1-2-4-trioxane and artemisinin

The biological activity of organic peroxides is usually associated with the antimalarial properties of artemisinin and its derivatives. However, the analysis of published data indicates that organic peroxides exhibit a variety of biological activity, which is still being given insufficient attention. In the present review, we deal with natural, semi-synthetic and synthetic peroxides exhibiting anthelmintic, antiprotozoal, fungicidal, antiviral and other activities that have not been described in detail earlier. The review is mainly concerned with the development of methods for the synthesis of biologically active natural peroxides, as well as its isolation from natural sources and the modification of natural peroxides. In addition, much attention is paid to the substantially cheaper biologically active synthetic peroxides. The present review summarizes 217 publications mainly from 2000 onwards.

Topics: Animals; Anthelmintics; Antifungal Agents; Antiprotozoal Agents; Antiviral Agents; Artemisinins; Dioxanes; Dioxolanes; Heterocyclic Compounds; Peroxides

The development of new efficient therapeutics for the treatment of malaria and cancer is an important endeavor. Over the past 15 years, much attention has been paid to the synthesis of dimeric structures, which combine two units of artemisinin, as lead compounds of interest. A wide variety of atemisinin-derived dimers containing different linkers demonstrate improved properties compared to their parent compounds (e.g., circumventing multidrug resistance), making the dimerization concept highly compelling for development of efficient antimalarial and anticancer drugs. The present Perspective highlights recent developments on different types of artemisinin-derived dimers and their structural and functional features. Particular emphasis is put on the respective in vitro and in vivo studies, exploring the role of the length and nature of linkers on the activities of the dimers, and considering the future prospects of the dimerization concept for drug discovery.

Topics: Animals; Antimalarials; Antineoplastic Agents, Phytogenic; Artemisinins; Dimerization; Heterocyclic Compounds; Humans; Malaria; Molecular Conformation; Neoplasms

Trioxane based compounds such as artemisinin and its synthetic and semi-synthetic analogues constitute promising class of antimalarial agents. The pharmaceutical development of artemisinin was started in 1971 after the isolation from Chinese medicinal plant Artemisia annua and this compound has drawn much attention from medical chemist and pharmacologist worldwide. Researchers from across the globe have independently and collaboratively conducted various studies on the artemisinin system in an attempt to identify lead molecules for malaria chemotherapy. This systematic study led to the discovery of artemether, arteether, dihydroartemisinin, and sodium artesunate which are being used as antimalarial drug for the treatment of Plasmodium falciparum related infections. These studies also revealed that the trioxane bridge is essential for the antimalarial activity of this class of compounds. Another class of structurally simple peroxides that emerged from these studies was the 1,2,4,5-tetraoxanes. Some of the tetraoxane based compounds have shown promising antimalarial potential, and much of work has been done on this type of compound in recent years. Apart from their antimalarial activity, these classes of compounds have also shown promising anticancer and antibacterial activity. To this end, an attempt has been made to describe the medicinal potential of trioxane and tetraoxane-based compounds. Literature from 1999 has been critically reviewed and an attempt has been made to discuss structure activity relationship study among the series of trioxane and tetraoxane based compounds.

Topics: Animals; Antimalarials; Antineoplastic Agents; Artemisia; Artemisinins; Heterocyclic Compounds; Humans; Malaria; Neoplasms; Plasmodium; Tetraoxanes

Heme is not only just the binding site responsible for oxygen transport by hemoglobin, but it is also the prosthetic group of many different heme-containing enzymes, such as cytochromes P450, peroxidases, catalase, and several proteins involved in electron transfer. Heme plays a key role in the mechanism of action of many different antimalarial drugs. In degrading the host's hemoglobin, the malaria parasite Plasmodium and several other heme-eating parasites are faced with this redox-active metal complex. Heme is able to induce the toxic reductive cascade of molecular oxygen, which leads to the production of destructive hydroxyl radicals. Plasmodium detoxifies heme by converting it into a redox-inactive iron(III) polymer called hemozoin. Artemisinin, a natural drug containing a biologically important 1,2,4-trioxane structure, is now the first-line treatment for multidrug-resistant malaria. The peroxide moiety in artemisinin reacts in the presence of the flat, achiral iron(II)-heme; the mechanism does not reflect the classical "key and lock" paradigm for drugs. Instead, the reductive activation of the peroxide function generates a short-lived alkoxy radical, which quickly rearranges to a C-centered primary radical. This radical alkylates heme via an intramolecular process to produce covalent heme-drug adducts. The accumulation of non-polymerizable redox-active heme derivatives, a consequence of heme alkylation, is thought to be toxic for the parasite. The alkylation of heme by artemisinin has been demonstrated in malaria-infected mice, indicating that heme is acting as the trigger and target of artemisinin. The alkylation of heme by artemisinin is not limited to this natural compound: the mechanism is invoked for a large number of antimalarial semisynthetic derivatives. Synthetic trioxanes or trioxolanes also alkylate heme, and their alkylation ability correlates well with their antimalarial efficacy. In addition, several reports have demonstrated the cytotoxicity of artemisinin derivatives toward several tumor cell lines. Deoxy analogues were just one-fiftieth as active or less, showing the importance of the peroxide bridge. The involvement of heme in anticancer activity has thus also been proposed. The anticancer mechanism of endoperoxide-containing molecules, however, remains a challenging area, but one that offers promising rewards for research success. Although it is not a conventional biological target, heme is the master piece of the mechanism of act

Topics: Antimalarials; Antineoplastic Agents; Artemisinins; Cell Line, Tumor; Cell Proliferation; Heme; Heterocyclic Compounds; Humans; Plasmodium

Topics: Animals; Antimalarials; Artemisinins; Heterocyclic Compounds; Molecular Structure; Plasmodium berghei; Sesquiterpenes; Structure-Activity Relationship

Antimalarial peroxides such as the phytochemical artemisinin or the synthetic ozonides arterolane and artefenomel undergo reductive cleavage of the pharmacophoric peroxide bond by ferrous heme, released by parasite hemoglobin digestion. The generated carbon-centered radicals alkylate heme in an intramolecular reaction and proteins in an intermolecular reaction. Here, we determine the proteinaceous alkylation signatures of artemisinin and synthetic ozonides in

Topics: Alkylation; Antimalarials; Artemisinins; Click Chemistry; Heterocyclic Compounds; Mass Spectrometry; Molecular Structure; Peroxides; Plasmodium falciparum; Proteomics; Protozoan Proteins; Stochastic Processes

The Fenton-like reductive cleavage of antimalarial peroxides like artemisinin by iron(II) species is a chemical reaction whose mechanistic pathway has not been yet fully understood; it is, however, known that there is considerable production of radical species centered at both the oxygen and carbon, which are important to the therapeutical effects of those compounds. This article reports kinetic data for the reaction of artemisinin and two model 1,2,4-trioxolanes with iron(II) species and also a mechanistic interpretation of this reductive cleavage from transition state thermodynamics. The suggestion of the presence of an enhancing specific factor inside the plasmodium is made.

Topics: Antimalarials; Artemisinins; Carbon; Drug Design; Ferrous Compounds; Free Radicals; Heterocyclic Compounds; Kinetics; Oxidation-Reduction; Oxygen; Thermodynamics

In spite of the recent increase in endoperoxide antimalarials under development, it remains unclear if all these chemotypes share a common mechanism of action. This is important since it will influence cross-resistance risks between the different classes. Here we investigate this proposition using novel clickable 1,2,4-trioxolane activity based protein-profiling probes (ABPPs). ABPPs with potent antimalarial activity were able to alkylate protein target(s) within the asexual erythrocytic stage of Plasmodium falciparum (3D7). Importantly, comparison of the alkylation fingerprint with that generated from an artemisinin ABPP equivalent confirms a highly conserved alkylation profile, with both endoperoxide classes targeting proteins in the glycolytic, hemoglobin degradation, antioxidant defence, protein synthesis and protein stress pathways, essential biological processes for plasmodial survival. The alkylation signatures of the two chemotypes show significant overlap (ca. 90 %) both qualitatively and semi-quantitatively, suggesting a common mechanism of action that raises concerns about potential cross-resistance liabilities.

Topics: Alkylation; Antimalarials; Artemisinins; Click Chemistry; Heterocyclic Compounds; Molecular Structure; Parasitic Sensitivity Tests; Plasmodium falciparum; Proteins; Proteomics

Fully synthetic endoperoxide antimalarials, namely, OZ277 (RBx11160; also known as arterolane) and OZ439 (artefenomel), have been approved for marketing or are currently in clinical development. We undertook an analysis of the kinetics of the in vitro responses of Plasmodium falciparum to the new ozonide antimalarials. For these studies we used a K13 mutant (artemisinin resistant) isolate from a region in Cambodia and a genetically matched (artemisinin sensitive) K13 revertant. We used a pulsed-exposure assay format to interrogate the time dependence of the response. Because the ozonides have physicochemical properties different from those of the artemisinins, assay optimization was required to ensure that the drugs were completely removed following the pulsed exposure. Like that of artemisinins, ozonide activity requires active hemoglobin degradation. Short pulses of the ozonides were less effective than short pulses of dihydroartemisinin; however, when early-ring-stage parasites were exposed to drugs for periods relevant to their in vivo exposure, the ozonide antimalarials were markedly more effective.

Topics: Antimalarials; Artemisinins; Heterocyclic Compounds; Parasitic Sensitivity Tests; Plasmodium falciparum

Evaluate the anti-tumor activity of ozonide antimalarials using a chemoresistant neuroblastoma cell line, BE (2)-c.. It was confirmed that five commonly used chemotherapy drugs had no cytotoxic activity in BE (2)-c cells. Six of 12 ozonides tested were active in-vitro at concentrations achievable in vivo with OZ513 being most active (IC50 = 0.5 mcg/ml). OZ513 activity was confirmed in IMR-32 and A673 cells. The Ao peak on cell-cycle analysis was increased after treatment with OZ513 in a concentration dependent fashion which when coupled with results from western blot analysis which showed an increase in cleaved capase-3 and cleaved PARP supported an increase in apoptosis. There was a concentration dependent decline in the MYCN and a cyclinD1 protein indicative of anti-proliferative activity and cell cycle disruption. OXPHOS metabolism was unaffected by OZ513 treatment while glycolysis was increased. There was a significant delay in time to tumor development in mice treated with OZ513 and a decline in the rate of tumor growth.. The antimalarial ozonide OZ513 has effective in-vitro and in-vivo activity against a pleiotropic drug resistant neuroblastoma cell-line. Treatment with OZ513 increased apoptotic markers and glycolysis with a decline in the MYCN oncogene and the cell cycle regulator cyclinD1. These effects suggest adaptation to cellular stress by mechanism which remain unclear.

Topics: Animals; Antimalarials; Antineoplastic Agents; Apoptosis; Artemisinins; Biomarkers; Caspase 3; Cell Cycle; Cell Line, Tumor; Disease Models, Animal; Drug Resistance, Neoplasm; Heterocyclic Compounds; Humans; Metabolome; Metabolomics; Mice; Neuroblastoma; Xenograft Model Antitumor Assays

The emerging cases of artemisinin and endoperoxide drug resistance are becoming a challenge to antimalarial drug discovery and therapy. The exact mode of action of this class of antimalarials is still unknown which presents a bottleneck for the understanding of drug resistance as well as designing new lead molecules of this class. To address this issue, the molecular docking and scoring studies of a homogeneous and structurally diverse dataset of artemisinin derived trioxanes have been performed on each of the two plausible targets of this class viz. heme and PfATP6. Since the crystal structure of PfATP6 is unknown, its homology model was built utilizing the human SERCA1 protein crystallized structure as a template. The binding energies of the heme binding site of the docked artemisinin derivatives showed very good correlation with the antimalarial activity (r(2) = 0.69), whereas the same study with the binding site of pfATP6 showed a very poor correlation (r(2) = 0.12), suggesting heme to be the possible target of artemisinin derived endoperoxides.

Topics: Amino Acid Sequence; Antimalarials; Artemisinins; Calcium-Transporting ATPases; Drug Design; Heme; Heterocyclic Compounds; Humans; Malaria, Falciparum; Models, Molecular; Molecular Docking Simulation; Molecular Sequence Data; Plasmodium falciparum; Sequence Alignment

In our ongoing search for highly active hybrid molecules exceeding their parent compounds in anticancer, antimalaria as well as antiviral activity and being an alternative to the standard drugs, we present the synthesis and biological investigations of 2nd generation 1,2,4-trioxane-ferrocene hybrids. In vitro tests against the CCRF-CEM leukemia cell line revealed di-1,2,4-trioxane-ferrocene hybrid 7 as the most active compound (IC50 of 0.01 μM). Regarding the activity against the multidrug resistant subline CEM/ADR5000, 1,2,4-trioxane-ferrocene hybrid 5 showed a remarkable activity (IC50 of 0.53 μM). Contrary to the antimalaria activity of hybrids 4-8 against Plasmodium falciparum 3D7 strain with slightly higher IC50 values (between 7.2 and 30.2 nM) than that of their parent compound DHA, hybrids 5-7 possessed very promising activity (IC50 values lower than 0.5 μM) against human cytomegalovirus (HCMV). The application of 1,2,4-trioxane-ferrocene hybrids against HCMV is unprecedented and demonstrated here for the first time.

Topics: Artemisinins; Cell Line, Tumor; Drug Resistance, Multiple; Ferrous Compounds; Heterocyclic Compounds; Heterocyclic Compounds, 4 or More Rings; Humans; Inhibitory Concentration 50; Leukemia; Metallocenes; Plasmodium falciparum

New, highly stable tricyclic antitubercular ozonides 9 and 10 derived from artemisinin are reported in 39 and 9% yields, respectively. The ozonide groups of 9 and 10 were found to be stable under strong basic and acidic conditions. The absolute configuration of ozonides 9 was confirmed by X-ray crystallography. Ozonide 10 shows promising antitubercular activity against M. tuberculosis H37Ra and M. tuberculosis H37Rv with MIC values of 0.39 and 3.12 μg/mL, respectively.

Topics: Antimalarials; Antitubercular Agents; Artemisinins; Crystallography, X-Ray; Heterocyclic Compounds; Molecular Conformation; Molecular Structure; Mycobacterium tuberculosis

Perhydrolysis of a sterically congested multifunctional epoxide was achieved in ethereal H2O2 with the aid of a recently developed Mo catalyst. The resulting hydroperoxide cyclized to give a 1,2,4-trioxane, which could be readily elaborated into qinghaosu and a range of novel analogues. Some of the compounds with two such trioxane moieties showed in vitro antimalarial activity comparable to or even better than that of artesunate or chloroquine.

Topics: Antimalarials; Artemisinins; Artesunate; Cyclization; Epoxy Compounds; Heterocyclic Compounds; Hydrogen Peroxide

Perkinsus olseni, the causative agent of Perkinsosis, can drastically affect the survival of target marine mollusks, with dramatic economic consequences for aquaculture. P. olseni is a member of the Alveolata group, which also comprises parasites that are highly relevant for medical and veterinary sciences such as Plasmodium falciparum and Toxoplasma. P. olseni shares several unique metabolic pathways with those pathological parasites but is not toxic to humans. In this work, six antimalarially active peroxides, derived from the natural product artemisinin or synthetic trioxolanes, were synthesized and tested on P. olseni proliferation and survival. All peroxides tested revealed an inhibitory effect on P. olseni proliferation at micromolar concentrations. The relevance of the peroxide functionality on toxicity and the effect of Fe(II)-intracellular concentration on activity were also evaluated. Results demonstrated that the peroxide functionality is the toxofore and intracellular iron concentration also proved to be a crucial co-factor on the activation of peroxides in P. olseni. These data points to a mechanism of bioactivation in P. olseni sharing similarities with the one proposed in P. falciparum parasites. Preliminary studies on bioaccumulation were conducted using fluorescent-labeled peroxides. Results show that synthetic trioxolanes tend to accumulate on a vacuole while the labeled artemisinin accumulates in the cytoplasm. Preliminary experiments on differential genes expression associated to Fe(II) transport protein (Nramp) and calcium transport protein (ATP6/SERCA) were also conducted by qPCR. Results point to a fourfold increase in expression of both genes upon exposure to trioxolanes and approximately twofold upon exposure to artemisinin derivatives. Data obtained in this investigation is relevant for better understanding of the biology of Perkinsus and may also be important in the development of new strategies for Perkinsosis prevention and control.

Topics: Adenosine Triphosphatases; Alveolata; Animals; Antiparasitic Agents; Artemisinins; Bivalvia; Cation Transport Proteins; Cell Proliferation; Ferrous Compounds; Heterocyclic Compounds; Humans; Peroxides; Protozoan Proteins

A series of 1,2,4-trioxanes were synthesized in which the key peroxy bonds were installed through a molybdenum-catalyzed perhydrolysis of the epoxy rings. A core structure was identified that may serve as a promising lead structure for further investigations because of its high antimalarial activity (comparable to that of artesunate and chloroquine), apparent potential for scale-up and derivatization, and facile monitoring/tracing by using UV light.

Topics: Antimalarials; Artemisinins; Catalysis; Cyclization; Epoxy Compounds; Heterocyclic Compounds; Molybdenum; Structure-Activity Relationship; Ultraviolet Rays

Four 5-carbon-linked trioxane dimer orthoesters (6a-6d) have been prepared in 4 or 5 chemical steps from the natural trioxane artemisinin (1). When administered orally to malaria-infected mice using a single dose of only 6 mg/kg body weight along with 18 mg/kg of mefloquine hydrochloride, trioxane dimer orthoester sulfone 6d completely and safely cured the mice; after 30 days, the cured mice showed no detectable parasitemia, gained at least as much weight as the control mice (no infection), and behaved normally.

Topics: Administration, Oral; Animals; Antimalarials; Artemisinins; Crystallography, X-Ray; Drug Therapy, Combination; Esters; Heterocyclic Compounds; Heterocyclic Compounds, 4 or More Rings; Malaria; Mefloquine; Mice; Molecular Structure; Plasmodium berghei

Ozonide OZ439 is a synthetic peroxide antimalarial drug candidate designed to provide a single-dose oral cure in humans. OZ439 has successfully completed Phase I clinical trials, where it was shown to be safe at doses up to 1,600 mg and is currently undergoing Phase IIa trials in malaria patients. Herein, we describe the discovery of OZ439 and the exceptional antimalarial and pharmacokinetic properties that led to its selection as a clinical drug development candidate. In vitro, OZ439 is fast-acting against all asexual erythrocytic Plasmodium falciparum stages with IC(50) values comparable to those for the clinically used artemisinin derivatives. Unlike all other synthetic peroxides and semisynthetic artemisinin derivatives, OZ439 completely cures Plasmodium berghei-infected mice with a single oral dose of 20 mg/kg and exhibits prophylactic activity superior to that of the benchmark chemoprophylactic agent, mefloquine. Compared with other peroxide-containing antimalarial agents, such as the artemisinin derivatives and the first-generation ozonide OZ277, OZ439 exhibits a substantial increase in the pharmacokinetic half-life and blood concentration versus time profile in three preclinical species. The outstanding efficacy and prolonged blood concentrations of OZ439 are the result of a design strategy that stabilizes the intrinsically unstable pharmacophoric peroxide bond, thereby reducing clearance yet maintaining the necessary Fe(II)-reactivity to elicit parasite death.

Topics: Adamantane; Animals; Antimalarials; Artemisinins; Dose-Response Relationship, Drug; Drug Stability; Heterocyclic Compounds; Iron; Malaria; Male; Mice; Peroxides; Plasmodium berghei; Rats; Rats, Sprague-Dawley; Time Factors; Treatment Outcome

A series of new amino functionalized 1,2,4-trioxepanes 8-16 and ester functionalized 1,2,4-trioxepanes 17-19 have been synthesized and evaluated against multi-drug resistant Plasmodium yoelii in Swiss mice. Amino functionalized trioxepanes 14, the most active compound of the series, showed 100% clearance of parasitaemia by oral route on day 4 and 75% protection to the treated mice beyond day 28.

Topics: Administration, Oral; Animals; Antimalarials; Artemisinins; Combinatorial Chemistry Techniques; Drug Resistance, Multiple; Heterocyclic Compounds; Mice; Parasitemia; Plasmodium yoelii; Propanols; Structure-Activity Relationship

It was found that iodine-catalyzed reactions of geminal bishydroperoxides with acetals proceed with the replacement of only one alkoxy group by the peroxide group to give previously unknown structures of 1-hydroperoxy-1'-alkoxyperoxides in yields up to 64%. The same compounds are formed in the iodine-catalyzed reactions of geminal bishydroperoxides with enol ethers. The nature of the solvent has a decisive influence on the formation of 1-hydroperoxy-1'-alkoxyperoxides. In the series of Et(2)O, THF, EtOH, CHCl(3), CH(3)CN, and hexane, the best results were obtained with the use of Et(2)O or THF as the solvent.

Topics: Acetals; Antimalarials; Artemisinins; Catalysis; Heterocyclic Compounds; Iodine; Peroxides