Amine Activation: Synthesis of N-(Hetero)arylamides from Isothioureas and Carboxylic Acids

Amine Activation: "Inverse" Dipeptide Synthesis and Amide Function Formation through Activated Amino Compounds

A copper(II)/HOBt-catalyzed procedure for the synthesis of dipeptides and "general" amides has been developed using microwave irradiation to considerably hasten the reaction. As an alternative to using traditional carboxylic acid activation, the method relies on the use of N-acyl imidazoles as activated amino partners. By doing so, a nonconventional way to reach dipeptides and amides has been proposed through the challenging and less studied N → C direction synthesis. A series of dipeptides and "general" amides have been successfully synthesized, and the applicability of the method has been illustrated in gram-scale syntheses. The mild reaction conditions proposed are completely adequate for couplings in the presence of sensitive amino acids, affording the products without detectable racemization. Furthermore, experimental observations prompted us to propose a plausible reaction pathway for the couplings.

Effect of gem-Difluorination on the Key Physicochemical Properties Relevant to Medicinal Chemistry: The Case of Functionalized Cycloalkanes

Physico-chemical properties important to drug discovery (pK_a , LogP, and aqueous solubility), as well as metabolic stability, were studied for a series of functionalized gem-difluorinated cycloalkanes and compared to those of non-fluorinated and acyclic counterparts to evaluate the impact of the fluorination. It was found that the influence of the CF₂ moiety on the acidity/basicity of the corresponding carboxylic acids and amines was defined by inductive the effect of the fluorine atoms and was nearly the same for acyclic and cyclic aliphatic compounds. Lipophilicity and aqueous solubility followed more complex trends and were affected by the position of the fluorine atoms, ring size, and even the nature of the functional group present; also, significant differences were found for the acyclic and cyclic series. Also, gem-difluorination either did not affect or slightly improved the metabolic stability of the corresponding model derivatives. The presented results can be used as a guide for rational drug design employing fluorine and establish the first chapter in a catalog of the key in vitro properties of fluorinated cycloalkanes.

Umpolung strategies for the functionalization of peptides and proteins

Umpolung strategies, defined as synthetic approaches which reverse commonly accepted reactivity patterns, are broadly recognized as enabling tools for small molecule synthesis and catalysis. However, methods which exploit this logic for peptide and protein functionalizations are comparatively rare, with the overwhelming majority of existing bioconjugation approaches relying on the well-established reactivity profiles of a handful of amino acids. This perspective serves to highlight a small but growing body of recent work that masterfully capitalizes on the concept of polarity reversal for the selective modification of proteinogenic functionalities. Current applications of umpolung chemistry in organic synthesis and chemical biology as well as the vast potential for further innovations in peptide and protein modification will be discussed.

Identification of novel Epac2 antagonists through in silico and in vitro analyses

cAMP-dependent guanine nucleotide exchange factor (Epac) is a key regulator in signal transduction and represents an excellent drug target to be investigated against various diseases. To date, very few modulators selective for Epac are available; however, there is still an unmet need of isoform-selective inhibitors. In the present study, ligand-based pharmacophores were designed to investigating structurally diverse molecules as Epac2 inhibitors. Pharmacophore models were developed using reported allosteric site inhibitors. The developed models were used to screen 95 thousand compounds from the National Cancer Institute (NCI), Maybride, and our in-house ICCBS Database. The binding mode and efficiency of the screened hits was investigated using molecular docking simulation on the allosteric site of Epac2 apo-protein (PDB ID: 2BYV) followed by ADMET (Absorption, Distribution, Metabolism, Excretion, and Toxicity) profiling Furthermore, obtained in silico screened hits were subjected to in vitro assay for insulin secretion. We identified, three lead molecules RDR02145, AAK-399, and AAD-026 reducing, insulin secretion. Remarkably, a higher inhibitory effect on insulin secretion was observed in AAK-399, and AAD-026 as compared to that of standard Epac2 non-competitive allosteric site inhibitor, MAY0132. Furthermore, Dynamic simulation studies of lead compounds proved the structural stability of the Epac2 auto-inhibited state. These findings underline the potential of these compounds as valuable pharmacological tools for designing future selective probes to inhibit the Epac-mediated signaling pathway.

Synthesis of heteroatom-containing pyrrolidine derivatives based on Ti(O-iPr)4 and EtMgBr-catalyzed carbocyclization of allylpropargyl amines with Et2Zn

The Ti(O-iPr)4 and EtMgBr-catalyzed regio and stereoselective carbocyclization of N-allyl-substituted 2-alkynylamines with Et2Zn, followed by deuterolysis or hydrolysis, affords the corresponding methylenepyrrolidine derivatives in high yields. It was found that Ti-Mg-catalyzed carbocyclization of N-allyl-substituted 2-alkynylamines with Et2Zn is equally selective in dichloromethane, hexane, toluene, and diethyl ether. The reaction was tolerant to the presence of aryl, alkyl, trimethylsilyl, methoxymethyl and aminomethyl substituents on the alkyne. A selective method was proposed for the preparation of bis-pyrrolidine derivatives using Ti-Mg-catalyzed carbocyclization of bis-allylpropargyl amines with Et2Zn.

Therapeutic potential of selanyl amide derivatives in the in vitro anticholinesterase activity and in in vivo antiamnesic action

The present study evaluated the in vitro acetylcholinesterase (AChE) inhibitor activity of two new selanyl amide derivatives in cerebral structures of mice. Our results demonstrated that N-(2-(3-(phenylselanyl)propoxy)phenyl)furan-2-carboxamide (1) and N-(2-(3-(phenylselanyl)propoxy)phenyl)thiophene-2-carboxamide (2) inhibited the in vitro AChE activity in mice. Another objective was to assess the effect of the best AChE inhibitor in an amnesic model induced by scopolamine (SCO) in male Swiss mice. The involvement of AChE activity and lipid peroxidation in the cerebral structures was investigated. Our results showed that compound 1 (10 mg/kg, intragastrically) attenuated the latency to find the escape box and the number of holes visited in the Barnes maze task, without altering the locomotor and exploratory activities in an open-field test. Compound 1 protected against increasing in lipid peroxidation levels and AChE activity caused by SCO in the cerebral cortex and hippocampus of mice. In conclusion, the present study evidenced the in vitro anticholinesterase effect of two new selanyl amide derivatives in the cerebral structures of mice. Moreover, compound 1, a selanyl amide derivative containing a furan ring, demonstrated antiamnesic action due to its antioxidant and anticholinesterase activities in cerebral structures.

Metal-free photocatalysts for the oxidation of non-activated alcohols and the oxygenation of tertiary amines performed in air or oxygen

This protocol describes the use of 9-fluorenone as a cheap and non-toxic photocatalyst for the oxidation of non-activated alcohols performed under the irradiation of a blue light-emitting diode. It also describes the use of the similarly cheap and non-toxic photocatalyst rose bengal for the selective α-oxygenation of tertiary amines to produce the corresponding amides in a selective way using the same light source. We have provided detailed instructions on how to assemble the light-emitting diode equipment and set up the photocatalytic reaction, where an oxygen atmosphere is created with an O₂-filled balloon. Further details are provided using four example reactions that illustrate how this system works: alcohol oxidation to prepare terephthlalaldehyde and androstanedione, and amine oxidation to make 2-phenyl-3,4-dihydroisoquinolin-1(2H)-one and (4-((4-chlorophenyl)(phenyl)methyl)piperazin-1-yl)m-tolyl)methanone. The times needed to perform these photocatalytic reactions are 18, 76, 22 and 54 h, respectively. We believe that this protocol represents a robust methodology for the late-stage modification of amines and the selective oxidation of steroids.

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.

Nitromethane as a nitrogen donor in Schmidt-type formation of amides and nitriles

The Schmidt reaction has been an efficient and widely used synthetic approach to amides and nitriles since its discovery in 1923. However, its application often entails the use of volatile, potentially explosive, and highly toxic azide reagents. Here, we report a sequence whereby triflic anhydride and formic and acetic acids activate the bulk chemical nitromethane to serve as a nitrogen donor in place of azides in Schmidt-like reactions. This protocol further expands the substrate scope to alkynes and simple alkyl benzenes for the preparation of amides and nitriles.

Palladium-Catalyzed Cross-Coupling Reactions: A Powerful Tool for the Synthesis of Agrochemicals

Pd-catalyzed cross-coupling reactions have become essential tools for the construction of carbon-carbon and carbon-heteroatom bonds. Over the last three decades, great efforts have been made with cross-coupling chemistry in the discovery, development, and commercialization of innovative new pharmaceuticals and agrochemicals (mainly herbicides, fungicides, and insecticides). In view of the growing interest in both modern crop protection and cross-coupling chemistry, this review gives a comprehensive overview of the successful applications of various Pd-catalyzed cross-coupling methodologies, which have been implemented as key steps in the synthesis of agrochemicals (on R&D and pilot-plant scales) such as the Heck, Suzuki, Sonogashira, Stille, and Negishi reactions, as well as decarboxylative, carbonylative, α-arylative, and carbon-nitrogen bond bond-forming cross-coupling reactions. Some perspectives and challenges for these catalytic coupling processes in the discovery of agrochemicals are briefly discussed in the final section. The examples chosen demonstrate that cross-coupling chemistry approaches open-up new, low-cost, and more efficient industrial routes to existing agrochemicals, and such methods also have the capability to lead the new generation of pesticides with novel modes of action for sustainable crop protection.

Artificial bioconjugates with naturally occurring linkages: the use of phosphodiester

Artificial orthogonal bond formations such as the alkyne–azide cycloaddition have enabled selective bioconjugations under mild conditions, yet naturally occurring linkages between native functional groups would be more straightforward to elaborate bioconjugates. Herein, we describe the use of a phosphodiester bond as a versatile option to access various bioconjugates. An opposite activation strategy, involving 5’-phosphitylation of the supported oligonucleotides, has allowed several biomolecules that possess an unactivated alcohol to be directly conjugated. It should be noted that there is no need to pre-install artificial functional groups and undesired and unpredictable perturbations possibly caused by bioconjugation can be minimized.

Direct Amidation of Carboxylic Acids through an Active α-Acyl Enol Ester Intermediate

The development of a highly efficient and simple protocol for the direct amidation of carboxylic acids is described employing ynoates as novel coupling reagents. The transformation proceeds in good to excellent yields via in situ α-acyl enol ester intermediates formation under mild reaction conditions. This useful method has been demonstrated for a range of substrates to provide a succinct access to structurally diverse amides, including key intermediates of glibenclamide, tiapride hydrochloride, and nateglinide, and can be conducted on a mole scale.

Palladium-catalyzed β-selective C(sp2)–H carboxamidation of enamides by isocyanide insertion: synthesis of N-acyl enamine amides

An efficient synthesis of N-acyl enamine amides via palladium-catalyzed alkene C–H activation and isocyanide insertion has been developed.

Recent Developments in Amide Synthesis Using Nonactivated Starting Materials

Amides are unquestionably one of the most important functional groups in organic chemistry because of their presence in numerous interesting molecules such as peptides, pharmaceutical agents, naturally occurring molecules, proteins and alkaloids, among others. This synopsis surveys the diverse recent approaches to amide synthesis from nonactivated carboxylic acids and derivatives as well as noncarboxylic compounds, highlighting the most innovative methodologies and those that are more eco-friendly compared to traditional methods while focusing on recent developments during the past two years.