- Rational design of bifunctional catalyst from KF and ZnO combination on alumina for cyclic urea synthesis from CO2 and diamine
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This study is mainly focused on the design of stable, active and selective catalyst for direct synthesis of 2-imidazolidinone (cyclic urea) from ethylenediamine and CO2. Based on the rationale for the catalyst properties needed for this reaction, KF, ZnO and Al2O3 combination was selected to design the catalyst. ZnO/KF/Al2O3 catalyst was prepared by stepwise wet-impregnation followed by the removal of physisorbed KF from the surface. High product yield could be achieved by tuning acid-base sites by varying the composition and calcination temperature. The catalysts were characterized by various techniques like XRD, N2-sorption, NH3-TPD, CO2-TPD, TEM, XPS and FT-IR measurements. It is shown that acidic and basic properties of the solvent can influence the activity and product selectivity for this reaction. Under optimized condition; 180 °C, 10 bar and 10 wt.% catalyst in batch mode, 96.3 % conversion and 89.6 % selectivity towards the 2-imidazolidinone were achieved.
- John, Crowny,Kulal, Nagendra,Shanbhag, Ganapati V.
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- Alkylamine-Substituted Perthiocarbamates: Dual Precursors to Hydropersulfide and Carbonyl Sulfide with Cardioprotective Actions
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The recent discovery of hydropersulfides (RSSH) in mammalian systems suggests their potential roles in cell signaling. However, the exploration of RSSH biological significance is challenging due to their instability under physiological conditions. Herein, we report the preparation, RSSH-releasing properties, and cytoprotective nature of alkylamine-substituted perthiocarbamates. Triggered by a base-sensitive, self-immolative moiety, these precursors show efficient RSSH release and also demonstrate the ability to generate carbonyl sulfide (COS) in the presence of thiols. Using this dually reactive alkylamine-substituted perthiocarbamate platform, the generation of both RSSH and COS is tunable with respect to half-life, pH, and availability of thiols. Importantly, these precursors exhibit cytoprotective effects against hydrogen peroxide-mediated toxicity in H9c2 cells and cardioprotective effects against myocardial ischemic/reperfusion injury, indicating their potential application as new RSSH- and/or COS-releasing therapeutics.
- Khodade, Vinayak S.,Pharoah, Blaze M.,Paolocci, Nazareno,Toscano, John P.
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supporting information
p. 4309 - 4316
(2020/03/05)
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- An approach towards more selective anticancer agents
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A promising approach towards better targeted anticancer drug therapy takes advantage of enhanced expression of proteases associated with human malignancies. Especially plasminogen activator activity has been found to be substantially increased, leading to an enhanced activity of the serine protease plasmin. Bifunctional alkylating agents, such as N-(2-chloroethyl)-N-nitrosoureas, display broad spectrum anticancer activity, but also exhibit considerable systemic toxicity. We describe here the synthesis of new N-nitrosourea-based prodrugs designed to become activated by tumor-associated proteases, to provide for enhanced antitumor activity and reduced systemic toxicity. Tripeptides representing substrates for plasmin were linked by an amide bond to N'-(2-aminoethyl)-N-(2-chloroethyl)-N-nitrosourea and the corresponding N'-methyl derivative. Synthesis and plasmin-triggered decomposition of these new tripeptide conjugates is described. Cancer cells expressing high plasminogen activator activity are highly sensitive to the new prodrugs in the presence of plasminogen, but not in its absence.
- Eisenbrand,Lauck-Birkel,Tang
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p. 1246 - 1258
(2007/10/03)
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This work is dealing with basic hydrolysis in water of allophanic esters as possible models of carboxybiotin. A complex mechanism is involved likely due to competition of nucleophilic attack on the two carbonyl groups of the substrate. The rate of hydrolysis is significantly increased by metallic cation (Mg++), a specific effect which allows to consider characterization of selectivity of bond breaking between nitrogen and carboxylate group with other nucleophiles.
- Monnier, Par E.,Klaebe,Perie
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p. 3269 - 3284
(2007/10/02)
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- 7-Alkylation and 7-Sulphonylation of 5,6-Dihydroimidazolo-thiazoles
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Reinvestigation of the alkylation of 3-phenyl-5,6-dihydroimidazolothiazole has shown that methylation occurs exclusively at the 7-position, and that the free base is readily solvolysed to a mixture of 1-methylimidazolidin-2-one, 1-methylimidazolidine-2-thione, and diphenacyl sulphide and disulphide. 3-Methyl-5,6-dihydroimidazolothiazole with methane- and arene-sulphonyl chlorides gave the corresponding 7-sulphonylthiazolium chlorides.On heating, these rearranged to 3-(2-chloroethyl)-4-methyl-3-aryl (or alkyl)sulphonylimido-2,3-dihydrothiazoles.The 7-(4-chlorophenylsulphonyl) derivative lost this substituent with aqueous base while concentrated aqueous ammonia attacked the 7a-position leading to a 3--2-imino-4-methyl-2,3-dihydrothiazole.
- Acheson, R. Morrin,Cooper, Martin W.,Cox, Ian R.
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p. 1773 - 1778
(2007/10/02)
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- Model Studies on the Mechanism of Biotin-Dependent Carboxylations. 2. Site of Protonation vs. CO2 Transfer
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Three irreversibly acidified model compounds (6-8) of N'-carboxybiotin (2) have been prepared to access the importance of proir protonation of the biotin ring system of the CO2-transfer potential of the N'-carboxy group.Substrates 6 and 7 can be considered model compounds of N'-carboxybiotin (2) in which protonation has occurred at the ureido carbonyl oxygen atom.Conversely, compound 8 was synthesized to evaluate the CO2-transfer potential of the N'-carboxy group, if protonation occurred at the N'-nitrogen atom.The reactivity of each substrate with nucleophiles has been evaluated.Of these three compounds, only 8 led to efficient transfer to the carbomethoxy group upon treatment with nitrogen-containing nucleophiles (morpholine, cyclohexylamine, and diisopropylamine).With smaller nucleophiles (i.e, water, methanol) reaction was centered at the ring C-2 position.Correspondingly, treatment of compound 6 with nucleophiles (i.e, alcohols, amines) led to products which can be explained in terms of two competing reactions.One pathway involves initial attack of the nucleophile at the C-2 position of the imidazolinium cation (an AAC2 process) to give a tetrahedral intermediate which then undergoes bond cleavage in either of two directions.The competing pathway observed was an irreversible SN2 displacement reactions (an AAL2 process) at the methylene position of the O-alkyl side chain.Factors are presented which account for the overall product distribution obtained from these reactions.Finally, the products obtained from the treatment of compound 7 with nucleophiles (i.e., alcohols, amines) could be accounted for solely by reactions which occurred at the C-2 position of the ring (an AAC2 process).The corresponding SN2 pathway is not a viably route for this substrate.The significance of these results to the mechanism of action of biotin is discussed.
- Cravey, Melanie J.,Kohn, Harold
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p. 3928 - 3939
(2007/10/02)
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