Synthesis and cytotoxic evaluation of novel amide–triazole-linked triterpenoid–AZT conjugates

The Use of Zidovudine Pharmacophore in Multi-Target-Directed Ligands for AIDS Therapy

The concept of polypharmacology embraces multiple drugs combined in a therapeutic regimen (drug combination or cocktail), fixed dose combinations (FDCs), and a single drug that binds to different targets (multi-target drug). A polypharmacology approach is widely applied in the treatment of acquired immunodeficiency syndrome (AIDS), providing life-saving therapies for millions of people living with HIV. Despite the success in viral load suppression and patient survival of combined antiretroviral therapy (cART), the development of new drugs has become imperative, owing to the emergence of resistant strains and poor adherence to cART. 3'-azido-2',3'-dideoxythymidine, also known as azidothymidine or zidovudine (AZT), is a widely applied starting scaffold in the search for new compounds, due to its good antiretroviral activity. Through the medicinal chemistry tool of molecular hybridization, AZT has been included in the structure of several compounds allowing for the development of multi-target-directed ligands (MTDLs) as antiretrovirals. This review aims to systematically explore and critically discuss AZT-based compounds as potential MTDLs for the treatment of AIDS. The review findings allowed us to conclude that: (i) AZT hybrids are still worth exploring, as they may provide highly active compounds targeting different steps of the HIV-1 replication cycle; (ii) AZT is a good starting point for the preparation of co-drugs with enhanced cell permeability.

Semisynthetic Derivatives of Pentacyclic Triterpenes Bearing Heterocyclic Moieties with Therapeutic Potential

Medicinal plants have been used by humans since ancient times for the treatment of various diseases and currently represent the main source of a variety of phytocompounds, such as triterpenes. Pentacyclic triterpenes have been subjected to numerous studies that have revealed various biological activities, such as anticancer, antidiabetic, anti-inflammatory, antimicrobial, and hepatoprotective effects, which can be employed in therapy. However, due to their high lipophilicity, which is considered to exert a significant influence on their bioavailability, their current use is limited. A frequent approach employed to overcome this obstacle is the chemical derivatization of the core structure with different types of moieties including heterocycles, which are considered key elements in medicinal chemistry. The present review aims to summarize the literature published in the last 10 years regarding the derivatives of pentacyclic triterpenes bearing heterocyclic moieties and focuses on the biologically active derivatives as well as their structure-activity relationships. Predominantly, the targeted positions for the derivatization of the triterpene skeleton are C-3 (hydroxyl/oxo group), C-28 (hydroxyl/carboxyl group), and C-30 (allylic group) or the extension of the main scaffold by fusing various heterocycles with the A-ring of the phytocompound. In addition, numerous derivatives also contain linker moieties that connect the triterpenic scaffold with heterocycles; one such linker, the triazole moiety, stands out as a key pharmacophore for its biological effect. All these studies support the hypothesis that triterpenoid conjugates with heterocyclic moieties may represent promising candidates for future clinical trials.

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.

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.

Pentacyclic Triterpenoids with Nitrogen-Containing Heterocyclic Moiety, Privileged Hybrids in Anticancer Drug Discovery

Pentacyclic triterpenoids are well-known phytochemicals with various biological activities commonly found in plants as secondary metabolites. The wide range of biological activities exhibited by triterpenoids has made them the most valuable sources of pharmacological agents. A number of novel triterpenoid derivatives with many skeletal modifications have been developed. The most important modifications are the formation of analogues or derivatives with nitrogen-containing heterocyclic scaffolds. The derivatives with nitrogen-containing heterocyclic compounds are among the most promising candidate for the development of novel therapeutic drugs. About 75% of FDA-approved drugs are nitrogen-containing heterocyclic moieties. The unique properties of heterocyclic compounds have encouraged many researchers to develop new triterpenoid analogous with pharmacological activities. In this review, we discuss recent advances of nitrogen-containing heterocyclic triterpenoids as potential therapeutic agents. This comprehensive review will assist medicinal chemists to understand new strategies that can result in the development of compounds with potential therapeutic efficacy.

Biocatalysis in the Chemistry of Lupane Triterpenoids

Pentacyclic triterpenes are important representatives of natural products that exhibit a wide variety of biological activities. These activities suggest that these compounds may represent potential medicines for the treatment of cancer and viral, bacterial, or protozoal infections. Naturally occurring triterpenes usually have several drawbacks, such as limited activity and insufficient solubility and bioavailability; therefore, they need to be modified to obtain compounds suitable for drug development. Modifications can be achieved either by methods of standard organic synthesis or with the use of biocatalysts, such as enzymes or enzyme systems within living organisms. In most cases, these modifications result in the preparation of esters, amides, saponins, or sugar conjugates. Notably, while standard organic synthesis has been heavily used and developed, the use of the latter methodology has been rather limited, but it appears that biocatalysis has recently sparked considerably wider interest within the scientific community. Among triterpenes, derivatives of lupane play important roles. This review therefore summarizes the natural occurrence and sources of lupane triterpenoids, their biosynthesis, and semisynthetic methods that may be used for the production of betulinic acid from abundant and inexpensive betulin. Most importantly, this article compares chemical transformations of lupane triterpenoids with analogous reactions performed by biocatalysts and highlights a large space for the future development of biocatalysis in this field. The results of this study may serve as a summary of the current state of research and demonstrate the potential of the method in future applications.

Synthesis, antibacterial, and cytotoxicity evaluation of oleanolic acid-4-aminoquinoline based hybrid compounds

AIM

To prepare a class of oleanolic-based compounds.

BACKGROUND

Conventional drugs used to treat infectious diseases suffer from limitations such as drug toxicity and drug resistance. The resistance of microbes to antimicrobial agents is a significant challenge in treating microbial infections. Combining two or more drugs with different modes of action to treat microbial infections results in a delay in developing drug resistance by the microbes. However, it is challenging to select the appropriate choice of drugs for combination therapy due to the differences in stability and pharmacokinetic profile of the drugs.Therefore, developing hybrid compounds using the existing drugs is a promising approach to design effective antimicrobial agents.

OBJECTIVES

To prepare oleanolic-based hybrid compounds followed by characterization, in vitro antibacterial, and cytotoxicity evaluation.

METHODS

Oleanolic acid-4-aminoquinoline-based hybrid compounds weresynthesized via esterification and amidation. The compounds werecharacterized using FTIR, NMR, and UHPLC-HRMS. Oleanolic acid was isolated from the flower buds of Syszygium aromaticum (L.) Merr. & L.M.Perry, a specie from Kingdom Plantae, order Mytales in Myrtaceae family. Their antibacterial and cytotoxicity activity was determined against selected strains of bacteria assessed using the microdilution assay and sulforhodamine B assay against selected cancer cell lines.

RESULTS

The synthesized hybrid compounds exhibited significant antibacterial activity against the Gram-positive bacteria Enterococcus faecalis (ATCC13047), Bacillus subtilis (ATCC19659), Staphylococcus aureus as well as Gram-negative bacteria,Klebsiella oxytoca (ATCC8724), Escherischia coli (ATCC25922), and Proteus vulgaris (ATCC6380)with minimum inhibitory concentrations of 1.25 mg/mLcompared to oleanolic acid (2.5 mg/mL). Compounds 13 and 14 displayed significant cytotoxic effectsin vitro against the cancer cell lines (MCF-7 and DU 145) compared to the oleanolic acid (IC50 ˃ 200 µM).

CONCLUSION

The present study revealed that the modification of C28 of OA enhanced its biological properties.

Synthesis and cytotoxicity of hybrids of 1,3,4- or 1,2,5-oxadiazoles tethered from ursane and lupane core with 1,2,3-triazole

Ursane and lupane type (1-((5-aryl-1,3,4-oxadiazol-2-yl)methyl)-1H-1,2,3-triazol-4-yl)methyl and (1-((4-methyl-2-oxido-1,2,5-oxadiazol-3-yl)methyl)-1H-1,2,3-triazol-4-yl)methyl hybrids were prepared by 1,3-cycloaddition reactions of azole-derived azides with alkyne esters connected to positions C-3 and C-28 of triterpene core and tested for cytotoxicity. Hybrid compounds of 1,3,4-oxadiazoles attached at positions 3- and 28- of triterpenoid frame via triazole spacer and combinations of 1,2,5-oxadiazole or 1,3,4-oxadiazole, tethered with succinate linker and 1,2,3-triazole at the position 3- of the ursane backbone, were inactive in relation to all the cancer cells tested. Eventually, combinations of furoxan fragment and 1,2,3-triazole linked to C-28 position of triterpene backbone demonstrated marked cytotoxic activity towards MCF-7 and HepG2 cells. The most active ester of ursolic acid with (1-((4-methyl-2-oxido-1,2,5-oxadiazol-3-yl)methyl)-1H-1,2,3-triazol-4-yl)methyl substituent and 3-O-acetyl group was superior in activity and selectivity over doxorubicin and ursolic acid on MCF-7 cells. The length of the carbon spacer group may be of crucial importance for cytotoxicity. The introduction of the additional ester linker between the C-28 of triterpenoid and triazole or changing triazole spacer between furoxan moiety and triterpenoid core resulted in activity decrease against all the tested cells. In accordance with molecular modeling results, the activity of new derivatives may be explained in terms of the interaction of the new hybrid molecules and Mdm2 binding sites.

Synthesis and Anticancer Activity of Dimeric Polyether Ionophores

Polyether ionophores represent a group of natural lipid-soluble biomolecules with a broad spectrum of bioactivity, ranging from antibacterial to anticancer activity. Three seem to be particularly interesting in this context, namely lasalocid acid, monensin, and salinomycin, as they are able to selectively target cancer cells of various origin including cancer stem cells. Due to their potent biological activity and abundant availability, some research groups around the world have successfully followed semi-synthetic approaches to generate original derivatives of ionophores. However, a definitely less explored avenue is the synthesis and functional evaluation of their multivalent structures. Thus, in this paper, we describe the synthetic access to a series of original homo- and heterodimers of polyether ionophores, in which (i) two salinomycin molecules are joined through triazole linkers, or (ii) salinomycin is combined with lasalocid acid, monensin, or betulinic acid partners to form 'mixed' dimeric structures. Of note, all 11 products were tested in vitro for their antiproliferative activity against a panel of six cancer cell lines including the doxorubicin resistant colon adenocarcinoma LoVo/DX cell line; five dimers (14-15, 17-18 and 22) were identified to be more potent than the reference agents (i.e., both parent compound(s) and commonly used cytostatic drugs) in selective targeting of various types of cancer. Dimers 16 and 21 were also found to effectively overcome the resistance of the LoVo/DX cancer cell line.

New Hybrids Derived from the Natural Compound (-)-β-Pinene and Amides or Acylthioureas as Antitumor Agents

Background:

Plant-derived natural compounds have a unique molecular structure and rich biological activity, hence, they are treated as important raw materials for the development of drugs.

Methods:

A natural compound (-)-β-pinene was used as a raw material, and twenty-six novel derivatives with amide or acylthiourea groups were synthesized based on the molecular hybridization method. In vitro antitumor activity of these derivatives on human breast cancer cell line MCF7 and human colon cancer cell line SW1116 were tested by MTT method. The effects of the synthesized derivatives on the morphology of MCF7 and SW1116 were observed by fluorescent inverted microscope.

Results:

The preliminary structure-activity relationship analysis demonstrates that the position and species of substituents on the aromatic ring of derivatives have an effect on the antitumor activity of derivatives. Observation of the cell morphology reveals that derivatives with antitumor activity can lead to rounding of the cell morphology, a decrease in cell volume and cell density, and ultimately inhibition of the proliferation of MCF7 and SW1116 cells. The antitumor activity evaluation results show that among these derivatives, compounds 5c, 5e, 5h, 7c, 7b and 7e exhibit good antitumor activity against MCF7, and compounds 5c, 5e, 5h and 7j exert moderate antitumor activity against SW1116.

Conclusion:

This study hopes to promote the high value-added utilization of natural compounds β-pinene and the development of novel antitumor drugs.

Design and synthesis of pentacyclic triterpene conjugates and their use in medicinal research

Triterpenoids are natural products from plants and many other organisms that have various biological activities, such as antitumor, antiviral, antimicrobial, and protective activities. This review covers the synthesis and biological evaluation of pentacyclic triterpene (PT) conjugates with other molecules that have been found to increase the IC₅₀ or improve the pharmacological profile of the parent PT. Some of these molecules are designed to target specific proteins or cellular organelles, which has resulted in highly selective lead structures for drug development. Other PT conjugates are useful for investigating their mechanism of action. This concept has been very successful: 1) Many compounds, especially mitochondria-targeting PT conjugates, have reached a selective cytotoxicity at low nanomolar concentrations in cancer cells. 2) A number of PT conjugates have had high activity against HIV or the influenza virus. 3) Fluorescent PT conjugates have been able to visualize the PT in living cells, which has allowed quantification of the uptake and distribution of the PT within the cell. 4) Biotinylated PT conjugates have been used to identify target proteins, which may help to show their mechanism of action. 5) A large number of PT conjugates with polyethylene glycol (PEG), polyamines, etc. form nanometer-sized micelles that have a much better pharmacological profile than the PT alone. In summary, the connection of a PT to an appropriate modifying molecule has resulted in extremely useful semisynthetic compounds with a high potential to treat cancer or viral infections or compounds that are useful for the study of the mechanism of action of PTs at the molecular level.

The potential of click reactions for the synthesis of bioactive triterpenes

Click reactions between alkynes and azides using the privileged scaffold of triterpenes have been of interest for biological chemistry. Many publications deal with the synthesis of novel bioactive molecules; these conjugates have also been used for bioanalytical and diagnostic purposes. As a result, conjugates of better physicochemical properties were obtained; even compounds of improved solubility in water and physiological fluids were made through the introduction of a triazol residue. "Hybrid-structures", i.e. molecules consisting of two independently bioactive subunits linked by a triazole residue were higher bioactive than their parent compounds but not as active as expected, and with a few exceptions the ultimate breakthrough has not yet been achieved. Only in the synthesis of compounds with anti-leishmanial activity some new and promising lead structures were found. As a consequence, triazole modified triterpenes seem to hold their greatest future prospect rather as diagnostic reagents and molecular probes than as drugs.

Recent Developments in the Functionalization of Betulinic Acid and Its Natural Analogues: A Route to New Bioactive Compounds

Betulinic acid (BA) and its natural analogues betulin (BN), betulonic (BoA), and 23-hydroxybetulinic (HBA) acids are lupane-type pentacyclic triterpenoids. They are present in many plants and display important biological activities. This review focuses on the chemical transformations used to functionalize BA/BN/BoA/HBA in order to obtain new derivatives with improved biological activity, covering the period since 2013 to 2018. It is divided by the main chemical transformations reported in the literature, including amination, esterification, alkylation, sulfonation, copper(I)-catalyzed alkyne-azide cycloaddition, palladium-catalyzed cross-coupling, hydroxylation, and aldol condensation reactions. In addition, the synthesis of heterocycle-fused BA/HBA derivatives and polymer‒BA conjugates are also addressed. The new derivatives are mainly used as antitumor agents, but there are other biological applications such as antimalarial activity, drug delivery, bioimaging, among others.

Synthesis and Cytotoxic Evaluation of Betulin–Triazole–AZT Hybrids

Betulin was converted to the corresponding alkyne-functionalized esters and amides and subsequently deployed as substrates for a ‘click’ chemistry-mediated coupling with 3'-azido-3'-deoxythydimine (AZT) to furnish a novel betulin–triazole–AZT hybrid compounds. Eleven new hybrids were thus successfully prepared and evaluated as cytotoxic agents, revealing an interesting anticancer activity in KB and HepG2 cancer cell lines.

Synthesis, Characterization, and Antibacterial Activity of Diethyl 1-((4-Methyl-2-phenyl-4,5-dihydrooxazol-4-yl)methyl)-1H-1,2,3-triazole-4,5-dicarboxylate

The compound, diethyl 1-((4-methyl-2-phenyl-4,5-dihydrooxazol-4-yl)methyl)-1H-1,2,3-triazole-4,5-dicarboxylate 2, was synthesized in high yield, through 1,3-dipolar cycloaddition reaction of 4-(azidomethyl)-4-methyl-2-phenyl-4,5-dihydrooxazole and diethyl but-2-ynedioate in the absence of a solvent. The structure of the synthesized compound was established on the basis of NMR spectroscopy (1H, 13C), X-ray crystallography, and MS data. The prepared compound was also tested in vitro for its antibacterial activity against Gram-positive bacteria (Staphylococcus aureus) and Gram-negative bacteria (Escherichia coli). The calculation of MBC/MIC ratio showed that this triazole derivative 2 had a bactericidal effect on the two strains tested.

Synthesis, characterization and augmented anticancer potential of PEG-betulinic acid conjugate

Betulinic acid (BA), a pentacyclic lupine-type triterpene, is reported to inhibit cell growth in a variety of cancers. However, its efficacy is limited by its poor aqueous solubility and relatively short half-life. In this study, BA-monomethoxy polyethylene glycol (mPEG) conjugate was synthesized by covalent coupling the C-28 carboxylic acid position of BA with amine groups of mPEG, in order to improve its solubility and anticancer efficacy. mPEG-BA conjugate was characterized using various analytical techniques including NMR, FT-IR and MALDI-MS. The mPEG-BA conjugate was cytotoxic, demonstrated internalization and induced cell apoptosis in Hep3B and Huh7 hepatic cancer cells. The western-blot analysis revealed, marked decrease in Bcl-2/Bax ratio, and increase in cleaved-PARP and cleaved-caspase-3 expressions. In vivo studies in Ehrlich ascites tumor (EAT) model following intravenous administration demonstrated significant reduction in tumor volume in case of PEGylated BA as compare to native BA. Furthermore, PEGylated BA treated EAT mice showed no biochemical and histological toxicities. These findings demonstrate the potential of PEGylated BA in cancer therapy, with improved water solubility and efficacy.

Green synthesis and anticancer potential of chalcone linked-1,2,3-triazoles

A series of chalcone linked-1,2,3-triazoles was synthesized via cellulose supported copper nanoparticle catalyzed click reaction in water. The structures of all the compounds were analyzed by IR, NMR and Mass spectral techniques. All the synthesized products were subjected to 3-(4,5-dimethylthiazole-2-yl)-2,5-diphenyltetrazolium bromide (MTT) cytotoxicity assay against a panel of four human cancer cell lines (MCF-7, MIA-Pa-Ca-2, A549, HepG2) to check their anticancer potential. Compound 6h was found to be most active against all the tested cancer cell lines with IC₅₀ values in the range of 4-11 μM and showed better or comparable activity to the reference drug against all the tested cell lines. Cell cycle analysis revealed that compound 6h induces apoptosis and G2/S arrest in MIA-Pa-Ca-2 cells. Compound 6h triggers mitochondrial potential loss in pancreatic cancer MIA-Pa-Ca-2 cells. Further, Compound 6h also triggers caspase-3 and PARP-1 cleavage, which increases in dose dependent manner.

Synthesis and cytotoxic evaluation of novel indenoisoquinoline-substituted triazole hybrids

The synthesis of various substituted triazole-indenoisoquinoline hybrids was performed based on a CuI-catalyzed 1,3-cycloaddition between propargyl-substituted derivatives and the azide-containing indenoisoquinoline. Besides, a variety of N-(alkyl)propargylindenoisoquinolines was used as substrates for the construction of triazole-indenoisoquinoline-AZT conjugated via a click chemistry-mediated coupling with 3'-azido-3'-deoxythymidine (AZT). Thus, twenty three new indenoisoquinoline-substituted triazole hybrids were successfully prepared and evaluated as cytotoxic agents, revealing an interesting anticancer activity of four triazole linker-indenoisoquinoline-AZT hybrids in KB and HepG2 cancer cell lines.