scholarly journals Non-Covalent Interactions in Enantioselective Organocatalysis: Theoretical and Mechanistic Studies of Reactions Mediated by Dual H-Bond Donors, Bifunctional Squaramides, Thioureas and Related Catalysts

Catalysts ◽  
2021 ◽  
Vol 11 (5) ◽  
pp. 569
Author(s):  
Ana Maria Faisca Phillips ◽  
Martin H. G. Prechtl ◽  
Armando J. L. Pombeiro
Keyword(s):  
Cascade Reactions ◽  
Cinchona Alkaloids ◽  
Chiral Amines ◽  
Theoretical Studies ◽  
Mechanistic Studies ◽  
Conjugate Additions ◽  
Non Covalent Interactions ◽  
High Yields ◽  
Covalent Interactions ◽  
Very High

Chiral bifunctional dual H-bond donor catalysts have become one of the pillars of organocatalysis. They include squaramide, thiosquaramide, thiourea, urea, and even selenourea-based catalysts combined with chiral amines, cinchona alkaloids, sulfides, phosphines and more. They can promote several types of reactions affording products in very high yields and excellent stereoselectivities in many cases: conjugate additions, cycloadditions, the aldol and Henry reactions, the Morita–Baylis–Hilman reaction, even cascade reactions, among others. The desire to understand mechanisms and the quest for the origins of stereoselectivity, in attempts to find guidelines for developing more efficient catalysts for new transformations, has promoted many mechanistic and theoretical studies. In this review, we survey the literature published in this area since 2015.

scholarly journals Mesoscale Assembly of Bisteroidal Esters from Terephthalic Acid

Molecules ◽  
2020 ◽  
Vol 25 (5) ◽  
pp. 1213 ◽  
Author(s):  
Gabriel Guerrero-Luna ◽  
María Guadalupe Hernández-Linares ◽  
Sylvain Bernès ◽  
Alan Carrasco-Carballo ◽  
Diana Montalvo-Guerrero ◽  
...  
Keyword(s):  
Self Assembly ◽  
Terephthalic Acid ◽  
Van Der Waals ◽  
Solvent System ◽  
Van Der Waals Interactions ◽  
Show Evidence ◽  
Non Covalent Interactions ◽  
Solvent Systems ◽  
High Yields ◽  
Covalent Interactions

A new series of bisteroidal esters was synthesized using a spacer group, sterols and sapogenins as substrates. Steroidal dimers were prepared in high yields employing diesters of terephthalic acid as linkages at the 3β, 3′β steroidal positions. In all attempts to crystallize bisteroids, it was observed that the compounds tended to self-organize in solution, which was detected when employing various solvent systems. The non-covalent interactions (van der Waals) of the steroidal moieties of this series of symmetrical bisteroids, the polarity of the solvents systems, and the different solubilities of the bisteroid aggregates, indeed induce the molecules to self-assemble into supramolecular structures with well-defined organization. Our results show that the self-assembled structures for the bisteroidal derivatives depend on the solvent system used: with hexane/EtOAc, membrane-shaped structures were obtained, while pure EtOAc afforded strand-shaped arrangements. In the CHCl3/CH3OH system, thin strands were formed, since van der Waals interactions are lowered in this system, as a consequence of the increased solubility of the bisteroids in CHCl3. Based on the characterization by SEM and XRD, we show evidence that the phenomenon of self-assembly of bisteroids occurs presenting different morphologies depending on the solvent used. The new steroidal dimer derivatives were characterized by NMR, TGA, DSC, SEM, and XRD. Finally, the molecular structure of one bisteroid was confirmed by single-crystal X-ray analysis.

Synthesis and theoretical studies of non‒covalent interactions within a newly synthesized chiral 1,2,4-triazolo[3,4-b][1,3,4]thiadiazine

2017 ◽  
Vol 1130 ◽  
pp. 688-698 ◽  
Author(s):  
Uzma Yunus ◽  
Shahbaz Ahmed ◽  
Mohammad Chahkandi ◽  
Moazzam H. Bhatti ◽  
Muhammad Nawaz Tahir
Keyword(s):  
Theoretical Studies ◽  
Non Covalent Interactions ◽  
Covalent Interactions

scholarly journals Conformational Dynamics in Asymmetric Catalysis: Is Catalyst Flexibility a Design Element?

Synthesis ◽  
2019 ◽  
Vol 51 (05) ◽  
pp. 1021-1036 ◽  
Author(s):  
Jennifer Crawford ◽  
Matthew Sigman
Keyword(s):  
Hydrogen Bond ◽  
Asymmetric Catalysis ◽  
Conformational Dynamics ◽  
Short Review ◽  
Cinchona Alkaloids ◽  
Design Element ◽  
Peptide Catalysts ◽  
Enzymatic Systems ◽  
Non Covalent Interactions ◽  
Covalent Interactions

Traditionally, highly selective low molecular weight catalysts have been designed to contain rigidifying structural elements. As a result, many proposed stereochemical models rely on steric repulsion for explaining the observed selectivity. Recently, as is the case for enzymatic systems, it has become apparent that some flexibility can be beneficial for imparting selectivity. Dynamic catalysts can reorganize to maximize attractive non-covalent interactions that stabilize the favored diastereomeric transition state, while minimizing repulsive non-covalent interactions for enhanced selectivity. This short review discusses catalyst conformational dynamics and how these effects have proven beneficial for a variety of catalyst classes, including tropos ligands, cinchona alkaloids, hydrogen-bond donating catalysts, and peptides.1 Introduction2 Tropos Ligands3 Cinchona Alkaloids4 Hydrogen-Bond Donating Catalysts5 Peptide Catalysts6 Conclusion

scholarly journals Catalytic reductive deoxygenation of esters to ethers driven by hydrosilane activation through non-covalent interactions with a fluorinated borate salt

2020 ◽  
Vol 10 (14) ◽  
pp. 4586-4592
Author(s):  
Vincent Rysak ◽  
Ruchi Dixit ◽  
Xavier Trivelli ◽  
Nicolas Merle ◽  
Francine Agbossou-Niedercorn ◽  
...  
Keyword(s):  
Reaction Mechanism ◽  
Noncovalent Interactions ◽  
Theoretical Studies ◽  
Non Covalent Interactions ◽  
Experimental And Theoretical Studies ◽  
Covalent Interactions

A fluorinated borate BArF salt catalyses the reductive deoxygenation of esters to ethers by using hydrosilanes. Experimental and theoretical studies highlight the role of noncovalent interactions in the reaction mechanism.

scholarly journals A mechanism for differential release of acrosomal enzymes during the acrosome reaction

1991 ◽  
Vol 275 (3) ◽  
pp. 759-766 ◽  
Author(s):  
D M Hardy ◽  
M N Oda ◽  
D S Friend ◽  
T T F Huang
Keyword(s):  
Electron Microscopy ◽  
Guinea Pig ◽  
Acrosome Reaction ◽  
Soluble Fraction ◽  
Dense Region ◽  
Immuno Electron Microscopy ◽  
Non Covalent Interactions ◽  
Covalent Interactions ◽  
Very High ◽  
Sperm Acrosome

To study the organization of fertilization enzymes in the sperm acrosome, we isolated and characterized two physicochemically distinct acrosomal fractions of guinea-pig spermatozoa. A soluble fraction contained the 25,000-Mr acrosomal autoantigen, AA1, and most of the acrosomal hyaluronidase and dipeptidyl peptidase II activity. A particulate fraction, designated acrosomal matrix (AM), consisted of membraneless crescent-shaped structures, and contained most of the acrosomal proacrosin. The AM also contained a 28,000-Mr putative proacrosin-binding protein, and a very-high-Mr component which, on reduction, was dissociated into 48,000-Mr and 67,000-Mr subunits. Autoproteolytic dissolution of the AM correlated with proteolysis by acrosin of the 28,000-Mr and 48,000-Mr AM molecules. Components of both the AM and the soluble fraction were localized by immuno-electron microscopy to the electron-dense region of the guinea-pig sperm acrosome. We conclude that acrosomal molecules are segregated into soluble and matrix compartments. This segregation is a function of disulphide bonding and non-covalent interactions among the relatively few components of the AM. Association of acrosin with the AM may be the mechanism by which this enzyme's release from the spermatozoon during the acrosome reaction is delayed relative to the release of other acrosomal molecules.

Photoelectron spectroscopy and theoretical studies of anion–π interactions: binding strength and anion specificity

2015 ◽  
Vol 17 (5) ◽  
pp. 3131-3141 ◽  
Author(s):  
Jian Zhang ◽  
Bin Zhou ◽  
Zhen-Rong Sun ◽  
Xue-Bin Wang
Keyword(s):  
Photoelectron Spectroscopy ◽  
Experimental Measurements ◽  
Theoretical Studies ◽  
Binding Strength ◽  
Π Interactions ◽  
Non Covalent Interactions ◽  
Covalent Interactions

Direct experimental measurements of non-covalent interactions between various anions and a π-electron-deficient cavity show significant binding strength and anion specificity.

scholarly journals Organocatalysts for enantioselective synthesis of fine chemicals: definitions, trends and developments

2015 ◽  
Author(s):  
Matteo Guidotti ◽  
Chiara Palumbo
Keyword(s):  
Asymmetric Catalysis ◽  
Organic Molecules ◽  
Optically Active ◽  
Fine Chemicals ◽  
Organic Transformations ◽  
Small Organic Molecules ◽  
Non Covalent Interactions ◽  
High Yields ◽  
Covalent Interactions ◽  
Covalent Activation

Abstract Organocatalysis, that is the use of small organic molecules to catalyze organic transformations, has been included among the most successful concepts in asymmetric catalysis, and it has been used for the enantioselective construction of C–C, C–N, C–O, C–S, C–P and C–halide bonds. Since the seminal works in early 2000, the scientific community has been paying an ever-growing attention to the use of organocatalysts for the synthesis, with high yields and remarkable stereoselectivities, of optically active fine chemicals of interest for the pharmaceutical industry. A brief overview is here presented about the two main classes of organocatalysis which are respectively characterized by covalent and non-covalent activation of the substrate. More detailed information about non-covalent interactions for organocatalysis are given. Finally, some successful examples of heterogenisation of organocatalysts are also discussed, in the view of a potential industrial exploitation.

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