Artemisinin derivatives bearing Mannich base group: synthesis and antimalarial activity

Synthesis of fusidane triterpenoid Mannich bases as potential antibacterial and antitumor agents

Mannich bases (8 examples) were synthesized via aminomethylation of fusidane propargyl esters. In vitro antimicrobial screening against key ESKAPE pathogens showed that the fusidic acid based Mannich products exhibit a high antimicrobial effect against Gram-positive bacteria Staphylococcus aureus and the fungus Cryptococcus neoformans. Moreover, the cytotoxic effect of fusidic acid and its analogs, which showed high antibacterial activity, was determined by MTT assay on cancer HepG2, HCT-116, SH-SY5Y, MCF-7, A549 and conditionally normal cells HEK293. A remarkable cytotoxic activity of fusidic acid propargyl ester and its aminomethylene derivatives against cancer and nontumoral HEK293 cells with IC50 values within 4.2-25 µM was found.

Synthesis, Characterization, and DFT Calculations of a New Sulfamethoxazole Schiff Base and Its Metal Complexes

A new Schiff base, 4-((1E,2E)-3-(furan-2-yl)allylidene)amino)-N-(5-methylisoxazol-3-yl) benzene-sulfonamide (L), was synthesized by thermal condensation of 3-(2-furyl)acrolein and sulfamethoxazole (SMX), and the furan Schiff base (L) was converted to a phenol Schiff base (L') according to the Diels-Alder [4 + 2] cycloaddition reaction and studied experimentally. The structural and spectroscopic properties of the Schiff base were also corroborated by utilizing density functional theory (DFT) calculations. Furthermore, a series of lanthanide and transition metal complexes of the Schiff base were synthesized from the nitrate salts of Gd, Sm, Nd, and Zn (L1, L2, L3, and L4), respectively. Various spectroscopic studies confirmed the chemical structures of the Schiff-base ligand and its complexes. Based on the spectral studies, a nine-coordinated geometry was assigned to the lanthanide complexes and a six-coordinated geometry to the zinc complex. The elemental analysis data confirmed the suggested structure of the metal complexes, and the TGA studies confirmed the presence of one coordinated water molecule in the lanthanide complexes and one crystalline water molecule in the zinc complex; in addition, the conductivity showed the neutral nature of the complexes. Therefore, it is suggested that the ligand acts as a bidentate through coordinates to each metal atom by the isoxazole nitrogen and oxygen atoms of the sulfur dioxide moiety of the SMX based on FTIR studies. The ligand and its complexes were tested for their anti-inflammatory, anti-hemolytic, and antioxidant activities by various colorimetric methods. These complexes were found to exhibit potential effects of the selected biological activities.

An insight into antimycobacterial and antioxidant potentials of INH-Schiff base complexes and in silico targeting of MtKasB receptor of M. tuberculosis

Isoniazid Schiff base complexes synthesized by the molecular hybridization strategy revealed enhanced anti-tubercular (100% killing of M. tb strain) and antioxidant activities.

Artemisinin inhibits NRas palmitoylation by targeting the protein acyltransferase ZDHHC6

Protein S-palmitoylation is a post-translational modification that plays a crucial role in cancer cells by regulating the function and localization of oncoproteins and tumor suppressor proteins. Here, we identify artemisinin (ART), a clinically approved antimalarial endoperoxide natural product with promising anticancer activities, as an inhibitor of the ER-residing palmitoyl transferase ZDHHC6 in cancer cells using a chemoproteomic approach. We show that ART covalently binds and inhibits ZDHHC6 to reduce palmitoylation of the oncogenic protein NRas, disrupt NRas subcellular localization, and attenuate the downstream pro-proliferative signaling cascades. Our study identifies artemisinin as a non-lipid-based palmitoylation inhibitor targeting a specific palmitoyl acyltransferase and provides valuable mechanistic insights into the anticancer activity of artemisinins that are currently being studied in human clinical trials for different cancers.

Design and synthesis of Mannich base-type derivatives containing imidazole and benzimidazole as lead compounds for drug discovery in Chagas Disease

The protozoan parasite Trypanosoma cruzi is the causative agent of Chagas disease, the most important parasitic infection in Latin America. The only treatments currently available are nitro-derivative drugs that are characterised by high toxicity and limited efficacy. Therefore, there is an urgent need for more effective, less toxic therapeutic agents. We have previously identified the potential for Mannich base derivatives as novel inhibitors of this parasite. To further explore this family of compounds, we synthesised a panel of 69 new analogues, based on multi-parametric structure-activity relationships, which allowed optimization of both anti-parasitic activity, physicochemical parameters and ADME properties. Additionally, we optimized our in vitro screening approaches against all three developmental forms of the parasite, allowing us to discard the least effective and trypanostatic derivatives at an early stage. We ultimately identified derivative 3c, which demonstrated excellent trypanocidal properties, and a synergistic mode of action against trypomastigotes in combination with the reference drug benznidazole. Both its druggability and low-cost production make this derivative a promising candidate for the preclinical, in vivo assays of the Chagas disease drug-discovery pipeline.

Schiff Bases and Complexes: A Review on Anti-Cancer Activity

Development in the field of bio-inorganic chemistry increased the interest in Schiff base and its complexes due to its biological importance in many fields, including anticancer activity. Discovery of the antitumor activity of Schiff base and its complexes against various tumor cell lines fascinates the researchers to develop new anticancer drugs without any side effects. Thus, the present review focuses on the anticancer activity of Schiff bases and their metal complexes.

Exploration of artemisinin derivatives and synthetic peroxides in antimalarial drug discovery research

Malaria is a life-threatening infectious disease caused by protozoal parasites belonging to the genus Plasmodium. It caused an estimated 405,000 deaths and 228 million malaria cases globally in 2018 as per the World Malaria Report released by World Health Organization (WHO) in 2019. Artemisinin (ART), a "Nobel medicine" and its derivatives have proven potential application in antimalarial drug discovery programs. In this review, antimalarial activity of the most active artemisinin derivatives modified at C-10/C-11/C-16/C-6 positions and synthetic peroxides (endoperoxides, 1,2,4-trioxolanes, 1,2,4-trioxanes, and 1,2,4,5-tetraoxanes) are systematically summarized. The developmental trend of ART derivatives, and cyclic peroxides along with their antimalarial activity and how the activity is affected by structural variations on different sites of the compounds are discussed. This compilation would be very useful towards scaffold hopping aimed at avoiding the unnecessary complexity in cyclic peroxides, and ultimately act as a handy resource for the development of potential chemotherapeutics against Plasmodium species.

Artemisinin-derived antimalarial endoperoxides from bench-side to bed-side: Chronological advancements and future challenges

According to WHO World Malaria Report (2018), nearly 219 million new cases of malaria occurred and a total no. of 435 000 people died in 2017 due to this infectious disease. This is due to the rapid spread of parasite-resistant strains. Artemisinin (ART), a sesquiterpene lactone endoperoxide isolated from traditional Chinese herb Artemisia annua, has been recognized as a novel class of antimalarial drugs. The 2015 "Nobel Prize in Physiology or Medicine" was given to Prof Dr Tu Youyou for the discovery of ART. Hence, ART is termed as "Nobel medicine." The present review article accommodates insights from the chronological advancements and direct statistics witnessed during the past 48 years (1971-2019) in the medicinal chemistry of ART-derived antimalarial endoperoxides, and their clinical utility in malaria chemotherapy and drug discovery.

Current scenario of artemisinin and its analogues for antimalarial activity

Human malaria, one of the most striking, reemerging infectious diseases, is caused by several types of Plasmodium parasites. Whilst advances have been made in lowering the numbers of cases and deaths, it is clear that a strategy based solely on disease control year on year, without reducing transmission and ultimately eradicating the parasite, is unsustainable. Natural products have served as a template for the design and development of antimalarial drugs currently in the clinic or in the development phase. Artemisinin combine potent, rapid antimalarial activity with a wide therapeutic index and an absence of clinically important resistance. The alkylating ability of artemisinin and its semi-synthetic analogues toward heme related to their antimalarial efficacy are underlined. Although impressive results have already been achieved in malaria research, more systematization and concentration of efforts are required if real breakthroughs are to be made. This review will concisely cover the clinical, preclinical antimalarial and current updates in artemisinin based antimalarial drugs. Diverse classes of semi-synthetic analogs of artemisinin reported in the last decade have also been extensively studied. The experience gained in this respect is discussed.

Novel aminohydrazide cross-linked chitosan filled with multi-walled carbon nanotubes as antimicrobial agents

Four chemically modified chitosan derivatives 1-4 were designed and synthesized via a series of four reactions; first by reaction with benzaldehyde to protect its amino groups (Derivative 1), second by reaction with epichlorohydrine (Derivative 2), third by reaction with aminobenzhydrazide (Derivative 3), and forth by removing of benzaldehyde to restore the free amino groups on the chitosan (Derivative 4). Two multi-walled carbon nanotube (MWCNT) biocomposites based on Derivative 4 were also prepared. The structure of the prepared derivatives and MWCNT composites was elucidated using elemental analyses, FTIR, XRD, SEM and TEM. The modified chitosan derivatives and MWCNT composites showed better antimicrobial activities than that of chitosan against Enterococcus faecalis, Staphylococcus epidermidis, Escherichia coli, Aspergillus niger, Cryptococcus neoformans and Candida tropicalis as judged by their higher inhibition zone diameters using the agar well diffusion technique. These derivatives and MWCNT composites are more potent against Gram-positive bacteria than against Gram-negative bacteria. The MWCNT composites displayed comparable or even better antimicrobial activities than the reference bactericides or fungicides. Thus, structural modification of chitosan through combination with functionalized moieties and MWCNTs in one system was taken as a way to achieve promising templates for antimicrobial agents and to be appropriate candidates for medical applications.

Design of Drug Delivery Systems Containing Artemisinin and Its Derivatives

Artemisinin and its derivatives have been reported to be experimentally effective for the treatment of highly aggressive cancers without developing drug resistance, they are useful for the treatment of malaria, other protozoal infections and they exhibit antiviral activity. However, they are limited pharmacologically by their poor bioavailability, short half-life in vivo, poor water solubility and long term usage results in toxicity. They are also expensive for the treatment of malaria when compared to other antimalarials. In order to enhance their therapeutic efficacy, they are incorporated onto different drug delivery systems, thus yielding improved biological outcomes. This review article is focused on the currently synthesized derivatives of artemisinin and different delivery systems used for the incorporation of artemisinin and its derivatives.

An Eco-Friendly Ultrasound-Assisted Synthesis of Novel Fluorinated Pyridinium Salts-Based Hydrazones and Antimicrobial and Antitumor Screening

The present work reports an efficient synthesis of fluorinated pyridinium salts-based hydrazones under both conventional and eco-friendly ultrasound procedures. The synthetic approach first involves the preparation of halogenated pyridinium salts through the condensation of isonicotinic acid hydrazide (1) with p-fluorobenzaldehyde (2) followed by the nucleophilic alkylation of the resulting N-(4-fluorobenzylidene)isonicotinohydrazide (3) with a different alkyl iodide. The iodide counteranion of 5–10 was subjected to an anion exchange metathesis reaction in the presence of an excess of the appropriate metal salts to afford a new series of fluorinated pyridinium salts tethering a hydrazone linkage 11–40. Ultrasound irradiation led to higher yields in considerably less time than the conventional methods. The newly synthesized ILs were well-characterized with FT-IR, ¹H NMR, ¹³C NMR, ¹¹B, ¹⁹F, ³¹P and mass spectral analyses. The ILs were also screened for their antimicrobial and antitumor activities. Within the series, the salts tethering fluorinated counter anions 11–13, 21–23, 31–33 and 36–38 were found to be more potent against all bacterial and fungal strains at MIC 4–8 µg/mL. The in vitro antiproliferative activity was also investigated against four tumor cell lines (human ductal breast epithelial tumor T47D, human breast adenocarcinoma MCF-7, human epithelial carcinoma HeLa and human epithelial colorectal adenocarcinoma Caco-2) using the MTT assay, which revealed that promising antitumor activity was exhibited by compounds 5, 12 and 14.

Iodine-catalyzed synthesis of dibenzo[b,h][1,6]naphthyridine-11-carboxamides via a domino reaction involving double elimination of hydrogen bromide

An iodine-catalyzed reaction of 2-aminobenzamides and mucobromic acid was described and utilized to synthesize a variety of 6-oxo-5,6-dihydrodibenzo[b,h][1,6]naphthyridine-11-carboxamide derivatives in refluxing THF. As the two bromine atoms in mucobromic acid were found missing in the dibenzonaphthyridine products, a domino-type reaction mechanism involving a double elimination of hydrogen bromide was proposed.

Mannich bases in medicinal chemistry and drug design

The biological activity of Mannich bases, a structurally heterogeneous class of chemical compounds that are generated from various substrates through the introduction of an aminomethyl function by means of the Mannich reaction, is surveyed, with emphasis on the relationship between structure and biological activity. The review covers extensively the literature reports that have disclosed Mannich bases as anticancer and cytotoxic agents, or compounds with potential antibacterial and antifungal activity in the last decade. The most relevant studies on the activity of Mannich bases as antimycobacterial agents, antimalarials, or antiviral candidates have been included as well. The review contains also a thorough coverage of anticonvulsant, anti-inflammatory, analgesic and antioxidant activities of Mannich bases. In addition, several minor biological activities of Mannich bases, such as their ability to regulate blood pressure or inhibit platelet aggregation, their antiparasitic and anti-ulcer effects, as well as their use as agents for the treatment of mental disorders have been presented. The review gives in the end a brief overview of the potential of Mannich bases as inhibitors of various enzymes or ligands for several receptors.

Synthesis, characterization and antimicrobial evaluation of some new schiff, mannich and acetylenic Mannich bases incorporating a 1,2,4-triazole nucleus

A series of Schiff and Mannich bases derived from 4-amino-5-(3-fluoro-phenyl)-2,4-dihydro-3H-1,2,4-triazole-3-thione were synthesized. The alkylation of 4-phenyl-5-(3-fluorophenyl)-2,4-dihydro-3H-1,2,4-triazole-3-thione with propargyl bromide afforded the corresponding thiopropargylated derivative which upon treatment with the appropriate secondary amines in the presence of CuCl₂ furnished the desired acetylenic Mannich bases. The synthesized compounds were characterized on the basis of their spectral (IR, ¹H- and ¹³C-NMR) data and evaluated for their biological activities. Some of the compounds were found to exhibit significant antimicrobial activity.

Synthesis and characterization of Schiff's bases of sulfamethoxazole

Background

Schiff's bases are excellent ligands which are synthesized from the condensation of primary amines with carbonyl groups.

Findings

The classical reaction for the synthesis of Schiff's bases in an ethanolic solution and glacial acetic acid as a catalyst was followed in the synthesis of substituted sulfamethoxazole compounds.

Conclusions

Some Schiff's bases containing sulfamethoxazole nucleus have been synthesized and characterized. The present compounds are hoped to be applied in the photostability of PVC.

Synthesis and biological activities of some novel aminomethyl derivatives of 4-substituted-5-(2-thienyl)-2,4-dihydro-3H-1,2,4-triazole-3-thiones

A novel series of compounds were synthesized by cyclic condensation reaction of substituted isothiocyanate (2a-c) with 2-thiophenecarboxylic acid hydrazide (1) in the presence of ethyl alcohol, to obtain intermediate thiosemicarbazides (3a-c), which were further treated with sodium hydroxide in the presence of ethanol to obtain triazole derivatives (4a-c). The latter were refluxed with substituted secondary amines and formaldehyde for 6-10 h to afford Mannich bases (5a-k). The synthesized compounds were characterized on the basis of their spectral (IR, (13)C and (1)H NMR) data and evaluated for biological activities. Some of the compounds were found to exhibit significant antimicrobial and antioxidant activity.

1-[4-({4-[(E)-(2-Hy-droxy-naphthalen-1-yl)methyl-idene-amino]-phen-yl}sulfan-yl)phen-yl]ethanone

The title Schiff base compound, C₂₅H₁₉NO₂S, crystallizes in a statistically disordered structure comprising keto and enol tautomeric forms. In the enol form, the benzenoid arrangment is promoted by a strong intra­molecular O—H⋯N hydrogen bond and adopts an E conformation about the imine bond. In the keto form there is an intramolecular N—H⋯O hydrogen bond. In the crystal, an extended network of C—H⋯O hydrogen bonds stabilizes columns parallel to the c axis, forming large voids (there are four cavities of 108 ų per unit cell) with highly disordered residual electron density. The SQUEEZE procedure in PLATON [Spek (2009 ▶). Acta Cryst. D65, 148–155] was used to eliminate the contribution of this electron density from the intensity data, and the solvent-free model was employed for the final refinement. The contribution of this undetermined solvent was ignored in the calculation of the unit-cell characteristics.

Synthesis and evaluation of hybrid drugs for a potential HIV/AIDS-malaria combination therapy

Malaria and HIV are among the most important global health problems of our time and together are responsible for approximately 3 million deaths annually. These two diseases overlap in many regions of the world including sub-Saharan Africa, Southeast Asia and South America, leading to a higher risk of co-infection. In this study, we generated and characterized hybrid molecules to target Plasmodium falciparum and HIV simultaneously for a potential HIV/malaria combination therapy. Hybrid molecules were synthesized by the covalent fusion of azidothymidine (AZT) with dihydroartemisinin (DHA), a tetraoxane or a 4-aminoquinoline derivative; and the small library was tested for antiviral and antimalarial activity. Our data suggests that compound 7 is the most potent molecule in vitro, with antiplasmodial activity comparable to that of DHA (IC(50)=26 nM, SI>3000), a moderate activity against HIV (IC(50)=2.9 μM; SI>35) and not toxic to HeLa cells at concentrations used in the assay (CC(50)>100 μM). Pharmacokinetics studies further revealed that compound 7 is metabolically unstable and is cleaved via O-dealkylation. These studies account for the lack of in vivo efficacy of compound 7 against the CQ-sensitive Plasmodium berghei N strain in mice, when administered orally at 20mg/kg.

Design, synthesis, biological evaluation, and comparative Cox1 and Cox2 docking of p-substituted benzylidenamino phenyl esters of ibuprofenic and mefenamic acids

Nonsteroidal anti-inflammatory drugs (NSAIDs) are frequently associated with gastric mucosal and renal adverse reactions, related to inhibition of cyclooxygenase1 (Cox1) in tissues where prostaglandins exert physiological effects. This led us to develop a set of ibuprofenic acid and mefenamic acid esters, namely: 4-((4-substituted benzylidene)amino)phenyl 2-(4-isobutylphenyl)propanoate and 4-((4-substituted benzylidene)amino)phenyl 2-((2,4-dimethylphenyl)amino)benzoate analogs, which were synthesized by condensation of the corresponding acids with Schiff's bases [4-(4-substituted benzylideneamino)phenols] involving dicyclohexyl carbodiimmide (DCC) as mild dehydrating agent. The main objective is to reduce the GIT toxicity associated with acute and chronic NSAIDs use. Anti-inflammatory, analgesic as well as ulcerogenic activities of the prepared esters were evaluated in vivo and compared with that of ibuprofen as reference standard in all screenings, involving the carrageenan induced paw oedema model and hot plate method. Most of the synthesized esters showed remarkable analgesic and anti-inflammatory activities. Interestingly, all of the compounds were found to be non-ulcerogenic under the tested conditions. This evidence have suggested that modification of the carboxyl function of representative NSAIDs results in retained or enhanced anti-inflammatory and analgesic activities with reduced ulcerogenic potential. Additionally, a comparative AutoDock study into Cox 1 and Cox2 has been done involving both of rigid and flexible docking for potential selectivity of our compounds within different Cox enzymes and to find out the binding orientation of these novel esters into their binding site. Some of the newly prepared aforementioned compounds showed considerable more Cox2 over Cox1 binding affinities by flexible docking better than rigid one.

Cellular electrophysiological effects of changrolin in isolated rat cardiac myocytes

Changrolin (2, 6-bis[pyrrolidin-1-ylmethyl]-4-[quinazolin-4-ylamino] phenol) is an anti-arrhythmic drug derived from β-dichroine, an active component of the Chinese medicinal herb, Dichroa febrifuga Lour. To elucidate the mechanism underlying the anti-arrhythmic effect of changrolin, we used the whole-cell patch-clamp technique to characterize the electrophysiological actions of changrolin in isolated rat cardiomyocytes. In this study, changrolin inhibited delayed rectified K(+) currents (I(K)) in a concentration-dependent manner with inhibiting the current by 11.9%±4.7%, 27.8%±3.4%, 31.5%±3.6% and 40.8%±3.7% at 10, 30, 100 and 300 μM, respectively (n=7-8). Changrolin was less effective against transient outward K(+) currents (I(to)), and only showed significantly inhibitory effect at the highest concentration (300 μM). Changrolin also induced a concentration-dependent inhibition of sodium currents (I(Na)) with an IC(50) of 10.19 μM (Hill coefficient=-1.727, n=6-7). In addition, changrolin exerted a holding potential-dependent block on Na(+) channels, produced a hyperpolarizing shift in the steady-state inactivation curve, as well as exhibited a marked frequency-dependent component to the blockade of Na(+) channels. Finally, calcium currents (I(Ca)) was decreased by changrolin in a concentration-dependent manner with an estimated IC(50) of 74.73 μM (Hill coefficient=-0.9082, n=6). In conclusion, changrolin blocks Na(+) and Ca(2+) channels, and also blocks K(+) channels (I(to) and I(K)) to some extent. Notably, changrolin preferentially blocks the inactivated state of Na(+) channels. These effects lead to a modification of electromechanical function and likely contribute to the termination of arrhythmia.

State-dependent blockade of human ether-a-go-go-related gene (hERG) K(+) channels by changrolin in stably transfected HEK293 cells

AIM

To study the effect of changrolin on the K(+) channels encoded by the human ether-a-go-go-related gene (hERG).

METHODS

hERG channels were heterologously stably expressed in human embryonic kidney 293 cells, and the hERG K(+) currents were recorded using a standard whole-cell patch-clamp technique.

RESULTS

Changrolin inhibited hERG channels in a concentration-dependent and reversible manner (IC(50)=18.23 mumol/L, 95% CI: 9.27-35.9 mumol/L; Hill coefficient=-0.9446). In addition, changrolin shifted the activation curve of hERG channels by 14.3+/-1.5 mV to more negative potentials (P<0.01, n=9) but did not significantly affect the steady-state inactivation of hERG (n=5, P>0.05). The relative block of hERG channels by changrolin was close to zero at the time point of channel opening by the depolarizing voltage step and quickly increased afterwards. The maximal block was achieved in the inactivated state, with no further development of the open channel block. In the "envelope of tails" experiments, the time constants of activation were found to be 287.8+/-46.2 ms and 174.2+/-18.4 ms, respectively, for the absence and presence of 30 mumol/L changrolin (P<0.05, n=7). The onset of inactivation was accelerated significantly by changrolin between -40 mV and +60 mV (P<0.05, n=7).

CONCLUSION

The results demonstrate that changrolin is a potent hERG blocker that preferentially binds to hERG channels in the open and inactivated states.

Artemisinin and its derivatives: a novel class of anti-malarial and anti-cancer agents

In this tutorial review, an effort towards presentation of a comprehensive account of the recent developments on various kinds of artemisinin derivatives including artemisinin dimers, trimers and tetramers has been made and their efficacy towards malaria parasites and different cancer cells lines was compared with that of artemisinins, and various other anti-malarial and anti-cancer drugs. It is expected that this review will provide first-hand information on artemisinin chemistry to organic/medicinal chemists, and pharmacologists working on anticancer and anti-malarial drug development.

Regioselective reaction: synthesis, characterization and pharmacological studies of some new Mannich bases derived from 1,2,4-triazoles

In the present investigation, a series of new 4[(3-substituted-1H-pyrazol-4-yl)methyleneamino]-5-substituted-2-[(4-methylpiperzine-1-yl)methyl]-2H-1,2,4-triazole-3(4H)-thiones (4) were synthesized by the aminomethylation of 4-(3-substituted-1H-pyrazol-3-yl)methyleneamino-5-substituted-4H-1,2,4-triazole-3-thiols (3) with formaldehyde and N-methylpiperzine. These newly synthesized Schiff and Mannich bases were characterized by IR, (1)H NMR, mass spectral data and elemental analyses. These compounds were screened for their antibacterial and antifungal activity. Some of the compounds were found to exhibit significant antimicrobial activity.