scholarly journals SnCl4-catalyzed solvent-free acetolysis of 2,7-anhydrosialic acid derivatives

2019 ◽  
Vol 15 ◽  
pp. 2990-2999
Author(s):  
Kesatebrhan Haile Asressu ◽  
Cheng-Chung Wang
Keyword(s):  
Sialic Acid ◽  
Lewis Acids ◽  
Ring Opening ◽  
Building Blocks ◽  
Solvent Free ◽  
Biologically Active ◽  
Protecting Group ◽  
Free Ring ◽  
Ring Opening Reactions ◽  
Acid Catalyzed

Sialic acid-containing glycans are found in different sialic acid forms and a variety of glycosidic linkages in biologically active glycoconjugates. Hence, the preparation of suitably protected sialyl building blocks requires high attention in order to access glycans in a pure form. In line with this, various C-5-substituted 2,7-anhydrosialic acid derivatives bearing both electron-donating and -withdrawing protecting groups were synthesized and subjected to different Lewis acid-catalyzed solvent-free ring-opening reactions at room temperature in the presence of acetic anhydride. Among the various Lewis acids tested, the desired acetolysis products were obtained in moderate yields under tin(IV) chloride catalysis. Our methodology could be extended to regioselective protecting group installations and manipulations towards a number of thiosialoside and halide donors.

scholarly journals SnCl4-catalyzed Solvent-free Acetolysis of 2,7-Anhydrosialic Acid Derivatives

2019 ◽  
Author(s):  
Kesatebrhan Haile Asressu ◽  
Cheng-Chung Wang
Keyword(s):  
Sialic Acid ◽  
Lewis Acids ◽  
Ring Opening ◽  
Building Blocks ◽  
Solvent Free ◽  
Biologically Active ◽  
Protecting Group ◽  
Free Ring ◽  
Ring Opening Reactions ◽  
Acid Catalyzed

Sialic acid-containing glycans are found in different sialic acid forms and a variety of glycosidic linkages in biologically active glycoconjugates. Hence, the preparation of suitably protected sialyl building blocks requires high attention in order to access glycans in pure form. In this line, various C-5 substituted 2,7-anhydrosialic acid derivatives bearing both electron donating and withdrawing protecting groups were synthesized and subjected to different Lewis acid-catalyzed solvent free ring opening reactions at room temperature in the presence of acetic anhydride. Among the various Lewis acids tested, the desired acetolysized products were obtained in moderate yields under a tin(IV) chloride catalysis system. Our methodology can be extended to regioselective protecting group installation and manipulation towards a number of thiosialoside and halide donors.

scholarly journals Low-temperature and purification-free stereocontrolled ring-opening polymerisation of lactide in supercritical carbon dioxide

2020 ◽  
Vol 22 (7) ◽  
pp. 2197-2202 ◽  
Author(s):  
Simon P. Bassett ◽  
Andrew D. Russell ◽  
Paul McKeown ◽  
Isabel Robinson ◽  
Thomas R. Forder ◽  
...  
Keyword(s):  
Carbon Dioxide ◽  
Low Temperature ◽  
Supercritical Carbon Dioxide ◽  
Ring Opening ◽  
Solvent Free ◽  
Free Ring ◽  
First Time ◽  
Supercritical Carbon

A stereoselective, solvent-free ring-opening polymerisation (ROP) of lactide (LA) in supercritical carbon dioxide (scCO2) is reported for the first time.

scholarly journals Microwave Heating Promotes the S-Alkylation of Aziridine Catalyzed by Molecular Sieves: A Post-Synthetic Approach to Lanthionine-Containing Peptides

Molecules ◽  
2021 ◽  
Vol 26 (20) ◽  
pp. 6135
Author(s):  
Valentina Verdoliva ◽  
Giuseppe Digilio ◽  
Michele Saviano ◽  
Stefania De Luca
Keyword(s):  
Microwave Irradiation ◽  
Molecular Sieves ◽  
Ring Opening ◽  
Cysteine Residue ◽  
Biologically Active ◽  
Synthetic Approach ◽  
Stepwise Approach ◽  
Valuable Alternative ◽  
Ring Opening Reactions ◽  
Nucleophilic Ring Opening

Aziridine derivatives involved in nucleophilic ring-opening reactions have attracted great interest, since they allow the preparation of biologically active molecules. A chemoselective and mild procedure to convert a peptide cysteine residue into lanthionine via S-alkylation on aziridine substrates is presented in this paper. The procedure relies on a post-synthetic protocol promoted by molecular sieves to prepare lanthionine-containing peptides and is assisted by microwave irradiation. In addition, it represents a valuable alternative to the stepwise approach, in which the lanthionine precursor is incorporated into peptides as a building block.

Nonmetal Schiff-Base Complex-Anchored Cellulose as a Novel and Reusable Catalyst for the Solvent-Free Ring-Opening Addition of CO2 with Epoxides

2019 ◽  
Vol 58 (37) ◽  
pp. 17255-17265 ◽  
Author(s):  
Shiyu Chen ◽  
Manoj Pudukudy ◽  
Zhongxiao Yue ◽  
Heng Zhang ◽  
Yunfei Zhi ◽  
...  
Keyword(s):  
Schiff Base ◽  
Ring Opening ◽  
Schiff Base Complex ◽  
Solvent Free ◽  
Reusable Catalyst ◽  
Free Ring ◽  
Base Complex

scholarly journals Palladium-catalyzed α-arylation for the addition of small rings to aromatic compounds

2019 ◽  
Vol 10 (1) ◽  
Author(s):  
Zhi-Tao He ◽  
John F. Hartwig
Keyword(s):  
Electronic Properties ◽  
Aromatic Compounds ◽  
Ring Opening ◽  
Biologically Active ◽  
High Yield ◽  
Protecting Group ◽  
Mechanistic Studies ◽  
Claisen Condensation ◽  
Wide Range ◽  
Palladium Catalyzed

Abstract Small, strained rings have rigid, defined conformations and unique electronic properties. For these reasons, many groups seek to use these subunits to form biologically active molecules. We report a generally applicable approach to attach small rings to a wide range of aromatic compounds by palladium-catalyzed α-arylation of cyclopropyl, cyclobutyl and azetidinyl esters. The direct α-arylation of cyclopropyl esters and cyclobutyl esters is achieved in high yield by ensuring that the rate of coupling exceeds the rate of Claisen condensation. The α-arylation of azetidines is achieved without ring opening of the strained saturated heterocycle by conducting the reactions with an azetidine derivative bearing a benzyl protecting group on nitrogen. Mechanistic studies show that the α-arylation of small rings is challenging because of the weak acidity of α C-H bond (cyclopropanes), strong sensitivity of the strained esters to Claisen condensation (cyclobutatanes), or facile decomposition of the enolates (azetidinyl esters).

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