Aerobic, Diselenide-Catalyzed Redox Dehydration: Amides and Peptides

Recent Advances in the Use of Diorganyl Diselenides as Versatile Catalysts

The importance of organoselenium compounds has been increasing in synthetic chemistry. These reagents are well-known as electrophiles and nucleophiles in many organic transformations, and in recent years, their functionality as catalysts has also been largely explored. The interest in organoselenium-based catalysts is due to their high efficacy, mild reaction conditions, strong functional compatibility, and great selectivity. Allied to organoselenium catalysts, the use of inorganic and organic oxidants that act by regenerating the catalytic species for the reaction pathway is common. Here, we provide a comprehensive review of the last five years of organic transformations promoted by diorganyl diselenide as a selenium-based catalyst. This report is divided into four sections: (1) cyclisation reactions, (2) addition reactions and oxidative functionalisation, (3) oxidation and reduction reactions, and (4) reactions involving phosphorus-containing starting materials.

A diselenobis-functionalized magnetic catalyst based on iron oxide/silica nanoparticles suggested for amidation reactions

In this study, a new heterogeneous magnetic catalytic system based on selenium-functionalized iron oxide nanoparticles is presented and suggested for facilitating amide/peptide bonds formation. The prepared nanocatalyst, entitled as “Fe₃O₄/SiO₂-DSBA” (DSBA stands for 2,2′-diselanediylbis benzamide), has been precisely characterized for identifying its physicochemical properties. As the most brilliant point, the catalytic performance of the designed system can be mentioned, where only a small amount of Fe₃O₄/SiO₂-DSBA (0.25 mol%) has resulted in 89% reaction yield, under a mild condition. Also, given high importance of green chemistry, convenient catalyst particles separation from the reaction medium through its paramagnetic property (ca. 30 emu·g⁻¹) should be noticed. This particular property provided a substantial opportunity to recover the catalyst particles and successfully reuse them for at least three successive times. Moreover, due to showing other excellences, such as economic benefits and nontoxicity, the presented catalytic system is recommended to be scaled up and exploited in the industrial applications.

Convenient synthesis of dipeptide structures in solution phase assisted by a thioaza functionalized magnetic nanocatalyst

In this study, a heterogeneous nanocatalyst is presented that is capable to efficiently catalyze the synthetic reactions of amide bond formation between the amino acids. This nanocatalyst which is named Fe₃O₄@SiO₂/TABHA (TABHA stands for thio-aza-bicyclo-hepten amine), was composed of several layers that increased the surface area to be functionalized with 2-aminothiazole rings via Diels-Alder approach. Firstly, various analytic methods such as Fourier-transform infrared (FTIR) and energy-dispersive X-ray (EDX) spectroscopic methods, thermogravimetric analysis (TGA), electron microscopy (EM), and UV-vis diffuse reflectance spectroscopy (UV-DRS) have been used to characterize the desired structure of the Fe₃O₄@SiO₂/TABHA catalyst. Afterward, the application of the presented catalytic system has been studied in the peptide bond formation reactions. Due to the existence of a magnetic core in the structure of the nanocatalyst, the nanoparticles (NPs) could be easily separated from the reaction medium by an external magnet. This special feature has been corroborated by the obtained results from vibrating-sample magnetometer (VSM) analysis that showed 24 emu g^-1 magnetic saturation for the catalytic system. Amazingly, a small amount of Fe₃O₄@SiO₂/TABHA particles (0.2 g) has resulted in ca. 90% efficiency in catalyzing the peptide bond formation at ambient temperature, over 4 h. Also, this nanocatalyst has demonstrated an acceptable recycling ability, where ca. 76% catalytic performance has been observed after four recycles. Due to high convenience in the preparation, application, and recyclization processes, and also because of lower cost than the traditional coupling reagents (like TBTU), the presented catalytic system is recommended for the industrial utilization.

Catalytic and non-catalytic amidation of carboxylic acid substrates

The present review offers an apt summary of amide bond formation with carboxylic acid substrates by taking advantage of several methods. Carboxamides can be regarded as a substantial part of organic and medicinal chemistry due to their utility in synthesizing peptides, lactams, and more than 25% of familiar drugs. Moreover, they play a leading role in the synthesis of bioactive products with anticancer, antifungal, and antibacterial properties. The data are arranged based on the type and amount of reagents used to conduct amidation and are also divided into the following categories: catalytic amidation of carboxylic acids, non-catalytic amidation, and transamidation.

Clickable coupling of carboxylic acids and amines at room temperature mediated by SO2F2: a significant breakthrough for the construction of amides and peptide linkages

The construction of amide bonds and peptide linkages is one of the most fundamental transformations in all life processes and organic synthesis. The synthesis of structurally ubiquitous amide motifs is essential in the assembly of numerous important molecules such as peptides, proteins, alkaloids, pharmaceutical agents, polymers, ligands and agrochemicals. A method of SO2F2-mediated direct clickable coupling of carboxylic acids with amines was developed for the synthesis of a broad scope of amides in a simple, mild, highly efficient, robust and practical manner (>110 examples, >90% yields in most cases). The direct click reactions of acids and amines on a gram scale are also demonstrated using an extremely easy work-up and purification process of washing with 1 M aqueous HCl to provide the desired amides in greater than 99% purity and excellent yields.

Rational Design of an Organocatalyst for Peptide Bond Formation

Amide bonds are ubiquitous in peptides, proteins, pharmaceuticals, and polymers. The formation of amide bonds is a straightforward process: amide bonds can be synthesized with relative ease because of the availability of efficient coupling agents. However, there is a substantive need for methods that do not require excess reagents. A catalyst that condenses amino acids could have an important impact by reducing the significant waste generated during peptide synthesis. We describe the rational design of a biomimetic catalyst that can efficiently couple amino acids featuring standard protecting groups. The catalyst design combines lessons learned from enzymes, peptide biosynthesis, and organocatalysts. Under optimized conditions, 5 mol % catalyst efficiently couples Fmoc amino acids without notable racemization. Importantly, we demonstrate that the catalyst is functional for the synthesis of oligopeptides on solid phase. This result is significant because it illustrates the potential of the catalyst to function on a substrate with a multitude of amide bonds, which may be expected to inhibit a hydrogen-bonding catalyst.

Facile Peptide Bond Formation: Effective Interplay between Isothiazolone Rings and Silanol Groups at Silver/Iron Oxide Nanocomposite Surfaces

Proportional to considerable progress in protein-drug conjugations, attention to the efficient peptide coupling reagents is being increased. Hence, in this study, a versatile heterogeneous nanoscale reagent is presented for chemical, biological, and medical purposes. A combination of silver and silica-coated iron oxide nanoparticles (Ag/Fe₃O₄) has been well functionalized with isothiazolone rings via a silver-modified Heck mechanism. An appropriate condition is provided for peptide bond formation through the surface interplay between silanol groups and the loaded isothiazolone rings. A logical mechanism including a series of successive covalent bonds onto the surface of Ag/Fe₃O₄ nanocomposites is suggested for this catalyzed peptide bond formation. Accurate comparisons have been made to obtain the optimum value of the nanocatalyst and suitable conditions. As an additional application, the biological activity of the desired product has also been investigated through antibacterial assay tests. The results showed that our desired product could also be used as an effective heterogeneous nanoscale antibacterial agent for different purposes. In this regard, all of the essential structural and practical analyses have been carried out and precisely interpreted.

Esterification by Redox Dehydration Using Diselenides as Catalytic Organooxidants

Ortho-functionalized aryl diselenides are catalytic (5.0 mol %) oxidants for the construction of esters from carboxylic acids and alcohols in the presence of stoichiometric triethyl phosphite and dioxygen in air as the terminal redox reagents (redox dehydration conditions). The reaction proceeds through the intermediacy of the anhydride and requires the presence of 10% DMAP to drive the esterification.

Recent progress in selenium-catalyzed organic reactions

Selenium-based catalysts, including organo- and inorganoselenium ones, in organic synthesis in the recent decade are reviewed.