Domino Reaction for the Synthesis of Substituted Pyrano[3',4':3,4]cyclopenta[1,2-c]chromenes Involving Double Ring Formation

Herein, we present a green cascade approach for synthesizing a range of chemoselective polysubstituted pyrano[3',4':3,4]cyclopenta[1,2-c]chromenes containing a chiral stereocenter. The strategy involves a metal-free nucleophilic reaction between dialkyl (2E)-2-{2-oxo-3-[(2E)-3-aryl-2-propenoyl]-2H-chromen-4-yl}-2-butenedioates and α,α-dicyanoolefins under reflux conditions in ethanol solvent. Mechanistic studies have shown that the reaction proceeds via a cascade of steps, including Michael addition, intramolecular C- and O-cyclization, intramolecular trans-esterification, [1,2]-H and [1,5]-methoxy- and ethoxy carbonyl shift, and finally aromatization to yield the desired product. In this method, three bonds (2C-C and C-O) form in one pot, simultaneously forming two new cyclopentane and pyrano rings by double cyclization reactions. Other advantages of this method are that it has a simple operation, readily available starting materials, a chemoselective cascade process, transition metal-free, synthetically useful yields, and green conditions by using ethanol as a solvent.

One-Pot Assembly of 2-Trifluoromethyl Benzothiazole and Benzoselenazole via Copper-Mediated Three-Component Cascade Reaction

A domino one-pot synthesis of 2-(trifluoromethyl) benzothiazole via copper-mediated three-component cascade reaction starting from the easily accessible starting materials such as o-iodoanilines, methyl trifluoropyruvate, and elemental sulfur is reported. The present strategy displayed a comprehensive substrate scope and good functional group tolerance and enabled access to a variety of substituted 2-(trifluoromethyl) benzothiazoles. A 2-(trifluoromethyl) benzoselenazole has also been synthesized utilizing this reaction methodology.

Facile synthesis and in silico studies of benzothiazole-linked hydroxypyrazolones targeting α-amylase and α-glucosidase

Aim: The objective of the present investigation was to design and synthesize new heterocyclic hybrids comprising benzothiazole and indenopyrazolone pharmacophoric units in a single molecular framework targeting α-amylase and α-glucosidase enzymatic inhibition. Materials & methods: 20 new benzothiazole-appended indenopyrazoles, 3a-t, were synthesized in good yields under environment-friendly conditions via cycloaddition reaction, and assessed for antidiabetic activity against α-amylase and α-glucosidase, using acarbose as the standard reference. Results: Among all the hydroxypyrazolones, 3p and 3r showed the best inhibition against α-amylase and α-glucosidase, which finds support from molecular docking and dynamic studies. Conclusion: Compounds 3p and 3r have been identified as promising antidiabetic agents against α-amylase and α-glucosidase and could be considered valuable leads for further optimization of antidiabetic agents.

Construction of benzoheterocycles by the reaction of α-arylglyoxylic acids and ortho-functionalized aniline under mild and minimal conditions

This work describes an environmentally friendly method for the synthesis of benzoxazinones, quinoxalinones and benzothiazoles by the reaction of α-arylglyoxylic acids and ortho-functionalized aniline. In this reaction, no other reagents are needed except for reactants and solvents. The reaction was carried out at a mild temperature of 50 °C with only water and/or carbon dioxide as the by-product. Therefore, the reaction has high practical atom economy. In addition, this strategy could be scaled up to the gram level, and the natural product Cephamandole A could be synthesized on a mass scale.

Solid-Phase Synthesis of 2-Benzothiazolyl and 2-(Aminophenyl)benzothiazolyl Amino Acids and Peptides

2-benzothiazoles and 2-(aminophenyl)benzothiazoles represent biologically interesting heterocycles with high pharmacological activity. The combination of these heterocycles with amino acids and peptides is of special interest, as such structures combine the advantages of amino acids and peptides with the advantages of the 2-benzothiazolyl and 2-(aminophenyl)benzothiazolyl pharmacophore group. In this work, we developed an easy and efficient method for the solid-phase synthesis of 2-benzothiazolyl (BTH) and 2-(aminophenyl)benzothiazolyl (AP-BTH) C-terminal modified amino acids and peptides with high chiral purity.

Design, Synthesis and Biological Activities of (Thio)Urea Benzothiazole Derivatives

(Thio)ureas ((T)Us) and benzothiazoles (BTs) each have demonstrated to have a great variety of biological activities. When these groups come together, the 2-(thio)ureabenzothizoles [(T)UBTs] are formed, improving the physicochemical as well as the biological properties, making these compounds very interesting in medicinal chemistry. Frentizole, bentaluron and methabenzthiazuron are examples of UBTs used for treatment of rheumatoid arthritis and as wood preservatives and herbicides in winter corn crops, respectively. With this antecedent, we recently reported a bibliographic review about the synthesis of this class of compounds, from the reaction of substituted 2-aminobenzothiazoles (ABTs) with iso(thio)cyanates, (thio)phosgenes, (thio)carbamoyl chlorides, 1,1'-(thio)carbonyldiimidazoles, and carbon disulfide. Herein, we prepared a bibliographic review about those features of design, chemical synthesis, and biological activities relating to (T)UBTs as potential therapeutic agents. This review is about synthetic methodologies generated from 1968 to the present day, highlighting the focus to transform (T)UBTs to compounds containing a range substituents, as illustrated with 37 schemes and 11 figures and concluded with 148 references. In this topic, the scientists dedicated to medicinal chemistry and pharmaceutical industry will find useful information for the design and synthesis of this interesting group of compounds with the aim of repurposing these compounds.

A Green Approach to 2-Substituted Benzo- and Naphthothiazoles via N-bromosuccinimide/Bromide-Mediated C(aryl)-S Bond Formation

2-Substituted benzo- and naphthothiazoles have been conveniently prepared from the intramolecular cyclization of phenylthioureas and activated thiobenzanilides or the coupling of isothiocyanates with amines under mild conditions using N-bromosuccinimide/tetrabutylammonium bromide in 1,2-dimethoxyethane (DME) under ambient conditions. The reactions produce moderate to excellent yields with good functional group tolerance and avoid the use of harsh thermal conditions, corrosive reagents, halogenated solvents, toxic metal salts, and expensive metal catalysts, and are amenable to preparations on a gram-scale.

[3 + 2] cycloaddition of nonstabilized azomethine ylides and 2-benzothiazolamines to access imidazolidine derivatives

A simple and practical method for the construction of 1,3,5-trisubstituted imidazolidine derivatives via [3 + 2] cycloaddition reaction has been developed. This reaction could smoothly proceed between nonstabilized azomethine ylides generated in situ and 2-benzothiazolamines to deliver a wide scope of differently substituted imidazolidines in high yields (up to 98%). The structure of one example was confirmed by X-ray single-crystal structure analysis.

Synthesis and Biological Importance of 2-(thio)ureabenzothiazoles

The (thio)urea and benzothiazole (BT) derivatives have been shown to have a broad spectrum of biological activities. These groups, when bonded, result in the 2-(thio)ureabenzothizoles (TBT and UBT), which could favor the physicochemical and biological properties. UBTs and TBTs are compounds of great importance in medicinal chemistry. For instance, Frentizole is a UBT derivative used for the treatment of rheumatoid arthritis and systemic lupus erythematosus. The UBTs Bentaluron and Bethabenthiazuron are commercial fungicides used as wood preservatives and herbicides in winter corn crops. On these bases, we prepared this bibliography review, which covers chemical aspects of UBTs and TBTs as potential therapeutic agents as well as their studies on the mechanisms of a variety of pharmacological activities. This work covers synthetic methodologies from 1935 to nowadays, highlighting the most recent approaches to afford UBTs and TBTs with a variety of substituents as illustrated in 42 schemes and 13 figures and concluded with 187 references. In addition, this interesting review is designed on chemical reactions of 2-aminobenzothiazoles (2ABTs) with (thio)phosgenes, iso(thio)cyanates, 1,1′-(thio)carbonyldiimidazoles [(T)CDI]s, (thio)carbamoyl chlorides, and carbon disulfide. This topic will provide information of utility for medicinal chemists dedicated to the design and synthesis of this class of compounds to be tested with respect to their biological activities and be proposed as new pharmacophores.

Cu-catalysed transamidation of unactivated aliphatic amides

Direct transamidation is gaining prominence as a ground-breaking technique that generates a wide variety of amides without the requirement of acid-amine coupling or other intermediate steps. However, transamidation of unactivated aliphatic amides, on the other hand, has been a long-standing issue in comparison to transamidation of activated amides. Herein, we report a transamidation approach of an unactivated aliphatic amide using a copper catalyst and chlorotrimethylsilane as an additive. In addition, we used transamidation as a tool for selective N-C(O) cleavage and O-C(O) formation to synthesise 2-substituted benzoxazoles and benzothiazoles. The reactions were carried out without using any solvents and offered wide substitution scope.

Synthesis of Homodrimane Sesquiterpenoids Bearing 1,3-Benzothiazole Unit and Their Antimicrobial Activity Evaluation

Based on some homodrimane carboxylic acids and their acyl chlorides, a series of fourteen 2-homodrimenyl-1,3-benzothiazoles, N-homodrimenoyl-2-amino-1,3-benzothiazoles, 4′-methyl-homodrimenoyl anilides and 4′-methyl-homodrimenthioyl anilides were synthesized and their biological activities were evaluated on five species of fungi (Aspergillus niger, Fusarium solani, Penicillium chrysogenum, P. frequentans, and Alternaria alternata) and two strains of bacteria (Bacillus sp. and Pseudomonas aeruginosa). The synthesis involved the decarboxylative cyclization, condensation and thionation of the said acids, anhydrides or their derivatives with 2-aminothiophenol, 2-aminobenzothiazole, p-toluidine and Lawesson’s reagent. As a result, together with the desired compounds, some unexpected products 8, 25, and 27 were obtained, and the structures and mechanisms for their formation have been proposed. Compounds 4, 9, and 25 showed higher antifungal and antibacterial activity compared to the standards caspofungin (MIC = 1.5 μg/mL) and kanamycin (MIC = 3.0 μg/mL), while compound 8 had comparable activities. In addition, compounds 6, 17, and 27 showed selective antifungal activity at MIC = 2.0, 0.25, and 1.0 μg/mL, respectively.

Transition Metal Complexes of Schiff Base Ligands Prepared from Reaction of Aminobenzothiazole with Benzaldehydes

Schiff bases have played significant roles in the development of inorganic or coordination chemistry. Three Schiff base (NB, CB and HB) ligands, prepared for the reaction of 2-amino-6-methoxy-benzothiazole with 2-Nitrobenzaldehyde, 2-chlorobenzaldehyde and 2,4-Dihydroxybenzaldehyed, respectively, were investigated for their transition metal complexes, which were prepared by reacting the ligand (2:1 molar ratio) with Co(II), Ni(II), Cu(II), Cd(II), Cr(III) and Fe(III) chlorides. The nature of the interaction between the metal ions and ligands (L) was studied with the aid of magnetic susceptibility, elemental analysis, FTIR and 1H-NMR spectroscopy. Based on the magnetic superstability and elemental analysis results, octahedral structures of the complexes, such as [ML2Cl2] or [ML2Cl(OH)], were proposed for Cu(II), Cd(II), Co(II) and Ni(II) in which the ligand (L:NB, CB or HB) is bidentate through the azomethine and benzothiazole nitrogen. For Cr(III) and Fe(III) complexes, octahedral ML2Cl(OH)2 or ML2(OH)3 structures were proposed, where one ligand is monodentate and the other is bidentate. The azomethine ν(-HC=N-) and 1H-NMR peaks of NB and CB were shifted to a higher frequency and downfield, respectively, upon complexation with metal ions. The bonding of OH groups of HB to Co(II), Cu(II) and Ni(II) enables π-backdonation from these metals to the azomethine of Schiff bases and the consequent shift of ν(-HC=N-) to a lower frequency and changes in the intensity of the 1H-NMR peak of OH. On the other hand, this backdonation was not evidenced in the FTIR of HB complexes with high-charge Cr(III) and Fe(III) ions.

A review on the design, synthesis, and structure-activity relationships of benzothiazole derivatives against hypoxic tumors

There has been a growing body of studies on benzothiazoles and benzothiazole derivatives as strong and effective antitumor agents against lung, liver, pancreas, breast, and brain tumors. Due to highly proliferative nature of the tumor cells, the oxygen levels get lower than that of a normal tissue in the tumor microenvironment. This situation is called as hypoxia and has been associated with increased ability for carcinogenesis. For the drug design and development strategies, hypoxic nature of the tumor tissues has been exploited more aggressively. Hypoxia itself acts as a signal initiating system to activate the pathways that eventually lead to the spread of the tumor cells into the different tissues, increases the rate of DNA damage and eventually ends up with more mutation levels that may increase the drug resistance. As one of the major mediators of hypoxic response, hypoxia inducible factors (HIFs) has been shown to activate to angiogenesis, metastasis, apoptosis resistance, and many other protumorigenic responses in cancer development. In the current review, we will be discussing the design, synthesis and structure-activity relationships of benzothiazole derivatives against hypoxic tumors such lung, liver, pancreas, breast and brain as potential anticancer drug candidates. The focus points of the study will be the biology behind carcinogenesis and how hypoxia contributes to the process, recent studies on benzothiazole and its derivatives as anti-cancer agents against hypoxic cancers, conclusions and future perspectives. We believe that this review will be useful for the researchers in the field of drug design during their studies to generate novel benzothiazole-containing hybrids against hypoxic tumors with higher efficacies.

Current Perspective of Synthesis of Medicinally Relevant Benzothiazole Based Molecules: Potential for Antimicrobial and Anti-Inflammatory Activities

The therapeutic potential of the majority of the marketed drugs is due to the presence of a heterocyclic nucleus, which constitutes a huge role in the field of medicinal chemistry. These heterocyclic scaffolds could act as a template in order to design potential therapeutic agents against several diseases. Benzothiazole scaffold is one of the influential heteroaromatic rings in the field of medicinal chemistry owing to its extensive pharmacological features. Herein, we have focused on the synthesis of benzothiazole based medicinal molecules, which possess antimicrobial and anti-inflammatory activities. This review covers a systematic description of synthetic routes for biologically relevant benzothiazole derivatives in the last five years. The main aim of this study is to show the diversification of benzothiazole based molecules into their pharmacologically more active derivatives. This review's synthetic protocols include metal-free, metal-catalyzed, and metal precursor azo dyes strategies for the development of benzothiazole derived bioactive compounds. The discussion under the various headings covers synthetic schemes and biological activities of the most potent molecules in the form of minimum inhibitory concentration.

Ionic Reactivity of 2-Isocyanoaryl Thioethers: Access to 2-Halo and 2-Aminobenzothia/Selenazoles

An ionic cascade insertion/cyclization reaction of thia-/selena-functionalized arylisocyanides has been successfully developed for the efficient and practical synthesis of 2-halobenzothiazole/benzoselenazole derivatives. This synthetic protocol, incorporating a halogen atom when forming the five-membered ring of benzothia/selenazoles, is different from the existing ones, where halogenation of the preformed benzothia/selenazole precursors happens. Additionally, a facile access to 2-aminobenzothiazoles is also achieved by the one-pot cascade reaction of 2-isocyanoaryl thioethers, iodine, and amines.

Catalyst-free reductive cyclization of bis(2-aminophenyl) disulfide with CO2 in the presence of BH3NH3 to synthesize 2-unsubstituted benzothiazole derivatives

An efficient and catalyst-free methodology for the reductive cyclization of various disulfides using BH3NH3 as a reductant and CO2 as a C1 resource was developed.

α-Keto Acids as Triggers and Partners for the Synthesis of Quinazolinones, Quinoxalinones, Benzooxazinones, and Benzothiazoles in Water

A general and efficient method for the synthesis of quinazolinones, quinoxalinones, benzooxazinones, and benzothiazoles from the reactions of α-keto acids with 2-aminobenzamides, benzene-1,2-diamines, 2-aminophenols, and 2-aminobenzenethiols, respectively, is described. The reactions were conducted under catalyst-free conditions, using water as the sole solvent with no additive required, and successfully applied to the synthesis of sildenafil. More importantly, these reactions can be conducted on a mass scale, and the products can be easily purified through filtration and washing with ethanol (or crystallized).

Benzothiazoles from Condensation of o-Aminothiophenoles with Carboxylic Acids and Their Derivatives: A Review

Nowadays, organic chemists are interested in the field of heterocyclic chemistry due to its use in the synthesis of a great variety of biologically active compounds. Heterocyclic compounds are widely found in nature and are essential for life. Among these, some natural nitrogen containing heterocyclic compounds have been used as chemotherapeutic agents. Their attachment to sugar molecules either as thioglycosides or as nucleosides analogues plays an important role in vital biological processes as well as in synthetic organic chemistry. Molecules containing benzothiazole (BT) nuclei are of this interesting class of compounds because some of them have been found to have a wide variety of biological activities. In this sense, we selected this topic to review and to then summarize the procedures related to the condensation reactions of o-aminothiophenoles (ATPs) as well as their disulfides with carboxylic acids, esters, orthoesters, acyl chlorides, amides, and nitriles. The condensation reactions with carbon dioxide (CO₂) are included. Conventional methods with the use of acid and metal catalysts as well as recent green techniques, such as microwave irradiation, the use of ionic liquids, and ultrasound (US) chemistry, which have proven to have many advantages, were found in the review.

Synthesis of biologically active derivatives of 2-aminobenzothiazole

The minireview considers the current trends in the synthesis of some biologically active compounds based on 2-aminobenzothiazole. The presented information covers publications of the last five years.

Modern Approaches to the Synthesis and Transformations of Practically Valuable Benzothiazole Derivatives

The review is devoted to modern trends in the chemistry of 2-amino and 2-mercapto substituted benzothiazoles covering the literature since 2015. The reviewed heterocycles belong to biologically active and industrially demanded compounds. Newly developed synthesis methods can be divided into conventional multistep processes and one-pot, atom economy procedures, realized using green chemistry principles and simple reagents. The easy functionalization of the 2-NH2 and 2-SH groups and the benzene ring of the benzothiazole moiety allows considering them as highly reactive building blocks for organic and organoelement synthesis, including the synthesis of pharmacologically active heterocycles. The review provides a summary of findings, which may be useful for developing new drugs and materials and new synthetic approaches and patterns of reactivity.

Tunable synthesis of benzothiophene fused pyranone and thiochromen fused furan derivatives via a domino process

A K₂CO₃-promoted tunable domino reaction between thioisatins and α-bromoketones was developed for the synthesis of benzothiophene fused pyranone and thiochromen fused furan derivatives via adjusting MgSO₄.

Current advances in the synthetic strategies of 2-arylbenzothiazole

Benzothiazole is a privileged scaffold in the field of synthetic and medicinal chemistry. Its derivatives and metal complexes possess a gamut of pharmacological properties and high degree of structural diversity that has proven it vital for the investigation for novel therapeutics. The 2nd position of benzothiazole is the most active site that makes 2-arylbenzothiazole as felicitous scaffolds in pharmaceutical chemistry. The extensive significance of benzo-fused heterocyclic moieties formation has led to broad and valuable different approaches for their synthesis. This review deals with the synthetic approaches developed so far for the synthesis of 2-arylbenzothiazoles. Moreover, this article abridges the publications devoted to the synthesis of this moiety over the last 6 years. This study gives a current precis of research on the fabrication of 2-arylbenzothiazoles through different synthetic pathways and shall be helpful for researchers and scientists who are working in this field to make more potent biologically active benzothiazole-based drugs.