Artemisinin inspired synthetic endoperoxide drug candidates: Design, synthesis, and mechanism of action studies

Synthesis and In Vivo Profiling of Desymmetrized Antimalarial Trioxolanes with Diverse Carbamate Side Chains

The recent withdrawal of artefenomel from clinical development leaves no endoperoxide-class agents in the antimalarial pipeline. Synthetic endoperoxides with a desymmetrized structure have demonstrated promising physiochemical and in vivo properties. Here we expand on our initial investigation of trans-3″ carbamate substitution with a diverse array of amine-, alcohol-, and sulfinyl-terminated analogues prepared in (S,S) and (R,R) configurations. In general, this chemotype combines low-nM antiplasmodial activity with excellent aqueous solubility but widely varying human liver microsome (HLM) stability. We evaluated 20 novel analogues in the P. berghei mouse malaria model, identifying new analogues such as RLA-4767 (9a) and RLA-5489 (9d), with HLM stability and pharmacokinetic profiles superior to analogues from our initial report (e.g., RLA-4776, 8a). These new leads approach or equal the efficacy of artefenomel after two daily oral doses of 10 mg/kg, thus revealing a promising chemotype with the potential to deliver development candidates.

Antiplasmodial potential of isolated xanthones from Mesua ferrea Linn. roots: an in vitro and in silico molecular docking and pharmacokinetics study

BACKGROUND

Malaria is a major global health concern, particularly in tropical and subtropical countries. With growing resistance to first-line treatment with artemisinin, there is an urgent need to discover novel antimalarial drugs. Mesua ferrea Linn., a plant used in traditional medicine for various purposes, has previously been investigated by our research group for its cytotoxic properties. The objective of this study was to explore the compounds isolated from M. ferrea with regards to their potential antiplasmodial activity, their interaction with Plasmodium falciparum lactate dehydrogenase (PfLDH), a crucial enzyme for parasite survival, and their pharmacokinetic and toxicity profiles.

METHODS

The isolated compounds were assessed for in vitro antiplasmodial activity against a multidrug-resistant strain of P. falciparum K1 using a parasite lactate dehydrogenase (pLDH) assay. In vitro cytotoxicity against Vero cells was determined using the MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay. The interactions between the isolated compounds and the target enzyme PfLDH were investigated using molecular docking. Additionally, pharmacokinetic and toxicity properties were estimated using online web tools SwissADME and ProTox-II, respectively.

RESULTS

Among the seven compounds isolated from M. ferrea roots, rheediachromenoxanthone (5), which belongs to the pyranoxanthone class, demonstrated good in vitro antiplasmodial activity, with the IC50 being 19.93 µM. Additionally, there was no toxicity towards Vero cells (CC50 = 112.34 µM) and a selectivity index (SI) of 5.64. Molecular docking analysis revealed that compound (5) exhibited a strong binding affinity of - 8.6 kcal/mol towards PfLDH and was stabilized by forming hydrogen bonds with key amino acid residues, including ASP53, TYR85, and GLU122. Pharmacokinetic predictions indicated that compound (5) possessed favorable drug-like properties and desired pharmacokinetic characteristics. These include high absorption in the gastrointestinal tract, classification as a non-substrate of permeability glycoprotein (P-gp), non-inhibition of CYP2C19, ease of synthesis, a high predicted LD50 value of 4,000 mg/kg, and importantly, non-hepatotoxic, non-carcinogenic, and non-cytotoxic effects.

CONCLUSIONS

This study demonstrated that compounds isolated from M. ferrea exhibit activity against P. falciparum. Rheediachromenoxanthone has significant potential as a scaffold for the development of potent antimalarial drugs.

Modulation of the Antimelanoma Activity Imparted to Artemisinin Hybrids by the Monoterpene Counterpart

Molecular hybridization is a widely used strategy in drug discovery and development processes that consists of the combination of two bioactive compounds toward a novel entity. In the current study, two libraries of hybrid derivatives coming from the linkage of sesquiterpene counterparts dihydroartemisinin and artesunic acid, with a series of monoterpenes, were synthesized and evaluated by cell viability assay on primary and metastatic melanoma cell lines. Almost all the obtained compounds showed micromolar antimelanoma activity and selectivity toward the metastatic form of this cancer. Four hybrid derivatives containing perillyl alcohol, citronellol, and nerol as monoterpene counterpart emerged as the best compounds of the series, with nerol being active in combination with both sesquiterpenes, dihydroartemisinin and artesunic acid. Preliminary studies on the mechanism of action have shown the dependence of the pharmacological activity of newly synthesized hybrids on the formation of carbon- and oxygen-centered radical species. This study demonstrated the positive modulation of the pharmacodynamic effect of artemisinin semisynthetic derivatives dihydroartemisinin and artesunic acid due to the hybridization with monoterpene counterparts.

Natural endoperoxides as promising anti-leishmanials

BACKGROUND

The discovery of artemisinin, an endoperoxide, encouraged the scientific community to explore endoperoxides as potential anti-parasitic molecules. Although artemisinin derivatives are rapidly evolving as potent anti-malarials, their potential as anti-leishmanials is emerging gradually. The treatment of leishmaniasis, a group of neglected tropical diseases is handicapped by lack of effective vaccines, drug toxicities and drug resistance. The weak antioxidant defense mechanism of the Leishmania parasites due to lack of catalase and a selenium dependent glutathione peroxidase system makes them vulnerable to oxidative stress, and this has been successful exploited by endoperoxides.

PURPOSE

The study aimed to review the available literature on the anti-leishmanial efficacy of natural endoperoxides with a view to achieve insights into their mode of actions.

METHODS

We reviewed more around 110 research and review articles restricted to the English language, sourced from electronic bibliographic databases including PubMed, Google, Web of Science, Google scholar etc. RESULTS: Natural endoperoxides could potentially augment the anti-leishmanial drug library, with artemisinin and ascaridole emerging as potential anti-leishmanial agents. Due to higher reactivity of the cyclic peroxide moiety, and exploiting the compromised antioxidant defense of Leishmania, endoperoxides like artemisinin and ascaridole potentiate their leishmanicidal efficacy by creating a redox imbalance. Furthermore, these molecules minimally impair oxidative phosphorylation; instead inhibit glycolytic functions, culminating in depolarization of the mitochondrial membrane and depletion of ATP. Additionally, the carbon-centered free radicals generated from endoperoxides, participate in chain reactions that can generate even more reactive organic radicals that are toxic to macromolecules, including lipids, proteins and DNA, leading to cell cycle arrest and apoptosis of Leishmania parasites. However, the precise target(s) of the toxic free radicals remains open-ended.

CONCLUSION

In this overview, the spectrum of natural endoperoxide molecules as major anti-leishmanials and their mechanism of action has been delineated. In view of the substantial evidence that natural endoperoxides (e.g., artemisinin, ascaridole) exert a noxious effect on different species of Leishmania, identification and characterization of other natural endoperoxides is a promising therapeutic option worthy of further pharmacological consideration.

Post-Translational Modifications of Proteins of Malaria Parasites during the Life Cycle

Post-translational modifications (PTMs) are essential for regulating protein functions, influencing various fundamental processes in eukaryotes. These include, but are not limited to, cell signaling, protein trafficking, the epigenetic control of gene expression, and control of the cell cycle, as well as cell proliferation, differentiation, and interactions between cells. In this review, we discuss protein PTMs that play a key role in the malaria parasite biology and its pathogenesis. Phosphorylation, acetylation, methylation, lipidation and lipoxidation, glycosylation, ubiquitination and sumoylation, nitrosylation and glutathionylation, all of which occur in malarial parasites, are reviewed. We provide information regarding the biological significance of these modifications along all phases of the complex life cycle of Plasmodium spp. Importantly, not only the parasite, but also the host and vector protein PTMs are often crucial for parasite growth and development. In addition to metabolic regulations, protein PTMs can result in epitopes that are able to elicit both innate and adaptive immune responses of the host or vector. We discuss some existing and prospective results from antimalarial drug discovery trials that target various PTM-related processes in the parasite or host.

A Radical-Generating Probe to Release Free Fluorophores and Identify Artemisinin-Sensitive Cancer Cells

The smart light-up probes have been extensively developed to image various enzymes and other bioactive molecules. Upon activation, these probes result in light-up fluorophores that exist in a protein-bound or a free form. The difference between these two forms has not yet been reported. Here, we present a pair of smart light-up probes that generate a protein-bound fluorophore and a free fluorophore upon activation by heme. Probe 8 generated a radical-attached fluorophore that predominantly existed in the free form, while probe 10 generated an α,β-unsaturated ketone-attached fluorophore that showed extensive labeling of proteins. In live-cell imaging, probe 8 showed greater fluorescence intensity than probe 10 when low concentrations (0.1-5 μM) of the probes were used, but probe 8 was less fluorescent than probe 10 when the concentrations of the probes were high (10 μM). Finally, probe 8 was used to reflect the activation level of the endoperoxide bond in cancer cells and to effectively distinguish ART-sensitive cancer cells from ART-insensitive ones.

Recent advances in the synthesis and antimalarial activity of 1,2,4-trioxanes

The increasing resistance of various malarial parasite strains to drugs has made the production of a new, rapid-acting, and efficient antimalarial drug more necessary, as the demand for such drugs is growing rapidly. As a major global health concern, various methods have been implemented to address the problem of drug resistance, including the hybrid drug concept, combination therapy, the development of analogues of existing medicines, and the use of drug resistance reversal agents. Artemisinin and its derivatives are currently used against multidrug- resistant P. falciparum species. However, due to its natural origin, its use has been limited by its scarcity in natural resources. As a result, finding a substitute becomes more crucial, and the peroxide group in artemisinin, responsible for the drugs biological action in the form of 1,2,4-trioxane, may hold the key to resolving this issue. The literature suggests that 1,2,4-trioxanes have the potential to become an alternative to current malaria drugs, as highlighted in this review. This is why 1,2,4-trioxanes and their derivatives have been synthesized on a large scale worldwide, as they have shown promising antimalarial activity in vivo and in vitro against Plasmodium species. Consequently, the search for a more convenient, environment friendly, sustainable, efficient, and effective synthetic pathway for the synthesis of 1,2,4-trioxanes continues. The aim of this work is to provide a comprehensive analysis of the synthesis and mechanism of action of 1,2,4-trioxanes. This systematic review highlights the most recent summaries of derivatives of 1,2,4-trioxane compounds and dimers with potential antimalarial activity from January 1988 to 2023.

An overview on the antimalarial activity of 1,2,4-trioxanes, 1,2,4-trioxolanes and 1,2,4,5-tetraoxanes

The demand for novel, fast-acting, and effective antimalarial medications is increasing exponentially. Multidrug resistant forms of malarial parasites, which are rapidly spreading, pose a serious threat to global health. Drug resistance has been addressed using a variety of strategies, such as targeted therapies, the hybrid drug idea, the development of advanced analogues of pre-existing drugs, and the hybrid model of resistant strains control mechanisms. Additionally, the demand for discovering new potent drugs grows due to the prolonged life cycle of conventional therapy brought on by the emergence of resistant strains and ongoing changes in existing therapies. The 1,2,4-trioxane ring system in artemisinin (ART) is the most significant endoperoxide structural scaffold and is thought to be the key pharmacophoric moiety required for the pharmacodynamic potential of endoperoxide-based antimalarials. Several derivatives of artemisinin have also been found as potential treatments for multidrug-resistant strain in this area. Many 1,2,4-trioxanes, 1,2,4-trioxolanes, and 1,2,4,5-tetraoxanes derivatives have been synthesised as a result, and many of these have shown promise antimalarial activity both in vivo and in vitro against Plasmodium parasites. As a consequence, efforts to develop a functionally straight-forward, less expensive, and vastly more effective synthetic pathway to trioxanes continue. This study aims to give a thorough examination of the biological properties and mode of action of endoperoxide compounds derived from 1,2,4-trioxane-based functional scaffolds. The present system of 1,2,4-trioxane, 1,2,4-trioxolane, and 1,2,4,5-tetraoxane compounds and dimers with potentially antimalarial activity will be highlighted in this systematic review (January 1963-December 2022).

Molecular and Crystal Structure, Spectroscopy, and Photochemistry of a Dispiro Compound Bearing the Tetraoxane Pharmacophore

The molecular structure and photochemistry of dispiro[cyclohexane-1,3'-[1,2,4,5]tetraoxane-6',2''-tricyclo[3.3.1.13,7 ]decan]-4-one (TX), an antiparasitic 1,2,4,5-tetraoxane was investigated using matrix isolation IR and EPR spectroscopies, together with quantum chemical calculations undertaken at the DFT(B3LYP)/6-311++G(3df,3pd) level of theory, with and without Grimme's dispersion correction. Photolysis of the matrix-isolated TX, induced by in situ broadband (λ>235 nm) or narrowband (λ in the range 220-263 nm) irradiation, led to new bands in the infrared spectrum that could be ascribed to two distinct photoproducts, oxepane-2,5-dione, and 4-oxohomoadamantan-5-one. Our studies show that these photoproducts result from initial photoinduced cleavage of an O-O bond, with the formation of an oxygen-centered diradical that regioselectivity rearranges to a more stable (secondary carbon-centered)/(oxygen-centered) diradical, yielding the final products. Formation of the diradical species was confirmed by EPR measurements, upon photolysis of the compound at λ=266 nm, in acetonitrile ice (T=10-80 K). Single-crystal X-ray diffraction (XRD) studies demonstrated that the TX molecule adopts nearly the same conformation in the crystal and matrix-isolation conditions, revealing that the intermolecular interactions in the TX crystal are weak. This result is in keeping with observed similarities between the infrared spectrum of the crystalline material and that of matrix-isolated TX. The detailed structural, vibrational, and photochemical data reported here appear relevant to the practical uses of TX in medicinal chemistry, considering its efficient and broad parasiticidal properties.

Artefenomel Regioisomer RLA-3107 Is a Promising Lead for the Discovery of Next-Generation Endoperoxide Antimalarials

Clinical development of the antimalarial artefenomel was recently halted due to formulation challenges stemming from the drug's lipophilicity and low aqueous solubility. The symmetry of organic molecules is known to influence crystal packing energies and by extension solubility and dissolution rates. Here we evaluate RLA-3107, a desymmetrized, regioisomeric form of artefenomel in vitro and in vivo, finding that the regioisomer retains potent antiplasmodial activity while offering improved human microsome stability and aqueous solubility as compared to artefenomel. We also report in vivo efficacy data for artefenomel and its regioisomer across 12 different dosing regimens.

Ring stage dormancy of Plasmodium falciparum tolerant to artemisinin and its analogues - A genetically regulated "Sleeping Beauty"

The appearance in 2008 in western Cambodia of Plasmodium falciparum tolerant to artemisinin, defined by longer parasite clearance time following drug administration and in vitro by a slightly higher survival rate of the ring stage after a 3-h treatment with 700 nM artemisinin (or analogues, collectively termed ART), has raised concerns of the possible loss of this frontline antimalarial [used in the form of an artemisinin combination therapy (ACT)], with its low IC₅₀ value against the ring stage and pleiotropic pro-drug/poison property. The key genetic marker of ART tolerance phenotype is a number of non-synonymous mutations in Pfkelch13 propeller domain. This results in defective assembly at the ring stage of a cytostome structure located at cytoplasmic side of the parasite membrane required for invagination of a double-membrane endosome carrying host cytosol haemoglobin to the digestive vacuole. The consequential deprivation of amino acids initiates ring stage parasites bearing the causal mutations in PfK13 (or other key cytostome components) entry into a dormant state ("Sleeping Beauty"), which, after a duration longer than that the short-lived ART, "Sleeping Beauty" ring parasite resumes its normal, but accelerated, development to maintain the 48-h intra-erythrocytic life-cycle. We posit that when ART-tolerant P. falciparum has acquired under ART stress the causative PfK13 mutation (not obligatory if mutations occur in other critical cytostome components), together with other necessary mutations to adjust to the new normalcy and to provide survival competitiveness, ART-tolerant parasite has now evolved into a genetically programmed "Sleeping Beauty". The onus of preventing the spread of ART-tolerant P. falciparum lies with the efficacy of ACT partner drug, hence the recommendation of a triple ACT (TACT). Nevertheless, attention should also be focussed on understanding the mechanisms of dormancy, such as induction, maintenance and recovery, to enable discovery and development of novel antimalarials targeting this unique parasite stage.

The Use of Medicinal Plant-Derived Metallic Nanoparticles in Theranostics

In the quest to effectively diagnose and treat the diseases that afflict mankind, the development of a tool capable of simultaneous detection and treatment would provide a significant cornerstone for the survival and control of these diseases. Theranostics denotes a portmanteau of therapeutics and diagnostics which simultaneously detect and treat ailments. Research advances have initiated the advent of theranostics in modern medicine. Overall, theranostics are drug delivery systems with molecular or targeted imaging agents integrated into their structure. The application of theranostics is rising exponentially due to the urgent need for treatments that can be utilized for diagnostic imaging as an aid in precision and personalised medicine. Subsequently, the emergence of nanobiotechnology and the green synthesis of metallic nanoparticles (MNPs) has provided one such avenue for nanoscale development and research. Of interest is the drastic rise in the use of medicinal plants in the synthesis of MNPs which have been reported to be potentially effective in the diagnosis and treatment of diseases. At present, medicinal plant-derived MNPs have been cited to have broad pharmacological applications and have been studied for their potential use in the treatment and management of cancer, malaria, microbial and cardiovascular diseases. The subject of this article regards the role of medicinal plants in the synthesis of MNPs and the potential role of MNPs in the field of theranostics.

Multigram Synthesis of a Combustion-Relevant δ-Ketohydroperoxide through Sulfonylhydrazine Substitution

A synthesis of a δ-ketohydroperoxide is described, addressing potential functional-group compatibilities in these elusive species relevant to combustion and atmospheric chemistries. The hydroperoxide is installed via sulfonylhydrazine substitution, which was found to be more effective than displacement of secondary halides. As part of this protocol, it was observed that 1,2-dimethoxyethane is an advantageous medium for the reaction, avoiding the formation of a tetrahydrofuran hydroperoxide side product. This discovery facilitated the multigram synthesis (6 steps, 41 % yield overall) and discrete characterization of the target δ-ketohydroperoxide.

On drug discovery against infectious diseases and academic medicinal chemistry contributions

This perspective is an attempt to document the problems that medicinal chemists are facing in drug discovery. It is also trying to identify relevant/possible, research areas in which academics can have an impact and should thus be the subject of grant calls. Accordingly, it describes how hit discovery happens, how compounds to be screened are selected from available chemicals and the possible reasons for the recurrent paucity of useful/exploitable results reported. This is followed by the successful hit to lead stories leading to recent and original antibacterials which are, or about to be, used in human medicine. Then, illustrated considerations and suggestions are made on the possible inputs of academic medicinal chemists. This starts with the observation that discovering a "good" hit in the course of a screening campaign still rely on a lot of luck - which is within the reach of academics -, that the hit to lead process requires a lot of chemistry and that if public-private partnerships can be important throughout these stages, they are absolute requirements for clinical trials. Concerning suggestions to improve the current hit success rate, one academic input in organic chemistry would be to identify new and pertinent chemical space, design synthetic accesses to reach these and prepare the corresponding chemical libraries. Concerning hit to lead programs on a given target, if no new hits are available, previously reported leads along with new structural data can be pertinent starting points to design, prepare and assay original analogues. In conclusion, this text is an actual plea illustrating that, in many countries, academic research in medicinal chemistry should be more funded, especially in the therapeutic area neglected by the industry. At the least, such funds would provide the intensive to secure series of hopefully relevant chemical entities which appears to often lack when considering the results of academic as well as industrial screening campaigns.

Advocacy for the Medicinal Plant Artabotrys hexapetalus (Yingzhao) and Antimalarial Yingzhaosu Endoperoxides

The medicinal plant Artabotrys hexapetalus (synonyms: A.uncinatus and A. odoratissimus) is known as yingzhao in Chinese. Extracts of the plant have long been used in Asian folk medicine to treat various symptoms and diseases, including fevers, microbial infections, ulcers, hepatic disorders and other health problems. In particular, extracts from the roots and fruits of the plant are used for treating malaria. Numerous bioactive natural products have been isolated from the plant, mainly aporphine (artabonatines, artacinatine) and benzylisoquinoline (hexapetalines) alkaloids, terpenoids (artaboterpenoids), flavonoids (artabotrysides), butanolides (uncinine, artapetalins) and a small series of endoperoxides known as yingzhaosu A-to-D. These natural products confer antioxidant, anti-inflammatory and antiproliferative properties to the plant extracts. The lead compound yingzhaosu A displays marked activities against the malaria parasites Plasmodium falciparum and P. berghei. Total syntheses have been developed to access yingzhaosu compounds and analogues, such as the potent compound C14-epi-yingzhaosu A and simpler molecules with a dioxane unit. The mechanism of action of yingzhaosu A points to an iron(II)-induced degradation leading to the formation of two alkylating species, an unsaturated ketone and a cyclohexyl radical, which can then react with vital parasitic proteins. A bioreductive activation of yingzhaosu A endoperoxide can also occur with the heme iron complex. The mechanism of action of yingzhaosu endoperoxides is discussed, to promote further chemical and pharmacological studies of these neglected, but highly interesting bioactive compounds. Yingzhaosu A/C represent useful templates for designing novel antimalarial drugs.

Antimalarial and anticancer activity evaluation of bridged ozonides, aminoperoxides and tetraoxanes

Bridged aminoperoxides, for the first time, were investigated for the in vitro antimalarial activity against the chloroquine-resistant Plasmodium falciparum strain K1 and for their cytotoxic activities against immortalized human normal liver (LO2) and lung (BEAS-2B) cell lines as well as human liver (HepG2) and lung (A549) cancer cell lines. Aminoperoxides exhibit good cytotoxicity against lung A549 cancer cells line. Synthetic ozonides were shown to have high activity against the chloroquine-resistant P. falciparum . A cyclic voltammetry study of peroxides was performed, and most of the compounds did not show a direct correlation in oxidative capacity-activity. Peroxides were analyzed for ROS production to understand their mechanism of action. However, none of the compounds has an impact on ROS generation, suggesting that ozonides induce apoptosis in HepG2 cells through ROS - independent dysfunction pathway.

Synthesis, Structure and Antileishmanial Evaluation of Endoperoxide–Pyrazole Hybrids

Leishmaniases are among the most impacting neglected tropical diseases. In attempts to repurpose antimalarial drugs or candidates, it was found that selected 1,2,4-trioxanes, 1,2,4,5-tetraoxanes, and pyrazole-containing chemotypes demonstrated activity against Leishmania parasites. This study reports the synthesis and structure of trioxolane–pyrazole (OZ1, OZ2) and tetraoxane–pyrazole (T1, T2) hybrids obtained from the reaction of 3(5)-aminopyrazole with endoperoxide-containing building blocks. Interestingly, only the endocyclic amine of 3(5)-aminopyrazole was found to act as nucleophile for amide coupling. However, the fate of the reaction was influenced by prototropic tautomerism of the pyrazole heterocycle, yielding 3- and 5-aminopyrazole containing hybrids which were characterized by different techniques, including X-ray crystallography. The compounds were evaluated for in vitro antileishmanial activity against promastigotes of L. tropica and L. infantum, and for cytotoxicity against THP-1 cells. Selected compounds were also evaluated against intramacrophage amastigote forms of L. infantum. Trioxolane–pyrazole hybrids OZ1 and OZ2 exhibited some activity against Leishmania promastigotes, while tetraoxane–pyrazole hybrids proved inactive, most likely due to solubility issues. Eight salt forms, specifically tosylate, mesylate, and hydrochloride salts, were then prepared to improve the solubility of the corresponding peroxide hybrids and were uniformly tested. Biological evaluations in promastigotes showed that the compound OZ1•HCl was the most active against both strains of Leishmania. Such finding was corroborated by the results obtained in assessments of the L. infantum amastigote susceptibility. It is noteworthy that the salt forms of the endoperoxide–pyrazole hybrids displayed a broader spectrum of action, showing activity in both strains of Leishmania. Our preliminary biological findings encourage further optimization of peroxide–pyrazole hybrids to identify a promising antileishmanial lead.

Autoxidation of a C2-Olefinated Dihydroartemisinic Acid Analogue to Form an Aromatic Ring: Application to Serrulatene Biosynthesis

Dihydroartemisinic acid (DHAA) is a plant natural product that undergoes a spontaneous endoperoxide-forming cascade reaction to yield artemisinin in the presence of air. The endoperoxide functional group gives artemisinin its biological activity that kills Plasmodium falciparum, the parasite that causes malaria. To enhance our understanding of the mechanism of this cascade reaction, 2,3-didehydrodihydroartemisinic acid (2,3-didehydro-DHAA), a DHAA derivative with a double bond at the C2-position, was synthesized. When 2,3-didehydro-DHAA was exposed to air over time, instead of forming an endoperoxide, this compound predominantly underwent aromatization. This olefinated DHAA analogue reveals the requirement of a monoalkene functional group to initiate the endoperoxide-forming cascade reaction to yield artemisinin from DHAA. In addition, this aromatization process was exploited to illustrate the autoxidation process of a different plant natural product, dihydroserrulatene, to form the aromatic ring in serrulatene. This spontaneous aromatization process has applications in other natural products such as leubethanol and erogorgiaene. Due to their similarity in structure to antimicrobial natural products, the synthesized compounds in this study were tested for biological activity. A group of the tested compounds had minimum inhibitory concentration (MIC) values ranging from 12.5 to 25 μg/mL against the bacterial pathogen Staphylococcus aureus and the fungal pathogen Cryptococcus neoformans.

Functionalized Boron Nanoparticles as Potential Promising Antimalarial Agents

Boron nanoparticles (BNPs), functionalized with hydroxyl groups, were synthesized in situ by a cascade process, followed by bromination and hydrolyzation reactions. These functionalized BNPs, (B _m (OH) _n ), were characterized using ¹H and ¹¹B NMR spectra, Fourier-transform infrared (FT-IR) spectroscopy, inductively coupled plasma-optical emission spectroscopy (ICP-OES), transmission electron microscopy (TEM), dynamic light scattering (DLS), and X-ray photoelectron spectroscopy (XPS) methods. These nanoparticles were also evaluated in vitro for their antimalarial activity against Plasmodium falciparum (3D7 strain) with an IC₅₀ value of 0.0021 μM and showed low toxicity to Uppsala 87 malignant glioma (U87MG) cell lines, malignant melanoma A375 cell lines, KB human oral cancer cell lines, rat cortical neuron cell lines, and rat fibroblast-like synoviocyte (FLS) cell lines.