Special Issue "Artemisinin (Qinghaosu): Commemorative Issue in Honor of Professor Youyou Tu on the Occasion of her 80th Anniversary"

Guest Editor
Dr. Geoff Brown
Department of Chemistry, The University of Reading, Whiteknights, Reading, RG6 6AD, UK
Website: http://www.reading.ac.uk/chemistry/about/staff/g-d-brown.asp
E-Mail:
Interests: *for Molecules specifically*: natural products; terpenes; biosynthesis; autoxidation chemistry; structure determination by NMR spectroscopy; prebiotic chemistry; *for Pharmaceuticals specifically*: natural products; antimalarial drugs; cannabinoids; NMR spectroscopy; metabonomics; oligosacharide structure determination

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TBA

Manuscript ID: Molecules-Artemisinin-20090512-Ferreira-us
Type of Paper: Review
Title: Flavonoid and Phenolics Antioxidants from Artemisia annua L. as Potential Synergizers of Artemisinin
Authors: Jorge F.S. Ferreira ^1,*, Davenand Luthria ² , Tomikazu Sasaki ³
Affiliations: ¹ USDA-ARS, Appalachian Farming Systems Research Center, 1224 Airport Rd., Beaver, WV 25813, USA; E-mail: Jorge.Ferreira@ars.usda.gov.
² Davenand Luthria, USDA-ARS, Food Composition and methods Development Lab, 10300 Baltimore Ave,. Bldg 161 BARC-East, Beltsville, MD 20705-2350, USA; E-mail: D.Luthria@ars.usda.gov
³ Department of Chemistry, Box 351700, University of Washington, Seattle, WA 98195-1700, USA; E-mail: sasaki@chem.washington.edu
Abstract: Since artemisinin was established as an active anti-malarial component from a diethyl ether extract of Artemisia annua in 1969, hundreds of papers have been published on the antimalarial effects of artemisinin and its semi-synthetic analogs, mainly dihydroartemisinin, artemether, arteether, and artesunate due to their better stability, higher bioavailability, and higher bioactivity against malaria. In the past decade, this work has been expanded to other bioactivities of artemisinin such as anti-cancer properties. Artemisinin, pharmacokinetics and bioavailability in animals and humans have not be well studied. Few, but growing, studies showing the potential synergistic effects of artemisinin with other compounds such as flavonoids and phenolics produced by A. annua have been reported. The growing idea that multi-component drug therapy might be better than monotherapy is illustrated by the recent resolution of the World Health Organization to support artemisinin-based combination therapies (ACTs), while phasing out monotherapy with artemisinins. In this critical review we will review the composition of phenolic phytochemicals extracted from A. annua. We will discuss the current research suggesting the possibility that artemisinin and its semi-synthetic analogs might become more potent if simultaneously delivered with natural antioxidant components (flavonoids and phenolics) present in A. annua traditional tea preparations and aqueous-alcoholic extracts for the treatment of malaria and other parasitic diseases that afflict humans and animals. These antioxidant molecules have been linked to suppression of the Cyt-P450 enzymes and p-glycoproteins, responsible for altering the absorption and metabolism of artemisinin in the body, and might also have immune modulatory activity in subjects afflicted with parasitic diseases. An approach for optimum extractions of both bioactive classes of phytochemicals (sesquiterpenoids and phenolics) from A. annua will be presented along with a brief discussion on influence of post harvest storage conditions on both groups of bioactive phytochemicals from A. annua.
Keywords: Artemisia annua, artemisinin, crude extracts, synergism, bioavailability, pharmacokinetics, extraction optimization, postharvest processing

Manuscript ID: Molecules- Artemisinin-20090517-Brown-uk
Title: The Biosynthesis of Artemisinin and the Phytochemistry of Artemisia annua L.
Type of Paper: Review
Author: Geoff Brown
Affiliation: Department of Chemistry, The University of Reading, Whiteknights, Reading, RG6 6AD, UK
Abstract: The Chinese medicinal plant Artemisia annua L. (Qinghao) is the only known source of the sesquiterpene, artemisinin (Qinghaosu), that is used in the treatment of malaria. Artemisinin is a highly oxygenated sesquiterpene, containing a unique 1,2,4-trioxane ring structure, which is responsible for the antimalarial activity of this natural product. The phytochemistry of A. annua is dominated by the presence of both sesquiterpenoids and flavonoids, as is the case for many other members of the Compositae family. A. annua is distinguished from other plants in this family, however, by the very large number of natural products which have been characterised (including around fifty amorphane and cadinane sesquiterpenes), as well as by the highly oxygenated nature of many of the terpene secondary metabolites. The discovery of an unusually wide variety of terpenoidal allylic hydroperoxidesfrom this species hasled to the proposal that the biogenesis of many of these highly oxygenated metabolites may be the result of oxidation reactions occurring at the tri-substituted double bond of a terpene precursor. Several studies into the biosynthesis of artemisinin were reported in the 1980’s and 1990’s, all of which required the prior synthesis of one or more sesquiterpene natural product in a radio-isotopically labelled form. These labelled precursors were then fed to either a homogenate or a cell-free preparation which was derived from the plant. Collectively, the results from these experiments were confusing, because they implied that an unfeasibly large number of different sesquiterpenes were all direct precursors to artemisinin. Some of these results were also contradictory, and as a result the complete biosynthetic pathway to artemisinin remained uncertain. More recent experiments, published within the last five years and employing stable isotopically-labelled precursors which were fed to intact A. annua plants, have provided a more conclusive picture of biosynthesis in this species. Thus, it has now been demonstrated that the sesquiterpene dihydroartemisinic acid is a late-stage precursor to artemisinin, while the closely related secondary metabolite, artemisinic acid, is not. In fact, feeding of these two precursors leads to the production of roughly half the sesquiterpenes which are known from A. annua. These experiments provide good circumstantial evidence for the hypothesis that many of the highly oxygenated terpenoids from A. annua arise by oxidation to an allylic hydroperoxide. In the particular case of artemisinin, it has now been shown explicitly by these in vivo experiments (as well as by additional in vitro studies) that the biosynthesis actually proceeds via a tertiary allylic hydroperoxide. Furthermore, there is evidence that the autoxidation of dihydroartemisinic acid to this allylic hydroperoxide is possibly a non-enzymatic process, and that the series of spontaneous rearrangement reactions which then convert the allylic hydroperoxide to the 1,2,4-trioxane ring of artemisinin, are almost certainly non-enzymatic in nature.

Manuscript ID: Molecules-Artemisinin-20090520-Djaman-fr
Title: In vitro Susceptibility of Plasmodium Falciparum Isolates to Artemisinin, Dihydro-Artemisinin, Chloroquine and Pyronaridine from Abidjan
Type of Paper: Article
Authors: Bla, K. B ¹, Yavo W ^1,2, Ouattara L ¹, Yapi H F ¹, Mazabraud A ³, Basco L K ⁴, Djaman A J ^1,3,*
Affiliation: ¹ Université de Cocody (22 BP 582 Abidjan 22), Institut Pasteur de Côte d’Ivoire, 01 BP 490 Abidjan
² Laboratoire de Microbiologie, Institut National de Santé Publique (INSP), BPV47 Abidjan, Côte d’Ivoire
³Institut de Biologie Animale Intégrative et Cellulaire (IBAIC), UMR 8080, Université Paris-Sud XI, Orsay, France
⁴Unité de Recherche Paludologie Afro-tropicale, Institut de recherche pour le développement (IRD)-Organisation de Coordination pour la lutte Contre les Endémies en Afrique Centrale (OCEAC), BP 288 Yaoundé, Cameroun
^*Corresponding author : Dr DJAMAN A. Joseph, Institut Pasteur de Côte d’Ivoire, 01 BP 490 Abidjan 01, Tél. : +225 22 48 10 00 poste 6807 djamanj@yahoo.fr
Abstract: We used standard in vitro drug sensitivity microtechnique recommended by the World Health Organization (WHO) to assess the sensitivity of Plasmodium falciparum isolates collected in Abidjan (Côte d’Ivoire) between April to December 2006. We tested antimalarial-drugs that are currently used (chloroquine, pyronaridine) and drugs newly introduced for malaria treatment in this country (artemisinin and its active metabolite, dihydroartemisinin). 32, 27, 25, and 28 P. falciparum isolates grew satisfactorily in chloroquine, pyronaridine, artemisinin, and dihydroartemisinin respectively and yielded interpretable results for these drugs. The proportions of resistant isolates were 56.2% for chloroquine, 48% for pyronaridine, 36% for artemisinin and 3.6% for dihydroartemisinin. The most potent antimalarial drug was dihydroartemisinin with a geometric mean IC₅₀ of 2.72 nM ranged from 1.45 to 3.99 nM. No multi-resistant isolates (showing resistance to more than three drugs) were found. A positive correlation was found between the 50% inhibitory concentration values for the following drugs: chloroquine and pyronaridine, pyronaridine and dihydroartemisinin, chloroquine and artemisinin, artemisinin and dihydroartemisinin. These data suggested cross-resistance between these drugs and justified an improved surveillance program for drug resistance to malaria in Côte d’Ivoire.
Keywords: artemisinin, chloroquine, dihydroartemisinin, Plasmodium falciparum, pyronaridine

Manuscript ID: Molecules- Artemisinin-20090527-it-Gasparrini
Type of Paper: Review Article
Title: Stereodynamic Investigation of Labile Stereogenic Centres in Dihydroartemisinin and Related Substances
Authors: Ilaria D’Acquarica ¹, Francesco Gasparrini ^{1, *}, Marco Pierini ¹, Claudio Villani ¹, Walter Cabri ², Michela Di Mattia ², Fabrizio Giorgi ²
Affiliations: ¹ Dipartimento di Chimica e Tecnologie del Farmaco, Sapienza Università di Roma, P. le Aldo Moro 5, 00185 Roma, Italy
² Analytical Development, R&D Department, sigma-tau S.p.A., Via Pontina km 30,400, 00040 Pomezia, Italy
Corresponding author: Francesco Gasparrini. Tel.: +390649912776. Fax: +390649912780; E-mail: francesco.gasparrini@uniroma1.it
Abstract: Since its identification in the 1970s, artemisinin, as well as semi-synthetic derivatives and synthetic trioxanes, have been used in therapy against malaria. Reduction of artemisinin by sodium borohydride produced dihydroartemisinin (DHA), which is also its main metabolite and provides improved antimalarial potency and a major elimination route. The synthesis of DHA opened pathways for further derivatization at C-10 to give ether and ester derivatives, largely exploited by the China Cooperative Research Group on Qinghaosu, with the aim of tuning water and/or oil solubility and improving bioavailability. The conversion of the lactone carbonyl group at C-10 of artemisinin into the hydroxyl (hemiacetal) group in DHA yields a new stereochemically labile centre in the molecule, which, in turn, provides two hemiacetal interconverting epimers (namely, a and b), the rate of interconversion and equilibrium position depending on buffer, pH and solvent polarity. Previous studies showing that interconversion of the two epimers occurred in a chromatographic time scale prompted us to fully investigate the phenomena as a crucial requisite of any analytical method aimed at quantitating this family of drugs. Investigations into dynamic molecular processes and determination of their kinetic parameters are commonly performed by dynamic nuclear magnetic resonance (DNMR). Such kinetic parameters can also be determined by chromatography, specifically for two species that interconvert during their passage through the column itself (on-column interconversion). During a Dynamic High Performance Liquid Chromatography (DHPLC) experiment, the chromatographic column acts at once as chemical reactor and separation device: first-order, reversible processes (diastereomerization, in our case) where the interconversion rates are on the same time-scale as the column separation rate typically yield temperature- and flow-dependent chromatographic profiles, with an interference regime (plateau) between the two resolved peaks. Computer simulation of the experimental deformed profiles can be used to obtain overall rate constants for the diastereomerization process during HPLC. In this critical review we will discuss the current importance of the on-column epimerization of DHA and related substances in the development of analytical methods aimed at quantitating the drugs, with the purpose of identifying the optimal conditions able to minimize on-column epimerization while achieving the best selectivity and efficiency of overall separation.
Keywords: antimalarials, dihydroartemisinin (DHA), epimerization, cryo-HPLC, dynamic HPLC (DHPLC), computer simulation.

Manuscript ID: Molecules-Artemisinin-20090610-us-Weina
Type of Paper: Review
Title: Embryotoxicity of Artemisinin and its Derivatives in Pregnant Animals
Authors: Qigui Li and Peter J. Weina
Affiliations: Division of Experimental Therapeutics, Walter Reed Army Institute of Research. 503 Robert Grant Avenue, Silver Spring, MD 20307-5100, USA: qigui.li@amedd.army.mil and peter.weina@amedd.army.mil
Abstract: Intravenous artesunate (AS) can cause fetal death and teratogenic effects in pregnant animals at a level (0.6-1.0 mg/kg) that below human therapeutic dose (2-4 mg/kg). Similar toxicity has also found for oral artemisinin (QHS), dihydroartemisinin (DHA), artemether (AM), and AS in various animal species with much higher doses (6.1-32.8 mg/kg). To date, however, this embryotoxicity has not been convincingly observed in pregnant women. Scientists have demonstrated that the DHA induce reprotoxicity primarily during yolk sac hematopoiesis of the embryos at a sensitive period of the early gestational days (GD) with high peak concentration, which effect inhibits angiogenesis and results in embryolethality. The severe embryotoxicity induced by injectable AS in animals is because that 1) the conversion rate of AS to DHA was significantly increased in the pregnant animals, resulting in a total AUC_D1-3 of DHA that was about 3.7-fold higher in pregnant than that in non-pregnant rats; 2) the buildup of high peak concentrations of AS and DHA totally in the blood of pregnant rats were also significantly higher than those of the non-pregnant animals; and 3) the injectable AS can provide a high peak concentration of drugs in blood, which could be even higher correspondingly risen in the location of the feto-placental unit since the drug distribution of AS and DHA in feto-placental tissues was always higher (2-4 folds) than that in the blood of the pregnant animals. The embryotoxicity can therefore be avoided or reduced by limiting the high-peak exposure level of artemisinins during this sensitive period in the fetal development (GD 9–14 in rats or GD 15 to week 6 in human.

Manuscript ID: Molecules-Artemisinin-20090610-us-Genovese
Type of Paper: Review
Title: Determinants of Neurotoxicity of Artemisinin and its Derivatives in Animal Species
Authors: Qigui Li ¹ and Raymond F. Genovese ²
Affiliations: ¹ Division of Experimental Therapeutics and ² Division of Psychiatry and Neurosciences, Walter Reed Army Institute of Research. Silver Spring, MD 20910-7500, USA: Qigui.Li@amedd.army.miland Raymond.Genovese@us.army.mil
Abstract: Artemisinin and its developed analogues, dihydroartemisinin (DHA), artemether (AM), arteether (AE), artesunate (AS) and artelinate (AL), are highly effective against the erythrocytic stages of P. falciparum. Studies with laboratory animals have demonstrated dose-dependent neurotoxicity that is associated with a number of adverse outcomes including movement disturbances, spasticity, balance deficits, brainstem tissue damage, and even death following administration of some intramuscular doses of oil-soluble AM and AE, or intragastric water-soluble AL. In contrast, few adverse effects have been observed after intravenous water-soluble AS and AL. Pharmacokinetic profiles suggest that the fatal neurotoxicity after administration with the oil-soluble artemisinins reflects a prolonged drug depot, which associated with damage of muscle cells at the intramuscular injection sites. Oral administration of AL also induces a gastrointestinal toxicity that is associated with a delayed gastric emptying. This effect suggests that a resulting accumulation of AL in stomach and blood prolonged the exposure time. In contrast, no toxicity was observed by intravenous injection with AS or AL with very short half-lives and a subsequent lack of accumulation of drug. In regard to the histopathological observations, select nuclei in the medulla, pons and mesencephalon are usually found to be most vulnerable to artemisinins. The occurrence of the brainstem lesion also seems to be strongly dependent upon a sustained exposure of circulating drug or metabolites. The sustained drug exposure time may, indeed, play a more important role in producing neurotoxicity than the peak drug exposure level, the degree of production of the active metabolite (DHA) and the mere penetration of the drug into the CNS. Therefore, considerations of the appropriate drug formulations as well as the appropriate drug regimens are critical factors necessary to avoiding neurotoxicity.

Manuscript ID: Molecules-Artemisinin-20090709-Romero-es
Title: Novel Anti-pathogen Activities of an Ancient Drug, Artemisinin
Authors: Romero MR¹, Marin JJG¹, Efferth T²
Affiliations: ¹ University of Salamanca, Laboratory of Experimental Hepatology and Drug Targeting, CIBERehd, Salmanca, Spain.
² German Cancer Research Center, Pharmaceutical Biology, Heidelberg, Germany; Email: marta.rodriguez@ciberehd.org, T.Efferth@dkfz-heidelberg.de, jjgmarin@usal.es
Abstract: Since a few decades the interest of western medicine in traditional Chinese medicine as a source of new compounds to treat diseases without available efficacious therapy has been increased. Among the vast experience acquired during millennia by Chinese medicine the use of artemisinin, as part of the extracts obtained from Artemisia annua (Qinghaosu), was included. These extracts were commonly used in decoctions against temblors and chills. Artemisinin emerges as a high interesting molecule since Professor Y. Tu discovered its antimalaria properties in 1972 and later on, when WHO recommended the use of artemisinin-based combinations therapies for the treatment of resistant strains of Plasmodium. Since then, several novel pharmacological activities for artemisinin and its derivatives have been described mainly based on the well-known properties endowed by its shared sesquiterpene structure. These include antiproliferative and cytostatic activity against tumour cells and protozoans other than Plasmodium, as well as antipathogen activity against certain human and animal viruses, bacteria and fungi. The present review summarizes the state of the art of artemisinin and its derivatives as novel drugs with a wide spectrum of activity against pathogens.

Manuscript ID: Molecules-Artemisinin-20091006-Zhou-cn
Type of Paper: Review
Title: Biological Action of Artemisinin: Insights from Medicinal Chemistry Studies
Authors: Jian Li and Bing Zhou
Affiliation: State Key Laboratory of Biomembrane and Membrane Biotechnology, School of Life Sciences, Tsinghua University, Beijing 100084, China; E-Mail: zhoubing@mail.tsinghua.edu.cn
Abstract: Artemisinins have become the essential antimalarial drugs since the finding of the artemisinin prototype. Although tramendous efforts have been devoted to decipher the mode of action for this class of molecules, their exact antimalarial mechanism remains an enigma. Several hypotheses have been proposed including alkylation of heme by carbon-centred free radicals, interference with proteins such as plasmodial Translationally Controlled Tumor Protein (TCTP) homolog and specifically, the sarcoplasmic/endoplasmic calcium ATPase (SERCA), in addition to damaging normal mitochondrial functions. Besides artemisinins, other endoperoxides with various backbones have also been synthesized, some of which showed comparable or even higher antimalarial effect. It is noteworthy that among these artemisinin derivatives, some enantiomers displayed similar in vitro malaria killing efficacy. In this article, the proposed mechanisms of action of artemisinins are reviewed in light of medicinal chemistry findings characterized by efficacy-structure studies, with the hope of gaining more insights into how these amazing drugs work.