Recent Advances in Synthesis of Benzothiazole Compounds Related to Green Chemistry

Benzothiazole a privileged scaffold for Cutting-Edges anticancer agents: Exploring drug design, structure-activity relationship, and docking studies

Cancer is a major societal, public health, and economic burden in the 21st century, with 9.7 million deaths in 2022 (9.96 million in 2020) and 20 million new cancer cases (19.6 million in 2020). Considering the increasing number of cancer cases and deaths, heterocyclic compounds always paved the gold mine for the development of potential anticancer drugs as these compounds have unique flexibility and dynamic cores. Benzothiazoles and their derivatives have potential anticancer properties, making them a desirable scaffold among different heterocycles. Title structures are a class of chemicals that may bind to various receptors with high affinity, particularly those engaged in oncogenic processes. The use of these compounds allows medicinal chemists to rapidly produce anticancer treatments across a large range of targets over an extended length of time. The current study presents a thorough success story of benzothiazole derivatives as anticancer agents. It discusses the current state of cancer, the profile of benzothiazole-based derivatives synthetic pathways, and its relevance as an anticancer agent on several oncogenic pathways. The structure-activity relationship was also added to offer insight into the connection of biological data with structure and the rational design of more active drugs.

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.

Exploring applications of non-targeted analysis in the characterization of the prenatal exposome

Capturing the breadth of chemical exposures in utero is critical in understanding their long-term health effects for mother and child. We explored methodological adaptations in a Non-Targeted Analysis (NTA) pipeline and evaluated the effects on chemical annotation and discovery for maternal and infant exposure. We focus on lesser-known/underreported chemicals in maternal and umbilical cord serum analyzed with liquid chromatography-quadrupole time-of-flight mass spectrometry (LC-QTOF/MS). The samples were collected from a demographically diverse cohort of 296 maternal-cord pairs (n = 592) recruited in San Francisco Bay area. We developed and evaluated two data processing pipelines, primarily differing by detection frequency cut-off, to extract chemical features from non-targeted analysis (NTA). We annotated the detected chemical features by matching with EPA CompTox Chemicals Dashboard (n = 860,000 chemicals) and Human Metabolome Database (n = 3140 chemicals) and applied a Kendrick Mass Defect filter to detect homologous series. We collected fragmentation spectra (MS/MS) on a subset of serum samples and matched to an experimental MS/MS database within the MS-Dial website and other experimental MS/MS spectra collected from standards in our lab. We annotated ~72 % of the features (total features = 32,197, levels 1-4). We confirmed 22 compounds with analytical standards, tentatively identified 88 compounds with MS/MS spectra, and annotated 4862 exogenous chemicals with an in-house developed annotation algorithm. We detected 36 chemicals that appear to not have been previously reported in human blood and 9 chemicals that were reported in less than five studies. Our findings underline the importance of NTA in the discovery of lesser-known/unreported chemicals important to characterize human exposures.

Revealing the Unique Role of Water in the Formation of Benzothiazoles: an Experimental and Computational Study

We present here a joint experimental and computational study on the formation of benzothiazoles. Our investigation reveals a green protocol for accessing benzothiazoles from acyl chlorides using either water alongside a reducing agent as the reaction medium or in combination with stoichiometric amounts of a weak acid, instead of the harsh conditions and catalysts previously reported. Specifically, we show that a protic solvent, particularly water, enables the formation of 2-substituted benzothiazoles from N-acyl 1,2-aminothiophenols already at room temperature, without the need for strong acids or metal catalysts. DFT Molecular Dynamics simulations coupled with advanced enhanced sampling techniques provide a clear understanding of the catalytic role of water. We demonstrate how bulk water - due to its extended network of hydrogen bonds and an efficient Grotthuss mechanism - provides a reaction path that strongly reduces the reaction barriers compared to aprotic environments, namely more than 80 kJ/mol for the first reaction step and 250 kJ/mol for the second. Finally, we discuss the influence of different aliphatic and aromatic substituents with varying electronic properties on chemical reactivity. Besides providing in-depth mechanistic insights, we believe that our findings pave the way for a greener route toward an important class of bioactive molecules.

Metal- and base-free, aerobic photoredox catalysis with riboflavin to synthesize 2-substituted benzothiazoles

Sustainable approaches for the synthesis of 2-substituted benzothiazoles are sought after for their use in organic chemistry, bioorganic chemistry, and industrial applications. Here, we described a visible light-driven photoredox catalytic cyclization of thioanilides to afford 2-substituted benzothiazoles using riboflavin as a photocatalyst, where oxygen is used as a clean oxidant and ethanol as a greener solvent. These results provide a new photochemical route for environmentally benign synthesis.

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.

Recent advances in the synthesis of new benzothiazole based anti-tubercular compounds

This review highlights the recent synthetic developments of benzothiazole based anti-tubercular compounds and their in vitro and in vivo activity. The inhibitory concentrations of the newly synthesized molecules were compared with the standard reference drugs. The better inhibition potency was found in new benzothiazole derivatives against M. tuberculosis. Synthesis of benzothiazole derivatives was achieved through various synthetic pathways including diazo-coupling, Knoevenagel condensation, Biginelli reaction, molecular hybridization techniques, microwave irradiation, one-pot multicomponent reactions etc. Other than recent synthetic developments, mechanism of resistance of anti-TB drugs is also incorporated in this review. Structure activity relationships of the new benzothiazole derivatives along with the molecular docking studies of selected compounds have been discussed against the target DprE1 in search of a potent inhibitor with enhanced anti-tubercular activity.

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.

Fe3O4@ABA-aniline-CuI nanocomposite as a highly efficient and reusable nanocatalyst for the synthesis of benzothiazole-sulfide aryls and heteroaryls

Studying diaryl sulfides and benzothiazoles is important in organic synthesis because numerous natural and medicinal products contain these scaffolds. Over the past few years, research on the synthesis of compounds containing benzothiazole-sulfide aryls, as important biological molecules, has received significant attention. Multicomponent reactions are the most popular strategy for performing difficult reactions and the synthesis of complexed molecules such as benzothiazole-sulfide aryls. In this work, CuI was successfully immobilized on the surface of magnetic Fe₃O₄ nanoparticles modified with aniline and 4-aminobenzoic acid [Fe₃O₄@ABA-Aniline-CuI nanocomposite] and its catalytic activity was investigated in the preparation of a broad range of benzothiazole-sulfide aryls and heteroaryls through the one-pot three-component reactions of 2-iodoaniline with carbon disulfide and aryl or heteroaryl iodides in the presence of KOAc as base in PEG-400 as solvent. TEM and SEM images revealed that the shape of the Fe₃O₄@ABA-Aniline-CuI particles is spherical and the size of the particles is approximately between 12-25 nanometers.

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.

Review on the Developments of Benzothiazole-containing Antimicrobial Agents

The infectious diseases caused by bacterial resistance to antibiotics constitute an increasing threat to human health on a global scale. An increasing number of infections, including tuberculosis, pneumonia, salmonellosis and gonorrhea, are becoming progressively challenging to cure owing to the ineffectiveness of current clinically used antibiotics and presents a serious health threat worldwide in medical community. The major concern of this global health threat is the ability of microorganisms to develop one or several mechanisms of resistance to antibiotics, making them inefficient to therapeutic treatment. The quest for discovering novel scaffold with antimicrobial property is particularly in great need to face future challenges in hospital and healthcare settings. Hence, the development of benzothiazoles is of considerable interest to medicinal chemists. Benzothiazole, being part of an important class of heterocyclic scaffold retains a wide spectrum of various attractive pharmacological activities. Antibiotic resistance represents an increasing burden comprising medical cost, hospital stay and mortality. Several derivatives containing a benzothiazole scaffold, reported in the literature, were found to display remarkable potencies towards diverse Grampositive and Gram-negative bacterial pathogens. The principal focus concerns the antibacterial potential of benzothiazole-based derivatives as antimicrobial agents interacting with targets in bacterial pathogens. In this review, we also disclose the significance of the benzothiazole moiety in the discovery of new antibacterial compounds, the potential of benzothiazole-based derivatives in the case of resistant bacterial strains, optimization of their antibacterial activity, and their future perspectives. The structure-activity relationship study and the mode of action of the title derivatives are highlighted too.

From (-)-sclareol to Norlabdane Heterocyclic Hybrid Compounds

This review relates to chemistry of the well-known biologically active natural labdane diterpenoid (-)-sclareol easily available from Clary sage (Salvia sclarea L.). It is mainly used in industry, especially for synthesis of fragrance compounds and natural analogs. The paper covers achievements on the synthesis, structure determination and biological activity of molecular hybrid compounds bearing hydrazide and thiosemicarbazone fragments or diazine, 1,2,4-triazole, carbazole, 1,3-thiazole, 1,3,4-oxadiazole, 1,3,4-thiadiazole units prepared based on it.

Synthesis of 2-Cyanobenzothiazoles via Pd-Catalyzed/Cu-Assisted C-H Functionalization/Intramolecular C-S Bond Formation from N-Arylcyanothioformamides

We report herein on a catalytic system involving palladium and copper to achieve the cyclization of N-arylcyanothioformamides and the synthesis of 2-cyanobenzothiazoles. The C-H functionalization/intramolecular C-S bond formation reaction was achieved in the presence of air, using 2.0 equiv of an inorganic additive (KI). In many cases, the reaction led to a sole product regioselectively obtained in good yields, allowing the synthesis of a wide range of substituted 2-cyanobenzothiazole derivatives, providing valuable building blocks for the design of more complex heterocyclic or molecular labeling systems.

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.

Oxidation of 2-Cyanothioacrylamides with Sodium Nitrite in Acidic Medium

Abstract

(E)-3-Aryl-2-cyanoprop-2-entioamides, prepared by Knoevenagel condensation between aromatic aldehydes and cyanothioacetamide, react with sodium nitrite in acetic acid to form (2E,2′E)-2,2′-(1,2,4-thiadiazole-3,5-diyl)bis[3-arylacrylonitriles]. A possible mechanism and limitations of the reaction are discussed. Molecular docking was carried out in order to search for possible protein targets for the obtained 1,2,4-thiadiazoles. One of the compounds showed a pronounced antidote effect against the herbicide 2,4-D in a laboratory experiment on sunflower seedlings and under field conditions.

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.

Design and Synthesis of New 2-Aminobenzamide Derivatives Containing Benzothiazole and Phenylamine Moiety and Their Cytotoxicity

Twelve new compounds including 2-aminobenzamide derivatives bearing benzothiazole and phenylamine moiety were designed and synthesized. The synthesized compounds were tested their cytotoxic activity against A549 and SW480 tumor cell lines. Compounds 3a and 3c exhibited cytotoxicity toward A549 cell line with IC50 values of 24.59 and 29.59 µM, respectively.

Thiazole and Related Heterocyclic Systems as Anticancer Agents: A Review on Synthetic Strategies, Mechanisms of Action and SAR Studies

Background:

Cancer is the second leading cause of death throughout the world. Many anticancer drugs are commercially available, but lack of selectivity, target specificity, cytotoxicity and development of resistance lead to serious side effects. There have been several experiments going on to develop compounds with minor or no side effects.

Objective:

This review mainly emphasizes synthetic strategies, SAR studies, and mechanism of action for thiazole, benzothiazole, and imidazothiazole containing compounds as anticancer agents.

Methods:

Recent literature related to thiazole and thiazole-related derivatives endowed with encouraging anticancer potential is reviewed. This review emphasizes contemporary strategies used for the synthesis of thiazole and related derivatives, mechanistic targets, and comprehensive structural activity relationship studies to provide perspective into the rational design of high-efficiency thiazole-based anticancer drug candidates.

Results:

Exhaustive literature survey indicated that thiazole derivatives are associated with properties of inducing apoptosis and disturbing tubulin assembly. Thiazoles are also associated with the inhibition of NFkB/mTOR/PI3K/AkT and regulation of estrogen-mediated activity. Furthermore, thiazole derivatives have been found to modulate critical targets such as topoisomerase and HDAC.

Conclusion:

Thiazole derivatives seem to be quite competent and act through various mechanisms. Some of the thiazole derivatives, such as compounds 29, 40, 62, and 74a with IC50 values of 0.05 μM, 0.00042 μM, 0.18 μM, and 0.67 μM, respectively not only have anticancer activity but they also have lower toxicity and better absorption. Therefore, some other similar compounds could be investigated to aid in the development of anticancer pharmacophores.

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.

Photochemical Csp2-H bond thiocyanation and selenocyanation of activated arenes, batch and continuous-flow approaches

Herein, we report an eco-friendly photochemical oxidative C_sp²-H thiocyanation and selenocyanation of activated arenes. The reaction proceeds under Violet LED irradiation in the presence of K₂S₂O₈, which quickly oxidizes KSCN and KSeCN, finally producing arylthio/selenocyanates. Using this benign, atom-economic protocol, the desired chalcogenide products were obtained regioselectively, with isolated yields that range from very good to excellent. Although, mechanistic study indicates that it is difficult to distinguish between a radical to a S_EAr reaction mechanism between the photo-induced formed ^•SCN, for the former, or NCSSCN, for the latter, to the aromatic heterocycles. The inhibition experiment together with the observed reactivity and regioselectivity, would be in agreement with the latter. The synthetic methodology designed could be successfully adapted to continuous-flow systems in a segmented-flow regime, employing the organic phase as the product reservoir. Using this setup, the advantage of the latter can be demonstrated by reducing the reaction time and improving the product yields. Similarly, the scaling up of the reaction to gram scale resulted in favorable outcomes by the flow setup, which installs the photo-flow chemistry as a powerful tool to be included into routine reaction procedures, which have great relevance for the pharmaceutical industry.

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.

Different patterns of supra-molecular aggregation in three amides containing N-(benzo[d]thia-zol-yl) substituents

Crystal structures are reported for three amides containing N-benzo[d]thia-zole substituents. In N-(benzo[d]thia-zol-6-yl)-3-bromo-benzamide, C14H9BrN2OS, where the two ring systems are nearly parallel to one another [dihedral angle = 5.8 (2)°], the mol-ecules are linked by N-H⋯O and C-H⋯N hydrogen bonds to form ribbons of R 3 3(19) rings, which are linked into sheets by short Br⋯Br inter-actions [3.5812 (6) Å]. N-(6-Meth-oxy-benzo[d]thia-zol-2-yl)-2-nitro-benzamide, C15H11N3O4S, crystallizes with Z' = 2 in space group Pna21: the dihedral angles between the ring systems [46.43 (15) and 66.35 (13)°] are significantly different in the independent mol-ecules and a combination of two N-H⋯N and five C-H⋯O hydrogen bonds links the mol-ecules into a three-dimensional network. The mol-ecules of 5-cyclo-propyl-N-(6-meth-oxy-ben-zo[d]thia-zol-2-yl)-isoxazole-3-carboxamide, C15H13N3O3S, exhibit two forms of disorder, in the meth-oxy group and in the cyclo-propyl-isoxazole unit; symmetry-related pairs of mol-ecules are linked into dimers by pairwise N-H⋯N hydrogen bonds. Comparisons are made with the structures of some related compounds.

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.

Two Approaches for the Synthesis of Fused Dihydropyridines via a 1,6-Electrocyclic Reaction: Fluorescent Properties and Prospects for Application

Reactions of penta-2,4-dienethioamides with acetylenedicarboxylic acid, methyl and ethyl esters, and methyl propiolate were systematically studied, and a number of new 2,3-dihydro-5H-thiazolo[3,2-a]pyridines (DTPs) and 4H,6H-pyrido[2,1-b][1,3]thiazines (PTZs) were prepared. A possible mechanism for a multistep domino transformation is suggested, and the key step is the 1,6-electrocyclic reaction. An additional alternative method for the synthesis of new heterocyclic systems was achieved. Evidence of the electrocyclic mechanism of a key step was collected from the analysis of the spatial structure of the synthesized bicyclic nonaromatic pyridines by X-ray diffraction and quantum chemical calculations, as well as from the thermodynamic quantities. DTPs exhibited yellow fluorescence in solution and yellow to red emissions in the solid state. Biological investigations demonstrated the ability of DTPs to penetrate living and fixed cells and presumably accumulate in lysosomes.

2-substituted benzothiazoles as antiproliferative agents: Novel insights on structure-activity relationships

Given the wide spectrum of biological activities, benzothiazoles represent privileged scaffolds in medicinal chemistry, useful in drug discovery programs to modulate biological activities of lead compounds. A large body of knowledge about benzothiazoles has been reported in scientific literature, describing their antimicrobial, anticonvulsant, neuroprotective, anti-inflammatory, and antiproliferative effects. This review summarizes the results obtained in the structure-activity relationship studies on antiproliferative benzothiazoles, focusing on 2-substituted derivatives and on mechanism of action responsible for the antitumor effects of this class of compounds.