10.1016/j.tet.2008.01.094
The research focuses on the isolation and structural determination of four novel bicyclic hexapeptides, RA-XIX, RA-XX, RA-XXI, and RA-XXII, derived from the roots of Rubia cordifolia L. The study employs a series of extraction and purification techniques, including partitioning between chloroform and water, column chromatography using silica gel, alumina, and aminopropyl-bonded silica gel, and reversed-phase HPLC. The structures of the peptides were established through semisynthesis from a cycloisodityrosine and chemical correlation with previously reported compounds. The cytotoxicity of these peptides against P-388 leukemia cells was evaluated using the MTT assay, with IC50 values ranging from 0.013 to 0.63 mg/mL. The experiments utilized various analytical techniques such as NMR, HRESIMS, and optical rotation to confirm the structures and purity of the isolated peptides.
10.1246/cl.2008.620
The study presents an efficient and recyclable heterogeneous catalyst, 16 wt% MoO3 supported on alumina, for the regioselective ring opening of epoxides with thiols, acetic anhydride, and alcohols under solvent-free conditions. The catalyst was prepared by impregnating alumina with ammonium heptamolybdate and then calcining it at high temperatures. The chemicals used in the study include various epoxides (alkyl, aryl, and cycloalkyl), nucleophiles (thiol derivatives like benzenethiol, acetic anhydride, and alcohols), and the catalyst itself. The purpose of these chemicals was to synthesize valuable synthetic intermediates such as β-hydroxysulphides, 1,2-diacetates, and β-alkoxyalcohols, which are key intermediates in the synthesis of biologically active compounds. The study highlights the advantages of using this catalyst, such as ease of handling, high yield, and recyclability without loss of activity, making it a green and efficient method for organic synthesis.
10.1016/S0040-4020(97)10136-3
The study investigates two methods for reducing ketene dithioacetals to produce substituted dithianes, which serve as building blocks for heterocyclic synthesis. The researchers, John M. Mellor, Stephen R. Schofield, and Stewart R. Korn, compared the effectiveness of magnesium in methanol and zinc in acetic acid for this reduction process. They found that zinc in acetic acid was more reliable than magnesium in methanol, which showed inconsistent results due to steric constraints in certain substrates. The study also involved the preparation of various ketene dithioacetals using two methods: reaction of carbon disulfide with the enolate anion of appropriate 1,3-dicarbonyl compounds in dimethylformamide or on alumina. The resulting dithianes were then successfully converted into heterocyclic aldehydes through cyclization and deprotection steps, demonstrating their utility in synthesizing complex heterocyclic structures.
10.1016/j.molcata.2010.09.006
The study presents the preparation and evaluation of ruthenium nanoparticles supported on multi-walled carbon nanotubes (RuL-MWCNT) for their catalytic efficiency in hydrogenation reactions. The nanoparticles were synthesized using a ligand stabilization method and characterized by elemental analysis and transmission electronic microscopy. The catalytic performance of the supported RuL-MWCNT was compared with non-supported ruthenium nanoparticles and ruthenium nanoparticles supported on other materials like silica, alumina, and activated carbon. The study found that the RuL-MWCNT catalyst demonstrated superior activity and selectivity in converting various unsaturated substrates to fully hydrogenated products, maintaining its catalytic behavior even after recycling. The support's nature significantly influenced the catalytic activity, with MWCNT showing the best results among the tested supports. The study concludes that the RuL-MWCNT system is an effective catalyst for hydrogenation processes, offering high activity, selectivity, and recyclability.
10.1016/S0040-4020(01)96527-5
The study investigates the Wittig, Wittig-Horner, and Knoevenagel reactions in the presence of alumina or potassium fluoride supported on alumina, without using organic solvents. The chemicals involved include phosphonium salts, which act as reactants to form ylides in the Wittig reaction, and phosphonates that participate in the Wittig-Horner reaction. Aldehydes and ketones serve as carbonyl compounds reacting with the ylides and phosphonates. Alumina and potassium fluoride supported on alumina function as catalysts and reaction media, with alumina selectively favoring the Knoevenagel reaction and potassium fluoride promoting the Wittig-Horner reaction. A small amount of water is found to increase the reaction rates of Wittig and Wittig-Horner reactions by solvating the catalyst surface and aiding in the formation of intermediates. The study demonstrates that these reactions can be effectively catalyzed without solvents, offering a more environmentally friendly approach to organic synthesis.
10.1007/BF02496342
The study investigates the influence of the acid-base properties of alumina supports on the performance of 12-tungstophosphoric heteropolyacid (HPWA)-supported catalysts containing platinum in n-pentane isomerization. The study employs DRIFT spectroscopy to analyze the interaction of HPWA with alumina and fluorinated alumina supports. It reveals that the Pt/HPWA/Al2O3 system is nearly inactive due to the interaction of HPWA with basic sites on alumina, leading to partial decomposition of HPWA. In contrast, fluorinated alumina, which has enhanced acidic sites, prevents HPWA destruction and promotes uniform HPWA distribution on the support surface. This results in significantly improved activity and selectivity for the Pt/HPWA/Al2O3-F catalyst in n-pentane isomerization. The study highlights the importance of support properties in determining the catalytic behavior of HPWA-based systems and demonstrates that fluorination can enhance the acidic properties of alumina supports, thereby improving the performance of HPWA catalysts in alkane isomerization.
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