scholarly journals Stereoselective organocascades: from fundamentals to recent developments

2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Elisabetta Massolo ◽  
Maurizio Benaglia
Keyword(s):  
Structural Change ◽  
Cascade Reactions ◽  
Reaction Sequence ◽  
One Pot ◽  
Chiral Catalyst ◽  
Recent Developments ◽  
Subsequent Step ◽  
Catalytic Cycles

Abstract Reaction sequences where more bonds are sequentially formed (cascade reactions) may be started either by a stoichiometric or by a catalytic reagent, and proceed in an enantio- diastereo- or non-stereo- selective manner. A wide variety of such strategies has been developed, including both stoichiometric and catalytic ones. Within the widely developed cascade reactions field, this chapter is not meant to be omni-comprehensive, but to offer an as much as possible complete overview on organocatalytic stereoselective methods. We embrace the more general definitions by Tietze and Denmark, considering as cascade reactions all those one-pot processes that involve two or more bond formations, where each subsequent step is enabled by a structural change caused by the previous one. We will include both two- and multi-component reactions where one or more organocatalysts may be responsible either for all or just some of the occurring transformations. Organocascades will be reported according to the number of involved catalytic cycles. In the following paragraphs, only cascade reactions that are stereoselective by means of a chiral catalyst will be considered. It will be shown that multiple possibilities, relying on different catalysis modes, are available to achieve the same reaction sequence.

Metal-, and Organocatalyst-Free One-Pot Assembly of Chiral Aza-Tricyclic Molecules: Creating Six Contiguous Stereocenters from 2-D-Structures and an Amino Acid

2020 ◽  
Author(s):  
Dung Do
Keyword(s):  
Amino Acid ◽  
Chemical Space ◽  
Structural Diversity ◽  
Therapeutic Agents ◽  
Chiral Molecules ◽  
One Pot ◽  
Complex Molecules ◽  
Chiral Catalyst ◽  
Chiral Complex ◽  
Free Process

<p>Chiral molecules with their defined 3-D structures are of paramount importance for the study of chemical biology and drug discovery. Having rich structural diversity and unique stereoisomerism, chiral molecules offer a large chemical space that can be explored for the design of new therapeutic agents.<sup>1</sup> Practically, chiral architectures are usually prepared from organometallic and organocatalytic processes where a transition metal or an organocatalyst is tailor-made for desired reactions. As a result, developing a method that enables rapid assembly of chiral complex molecules under metal- and organocatalyst-free condition represents a daunting challenge. Here we developed a straightforward route to create a chiral 3-D structure from 2-D structures and an amino acid without any chiral catalyst. The center of this research is the design of a <a>special chiral spiroimidazolidinone cyclohexadienone intermediate</a>, a merger of a chiral reactive substrate with multiple nucleophillic/electrophillic sites and a transient organocatalyst. <a>This unique substrate-catalyst (“subcatalyst”) dual role of the intermediate enhances </a><a>the coordinational proximity of the chiral substrate and catalyst</a> in the key Aza-Michael/Michael cascade resulting in a substantial steric discrimination and an excellent overall diastereoselectivity. Whereas the “subcatalyst” (hidden catalyst) is not present in the reaction’s initial components, which renders a chiral catalyst-free process, it is strategically produced to promote sequential self-catalyzed reactions. The success of this methodology will pave the way for many efficient preparations of chiral complex molecules and aid for the quest to create next generation of therapeutic agents.</p>

scholarly journals PRODUCTION OF ULTRASTRUCTURAL MEMBRANE LESIONS BY THE FIFTH COMPONENT OF COMPLEMENT

1971 ◽  
Vol 133 (1) ◽  
pp. 53-62 ◽  
Author(s):  
Margaret J. Polley ◽  
Hans J. Müller-Eberhard ◽  
Joseph D. Feldman
Keyword(s):  
Structural Change ◽  
Cell Membrane ◽  
Quantitative Relationship ◽  
Intermediate Complex ◽  
Reaction Sequence ◽  
Immune Hemolysis ◽  
Physical Presence ◽  
Reverse Situation

A direct quantitative relationship has been demonstrated between the number of cell bound C4,2 complexes or C5 molecules and the number of ultrastructural lesions visualized on the cell membrane subsequent to immune hemolysis. When bound C4,2 complexes exceeded bound C5 molecules, the number of ultrastructural lesions seen corresponded to the number of C5 molecules. However, in the reverse situation, with bound C5 molecules in excess of bound C4,2 complexes, the latter determined the number of lesions. During the complement-reaction sequence, the lesions first became visible in the nonlytic intermediate complex EAC1,4,2,3,5 and their number was unaffected when lysis was induced by C6–C9. Since the lesions were also demonstrable on the intermediate complex EC5,6,7, it is concluded that the protein C5 is responsible for their production. Once formed, the physical presence of the C5 molecule is no longer required for the manifestation of the lesions as indicated by persistence of lesions after removal of C5 protein by trypsin. The C5-dependent ultra-structural phenomenon has therefore been interpreted to represent a true structural change of the membrane which, however, is not accompanied by a permeability defect.

Amino- and sulfo-bifunctionalized hyper-crosslinked organic nanotube frameworks as efficient catalysts for one-pot cascade reactions

2019 ◽  
Vol 43 (5) ◽  
pp. 2269-2273 ◽  
Author(s):  
Guojie Meng ◽  
Shengguang Gao ◽  
Ying Liu ◽  
Li Zhang ◽  
Chunmei Song ◽  
...  
Keyword(s):  
Cascade Reactions ◽  
One Pot ◽  
First Time

The synthesis of amino- and sulfo-bifunctionalized hyper-crosslinked organic nanotube frameworks for one-pot cascade reactions was reported for the first time.

Recent developments in enantioselective organocatalytic cascade reactions for the construction of halogenated ring systems

2021 ◽  
Author(s):  
Ana Maria Madeira Martins Faisca Phillips ◽  
Ana Maria Madeira Martins Faisca Phillips ◽  
Armando J. L. Pombeiro
Keyword(s):  
Cascade Reactions ◽  
Ring Systems ◽  
Recent Developments

Recent advance in ester synthesis by Multi Component Reactions (MCRs): A Review

2021 ◽  
Vol 25 ◽  
Author(s):  
Dhaval B. Patel ◽  
Jagruti A. Parmar ◽  
Siddharth S. Patel ◽  
Unnati J. Naik ◽  
Hitesh D. Patel
Keyword(s):  
Multicomponent Reactions ◽  
Medicinal Chemistry ◽  
Reaction Times ◽  
Synthetic Methods ◽  
Ester Synthesis ◽  
One Pot ◽  
Wide Range ◽  
Recent Developments ◽  
Ester Linkage ◽  
The One

: The synthesis of ester containing heterocyclic compounds via multicomponent reaction is one of the most preferable process in the synthetic organic chemistry and medicinal chemistry. Compounds containing ester linkage have a wide range of biological application in the pharmaceutical field. Therefore, many method have been developed for the synthesis of these type of derivatives. However, some of them are carried out in the presence of toxic solvents and catalysts, with lower yields, longer reaction times, low selectivities and by-products. Thus, the development of new synthetic methods for the ester synthesis is required in the medicinal chemistry. As we know, multicomponent reactions (MCRs) are a powerful tool towards the one-pot ester synthesis, so in this article we have reviewed the recent developments in ester synthesis. This work covers selected explanation of methods via multicomponent reactions to explore the methodological development in ester synthesis.

scholarly journals Engineering P450 TamI as an Iterative Biocatalyst for Selective Late-Stage C-H Functionalization and Epoxidation of Tirandamycin Antibiotics

2021 ◽  
Author(s):  
Rosa V. Espinoza ◽  
Kersti Caddell Haatveit ◽  
S. Wald Grossman ◽  
Jin Yi Tan ◽  
Caylie A. McGlade ◽  
...  
Keyword(s):  
Natural Product ◽  
Late Stage ◽  
Md Simulations ◽  
Cascade Reactions ◽  
Direct Access ◽  
Tetramic Acid ◽  
Reaction Sequence ◽  
Substrate Reactivity ◽  
Continuous Oxidation

<div> <div> <div> <p>Iterative P450 enzymes are powerful biocatalysts for selective late-stage C-H oxidation of complex natural product scaffolds. These enzymes represent new tools for selectivity and cascade reactions, facilitating direct access to core structure diversification. Recently, we reported the structure of the multifunctional bacterial P450 TamI and elucidated the molecular basis of its substrate binding and strict reaction sequence at distinct carbon atoms of the substrate. Here, we report the design and characterization of a toolbox of TamI biocatalysts, generated by mutations at Leu101, Leu244 and/or Leu295, that alter the native selectivity, step sequence and number of reactions catalyzed, including the engineering of a variant capable of catalyzing a four-step oxidative cascade without the assistance of the flavoprotein and oxidative partner TamL. The tuned enzymes override inherent substrate reactivity enabling catalyst- controlled C-H functionalization and alkene epoxidation of the tetramic acid-containing natural product tirandamycin. Five new, bioactive tirandamycin derivatives (6-10) were generated through TamI-mediated enzymatic synthesis. Quantum mechanics calculations and MD simulations provide important insights on the basis of altered selectivity and underlying biocatalytic mechanisms for enhanced continuous oxidation of the iterative P450 TamI. </p> </div> </div> </div>

scholarly journals Appel-reagent-mediated transformation of glycosyl hemiacetal derivatives into thioglycosides and glycosyl thiols

2013 ◽  
Vol 9 ◽  
pp. 974-982 ◽  
Author(s):  
Tamashree Ghosh ◽  
Abhishek Santra ◽  
Anup Kumar Misra
Keyword(s):  
Reaction Sequence ◽  
Reaction Conditions ◽  
One Pot ◽  
Carbon Tetrabromide

A series of glycosyl hemiacetal derivatives have been transformed into thioglycosides and glycosyl thiols in a one-pot two-step reaction sequence mediated by Appel reagent (carbon tetrabromide and triphenylphosphine). 1,2-trans-Thioglycosides and β-glycosyl thiol derivatives were stereoselectively formed by the reaction of the in situ generated glycosyl bromides with thiols and sodium carbonotrithioate. The reaction conditions are reasonably simple and yields were very good.

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