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Topic Review
Tetrasubstituted α-Aminophosphonic Acid Derivatives
Due to their structural similarity with natural α-amino acids, α-aminophosphonic acid derivatives are known biologically active molecules. In view of the relevance of tetrasubstituted carbons in nature and medicine and the strong dependence of the biological activity of chiral molecules into their absolute configuration, the synthesis of α-aminophosphonates bearing tetrasubstituted carbons in an asymmetric fashion has grown in interest in the last decades. In the following lines, the existing literature for the synthesis of optically active tetrasubstituted α-aminophosphonates are summarized, comprising diastereoselective and enantioselective approaches.
  • 998
  • 19 Jun 2021
Topic Review
Copper-Catalyzed Intramolecular Borylative Coupling with Imines
Copper-catalyzed enantioselective borylative cyclization with various electrophiles via difunctionalization of unsaturated hydrocarbons is a powerful tool for the generation of interesting boron-containing carbocycles and heterocycles processes involving a chiral organocopper intermediate. Alkenes, allenes, and alkynes are versatile and easily accessible substrates that can be subjected to a wide range of reactions to produce densely functionalized, enantioenriched products.
  • 988
  • 17 Jul 2022
Topic Review
Asymmetric Catalytic Ketimine Mannich Reactions
These ketimines are less electrophilic and thus, arguably, more challenging substrates. 3-Aryl-3-hydroxyisoindolin-1-ones are often employed as stable precursors for the corresponding endocyclic N-carbonyl diaryl ketimines. This class of ketimines is useful synthons to access chiral isoindolin-1-ones that are an important motif found in numerous biologically relevant molecules and natural products.
  • 979
  • 05 Aug 2021
Topic Review
Hydrogen Sources in Catalytic Transfer Hydrogenation
Catalytic transfer hydrogenation has emerged as a pivotal chemical process with transformative potential in various industries. Unlike conventional direct hydrogenation, catalytic transfer hydrogenation offers numerous advantages, such as enhanced safety, cost-effective hydrogen donors, byproduct recyclability, catalyst accessibility, and the potential for catalytic asymmetric transfer hydrogenation, particularly with chiral ligands. Alcohols such as methanol and isopropanol are prominent hydrogen donors, demonstrating remarkable efficacy in various reductions. Formic acid offers irreversible hydrogenation, preventing the occurrence of reverse reactions, and is extensively utilized in chiral compound synthesis. Unconventional donors such as 1,4-cyclohexadiene and glycerol have shown a good efficiency in reducing unsaturated compounds, with glycerol additionally serving as a green solvent in some transformations. 
  • 976
  • 14 Nov 2023
Topic Review
Isoquinolone
Isoquinolones (isoquinolin-1(2H)-ones): the atom- and step-economic syntheses.
  • 972
  • 14 Jul 2021
Topic Review
Lipid-Oligonucleotide Conjugates and the Development of RNA-Based Therapeutics
Antisense and small interfering RNA (siRNA) oligonucleotides have been recognized as powerful therapeutic compounds for targeting mRNAs and inducing their degradation. However, a major obstacle is that unmodified oligonucleotides are not readily taken up into tissues and are susceptible to degradation by nucleases. For these reasons, the design and preparation of modified DNA/RNA derivatives with better stability and an ability to be produced at large scale with enhanced uptake properties is of vital importance.
  • 969
  • 01 Feb 2023
Topic Review
Supramolecular Chemistry: Host–Guest Molecular Complexes
The host–guest (HG) interactions in two-dimensional (2D) permeable porous linkages are growing expeditiously due to their future applications in biocatalysis, separation technology, or nanoscale patterning. In host–guest (HG) interaction, distinctive structural complexes development occurs via non-covalent associations. There is a growing curiosity in executing supramolecular HG structures for assembling organic solvents and aqueous solutions on compact planes.
  • 967
  • 09 Jul 2021
Topic Review
Albumin Conjugates as MRI Agents
Human serum albumin (HSA) is the most abundant protein in plasma. It is found at a concentration of roughly 0.7 mM in the vasculature. HSA is a monomeric multidomain biomolecule, representing the main determinant of plasma oncotic pressure and displays an extraordinary ligand binding capacity. HSA represents the main carrier for fatty acids, affects the pharmacokinetics of many drugs, can be a platform for drug discovery, suitable transport for therapy and diagnostics. Here we develop a class of macromolecular constructs from nitroxides conjugated to a human carrier protein as potential Organic radical contrast agents (ORCAs) for magnetic resonance imaging (MRI). MRI is a powerful non-invasive tool for clinics. The MRI specificity can be improved by enhancing by the addition of a contrast agent. The most efficient of the currently-used contrast agents are paramagnetic gadolinium chelates. However, the low stability of some chelates and therefore release toxic metal ions from the chelates provide harmful oxidative stress, mitochondrial membrane dysfunction, changes in gene expression, DNA damage, mutagenicity, etc. Therefore, there is sufficient interest in the production of “metal-free” MRI contrast agents.
  • 947
  • 29 Dec 2021
Topic Review
Central-Units/Terminal-Chains on Banana-Shaped Liquid Crystals
Azo-functionalized materials are one of the appealing groups of the functionalized materials owing to their photoswitching behaviour and have been explored for various potential applications viz., optical data storage, sensor, display devices, nonlinear materials and molecular switches. Recently, azo-functionalized bent-core liquid crystals (BCLCs) have gained significant attention because they have dual properties of BCLCs and azobenzene, which enables to generate new multifaceted functional and smart materials. In this report, the recently synthesized azobenzene containing bent-core mesogens and its subclass, the so-called hockey stick and V-shaped molecules are summarized. The mesomorphic behaviour of reported BCLCs affected by the type of central core unit, the nature, number and position of the lateral substituents and the type and length of the terminal chain are discussed. The photoisomerization process of these photoresponsive BCLCs in solid, solution and mesophase, as well as the impact of light on the chemical and electrical properties of them, are discussed.
  • 946
  • 09 Oct 2020
Topic Review
Mechanism of Heterogeneous Alkaline Deacetylation of Chitin
Chitosan can be obtained from chitin chemically or by using enzymatic preparations. From a chemical point of view, both acids and alkalis can be used to deacetylate chitin. However, alkaline deacetylation is used more often since glycosidic bonds are very sensitive to an acidic environment, in which they are destroyed. A mechanism for the chitin deacetylation reaction is proposed, taking into account its kinetic features in which the decisive role is assigned to the effects of hydration. It has been shown that the rate of chitin deacetylation increases with a decrease in the degree of hydration of hydroxide ions in a concentrated alkali solution. When the alkali concentration is less than the limit of complete hydration, the reaction practically does not occur. Hypotheses have been put forward to explain the decrease in the rate of the reaction in the second flat portion of the kinetic curve. The first hypothesis is the formation of “free” water, leading to the hydration of chitin molecules and a decrease in the reaction rate. The second hypothesis postulates the formation of a stable amide anion of chitosan, which prevents the nucleophilic attack of the chitin macromolecule by hydroxide ions.
  • 945
  • 19 Jun 2023
Topic Review
Yucca Saponins. Bioactivity and analytical methods
Yucca is one of the main sources of steroidal saponins, hence different extracts are commercialized for use as surfactant additives by beverage, animal feed, cosmetics or agricultural products. For a deeper understanding of the potential of the saponins that can be found in this genus, an exhaustive review of the structural characteristics, bioactivities and analytical methods that can be used with these compounds has been carried out, since there are no recent reviews on the matter. Thus, a total of 108 saponins from eight species of the genus Yucca have been described.
  • 936
  • 08 Oct 2021
Topic Review
Methods of Lysergic Acid Synthesis
Ergot is the spore form of the fungus Claviceps purpurea. Ergot alkaloids are indole compounds that are biosynthetically derived from L-tryptophan and represent the largest group of fungal nitrogen metabolites found in nature. The common part of ergot alkaloids is lysergic acid. 
  • 936
  • 01 Dec 2022
Topic Review
Copper-Catalyzed Synthesis of Coumarins
Coumarin (2H-chromen-2-one) derivatives have important uses in medicinal and synthetic chemistry, for example, as fluorescent probes. These properties have prompted chemists to develop efficient synthetic methods to synthesize the coumarin core and/or to functionalize it. In this context, many metal-catalyzed syntheses of coumarins have been introduced; among them, copper-catalyzed reactions appear to be very promising owing to the non-toxicity and cheapness of copper complexes.
  • 934
  • 10 Dec 2021
Topic Review
Functional Pyrazolo[1,5-a]pyrimidines
Pyrazolo[1,5-a]pyrimidine (PP) derivatives are an enormous family of N-heterocyclic compounds that possess a high impact in medicinal chemistry and have attracted a great deal of attention in material science recently due to their significant photophysical properties.
  • 933
  • 14 Jul 2021
Topic Review
Sesquiterpenoids Specially Produced by Fungi
Fungi are widely distributed in the terrestrial environment, freshwater, and marine habitat. Only approximately 100,000 of these have been classified although there are about 5.1 million characteristic fungi all over the world. These eukaryotic microbes produce specialized metabolites and participate in a variety of ecological functions, such as quorum detection, chemical defense, allelopathy, and maintenance of symbiosis. Fungi therefore remain an important resource for the screening and discovery of biologically active natural products. Sesquiterpenoids are arguably the richest natural products from plants and micro-organisms. The rearrangement of the 15 high-ductility carbons gave rise to a large number of different skeletons. At the same time, abundant structural variations lead to a diversification of biological activity. 
  • 927
  • 06 Dec 2021
Biography
Pierre Vogel
Professor Pierre Vogel was born in Cully (Switzerland). He did his Ph. D under supervision of Prof. H. Prinzbach, at the Institute of Organic Chemistry, in the University of Lausanne. He carried out post-doctoral research at Yale University (New Haven, Connecticut, USA), collaborating with Profs. M. Saunders, J.A. Berson, K.A. Wiberg and P.v.R. Schleyer (Princeton University). He then moved to M
  • 926
  • 22 Sep 2022
Topic Review
Actual Symmetry of Symmetric Adducts
This review discusses molecular adducts, whose composition allows a symmetric structure. Such adducts are popular model systems, as they are useful for analyzing the effect of structure on the property selected for study since they allow one to reduce the number of parameters. The main objectives of this discussion are to evaluate the influence of the surroundings on the symmetry of these adducts, steric hindrances within the adducts, competition between different noncovalent interactions responsible for stabilizing the adducts, and experimental methods that can be used to study the symmetry at different time scales. This review considers the following central binding units: hydrogen (proton), halogen (anion), metal (cation), water (hydrogen peroxide). 
  • 921
  • 10 Feb 2022
Topic Review
Trends in Cu-Catalyzed Ar-Xs Transformations with Amines
Aromatic compounds (Ar-Xs) are technologically important inert low-cost solvents (chlorobenzene or o-dichlorobenzene) and intermediates for the manufacture of flame-retardant polymers used in electronics and furniture. Furthermore, Ar-Xs are the chemicals necessary for the production of industrially important dyes, pigments, and a broad group of biologically active species such as pesticides and drugs. Utilization of Ar-Xs as arylating agents based on Cu-catalyzed substitution of bound halogen (X) applying different nucleophiles serves as the technique for production of a broad scale of useful chemicals.
  • 918
  • 16 Sep 2022
Topic Review
Synthesis of N,N'-Chelate Organoboron Derivatives
N,N′-chelate organoboron compounds have been successfully applied in bioimaging, organic light-emitting diodes (OLEDs), functional polymer, photocatalyst, electroluminescent (EL) devices, and other science and technology areas. However, the concise and efficient synthetic methods become more and more significant for material science, biomedical research, or other practical science.
  • 915
  • 31 Mar 2021
Topic Review Peer Reviewed
Cycloadditions and Cyclization Reactions via Post-Synthetic Modification and/or One-Pot Methodologies for the Stabilization of Imine-Based Covalent Organic Frameworks
Interest in covalent organic frameworks as high-value materials has grown steadily since their development in the 2000s. However, the great advantage that allows us to obtain these crystalline materials—the reversibility of the bonds that form the network—supposes a drawback in terms of thermal and chemical stability. Among the different strategies employed for the stabilization of imine-based Covalent Organic Frameworks (COFs), cycloaddition and other related cyclization reactions are especially significant to obtain highly stable networks with extended π-delocalization and new functionalities, expanding even further the potential application of these materials. Therefore, this entry gathered the most recent research strategies for obtaining stable COFs by means of cyclization reactions, including the Povarov reaction and intramolecular oxidative cyclization reactions as well as some other recent innovative approaches.
  • 913
  • 26 Jun 2023
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