Multibond Forming Tandem Reactions of Anilines via Stable Aryl Diazonium Salts: One-Pot Synthesis of 3,4-Dihydroquinolin-2-ones

Fluorescent α-amino acids via Heck-Matsuda reactions of phenylalanine-derived arenediazonium salts

The Heck-Matsuda coupling reaction of arenediazonium salts derived from L-phenylalanine with various alkenes has been developed. A two-step process involving the preparation of a tetrafluoroborate diazonium salt from a 4-aminophenylalanine derivative, followed by a palladium(0)-catalysed Heck-Matsuda coupling reaction allowed access to a range of unnatural α-amino acids with cinnamate, vinylsulfone and stilbene side-chains. Analysis of the photophysical properties of these unnatural α-amino acids demonstrated that the (E)-stilbene analogues exhibited fluorescent properties with red-shifted absorption and emission spectra and larger quantum yields than L-phenylalanine.

Synthesis and Fluorescent Properties of Alkynyl- and Alkenyl-Fused Benzotriazole-Derived α-Amino Acids

Fluorescent unnatural α-amino acids are widely used as probes in chemical biology and medicinal chemistry. While a variety of structural classes have been developed, there is still a requirement for new environmentally sensitive analogues that can closely mimic proteinogenic α-amino acids. Here, we report the synthesis and fluorescent properties of highly conjugated, benzotriazole-derived α-amino acids designed to mimic l-tryptophan. Alkynyl-substituted analogues were prepared using three key steps, nucleophilic aromatic substitution with a 3-aminoalanine derivative, benzotriazole formation via a one-pot diazotization and cyclization process, and a Sonogashira cross-coupling reaction. E-Alkenyl-substituted benzotriazoles were accessed by stereoselective partial hydrogenation of the alkynes using zinc iodide and palladium catalysis. The alkynyl analogues were found to possess higher quantum yields and stronger brightness and, a solvatochromic study with the most fluorogenic α-amino acids demonstrated sensitivity to polarity.

One-Pot Synthesis and in Silico Molecular Docking Studies of Arylselanyl Hydrazides as Potential Antituberculosis Agents

The present study reports a simple two-step method for the synthesis of arylselanyl hydrazide derivatives using hypophosphorous acid and polyethylene glycol (H₃ PO₂ /PEG-400) as an alternative reducing system and hydrazine hydrate (NH₂ NH₂ ⋅xH₂ O/50-60 %). This single-vessel procedure was employed with methyl acrylate 2a and methyl bromoacetate 2b using diaryl diselenides to generate the nucleophile species to produce, respectively, 3-(arylselanyl)propane-hydrazides 4a-e and 2-(arylselanyl)acetohydrazides 5a-e with good yields by accelerating the reduction of -Se-Se- bond, when compared to available methods. The synthesized molecules are structurally similar to the isoniazid (INH). Therefore, we perform in silico molecular docking studies, using the lactoperoxidase enzyme, in order to verify whether the INH Se derivatives could interact in a similar way to INH at the active site of the mammalian enzyme. The in silico results indicated a similar type of interaction of the arylselanyl hydrazide derivatives with that of INH. In view of the similar in silico interaction of the selenium derivatives of INH, the arylselanyl hydrazide derivatives reported here should be tested against Mycobacterium tuberculosis in vitro.

A late-stage diversification via Heck-Matsuda arylation: Straightforward synthesis and cytotoxic/antiproliferative profiling of novel aryl-labdane-type derivatives

In the current study a late-stage diversification of unactivated olefins labd-8(17)-en-15-oic acid (1a) and methyl labd-8(17)-en-15-oate (1b) via Heck-Matsuda arylation is described. The reaction provided straightforward and practical access to a series of novel aryl-labdane-type derivatives (HM adducts 3a-h) in moderate to good yields in a highly regio- and stereoselective manner at room temperature under air atmosphere. The cytotoxic activity of these compounds was investigated in vitro against three different human cell lines (THP-1, K562, MCF-7). Of these, HM adduct 3h showed a selective effect in all cancer cell lines tested and was selected for extended biological investigations in a leukemia cell line (K562), which demonstrated that the cytotoxic/antiproliferative activity observed in this compound might be mediated by induction of cell cycle arrest at the sub-G1 phase and by autophagy-induced cell death. Taken together, these findings indicate that further investigation into the anticancer activity against chronic myeloid leukemia from aryl-labdane-type derivatives may be fruitful.

One-pot synthesis of N-substituted benzannulated triazoles via stable arene diazonium salts

A mild and effective one-pot synthesis of 1,2,3-benzotriazin-4(3H)-ones and benzothiatriazine-1,1(2H)-dioxide analogues has been developed. The method involves the diazotisation and subsequent cyclisation of 2-aminobenzamides and 2-aminobenzenesulfonamides via stable diazonium salts, prepared using a polymer-supported nitrite reagent and p-tosic acid. The transformation was compatible with a wide range of aryl functional groups and amide/sulfonamide-substituents and was used for the synthesis of pharmaceutically important targets. The synthetic utility of the one-pot diazotisaton-cyclisation process was further demonstrated with the preparation of an α-amino acid containing 1,2,3-benzotriazin-4(3H)-one.

Enantioselective Heck-Matsuda Reactions: From Curiosity to a Game-Changing Methodology

The enantioselective palladium-catalyzed Heck arylation of olefins using arenediazonium salts is one of the last features in the evolution of a synthetic method known as the Heck-Matsuda reaction. This personal account highlights the development of the enantioselective Heck-Matsuda reaction in its initial stages, the challenges faced along the way, and the interesting findings that opened new synthetic opportunities, mainly from our laboratory, featuring the Heck-Matsuda reaction as a central player in the synthesis of bioactive and functional molecules.

Novel N-transfer reagent for converting α-amino acid derivatives to α-diazo compounds

A novel universal N-transfer reagent for direct and effective transformation of α-amino ketones, acetamides, and esters to the corresponding α-diazo products under mild basic conditions has been developed. This one-step synthetic approach not only allows for generation of α-substituted-α-diazo carbonyl compounds from α-amino acid derivatives but also permits preparation of α-diazo dipeptides from N-terminal dipeptides (32 examples, up to 91%).

One-pot ortho-amination of aryl C-H bonds using consecutive iron and copper catalysis

A one-pot approach for ortho-coupling of arenes with non-actived N-nucleophiles has been developed using sequential iron and copper catalysis. Regioselective ortho-activation of anisoles, anilines and phenols was achieved through iron(iii) triflimide catalysed iodination, followed by a copper(i)-catalysed, ligand-assisted coupling reaction with N-heterocycle, amide and sulfonamide-based nucleophiles. The synthetic utility of this one-pot, two-step method for the direct amination of ortho-aryl C-H bonds was demonstrated with the late-stage functionalisation of 3,4-dihydroquinolin-2-ones. This allowed the preparation of a TRIM24 bromodomain inhibitor and a series of novel analogues.

Transition-Metal-Free Catalytic Carboalkoxylation of Styrenes at Room Temperature

Herein, we describe the first transition-metal-free catalytic carboalkoxylation of styrenes with aryl diazonium salts by Meerwein addition in the presence of a phenalenyl ligand at room temperature without requiring any light stimulation. This three-component reaction allows facile difunctionalization of styrene derivatives with various alcohols (such as 1, 2, and 3°) as the source of alkoxy group during this transformation. The key intermediates and the transition states involved in this reaction path were unraveled by a series of control experiments coupled with density functional theory calculations. The full mechanistic investigation provides an understanding of the selectivity toward carboalkoxylation (Meerwein arylation addition elimination) in the presence of various alcohols over the simple arylation to multiple bond (Meerwein arylation-elimination) reaction.

Silver-promoted decarboxylative radical addition/annulation of oxamic acids with gem-difluoroolefins: concise access to CF2-containing 3,4-dihydroquinolin-2-ones

Described is a silver-promoted decarboxylative radical addition/annulation of oxamic acids with gem-difluoroalkenes. This reaction proceeded under mild reaction conditions with broad functional group compatibility, enabling the convenient synthesis of various structurally diverse CF2-containing 3,4-dihydroquinolin-2-ones that might find applications in medical chemistry.