Synthesis and biological evaluation of polymethoxylated 4-heteroarylcoumarins as tubulin assembly inhibitor

Sugar functionalized coumarin motifs: Synthesis and applications

Sugars are vital biomolecules widely found in nature, playing an indispensable role in a plethora of biological processes. Similarly, coumarins are heterocycles with an effective pharmacophore skeleton, making them crucial in drug design and development. Coupling carbohydrate moieties to the small biologically active molecules creates a vast library of glycoconjugates with impressive structural diversity. The potential of coumarin glycosides is being extensively explored due to their broad spectrum of applications, including antibacterial, anticancer, and anticoagulant properties, etc. This review highlights various chemical methodologies for synthesizing diverse coumarin glycohybrids with distinct linkages and explores their immense biological potential, making a significant contribution to the field of organic synthesis.

In Vitro and In Silico Biological Studies of 4-Phenyl-2-quinolone (4-PQ) Derivatives as Anticancer Agents

Our previous study found that 2-phenyl-4-quinolone (2-PQ) derivatives are antimitotic agents, and we adopted the drug design concept of scaffold hopping to replace the 2-aromatic ring of 2-PQs with a 4-aromatic ring, representing 4-phenyl-2-quinolones (4-PQs). The 4-PQ compounds, whose structural backbones also mimic analogs of podophyllotoxin (PPT), maybe a new class of anticancer drugs with simplified PPT structures. In addition, 4-PQs are a new generation of anticancer lead compounds as apoptosis stimulators. On the other hand, previous studies showed that 4-arylcoumarin derivatives with 5-, 6-, and 7-methoxy substitutions displayed remarkable anticancer activities. Therefore, we further synthesized a series of 5-, 6-, and 7-methoxy-substituted 4-PQ derivatives (19-32) by Knorr quinoline cyclization, and examined their anticancer effectiveness. Among these 4-PQs, compound 22 demonstrated excellent antiproliferative activities against the COLO205 cell line (50% inhibitory concentration (IC50) = 0.32 μM) and H460 cell line (IC50 = 0.89 μM). Furthermore, we utilized molecular docking studies to explain the possible anticancer mechanisms of these 4-PQs by the docking mode in the colchicine-binding pocket of the tubulin receptor. Consequently, we selected the candidate compounds 19, 20, 21, 22, 25, 27, and 28 to predict their absorption, distribution, metabolism, excretion, and toxicity (ADMET) profiles. Pharmacokinetics (PKs) indicated that these 4-PQs displayed good drug-likeness and bioavailability, and had no cardiotoxic side effects or carcinogenicity, but we detected risks of drug-drug interactions and AMES toxicity (mutagenic). However, structural modifications of these 4-PQs could improve their PK properties and reduce their side effects, and their promising anticancer activities attracted our attention for further studies.

[5]-Helistatins: Tubulin-Binding Helicenes with Antimitotic Activity

Helicenes are high interest synthetic targets with unique conjugated helical structures that have found important technological applications. Despite this interest, helicenes have had limited impact in chemical biology. Herein, we disclose a first-in-class antimitotic helicene, helistatin 1 (HA-1), where the helicene scaffold acts as a structural mimic of colchicine, a known antimitotic drug. The synthesis proceeds via sequential Pd-catalyzed coupling reactions and a π-Lewis acid cycloisomerization mediated by PtCl2. HA-1 was found to block microtubule polymerization in both cell-free and live cell assays. Not only does this demonstrate the feasibility of using helicenes as bioactive scaffolds against protein targets, but also suggests wider potential for the use of helicenes as isosteres of biaryls or cis-stilbenes-themselves common drug and natural product scaffolds. Overall, this study further supports future opportunities for helicenes for a range of chemical biological applications.

Rational approaches, design strategies, structure activity relationship and mechanistic insights for therapeutic coumarin hybrids

Hybrid molecules, furnished by combining two or more pharmacophores is an emerging concept in the field of medicinal chemistry and drug discovery that has attracted substantial traction in the past few years. Naturally occurring scaffolds such as coumarins display a wide spectrum of pharmacological activities including anticancer, antibiotic, antidiabetic and others, by acting on multiple targets. In this view, various coumarin-based hybrids possessing diverse medicinal attributes were synthesized in the last five years by conjugating coumarin moiety with other therapeutic pharmacophores. The current review summarizes the recent development (2014 and onwards) of these pharmacologically active coumarin hybrids and demonstrates rationale behind their design, structure-activity relationships (SAR) and mechanistic studies performed on these hybrid molecules. This review will be beneficial for medicinal chemist and chemical biologist, and in general to the drug discovery community and will facilitate the synthesis and development of novel, potent coumarin hybrid molecules serving as lead molecules for the treatment of complex disorders.

Applications of Friedel-Crafts reactions in total synthesis of natural products

Over the years, Friedel-Crafts (FC) reactions have been acknowledged as the most useful and powerful synthetic tools for the construction of a special kind of carbon-carbon bond involving an aromatic moiety. Its stoichiometric and, more recently, its catalytic procedures have extensively been studied. This reaction in recent years has frequently been used as a key step (steps) in the total synthesis of natural products and targeted complex bioactive molecules. In this review, we try to underscore the applications of intermolecular and intramolecular FC reactions in the total syntheses of natural products and complex molecules, exhibiting diverse biological properties.

Hybrid Molecules Composed of 2,4-Diamino-1,3,5-triazines and 2-Imino-Coumarins and Coumarins. Synthesis and Cytotoxic Properties

A series of 2-imino-2H-chromen-3-yl-1,3,5-triazine compounds 5⁻12, which are namely hybrids of 2,4-diamino-1,3,5-triazines and 2-imino-coumarins, was synthesized by reacting 2-(4,6-diamine-1,3,5-triazin-2-yl)acetonitriles 1⁻4 with 2-hydroxybenzaldehydes. After this, upon heating in aqueous DMF, 2-imino-2H-chromen-3-yl-1,3,5-triazines 10 and 12 were converted into the corresponding 2H-chromen-3-yl-1,3,5-triazines 13 and 14, which are essentially hybrids of 2,4-diamino-1,3,5-triazines and coumarins. The in vitro anticancer activity of the newly prepared compounds was evaluated against five human cancer cell lines: DAN-G, A-427, LCLC-103H, SISO and RT-4. The greatest cytotoxic activity displayed 4-[7-(diethylamino)-2-imino-2H-chromen-3-yl]-6-(4-phenylpiperazin-1-yl)-1,3,5-triazin-2-amine (11, IC₅₀ in the range of 1.51⁻2.60 μM).

Synthesis and antimycobacterial activity of 1-(β-d-Ribofuranosyl)-4-coumarinyloxymethyl- / -coumarinyl-1,2,3-triazole

A series of β-d-ribofuranosyl coumarinyl-1,2,3-triazoles have been synthesized by Cu-catalyzed cycloaddition reaction between azidosugar and 7-O-/7-alkynylated coumarins in 62-70% overall yields. The in vitro antimycobacterial activity evaluation of the synthesized triazolo-conjugates against Mycobacterium tuberculosis revealed that compounds were bactericidal in nature and some of them were found to be more active than one of the first line antimycobacterial drug ethambutol against sensitive reference strain H37Rv, and 7 to 420 times more active than all four first line antimycobacterial drugs (isoniazid, rifampicin, ethambutol and streptomycin) against multidrug resistant clinical isolate 591. Study of in silico pharmacokinetic profile indicated the drug like characters for the test molecules. Further, transmission electron microscopic experiments revealed that these compounds interfere with the constitution of bacterial cell wall possibly by targeting mycobacterial InhA and DNA gyrase enzymes. Study conducted on the activities of the test compounds on bacterial InhA and DNA gyrase revealed that the most bactericidal test compound, N¹-(β-d-ribofuranosyl)-C⁴-(4-methylcoumarin-7-oxymethyl)-1,2,3-triazole (6b) and its corresponding directly linked conjugate N¹-(β-d-ribofuranosyl)-C⁴-(4-methylcoumarin-7-yl)-1,2,3-triazole (11b) significantly inhibited the activity of both the enzymes. The results were further supported by molecular docking studies of the compound 6b and 11b with bacterial InhA and DNA gyrase B enzymes. Further, the cytotoxicity study of some of the better active compounds on THP-1 macrophage cell line using MTT assay showed that the synthesized compounds were non-cytotoxic.

Coumarin: A Natural, Privileged and Versatile Scaffold for Bioactive Compounds

Many naturally occurring substances, traditionally used in popular medicines around the world, contain the coumarin moiety. Coumarin represents a privileged scaffold for medicinal chemists, because of its peculiar physicochemical features, and the versatile and easy synthetic transformation into a large variety of functionalized coumarins. As a consequence, a huge number of coumarin derivatives have been designed, synthesized, and tested to address many pharmacological targets in a selective way, e.g., selective enzyme inhibitors, and more recently, a number of selected targets (multitarget ligands) involved in multifactorial diseases, such as Alzheimer's and Parkinson's diseases. In this review an overview of the most recent synthetic pathways leading to mono- and polyfunctionalized coumarins will be presented, along with the main biological pathways of their biosynthesis and metabolic transformations. The many existing and recent reviews in the field prompted us to make some drastic selections, and therefore, the review is focused on monoamine oxidase, cholinesterase, and aromatase inhibitors, and on multitarget coumarins acting on selected targets of neurodegenerative diseases.

Microwave-assisted synthesis and antitumor evaluation of a new series of thiazolylcoumarin derivatives

A new series of thiazolylcoumarin derivatives was synthesized. The designed strategy embraced a molecular hybridization approach which involves the combination of the thiazole and coumarin pharmacophores together. The new hybrid compounds were tested for in vitro antitumor efficacy over cervical (Hela) and kidney fibroblast (COS-7) cancer cells. Compounds 5f, 5h, 5m and 5r displayed promising efficacy toward Hela cell line. In addition, 5h and 5r were found to be the most active candidates toward COS-7 cell line. The four active analogs, 5f, 5h, 5m and 5r were screened for in vivo antitumor activity over EAC cells in mice, as well as in vitro cytotoxicity toward W138 normal cells. Results illustrated that 5r has the highest in vivo activity, and that the four analogs are less cytotoxic than 5-FU toward W138 normal cells. In this study, 3D pharmacophore analysis was performed to investigate the matching pharmacophoric features of the synthesized compounds with trichostatin A. In silico studies showed that the investigated compounds meet the optimal needs for good oral absorption with no expected toxicity hazards.

The value of pyrans as anticancer scaffolds in medicinal chemistry

Pyran-based heterocycles are promising for anticancer drug discovery.

Synthesis and cytostatic properties of polyfunctionalized furanoallocolchicinoids

A series of furan-based allocolchicinoids was prepared from commercially available colchicine via a nine-step reaction sequence. Cytostatic activity, cell cycle arrest, apoptosis, tubulin and F-actin expression were studied in vitro in 2D and 3D cultures of normal and tumor epithelial keratinocytes, endothelial and mesenchymal cells. Among the prepared furanoallocolchicine analogues, 14a and 7a displayed the most pronounced anti-cancer activity. These compounds induced two types of effects: (a) cell cycle arrest in the G2/M phase as a direct consequence of effective tubulin binding (metaphase effect), and (b) pronounced cell stress (as evidenced by the overexpression of tubulin and F-actin), which was caused by the hyperpolarization of mitochondrial and lysosomal membranes (interphase effect).

Synthesis and evaluation of anticancer activity of 6-pyrazolinylcoumarin derivatives

A series of novel 6-pyrazolinylcoumarins has been synthesized via multi-step protocol. The synthetic procedure was based on the acetylation of hydroxycoumarins; Fries rearrangement and Claisen–Schmidt condensation; the target 6-[5-aryl-4,5-dihydropyrazol-3-yl]-5-hydroxy-7-methylcoumarins (33–49) were obtained under reactions of hydrazine and 2-aryl-5-methyl-2,3-dihydropyrano[2,3-f]chromen-4,8-diones as the last phase of the protocol. Anticancer activity screening in NCI60-cell lines assay allowed identification of compound 47 with the highest level of antimitotic activity with mean GI₅₀ value of 10.20 μM and certain sensitivity profile toward the Leukemia cell lines CCRF-CEM and MOLT-4 (GI₅₀/TGI values 1.88/5.06 μM and 1.92/4.04 μM respectively).

Recent developments of C-4 substituted coumarin derivatives as anticancer agents

Cancer is a prominent cause of death in global. Currently, the numbers of drugs that are in clinical practice are having a high prevalence of side effect and multidrug resistance. Researchers have made an attempt to expand a suitable anticancer drug that has no MDR and side effect. Coumarin scaffold became an attractive subject due to their broad spectrum of pharmacological activities. Coumarin derivatives extensively explored for anticancer activities as it possesses minimum side effect along with multi-drug reversal activity. Coumarin derivatives can act by various mechanisms on different tumor cell lines depending on substitution pattern of the core structure of coumarin. Substitution on coumarin nucleus leads to the search for more potent compounds. In this review, we have made an effort to give a synthetic strategy for the preparation of C-4 substituted coumarin derivatives as anticancer agents based on their mechanism of action and also discuss the SAR of the most active compound.

Synthesis and anticancer activity of 6-heteroarylcoumarins

A series of novel 7-hydroxy-8-methyl-coumarins with indole, pyrimidine, pyrazole, pyran, tetrazolo[1,5-a]pyrimidine, pyrimido[1,2-a]benzimidazol, 2-oxo-1,2-dihydropyridine and dihydropyrazolo[3,4-b]pyridine moieties at C6 position of heterocyclic core have been synthesized. Anticancer activity screening on NCI60 cell lines allowed identification of 6-(6-fluoro-1H-indol-2-yl)-7-hydroxy-4,8-dimethyl-2H-chromen-2-one (23) with the highest level of antimitotic activity with mean GI50/TGI values of 3.28/13.24 μM and certain sensitivity profile towards the Non-Small Cell Lung Cancer cell line НОР-92 (GI50/TGI/LC50 values 0.95/4.17/29.9 μM).

Synthesis of indole-derived allocolchicine congeners exhibiting pronounced anti-proliferative and apoptosis-inducing properties

The synthesis and biological assessment of indole-based allocolchicine congeners with potent anti-proliferative and apoptosis-inducing activity are reported.

Application of the Suzuki-Miyaura reaction in the synthesis of flavonoids

The application of the Suzuki-Miyaura reaction in the synthesis of flavonoids, an important class of natural products, is reviewed. This reaction has not only been employed to provide access to flavonoid nuclei, but has also been applied to the synthesis of dimeric flavonoids and in the synthesis of libraries of flavonoid derivatives for biological activity studies. The classes of flavonoids that are discussed are the chalcones, flavones, isoflavones, neoflavones, biflavones and derivatives of flavonoids obtained by C-C bond formation via the Suzuki-Miyaura reaction.

[Liposome formulations of combretastatin A4 and 4-arylcoumarin analog prodrugs: antitumor effect in the mouse model of breast cancer]

The antimitotic agent combretastatin A4 (CA-4) has been suggested as an antivascular agent for anticancer therapy relatively recently. To reduce systemic toxicity by means of administration in liposome formulations, in this study new lipophilic prodrugs, oleic derivatives of CA-4 and its 4-arylcoumarin analog (CA4-Ole and ArC-Ole, respectively), have been synthesized: Liposomes of 100 nm mean diameter prepared on the basis of egg phosphatidylcholine and phosphatidylinositol from bakers yeast have been shown to include completely up to 10 mol. % of CA4-Ole, or 7 mol. % of ArC-Ole. Also, prodrug bearing liposomes decorated with tetrasaccharide selectin ligand Sialyl Lewis X (SiaLe(x)) have been constructed to achieve targeting to endothelium under neovascularization. The antitumor activity in vivo was studied in the model of slowly growing mouse breast cancer. Under the used dose (22 mg/kg) as well as the regimen of treatment (four injections, one per a week, starting from the appearance of palpable tumors) cytostatic CA-4 did not reveal any anticancer effect, and oppositely even stimulated tumor growth. Liposome formulations of CA4-Ole did not show such stimulation. However, to achieve pronounced antitumor effect, number of injections of liposomes should be apparently elevated. New antimitotic agent ArC revealed cytotoxic activity of only one tenth value obtained for CA-4 in vitro in the culture of human breast carcinoma cells. Nevertheless, in vivo in the mouse model of breast cancer this compound showed antitumor effect under double CA-4 equivalent dose. The results demonstrate availability of SiaLe(x)-liposomes loaded with ArC-Ole: this preparation began to inhibit tumor growth already after the second injection. It is necessary further to choose doses and regimens of administration both for ArC and liposome formulations bearing ArC-Ole.

A facile synthesis of highly functionalized 4-arylcoumarins via Kostanecki reactions mediated by DBU

An efficient synthesis of 4-arylcoumarins has been accomplished via Kostanecki reactions of 2-hydroxybenzophenones with acetic anhydride employing DBU at ambient temperature. Using the same strategy, several 2-acyloxybenzophenone derivatives were readily converted to 3,4-difunctionalized coumarins. This protocol offers a notable improvement in reaction conditions for coumarin synthesis and takes advantage of its synthetic capability, especially for highly functionalized 4-arylcoumarins with structural diversity.

Synthesis and biological evaluation of 4-arylcoumarin analogues of combretastatins. Part 2

A series of A-ring variously methoxylated 4-(3-hydroxy-4-methoxyphenyl)coumarins related to combretastatin A-4 was prepared by cross-coupling reactions. Cytotoxicity studies indicated a potent activity against HBL100 cell line. Substitution patterns on A-ring had only a slight effect on antiproliferative activity. For most cytotoxic compounds, the activity as potential modulators of P-gp and BCRP efflux pumps was evaluated. The results show that compounds 2 and 7 were able to restore mitoxantrone accumulation (BCRP) at concentrations similar to that of cyclosporine A. Compound 7 was the most efficient to reverse P-gp activity. All compounds were found to potently inhibit in vitro microtubule formation via a substoichiometric mode of action for the most part. Compounds 1 and 2 were found to have an apparent affinity binding constant similar to that of combretastatin A-4, i.e., 1 × 10 (6) M(-1). The molecular modeling of coumarin derivatives was performed on the basis of the molecular structure of 7, as determined by single-crystal X-ray crystallography. The calculations suggested that the presence of a methoxy group out of the plane of the chromenone moiety is an important steric hindrance factor embedding the accessibility of those molecules inside the binding pocket on tubulin.

Synthesis and evaluation of azetidinone analogues of combretastatin A-4 as tubulin targeting agents

The synthesis and antiproliferative activity of a new series of rigid analogues of combretastatin A-4 are described which contain the 1,4-diaryl-2-azetidinone (β-lactam) ring system in place of the usual ethylene bridge present in the natural combretastatin stilbene products. These novel compounds are also substituted at position 3 of the β-lactam ring with an aryl ring. A number of analogues showed potent nanomolar activity in human MCF-7 and MDA-MB-231 breast cancer cell lines, displayed in vitro inhibition of tubulin polymerization, and did not cause significant cytotoxicity in normal murine breast epithelial cells. 4-(4-Methoxyaryl)-substituted compound 32, 4-(3-hydroxy-4-methoxyaryl)-substituted compounds 35 and 41, and the 3-(4-aminoaryl)-substituted compounds 46 and 47 displayed the most potent antiproliferative activity of the series. β-Lactam 41 in particular showed subnanomolar activity in MCF-7 breast cancer cells (IC₅₀= 0.8 nM) together with significant in vitro inhibition of tubulin polymerization and has been selected for further biochemical assessment. These novel β-lactam compounds are identified as potentially useful scaffolds for the further development of antitumor agents that target tubulin.

Lead identification of conformationally restricted β-lactam type combretastatin analogues: synthesis, antiproliferative activity and tubulin targeting effects

The synthesis and study of the structure-activity relationships of a series of rigid analogues of combretastatin A-4 are described which contain the 1,4-diaryl-2-azetidinone (β-lactam) ring system in place of the usual ethylene bridge present in the natural combretastatin stilbene products. The 1,4-diaryl-2-azetidinones are unsubstituted at C-3, or contain methyl substituent(s) at C-3. The most potent compounds 12d and 12e display antiproliferative activity at nanomolar concentrations when evaluated against the MCF-7 and MDA-MB-231 human breast carcinoma cell lines. 12d exerts antimitotic effects through an inhibition of tubulin polymerisation and subsequent G2/M arrest of the cell cycle in human MDA-MB-231 breast cancer cells, with similar activity to that of CA-4. These novel β-lactam compounds are identified as potentially useful scaffolds for the further development of antitumour agents which target tubulin.

Lead identification of conformationally restricted benzoxepin type combretastatin analogs: synthesis, antiproliferative activity, and tubulin effects

We have synthesized a series of polymethoxylated rigid analogs of combretastatin A-4 which contain a benzoxepin ring in place of the usual ethylene bridge present in the natural combretastatin products. The compounds display antiproliferative activity when evaluated against the MCF-7 and MDA human breast carcinoma cell lines. 5-(3-Hydroxy-4-methoxyphenyl)-4-(3,4,5-trimethoxyphenyl)-2,3-dihydro-benzoxepine (11g) was found to be the most potent product when evaluated against the MCF-7 breast cancer cell line. A brief computational study of the structure-activity relationship for the synthesized compounds is presented. These 4,5-diarylbenzoxepins are identified as potentially useful scaffolds for the further development of antitumor agents which target tubulin.