microspheres). Fe3O4@GEM with a specific surface area of 30.41 m2/g, average pore diameter of 17.13 nm, and pore volume of 0.13 cm3/g exhibited superparamagnetic behavior with the saturation magnetization of 7.1 emu/g. The content of epoxy groups on Fe3O4@GEM was 0.22 mmol/g. Pseudomonas sp. lipase (PSL) was covalently immobilized onto the Fe3O4@GEM microspheres through the reaction between the amino groups of the enzyme and the epoxy groups on the microspheres. PSL/Fe3O4@GEM exhibited enhanced enantioselectivity for the resolution of allylic alcohol to the corresponding optically active (S)-allylic alcohol and (R)-allylic alcohol acetate compared to free PSL. The enantiomeric excess of (S)-l-pheny-2-propen-1-ol for the former (98.1%) was 81.7 times that of the latter (1.2%) when the immobilized PSL was used for transesterification resolution of (R,S)-l-pheny-2-propen-1-ol. Furthermore, the ees and eep values were still retained at 95.2% and 95.4% after PSL/Fe3O4@GEM was recycled 10 times, indicating that PSL/Fe3O4@GEM had very good reusability. In addition, the transesterification resolution of (R,S)-1-(4-methylphenyl)-2-propen-1-ol and (R,S)-1-(4-bromophenyl)-2-propen-1-ol was catalyzed by PSL/Fe3O4@GEM, affording ideal ees and eep values of 99.3%, 97.4% and 99.6%, 98.2%, respectively. Therefore, PSL/Fe3O4@GEM demonstrated its potential as a highly efficient enzymatic reactor and Fe3O4@GEM would be very promising carriers for immobilizing enzymes in industrial application.
- Gu, Yaohua,Xue, Ping
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p. 696 - 705
(2018/06/27)
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- Anti-proliferative, apoptotic induction, and anti-migration effects of hemi-synthetic 1’S-1’-acetoxychavicol acetate analogs on MDA-MB-231 breast cancer cells
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Nine analogs of 1′S-1′-acetoxychavicol acetate (ACA) were hemi-synthesized and evaluated for their anticancer activities against seven human cancer cell lines. The aim of this study was to investigate the anti-proliferative, apoptotic, and anti-migration effects of these compounds and to explore the plausible underlying mechanisms of action. We found that ACA and all nine analogs were non toxic to human mammary epithelial cells (HMECs) used as normal control cells, and only ACA, 1′-acetoxyeugenol acetate (AEA), and 1′-acetoxy-3,5-dimethoxychavicol acetate (AMCA) inhibited the growth of MDA-MB-231 breast cancer cells with a half-maximal inhibitory concentration (IC50) value of 30.0 μM based on 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay results, and were selected for further investigation. DNA fragmentation assays showed that these three compounds markedly induced apoptosis of MDA-MB-231 cells. Western blot analysis revealed increased expression levels of cleaved PARP, p53, and Bax, while decreased expression levels of Bcl-2 and Bcl-xL were seen after treatment, indicating that apoptosis was induced via the mitochondrial pathway. Moreover, ACA, AEA, and AMCA effectively inhibited the migration of MDA-MB-231 cells. They also downregulated the expression levels of pFAK/FAK and pAkt/Akt via the integrin β1-mediated signaling pathway. Collectively, ACA and its hemi-synthetic analogs, AEA and AMCA are seen as potential anticancer agents following their abilities to suppress growth, induce apoptosis, and inhibit migration of breast cancer cells.
- Liew, Su Ki,Azmi, Mohamad Nurul,In, Lionel L. A.,Awang, Khalijah,Nagoor, Noor Hasima
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p. 2763 - 2776
(2017/10/11)
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- Kinetic resolution of allylic alcohols via stereoselective acylation catalyzed by lipase PS-30
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By using lipase PS-30 as catalyst, the kinetic resolution of a series of racemic allylic alcohols has been achieved via stereoselective acylation. The value of kinetic enantiomeric ratio (E) reached up to 968. Substituent effect is briefly discussed.
- Chen, Peiran,Xiang, Peng
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p. 5758 - 5760
(2011/12/03)
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- A new mathematical method for determining the enantiomeric ratio in lipase-catalyzed reactions
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We present a new mathematical method for determining the enantiomeric ratio (E) during lipase-catalyzed kinetic resolutions. The method involves the fitting of a model to profiles of adimensionalized concentrations of the two enantiomers of the chiral substrate, plotted against degree of conversion. The model equations are presented for a reversible reaction involving bi-bi ping-pong kinetics in which the chiral substrate enters second and the chiral product leaves second. However, it is also shown that the method is easy to modify for analysis of resolutions involving other chiral substrate-product pairs and of resolutions in which the behavior of the system can be approximated by irreversible uni-uni kinetics. We show that our method retains several advantageous features of existing methods that help to ensure accuracy.
- Mitchell, David Alexander,Moure, Vivian Rotuno,Marques, Francisco de Assis,Krieger, Nadia
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experimental part
p. 23 - 28
(2010/11/02)
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- Enantioselective hydrolysis of 1-arylallyl acetates catalyzed by Candida antarctica lipase
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(R)-1-Arylallyl alcohols were obtained with excellent enantioselectivities via kinetic resolution of the corresponding acetates using immobilized Candida antarctica lipase. The scope and limitations of this reaction were investigated. The best results are obtained using the water/acetonitrile solvent system, and the reaction tolerates a variety of aryl and heteroaryl substituents.
- Kadnikova, Ekaterina N.,Thakor, Vikalp A.
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p. 1053 - 1058
(2008/09/19)
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- Structure-activity relationships of 1′S-1′-acetoxychavicol acetate for inhibitory effect on NO production in lipopolysaccharide-activated mouse peritoneal macrophages
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1′S-1′-Acetoxychavicol acetate from the rhizomes of Alpinia galanga inhibited nitric oxide (NO) production in lipopolysaccharide-activated mouse peritoneal macrophages with an IC50 value of 2.3 μM. To clarify the structure-activity relationship of 1′S-1′- acetoxychavicol acetate, various natural and synthetic phenylpropanoids and synthetic phenylbutanoids were examined, and the following structural requirements were clarified. (1) The para or ortho substitution of the acetoxyl and 1-acetoxypropenyl groups at the benzene ring was essential. (2) The S configuration of the 1′-acetoxyl group was preferable. (3) The presence of the 3-methoxyl group and disappearance of the 2′-3′ double bond by hydrogenation reduced the activity. (4) The substitution of acetyl groups with propionyl or methyl groups reduced the activity. (5) Lengthening of the carbon chain between the 1′- and 2′-positions reduced the activity.
- Matsuda, Hisashi,Ando, Shin,Morikawa, Toshio,Kataoka, Shinya,Yoshikawa, Masayuki
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p. 1949 - 1953
(2007/10/03)
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- Aminocyclopentadienyl Ruthenium Complexes as Racemization Catalysts for Dynamic Kinetic Resolution of Secondary Alcohols at Ambient Temperature
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Aminocyclopentadienyl ruthenium complexes, which can be used as room-temperature racemization catalysts with lipases in the dynamic kinetic resolution (DKR) of secondary alcohols, were synthesized from cyclopenta-2,4-dienimines, Ru3(CO)12, and CHCl 3: [2,3,4,5-Ph4(η5-C 4CNHR)]Ru-(CO)2Cl (4: R = i-Pr; 5: R = n-Pr; 6: R = t-Bu), [2,5-Me2-3,4-Ph2(η5-C 4CNHR)]Ru(CO)2Cl (7: R = i-Pr; 8: R = Ph), and [2,3,4,5-Ph4(η5-C4CNHAr)]Ru(CO) 2Cl (9: Ar =p-NO2C6H4; 10: Ar = p-ClC6H4; 11: Ar = Ph; 12: Ar = p-OMeC6H 4; 13: Ar = p-NMe2C6H4). The tests in the racemization of (S)-4-phenyl-2-butanol showed that 7 is the most active catalyst, although the difference decreased in the DKR. Complex 4 was used in the DKR of various alcohols; at room temperature, not only simple alcohols but also functionalized ones such as allylic alcohols, alkynyl alcohols, diols, hydroxyl esters, and chlorohydrins were successfully transformed to chiral acetates. In mechanistic studies for the catalytic racemization, ruthenium hydride 14 appeared to be a key species. It was the major organometallic species in the racemization of (S)-1-phenylethanol with 4 and potassium tert-butoxide. In a separate experiment, (S)-1-phenylethanol was racemized catalytically by 14 in the presence of acetophenone.
- Choi, Jun Ho,Choi, Yoon Kyung,Kim, Yu Hwan,Park, Eun Sil,Kim, Eun Jung,Kim, Mahn-Joo,Park, Jaiwook
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p. 1972 - 1977
(2007/10/03)
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- Solvent-dependent dynamic kinetic asymmetric transformation/kinetic resolution in molybdenum-catalyzed asymmetric allylic alkylations
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Catalytic asymmetric alkylation reactions of branched racemic carbonates 1a and 1b with sodium dimethyl malonate, promoted by molybdenum and ligand 5, proceed by a kinetic resolution in toluene, THF, tetrahydropyran, i-PrOAc, 1,2-dichloroethane, and MeCN with krel of 7-16. In THF, MeCN, tetrahydropyran, and i-PrOAc using the (S,S)-5 ligand, the fast reacting (S)-carbonate enantiomer provides the branched product with high ee (97-99.5%) and branched/linear selectivity, but the ee erodes as the reaction of the slow-reacting (R)-enantiomer takes place. This implies that the rate of equilibration of the oxidative addition complexes in these solvents is competitive with the subsequent malonate displacement step. In toluene and dichloroethane, the ee and branched/linear ratios diminish during the reaction of the slow-reacting (R)-isomer, but not nearly as much as in the other solvents. This is most likely due to either an increase in the rate of equilibration of the oxidative addition complexes relative to the malonate displacement step, or vice versa. Because of the minimal stereochemical memory effect in toluene and 1,2-dichloroethane, the reactions in these solvents can be carried to completion (dynamic kinetic asymmetric transformation) and still provide product with excellent ee (>95%). The anion of dimethyl methylmalonate also reacts via a kinetic resolution, although the ee's, rates, and krel values differ from those of the reactions with dimethyl malonate.
- Hughes, David L.,Palucki, Michael,Yasuda, Nobuyoshi,Reamer, Robert A.,Reider, Paul J.
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p. 2762 - 2768
(2007/10/03)
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