Synthesis of 3′-azido-3′-deoxythymidine (AZT)—Cinchona alkaloid conjugates via click chemistry: Toward novel fluorescent markers and cytostatic agents

Ligand assisted CuAAC labelling and RP-HPLC analysis of zidovudine and Retrovir using propargyl-Fmoc probe

The extensive application of zidovudine (ZDV) as a stand-alone anti-HIV drug and a component in antiviral combination therapies, has made its analysis important both in the pharmaceutical and environmental context. The azide group in ZDV structure makes it a ready-to-use substrate for copper-catalyzed azide-alkyne cycloaddition (CuAAC), which is an efficient method for "click chemistry" labeling. In this paper, we describe a ligand-assisted CuAAC procedure for the precolumn derivatization of ZDV. We used propargyl-Fmoc fluorescent label and trans-2-(4-((dimethylamino)methyl)-1H-1,2,3-triazol-1-yl)cyclohexan-1-ol (AMTC) as a copper-binding ligand. We tested the applicability of AMTC for precolumn derivatization and developed chromatographic analytical procedures for ZDV and its formulation (50 mg/5 ml oral solution, Retrovir™ syrup). Our research aimed to improve labeling efficiency with a Cu-chelating ligand, using an accessible and affordable fluorescent probe. We also developed a sustainable mechanochemical synthesis procedure for obtaining propargyl-Fmoc in a gram scale and thus boosted the accessibility of this probe. The advantages of the developed derivatization procedure are its simplicity and easy availability of the propargyl-Fmoc probe. Moreover, the high lipophilicity of the propargyl-Fmoc probe enables efficient separation of the analyte from polar matrix components. In addition, the derivatization procedure can be performed directly on a sample solution. We tested its usability for samples in environmental and biological matrices, including tap water, river water, urine, and human serum.

Cytotoxicity of cinchona alkaloid organocatalysts against MES-SA and MES-SA/Dx5 multidrug-resistant uterine sarcoma cell lines

Since the first application of natural quinine as an anti-malarial drug, cinchona alkaloids and their derivatives have been exhaustively studied for their biological activity. In our work, we tested 13 cinchona alkaloid organocatalysts, synthesised from quinine. These derivatives were screened against MES-SA and Dx5 uterine sarcoma cell lines for in vitro anticancer activity and to investigate their potential to overcome P-glycoprotein (P-gp) mediated multidrug resistance (MDR). Decorating quinine with hydrogen-bond donor units, such as thiourea and (thio)squaramide, resulted in decreased half-maximal growth inhibition values on both cell lines (1.3-21 µM) compared to quinine and other cinchona alcohols (47-111 µM). Further cytotoxicity studies conducted in the presence of the P-gp inhibitor tariquidar indicated that several analogues, especially cinchona amines and squaramides, but not thiosquaramide, were expelled from MDR cells by P-gp. Similarly to the established P-gp inhibitor quinine, 6 cinchona analogues were shown to inhibit calcein-AM efflux. Interestingly, quinine and didehydroquinine exhibited a marginally increased toxicity against the multidrug resistant Dx5 cells. Collateral sensitivity of the MDR cell line was more pronounced when the cinchona thiosquaramide was complexed with Cu(II) acetate. Based on the results, cinchona derivatives are good anticancer candidates for further drug development.

The Sulfo-Click Reaction and Dual Labeling of Nucleosides

This article contains detailed synthetic procedures for the implementation of the sulfo-click reaction to nucleoside derivatives. First, 3'-O-TBDMS-protected nucleosides are converted to their corresponding 4'-thioacid derivatives in three steps. Then, various conjugates are synthetized via a biocompatible and chemoselective coupling procedure using sulfonyl azide partners. Finally, to illustrate the potential of the sulfo-click reaction, a nucleoside bearing two orthogonal azido groups is synthesized and engaged in one-pot dual labeling through a sulfo-click/copper-catalyzed azide-alkyne cycloaddition (CuAAC) cascade. The high efficiency of the sulfo-click reaction as applied to nucleosides opens up new possibilities in the context of bioconjugation. © 2020 Wiley Periodicals LLC. Basic Protocol 1: General protocol for the synthesis of 4'-thioacid-nucleoside derivatives Basic Protocol 2: Implementation of the sulfo-click reaction Basic Protocol 3: Synthesis of 3'-azido-4'-(carboxamido)ethane-sulfonyl azide-3'-deoxythymidine Basic Protocol 4: Detailed synthetic procedure for one-pot double-click conjugations.

Click chemistry based regioselective one-pot synthesis of coumarin-3-yl-methyl-1,2,3-triazolyl-1,2,4-triazol-3(4H)-ones as newer potent antitubercular agents

Coumarin-3-yl-methyl-1,2,3-triazolyl-1,2,4-triazol-3(4H)-ones (8k-z) were synthesized via copper(I)-catalyzed azide-alkyne cycloaddition click chemistry. The synthesized hybrid molecules were characterized by spectral studies. Compounds 8k-z were screened for their in vitro anti-TB activity by using the Microplate Alamar Blue assay and for cytotoxicity using the MTT assay. Some of the compounds were found to be most potent against the tested Mycobacterium tuberculosis H37Rv strain with a MIC of 1.60 µg/ml. Further, docking the compounds into the InhA binding pocket showed strong binding interactions and effective overall docking scores were recorded. The drug-likeness and toxicity studies were computed using Molinspiration and Protox, respectively.

Synthesis of novel 1,2,3-triazole-substituted tomentosins

A series of 1,2,3-triazole-containing tomentosin scaffolds was obtained from tomentosin 1. The synthesis involved a Michael addition of trimethylsilylazide on the α-methylene-γ-lactone function of the natural sesquiterpene lactone 1 to give the diastereoisomers 2 and 3, which were readily separated by column chromatography. These compounds underwent copper-catalyzed Huisgen 1,3-dipolar cycloaddition with various terminal alkynes to provide compounds 4a–h and 5a–h in good yields.

Synthesis and Biological Evaluation of Novel Triazoles Linked 7-hydroxycoumarin as Potent Cytotoxic Agents

Background:

BacCancer is regarded as second leading cause of death worldwide. Therefore, there is a high demand for the discovery, development and improvement of novel anti-cancer agents which could efficiently prevent proliferative pathways and clonal expansion of cells.

Objective:

In view of this, a new series of bioactive scaffolds viz triazoles linked 7-hydroxycoumarin (1) were synthesized using click chemistry approach.

Method:

All the synthesized compounds were screened for cytotoxicity against a panel of seven different human cancer cell lines viz. Colon (Colo-205 and HCT-116), breast (MCF-7), lung (NCI-H322 and A549), prostate (PC-3) and skin (A-431) using 3-(4,5-Dimethylthiazol-yl)-diphenyl tetrazoliumbromide (MTT) assay.

Results:

Among all tested analogs, compound 5, displayed better cytotoxic activity as compared to the parent 7- hydroxycoumarin (1) with IC50 of 5.1, 22.7, 14.3 and 10.2 µM against breast (MCF-7), lung (NCI- H322), prostate (PC-3) and skin (A-431) cancer cell lines, respectively; the compound 5 was 8-fold more sensitive against MCF-7 than the parent 7-hydroxycoumarin. Moreover, Compound 5 induced both cytotoxic as well as cytostatic effects via induction of apoptosis and G1 phase arrest, respectively in breast cancer cells (MCF-7). The apoptotic cell population enhanced to 18.8% at 8 µM of 5 from 9.8% in case of negative control, while G1 phase arrest increased to 54.4% at 8 µM compared to negative control of 48.1%. Moreover, Compound 5 also exhibited a remarkable decrease in mitochondrial membrane potential (ΛΨm) leading to apoptosis of cancer cells used.

Conclusion:

The structure-activity relationship study revealed that the derivatives bearing electron-withdrawing substituents were more effective. The present study resulted in identification of the compounds demonstrating broad spectrum cytotoxic activity.

Synthesis and biological evaluation of novel 3-O-tethered triazoles of diosgenin as potent antiproliferative agents

Diosgenin, a promising anticancer steroidal sapogenin, was isolated from Dioscorea deltoidea. Keeping its stereochemistry rich architecture intact, a scheme for the synthesis of novel diosgenin analogues was designed using Cu (I)-catalysed alkyne-azide cycloaddition in order to study their structure-activity relationship. Both diosgenin and its analogues exhibited interesting anti-proliferative effect against four human cancer cell lines viz. HBL-100 (breast), A549 (lung), HT-29 (colon) and HCT-116 (colon) using [3-(4,5-dimethylthiazolyl-2)-2,5-diphenyltetrazoliumbromide] (MTT) assay. Among the synthesized analogues, Dgn-1 bearing a simple phenyl R moiety attached via triazole to the parent molecule was identified as the most potent analogue against A549 cancer cell line having IC₅₀ of 5.54μM, better than the positive control (BEZ-235). Dgn-2 and Dgn-5 bearing o-nitrophenyl and o-cyanophenyl R moieties respectively, displayed impressive anti-proliferative activity against all the tested human cancer cell lines with IC₅₀ values ranging from 5.77 to 9.44μM. The structure-activity relationship (SAR) revealed that the analogues with simple phenyl R moiety or electron withdrawing ortho substituted R moieties seem to have beneficial impact on the anti-proliferative activity.

Exposure to air boosts CuAAC reactions catalyzed by PEG-stabilized Cu nanoparticles

The catalytic activity of Cu(0) NPs is boosted upon aerobic oxidation, forming Cu₂O NPs, and further improved on an SBA-15 support.

Ferrocene–cinchona hybrids with triazolyl-chalcone linkers act as pro-oxidants and sensitize human cancer cell lines to paclitaxel

Epimeric ferrocene–quinidine hybrids with triazolyl-chalcone linkers act as pro-oxidative agents and autophagy modulators in paclitaxel resistant cancer cells.

Synthesis of α-santonin derived acetyl santonous acid triazole derivatives and their bioevaluation for T and B-cell proliferation

A new series of α-santonin derived acetyl santonous acid 1,2,3-triazole derivatives were synthesised using Huisgen 1,3-dipolar cyclo-addition reaction (click chemistry approach) and evaluated for their in vitro inhibition activity on concanavalin A (ConA) induced T cell proliferation and lipopolysaccharide (LPS) induced B cell proliferation. Among the synthesised series, compounds 2-10 and 19 exhibited significant inhibition against ConA and LPS stimulated T-cell and B-cell proliferation in a dose dependent manner. More significantly compounds 4, 9-10 and 19 exhibited potent inhibition activity with remarkably lower cytotoxicity on the mitogen-induced T cell and B cell proliferation at 1 μM concentration. The compound 6 displayed potent immunosuppressive effects with ∼89% against LPS induced B-cell and ∼83% against ConA stimulated T-cell proliferation at 100 μM concentration without cytotoxicity. Compound 10 was more selective against B cell proliferation and exhibited 81% and 69% suppression at 100 and 1 μM concentration respectively. The present study led to the identification of several santonin analogs with reduced cytotoxicity and strong inhibition activity against the cell proliferation induced by the mitogens.

Novel triazole hybrids of myrrhanone C, a natural polypodane triterpene: Synthesis, cytotoxic activity and cell based studies

The 3-keto functionality in ring A of myrrhanone C, a natural bicyclic triterpene has been chemically modified and synthesized 27 novel triazole hybrids belonging to two different series in very good to excellent yields (66-83%). The synthesized compounds were thoroughly characterized by their spectroscopic data (IR, (1)H&(13)C NMR, HRMS). All the synthesized compounds were evaluated for their cytotoxic potential against a panel of five human cancer cell lines by employing MTT assay using doxorubicin as the standard. In general the synthesized compounds showed anticancer activity against almost all the cell lines screened. Interestingly, the oxime based triazoles (4a-4n) showed higher activity than the benzylidene triazoles (6a-6m). Most significantly compound 4a showed potent activity against all the tested cell lines, especially against lung cancer (A-549) with an IC 50 of 6.16 μm. In view of their significant activity against lung cancer cell lines, compounds 4a and 4l were subjected to detailed biological studies, which revealed that they arrested cell cycle in G2/M phase and induced cell death by apoptosis that was further confirmed by Hoechst staining, measurement of mitochondrial membrane potential (ΔΨm) and Annexin V-FITC assay. These compounds will serve as lead molecules in the development of potent anticancer drug candidates especially for lung cancer.

Double helix quinine-based supergelator

10,11-Didehydroquinine is a simple, low molecular weight supergelator which forms, in nonpolar media, stable chiral organogels composed of unique double-helix nano-sized fibers. A novel gelation mechanism involves a hydrogen bonding network formed by an acidic alkyne proton of the Cinchona gelator and the carbonyl group of ethyl acetate used as a solvent.

Synthesis, characterization, and antibacterial property of novel starch derivatives with 1,2,3-triazole

Four novel starch-linked-1,2,3-triazole derivatives were synthesized including 6-hydroxymethyltriazole-6-deoxy starch (HMTST), 6-bromomethyltriazole-6-deoxy starch (BMTST), 6-chloromethyltriazole-6-deoxy starch (CMTST), and 6-carboxyltriazole-6-deoxy starch (CBTST). Their antibacterial properties against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) were evaluated in vitro, respectively. The inhibitory property of the obtained amphiprotic starch derivatives exhibited a remarkable improvement over starch. And the antibacterial indices of most of the products were higher than 60% and 40% at 1.0 mg/mL when the culture time was 8 h and 16 h, respectively. Moreover, the inhibitory index of CBTST attained 97% above at 1.0 mg/mL. Generally, the inhibitory activity decreased in the order: CBTST>CMTST>BMTST>HMTST>starch. Furthermore, the order of their antibacterial activity was consistent with the electron-withdrawing property of different substituted groups of the 1,2,3-triazole groups. The substituted groups with stronger electron withdrawing ability relatively possessed greater antibacterial activity.

Synthesis, structure and in vitro cytostatic activity of ferrocene-Cinchona hybrids

Exploring copper(I)- and ruthenium(II)-catalyzed azide-alkyne cycloadditions and a Sonogashira protocol, novel cytostatic ferrocene-cinchona hybrids were synthetized displaying significant in vitro activity on HepG-2 and HT-29 cells. Preliminary SAR studies disclosed that compounds incorporating linkers with 1,2,3-triazole and chalchone residues can be considered as promising lead structures. According to the best of our knowledge this is the first letter on the incorporation of ferrocene nucleus in the reputed cinchona family via triazole and chalcone linkers with established pharmaceutical profile.

Nucleic Acid Bioconjugates in Cancer Detection and Therapy

Nucleoside- and nucleotide-based chemotherapeutics have been used to treat cancer for more than 50 years. However, their inherent cytotoxicities and the emergent resistance of tumors against treatment has inspired a new wave of compounds in which the overall pharmacological profile of the bioactive nucleic acid component is improved by conjugation with delivery vectors, small-molecule drugs, and/or imaging modalities. In this manner, nucleic acid bioconjugates have the potential for targeting and effecting multiple biological processes in tumors, leading to synergistic antitumor effects. Consequently, tumor resistance and recurrence is mitigated, leading to more effective forms of cancer therapy. Bioorthogonal chemistry has led to the development of new nucleoside bioconjugates, which have served to improve treatment efficacy en route towards FDA approval. Similarly, oligonucleotide bioconjugates have shown encouraging preclinical and clinical results. The modified oligonucleotides and their pharmaceutically active formulations have addressed many weaknesses of oligonucleotide-based drugs. They have also paved the way for important advancements in cancer diagnosis and treatment. Cancer-targeting ligands such as small-molecules, peptides, and monoclonal antibody fragments have all been successfully applied in oligonucleotide bioconjugation and have shown promising anticancer effects in vitro and in vivo. Thus, the application of bioorthogonal chemistry will, in all likelihood, continue to supply a promising pipeline of nucleic acid bioconjugates for applications in cancer detection and therapy.

Activity guided isolation and modification of juglone from Juglans regia as potent cytotoxic agent against lung cancer cell lines

Background

Juglans regia has been found to exhibit significant anticancer activity against various human cancer cell lines. This study was undertaken to isolate the active chemical constituent (Juglone) and to investigate its cytotoxic activity along with its various analogs against different human cancer cell lines.

Methods

Isolation of juglone, a napthoquinone, from the chloroform extract of the root part of Juglans regia was executed by flash chromatography using silica gel as stationary phase. The isolated Juglone was used as starting material for the further synthesis of a novel series of triazolyl analogs using click chemistry approach to investigate their cytotoxic potential against different human cancer cell lines using 3-(4,5-Dimethylthiazol-yl)-diphenyl tetrazoliumbromide (MTT) assay.

Results

The different extracts of Juglans regia and the isolated compound (juglone) exhibited satisfactory cytotoxic activity against a panel of eight different human cancer cell lines namely, prostate colon (Colo-205 and HCT-116), breast (T47D), prostate (PC-3 and DU-145), skin (A-431) and lung (NCI-H322 and A549). Interestingly, all the synthesised analogs displayed enhanced and selective cytotoxic activity against lung cancer cell lines only. Of the synthesized derivatives, 15a and 16a displayed the best activity with IC₅₀ of 4.72 and 4.67 μM against A549 cells. Both these derivatives exhibited superior potency to BEZ-235 against both the lung cancer cell lines. So far as the structural aspects are concerned, electron withdrawing substituents at the ortho position of R moiety of the triazolyl analogs seem to be essential for attaining better activity.

Conclusion

The present study demonstrates the selective and enhanced cytotoxic activity of the triazolyl analogs of juglone against NCI-H322 and A549 human lung cancer cell lines. Some derivatives exhibited superior potency to BEZ-235, a commercially available anticancer agent.

Fluorescent 1,2,3-triazole derivative of 3′-deoxy-3-azidothymidine: synthesis and absorption/emission spectra

3′-Deoxy-3-azidothymidine (AZT, zidovudine) is a nucleoside-analog reverse transcriptase inhibitor, successfully used against the human immunodeficiency virus (HIV). Its structure contains an azide function, which makes it a useful substrate for 1,2,3-triazole synthesis, using the copper-catalyzed azide-alkyne cycloaddition, the flagship reaction of ‘click chemistry’. Herein we present the synthesis and spectral characterization of its 1,2,3-triazole derivative containing a fluorenylmethyloxycarbonyl (fmoc) fluorescent fragment. The preparation and characteristics of a novel fluorescent probe, 9H-fluoren-9-ylmethyl prop-2-yn-1-yl carbonate (propargyl-fmoc) is also presented.

Quinine conjugates and quinine analogues as potential antimalarial agents

Malaria is a tropical disease, prevalent in Southeast Asia and Africa, resulting in over half a million deaths annually; efforts to develop new antimalarial agents are therefore particularly important. Quinine continues to play a role in the fight against malaria, but quinoline derivatives are more widely used. Drugs based on the quinoline scaffold include chloroquine and primaquine, which are able to act against the blood and liver stages of the parasite's life cycle. The purpose of this review is to discuss reported biologically active compounds based on either the quinine or quinoline scaffold that may have enhanced antimalarial activity. The review emphasises hybrid molecules, and covers advances made in the last five years. The review is divided into three sections: modifications to the quinine scaffold, modifications to aminoquinolines and finally metal-containing antimalarial compounds.

Click chemistry inspired synthesis and bioevaluation of novel triazolyl derivatives of osthol as potent cytotoxic agents

A new series of diverse triazoles linked through the hydroxyl group of lactone ring opened osthol (1) were synthesized using click chemistry approach. All the derivatives were subjected to 3-(4,5-Dimethylthiazol-yl)-diphenyl tetrazoliumbromide (MTT) cytotoxicity screening against a panel of seven different human cancer cell lines viz. colon (colo-205), colon (HCT-116), breast (T47D), lung (NCI-H322), lung (A549), prostate (PC-3) and Skin (A-431) to check their cytotoxic potential. Interestingly, among the tested molecules, most of the analogs displayed better cytotoxic activity than the parent osthol (1). Of the synthesized triazoles, compounds 8 showed the best activity with IC50 of 1.3, 4.9, 3.6, 41.0, 35.2, 26.4 and 7.2 μM against colon (Colo-205 and HCT-116), breast (T47D), lung (NCI-H322 and A549), prostate (PC-3) and Skin (A-431) cancer lines respectively. Compound 8 induced potent apoptotic effects in Colo-205 cells. The population of apoptotic cells increased from 11.4% in case of negative control to 24.1% at 25 μM of 8. Compound 8 also induced a remarkable decrease in mitochondrial membrane potential (ΛΨm) leading to apoptosis of cancer cells used. The present study resulted in identification of broad spectrum cytotoxic activity of analogs bearing electron withdrawing substituents, besides the enhanced selective activity of analogs with electron donating moieties.

1,2,3-triazole-substituted oleanolic Acid derivatives: synthesis and antiproliferative activity

Hybrid compounds are relevant products when searching for structure-activity relationships of natural products. Starting from the naturally occurring triterpene oleanolic acid, alkyl esters were prepared and treated with different aromatic azides using click chemistry to produce hybrid compounds. Some 18 new oleanolic acid derivatives were synthesized and the structures were confirmed by spectroscopic and spectrometric means. The antiproliferative activity of the new derivatives was evaluated towards normal lung fibroblasts (MRC-5), gastric epithelial adenocarcinoma (AGS), promyelocytic leukemia (HL-60), lung cancer (SK-MES-1) and bladder carcinoma (J82) cells. The alkyne esters 1 and 3 showed activity on all cell lines but without selectivity (19.6-23.1 μM and 14.1-56.2 μM, respectively), their respective methyl esters were inactive. Compounds with a benzene and p-anisole attached to the triazole ring, showed no antiproliferative effect. Introduction of a chlorine atom into the benzene ring (compound 9) elicited a selective effect against AGS cells (IC50 value: 8.9 μM). The activity was lost when the COOH function at C-28 was methylated. Better antiproliferative effect was found for compounds 11 and 15 bearing a p-toluenesulphonyl group, with values in the range of 10.8-47.1 μM and 11.5-22.2 μM, respectively. The effect, however, was not associated with selectivity.

Chemical architecture and applications of nucleic acid derivatives containing 1,2,3-triazole functionalities synthesized via click chemistry

There is considerable attention directed at chemically modifying nucleic acids with robust functional groups in order to alter their properties. Since the breakthrough of copper-assisted azide-alkyne cycloadditions (CuAAC), there have been several reports describing the synthesis and properties of novel triazole-modified nucleic acid derivatives for potential downstream DNA- and RNA-based applications. This review will focus on highlighting representative novel nucleic acid molecular structures that have been synthesized via the “click” azide-alkyne cycloaddition. Many of these derivatives show compatibility for various applications that involve enzymatic transformation, nucleic acid hybridization, molecular tagging and purification, and gene silencing. The details of these applications are discussed. In conclusion, the future of nucleic acid analogues functionalized with triazoles is promising.

Acylated mono-, bis- and tris- cinchona-based amines containing ferrocene or organic residues: synthesis, structure and in vitro antitumor activity on selected human cancer cell lines

A series of novel functionalized mono-, bis- and tris-(S)-{[(2S,4R,8R)-8-ethyl-quinuclidin-2-yl](6-methoxyquinolin-4-yl)}methanamines including ferrocene-containing derivatives was obtained by the reaction of the precursor amine with a variety of acylation agents. Their in vitro antitumor activity was investigated against human leukemia (HL-60), human neuroblastoma (SH-SY5Y), human hepatoma (HepG2) and human breast cancer (MCF-7) cells by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT)-assay and the 50% inhibitory concentration (IC₅₀) values were determined. Our data indicate that the precursor amine has no antitumor activity in vitro, but the bis-methanamines with ureido-, thioureido and amide-type linkers display attractive in vitro cytotoxicity and cytostatic effects on HL-60, HepG2, MCF-7 and SH-SY5Y cells. Besides ¹H- and ¹³C-NMR methods the structures of the new model compounds were also studied by DFT calculations.