Synthesis of a new 4-aza-2,3-didehydropodophyllotoxin analogues as potent cytotoxic and antimitotic agents

Synthesis, molecular docking analysis and in vitro evaluation of new heterocyclic hybrids of 4-aza-podophyllotoxin as potent cytotoxic agents

Two different synthetic approaches to novel heterocyclic hybrid compounds of 4-azapodophyllotoxin were investigated. The obtained products were characterized by infrared spectroscopy, nuclear magnetic resonance spectroscopy, and high-resolution mass spectrometry. MTT protocol was then performed to examine the cytotoxic activity of these products against KB, HepG2, A549, MCF7, and Hek-293 cell lines. The cytotoxic assessment indicated that all products displayed moderate to high cytotoxicity against all tested cancer cell lines. The most active compound 13k containing the 2-methoxypyridin-4-yl group exhibited selective cytotoxicity against KB, A549, and HepG2 cell lines with the IC50 values ranging from 0.23 to 0.27 μM, which were between 5- to 10-fold more potent than the positive control ellipticine. Compounds 13a (HetAr = thiophen-3-yl) and 13d (HetAr = 5-bromofuran-2-yl) displayed high cytotoxic selectivity for A549 and HepG2 cancer cell lines when compared to the other cancer cell lines and low toxicity to the normal Hek-293 cell line. Molecular docking study was conducted to evaluate the interaction of new synthesized compounds with the colchicine-binding-site of tubulin. Besides that, physicochemical and pharmacokinetic properties of the most active compounds 13h,k were predicted.

Synthesis, Molecular Docking, and Cytotoxic Evaluation of Fluorinated Podophyllotoxin Derivatives

Objective: The study was conducted to evaluate the in vitro and in silico anticancer activity of fluorinated podophyllotoxin derivatives. Methods: Microwave-assisted multicomponent reactions were carried out in an Anton Paar Microwave Synthetic Reactor Monowave 400 in order to synthesize fluorinated podophyllotoxin derivatives. These products were identified by spectral analysis and evaluated for their cytotoxicity against 4 types of human cancer cell lines (KB, HepG2, A549, and MCF7), as well as human embryonic kidney (Hek) 293 cells using MTT protocol. Molecular docking was conducted using 2 crystal structures of tubulin—colchicine (PDB ID: 4O2B) and topoisomerase II—etoposide (PDB ID: 3QX3) complexes. Results: Two potent cytotoxic fluorinated podophyllotoxin–naphthoquinone compounds were synthesized in good yields. They displayed high cytotoxic activity against all the tested cell lines, with IC50 values ranging from 0.58 to 3.17 µM. Notably, product 8a showed low toxicity against the Hek-293 cell line. Molecular docking results showed that products 8a and 8b participated in the same key interactions provided by etoposide with both topoisomerase and DNA chain domains. The binding energy values calculated for 8a and 8b are acceptable. Conclusion: This study revealed that products 8a and 8b exhibited promising in vitro and in silico anticancer activity and could be recognized as promising anticancer agents.

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.

Synthesis and Cytotoxic Evaluation of Fluoro and Trifluoromethyl Substituents Containing Novel Naphthoquinone-Fused Podophyllotoxins

A series of novel naphthoquinone-fused podophyllotoxins containing fluoro and trifluoromethyl substituents were synthesized in a medium with good yields using two different synthetic approaches: microwave-assisted four-component reactions of 2-hydroxy-1,4-naphthoquinone, tetronic acid, fluorinated arylaldehydes, and ammonium acetate, and microwave-assisted three-component reactions of 2-amino-1,4-naphthoquinone, tetronic acid, and fluorinated arylaldehydes. The structures of all products were confirmed by spectral analysis. Together, cytotoxicity assessment of the products against four human cancer cell lines (human carcinoma [KB], human hepatocellular carcinoma [HepG2], lung cancer [A549], breast carcinoma [MCF7], and human embryonic kidney [Hek-293]) was performed by MTT assay. Among the obtained compounds, compound 7f turned out to be the most potent anticancer agent with significant cytotoxic activity against KB, HepG2, and MCF cancer cell lines.

Synthesis and biological activity, and molecular modelling studies of potent cytotoxic podophyllotoxin-naphthoquinone compounds

A new approach for the synthesis of podophyllotoxin-naphthoquinone compounds using microwave-assisted three-component reactions is reported in this study. Novel podophyllotoxin-naphthoquinone derivatives with modification on ring E were synthesized. All the synthetic compounds were assessed in terms of their cytotoxicity profile against four cancer cell lines (KB, HepG2, A549, and MCF7), and noncancerous Hek-293 cell lines. Notably, treatment of SK-LU-1 cells with compounds 5a and 5b resulted in G2/M phase arrest of the cell cycle, caspase-3/7 activation, and apoptosis. Additionally, molecular docking studies were performed and showed important interaction of two compounds against residues in the colchicine-binding-site of tubulin as well. Taken together, compounds 5a and 5b were identified as potent anticancer agents.

A new approach for the synthesis of podophyllotoxin-naphthoquinone compounds using microwave-assisted three-component reactions is reported in this study.

Synthesis and medicinal chemistry of tetronamides: Promising agrochemicals and antitumoral compounds

Butenolides and tetronic acids occupy a prominent position in synthetic chemistry due to their ubiquitous distribution in nature. This has stimulated investigations firstly in the synthesis of such systems and, laterly, the interest has turned to the understanding of the quantum structure of such systems, allowing a deeper understanding of the mechanism and reactivity of this cyclic scaffold. In contrast, tetronamides, which consist of compounds bearing a 4-aminofuran-2(5H)-one backbone, are relatively rare in nature and synthetic routes to such compounds are poorly explored. This review highlights both the importance of the tetronamide scaffold in medicinal chemistry and the most relevant recondite synthetic strategies for obtaining compounds of this class.

Insight Into the Molecular Mechanism of Podophyllotoxin Derivatives as Anticancer Drugs

Podophyllotoxin (PTOX) is a biologically active compound derived from the podophyllum plant, and both it and its derivatives possess excellent antitumor activity. The PTOX derivatives etoposide (VP-16) and teniposide (VM-26) have been approved by the U.S. Food and Drug Administration (FDA) for cancer treatment, but are far from perfect. Hence, numerous PTOX derivatives have been developed to address the major limitations of PTOX, such as systemic toxicity, drug resistance, and low bioavailability. Regarding their anticancer mechanism, extensive studies have revealed that PTOX derivatives can induce cell cycle G2/M arrest and DNA/RNA breaks by targeting tubulin and topoisomerase II, respectively. However, few studies are dedicated to exploring the interactions between PTOX derivatives and downstream cancer-related signaling pathways, which is reasonably important for gaining insight into the role of PTOX. This review provides a comprehensive analysis of the role of PTOX derivatives in the biological behavior of tumors and potential molecular signaling pathways, aiming to help researchers design and develop better PTOX derivatives.

Intercepted-Knoevenagel condensation for the synthesis of unsymmetrical fused-tricyclic 4H-pyrans

4H-Pyrans (4H-Pys) and 1,4-dihydropyridines (1,4-DHPs) are important classes of heterocyclic scaffolds in medicinal chemistry. Herein, an indium(III)-catalyzed one-pot domino reaction for the synthesis of highly functionalized 4H-Pys, and a model of 1,4-DHP is reported. This alternative approach to the challenging Hantzsch 4-component reaction enables the synthesis of fused-tricyclic heterocycles, and the mechanistic studies underline the importance of an intercepted-Knoevenagel adduct to achieve higher chemoselectivity towards these types of unsymmetrical heterocycles.

Synthesis and biological evaluation of bergenin-1,2,3-triazole hybrids as novel class of anti-mitotic agents

In continuation of our investigation of pharmacologically-motivated natural products, we have isolated bergenin (1) as a major compound from Mallotus philippensis, which is deployed in different Indian traditional systems of medicine. Here, a series of bergenin-1,2,3-triazole hybrids were synthesized and evaluated for their potentials against a panel of cancer cell lines. Several of the hybrid derivatives were found more potent in comparison to parent compound bergenin (1). Among them, 4j demonstrated potent activity against A-549 and HeLa cell lines with IC₅₀ values of 1.86 µM and 1.33 μM, respectively, and was equipotent to doxorubicin. Cell cycle analysis showed that 4j arrested HeLa cells at G2/M phase and lead to accumulation of Cyclin B1 protein. Cell based tubulin polymerization assays and docking studies demonstrated that 4j disrupts tubulin assembly by occupying colchicine binding pocket of tubulin.

Aminoazole-Based Diversity-Oriented Synthesis of Heterocycles

The comprehensive review contains the analysis of literature data concerning reactions of heterocyclization of aminoazoles and demonstrates the application of these types of transformations in diversity-oriented synthesis. The review is oriented to wide range of chemists working in the field of organic synthesis and both experimental and theoretical studies of nitrogen-containing heterocycles.

An Efficient One-Pot, Four-Component Synthesis of Pyrazolo[3,4-b]pyridines Catalyzed by Tetrapropylammonium Bromide (TPAB) in Water

A novel and one-pot pseudo-four-component reaction between a series of arylglyoxals, malononitrile, 3-methyl-1-phenyl-1H-pyrazol-5-amine, and acetone in the presence of tetrapropylammonium bromide (TPAB) has been developed to synthesize a series of new substituted pyrazolo[3,4-b]pyridines, using water as an environmentally friendly solvent, in high to excellent yields.

Click chemistry-assisted synthesis of triazolo linked podophyllotoxin conjugates as tubulin polymerization inhibitors

A series of new triazolo linked 4β-amidopodophyllotoxin conjugates (9a-l) were synthesized using click chemistry and evaluated for their antitumor activity against four human cancer cell lines. Among them, two compounds (9c and 9j) showed significant anticancer activity with IC50 values of 0.9 and 0.07 μM, respectively. Biological studies are conducted into the cell-cycle distribution of these conjugates inducing G2/M-phase arrest, apart from an increase in the levels of caspase-3 proteins, followed by apoptotic cell death. A tubulin polymerization assay analysis showed that these compounds effectively inhibit microtubule assembly in HeLa cells and, moreover, Hoechst 33258 and Immunohistochemistry staining suggest that these compounds induce cell death by apoptosis. The docking studies showed that compounds 9c and 9j interact and bind efficiently with the tubulin protein at the colchicine site.

BET Bromodomain Inhibitors with One-Step Synthesis Discovered from Virtual Screen

Chemical inhibition of epigenetic regulatory proteins BrdT and Brd4 is emerging as a promising therapeutic strategy in contraception, cancer, and heart disease. We report an easily synthesized dihydropyridopyrimidine pan-BET inhibitor scaffold, which was uncovered via a virtual screen followed by testing in a fluorescence anisotropy assay. Dihydropyridopyimidine 3 was subjected to further characterization and is highly selective for the BET family of bromodomains. Structure-activity relationship data and ligand deconstruction highlight the importance of the substitution of the uracil moiety for potency and selectivity. Compound 3 was also cocrystallized with Brd4 for determining the ligand binding pose and rationalizing subsequent structure-activity data. An additional series of dihydropyridopyrimidines was synthesized to exploit the proximity of a channel near the ZA loop of Brd4, leading to compounds with submicromolar affinity and cellular target engagement. Given these findings, novel and easily synthesized inhibitors are being introduced to the growing field of bromodomain inhibitor development.

One-Pot Synthesis of Densely Substituted Pyrazolo[3,4-b]-4,7-dihydropyridines

We have achieved a facile synthesis of a combinatorial library of densely substituted pyrazolo[3,4-b]-4,7-dihydropyridines- the mimics of antigenital wart drug podophyllotoxin-from 5-aminopyrazoles and 4-(methylthio) 4H-chromenes. The C(4) pyrazolyl 4H-chromenes, which also possess structural features of podophyllotoxin, were isolable intermediates in the two-step, one-pot condensation. The condensation took place in a one-pot, multicomponent manner when 3-oxo-3-phenylpropanenitriles, hydrazine (precursors for 5-aminopyrazoles) and 4-(methylthio)-4H-chromenes were heated in refluxing ethanol. The condensation, however, stops at 4H-chromene stage when methyl hydrazine or phenylhydrazine were employed. Our findings offer an opportunity for synthesis of a combinatorial library of podophyllotoxin mimics, thus paving the way for discovery of lead candidates for cancer treatment.

Recent Advances in the Chemistry and Biology of Podophyllotoxins

Podophyllotoxin and its related aryltetralin cyclolignans belong to a family of important products that exhibit various biological properties (e.g., cytotoxic, insecticidal, antifungal, antiviral, anti-inflammatory, neurotoxic, immunosuppressive, antirheumatic, antioxidative, antispasmogenic, and hypolipidemic activities). This Review provides a survey of podophyllotoxin and its analogues isolated from plants. In particular, recent developments in the elegant total chemical synthesis, structural modifications, biosynthesis, and biotransformation of podophyllotoxin and its analogues are summarized. Moreover, a deoxypodophyllotoxin-based chemosensor for selective detection of mercury ion is described. In addition to the most active podophyllotoxin derivatives in each series against human cancer cell lines and insect pests listed in the tables, the structure-activity relationships of podophyllotoxin derivatives as cytotoxic and insecticidal agents are also outlined. Future prospects and further developments in this area are covered at the end of the Review. We believe that this Review will provide necessary information for synthetic, medicinal, and pesticidal chemistry researchers who are interested in the chemistry and biology of podophyllotoxins.

Synthesis of Isoxazolopyridines and Spirooxindoles under Ultrasonic Irradiation and Evaluation of Their Antioxidant Activity

New polycyclic-fused isoxazolo[4,5-e]pyridines and spirooxindoles were obtained via multicomponent reaction of 5-amino-3-methylisoxazole, indan-1,3-dione, and aromatic aldehydes and reaction of 5-amino-3-methylisoxazole, isatin, and β-diketones in the presence of (±)-camphor-10-sulfonic acid as an effective and nontoxic organocatalyst under ultrasound-promoted conditions. The antioxidant activity of the novel synthesized compounds was studied.

Synthesis and biological evaluation of 4β-benzoxazolepodophyllotoxin hybrids as DNA topoisomerase-II targeting anticancer agents

A series of new 4β-benzoxazolepodophyllotoxin compounds (9a–j) were prepared and screened for molecular modelling and cytotoxicity against various human tumour cell lines. Cell apoptosis evaluation was performed using Hoechst staining.

Catalytic one-pot microwave assisted synthesis of 4-azapodophyllotoxin derivatives and rational design of experiment

A catalytic one-pot microwave assisted synthesis of 4-azapodophyllotoxin has been described. Rational design of experiment has been used to obtain the reaction yield.

l-Proline catalyzed three-component synthesis of para-naphthoquinone–4-aza-podophyllotoxin hybrids as potent antitumor agents

A series of novelpara-naphthoquinone embodied 4-aza-podophyllotoxin hybrids were synthesized and some of the compounds exhibited excellent antitumor activities.

Synthesis of novel anticancer iridoid derivatives and their cell cycle arrest and caspase dependent apoptosis

Nyctanthes arbortristis Linn (Oleaceae) is widely distributed in sub-Himalayan regions and southwards to Godavari, India commonly known as Harsingar and Night Jasmine. In continuation of our drug discovery programme on Indian medicinal plants, we isolated arbortristoside-A (1) and 7-O-trans-cinnamoyl 6β-hydroxyloganin (2) from the seeds of N. Arbortristis, which exhibited moderate in vitro anticancer activity. Chemical transformation of 2 led to significant improvement in the activity in derivative 8 and 15 against HepG2 (human hepatocellular carcinoma), MCF-7 (breast adenocarcinoma) cell lines. The compounds 8 and 15 were also capable of cell cycle arrest and caspase dependent apoptosis in HepG2 cell lines. These iridoid derivatives hold promise for developing safer alternatives to the marketed drugs.

Quinazolino linked 4β-amidopodophyllotoxin conjugates regulate angiogenic pathway and control breast cancer cell proliferation

A series of new conjugates of quinazolino linked 4β-amidopodophyllotoxins 10aa-af and 10ba-bf were synthesized and evaluated for their anticancer activity against human pancreatic carcinoma (Panc-1) as well as breast cancer cell lines such as MCF-7 and MDA-MB-231 by employing MTT assay. Among these conjugates, some of them like 10bc, 10bd, 10be and 10bf exhibited high potency of cytotoxicity. Flow cytometric analysis showed that these conjugates arrested the cell cycle in the G2/M phase and caused the increase in expression of p53 and cyclin B1 protein with concomitant decrease in Cdk1 thereby suggesting the inhibitory action of these conjugates on mitosis. Interestingly, we observed a decrease in expression of proteins that control the tumor micro environment such as VEGF-A, STAT-3, ERK1/2, ERK-p, AKT-1 ser 473 phosphorylation in compounds treated breast cancer cells. Further, these effective conjugates have exhibited inhibitory action on integrin (αVβIII). Furthermore, the MCF-7 cells that were arrested and lost the proliferative capacity undergo mitochondrial mediated apoptosis by activation of caspases-9. Thus these conjugates have the potential to control breast cancer cell growth by effecting tumor angiogenesis and invasion.

Preparation of novel antiproliferative emodin derivatives and studies on their cell cycle arrest, caspase dependent apoptosis and DNA binding interaction

Emodin (1) is the major bioactive compound of several herb species, which belongs to anthraquinone class of compound. As a part of our drug discovery program, large quantities of emodin (1) was isolated from the roots of Rheum emodi and a library of novel emodin derivatives 2-15 were prepared to evaluate their antiproliferative activities against HepG2, MDA-MB-231 and NIH/3T3 cells lines. The derivatives 3 and 12 strongly inhibited the proliferation of HepG2 and MDA-MB-231 cancer cell line with an IC₅₀ of 5.6, 13.03 and 10.44, 5.027, respectively, which is comparable to marketed drug epirubicin (III). The compounds 3 and 12 were also capable of inducing cell cycle arrest and caspase dependent apoptosis in HepG2 cell lines and exhibit DNA intercalating activity. These emodin derivatives hold promise for developing safer alternatives to the marketed epirubicin.

Synthesis and biological evaluation of 4β-sulphonamido and 4β-[(4'-sulphonamido)benzamide]podophyllotoxins as DNA topoisomerase-IIα and apoptosis inducing agents

A series of new 4β-sulphonamido and 4β-[(4'-sulphonamido)benzamide] conjugates of podophyllotoxin (11a-j and 15a-g) were synthesized and evaluated for anticancer activity against six human cancer cell lines and found to be more potent than etoposide. Some of the compounds 11b, 11d and 11e that showed significant antiproliferative activity in Colo-205 cells, were superior to etoposide. The flow cytometric analysis indicates that these compounds (11b, 11d and 11e) showed G2/M cell cycle arrest and among them 11e is the most effective. It is observed that this compound (11e) caused both single-strand DNA breaks as observed by comet assay as well as double-strand DNA breaks as indicated by γ-H2AX. Further 11e showed inhibition of topo-IIα as observed from Western blot analysis and related studies. Compounds caused activation of ATM as well as Chk1 protein indicating that the compound caused effective DNA damage. Moreover activation of caspase-3, p21, p16, NF-kB and down regulation of Bcl-2 protein suggests that this compound (11e) has apoptotic cell death inducing ability, apart from acting as a topo-IIα inhibitor.