Acid catalyzed Michael additions to artemisitene

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.

The molecular and cellular action properties of artemisinins: what has yeast told us?

Artemisinin (ART) or Qinghaosu is a natural compound possessing superior anti-malarial activity. Although intensive studies have been done in the medicinal chemistry field to understand the structure-effect relationship, the biological actions of artemisinin are poorly understood and controversial. Due to the current lack of a genetic amiable model to address this question, and an accidental finding made more than a decade ago during our initial exploratory efforts that yeast Saccharomyces cerevisiae can be inhibited by artemisinin, we have since been using the baker's yeast as a model to probe the molecular and cellular properties of artemisinin and its derivatives (ARTs) in living cells. ARTs were found to possess potent and specific anti-mitochondrial properties and, to a lesser extent, the ability to generate a relatively general oxidative damage. The anti-mitochondrial effects of artemisinin were later confirmed with purified mitochondria from malaria parasites. Inside some cells heme appears to be a primary reducing agent and reduction of ARTs by heme can induce a relatively nonspecific cellular damage. The molecular basis of the anti-mitochondrial properties of ARTs remains not well elucidated yet. We propose that the anti-mitochondrial and heme-mediated ROS-generating properties constitute two cellcidal actions of ARTs. This review summarizes what we have learned from yeast about the basic biological properties of ARTs, as well as some key unanswered questions. We believe yeast could serve as a window through which to peek at some of the biological action secrets of ARTs that might be difficult for us to learn otherwise.

Biological actions of artemisinin: insights from medicinal chemistry studies

Artemisinins have become essential antimalarial drugs for increasingly widespread drug-resistant malaria strains. Although tremendous efforts have been devoted to decipher how this class of molecules works, their exact antimalarial mechanism is still an enigma. Several hypotheses have been proposed to explain their actions, including alkylation of heme by carbon-centered free radicals, interference with proteins such as the sarcoplasmic/endoplasmic calcium ATPase (SERCA), as well as damaging of normal mitochondrial functions. Besides artemisinins, other endoperoxides with various backbones have also been synthesized, some of which showed comparable or even higher antimalarial effects. 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 insight into how these potent drugs work.

Spectroscopic study of the dispiro-1,2,4,5-tetroxane (cyclohexanone diperoxide)

The aim of this work is to present results derived from experimental IR and UV spectra and theoretical studies of DPCH, in order to get a more deeper insight on the physicochemical properties of this compound to gain a more deep knowledge of its action, helping in the design of new compounds with antimalaric effects. Experimental results are analyzed on the basis of theoretical calculations, which allow to derive suitable interpretations of spectral data.

Fluoroartemisinins: Metabolically More Stable Antimalarial Artemisinin Derivatives

This report is an overview on the design, preparation, and evaluation of metabolically stable artemisinins, using fluorine substitution. The chemical challenges encountered for the incorporation of fluorine-containing elements and the preparation of a large range of 10-trifluoromethyl artemisinin derivatives are detailed. Impact of the fluorine substitution on the antimalarial activity is also highlighted. Preclinical data of lead compounds, and evidence for their strong and prolonged antimalarial activity are presented.

Antimalarial activities of (+)-deoxoartemisitene and its novel C-11, 13 derivatives

(+)-Deoxoartemisitene and its C-11, 13 derivatives were synthesized from artemisinic acid via a short and regiospecific process and several derivatives show 10-20 times more in vitro antimalarial activities against Plasmodium falciparum than artemisinin.

Development of artemisinin and its structurally simplified trioxane derivatives as antimalarial drugs

Artemisinin and simplified trioxane analogs constitute a promising class of antimalarial chemotherapeutic agents. Their development since the early 1970s into clinical trials and clinical use has drawn much attention from medical scientists worldwide although the crude extract containing artemisinin has been used in China for treatment of fever for many centuries. Many research groups have independently and collaboratively conducted various studies on the artemisinin system both in search for the new compounds more antimalarially active than the parent artemisinin and in an attempt to understand its molecular mechanism(s) of action. Ongoing studies have provided a better understanding of the putative intermediates essential for the antimalarial activity and have led to designer trioxanes whose chemical structures have been simplified and modified to increase efficacy while lowering toxicity. Other desirable features beneficial to clinical uses such as bioavailability, drug stability and water solubility have been considered, and portions of the trioxane skeleton have been added or modified to accommodate these parameters accordingly.

Antimalarial chemotherapeutic peroxides: artemisinin, yingzhaosu A and related compounds

Mechanism-based rational design and gram-scale chemical synthesis have produced some new trioxane and endoperoxide antimalarial drug candidates that are efficacious and safe. This review summarises recent achievements in this area of peroxide drug development for malaria chemotherapy.

Artemisinin and derivatives: the future for malaria treatment?

The isolation in 1972 of artemisinin by Chinese scientists, and their development of all the derivatives now used in the treatment of malaria today, were of outstanding importance. The results which have accumulated both from the Chinese work and from that subsequently conducted on a worldwide basis provide for a relatively comprehensive understanding of the chemistry, pharmacological profiles, toxicology, metabolism, and effects on the malaria parasite. The optimal regimens for use in the field are also apparent, particularly in combinations with longer half-life quinoline antimalarials. Thus the future use of the artemisinin class of drug appears assured. However, the mechanism of action needs to be clarified. More importantly from a clinical viewpoint, problems inherent in the current derivatives must be addressed, particularly that of neurotoxicity, if new artemisinin derivatives are to be introduced in a normal drug regulatory environment. The application of established principles of modern drug design should indeed allow for the first truly rationally designed, in so far as the target is still unknown, derivatives to come to hand.