Artemisinin structure

Besides their essential roles in nature, isoprenoids are of commercial importance in industry. Some isoprenoids have been used as flavors, fragrances, spices, and food additives, while many are used as pharmaceuticals to treat an array of human diseases, such as cancer (Taxol), malaria (artemisinin), and HIV (coumarins). In contrast to the huge market demand, isoprenoids are present only in low abundance in their host organisms. Thus, isolation of the required isoprenoids consumes a large quantity of natural resources. Furthermore, owing to their structural complexity, total chemical synthesis is often not commercially feasible. For these reasons, metabolic engineering may provide an alternative to produce these valuable isoprenoids [88,89]. 

The antiproliferative structure-activity relationships of 96 artemisinin derivatives are also discussed. 

FDA) for use in humans to treat malaria because this drug is considered a safe drug with few side effects.These features prompted various scientists around the world to evaluate the potential of artemisinin (1) and derivatives to control cancer cells proliferation. This chapter reviews the recent advances on analytical methods for extraction and quantification of artemisinin (1) from A. annua. Examples of artemisinin-derivatives with antiproliferative activities are listed, describing the structure-activity relationships of 96 compounds. This knowledge is essential for future development and use of artemisinin derivatives in cancer therapy. The mechanism of action of artemisinin and derivatives on cancer cells have been well reviewed in literature and therefore is not discussed in this chapter. 

Woerdenbag et al also evaluated the influence of chiral center configurations present in artemisinin (1) structure on the proliferation of Ehrlich ascites tumor (ETA) cells. Compounds 11-hydroxyartemisinin (47) and 11-hydroxy-11-epi-artemisinin (48) (Fig. 4) were synthesized and the... 

Fig. 6. Chemical structure of artemisinin (l)-derived trimers and tetramers.

Quinghaosu is the latest fundamental discovery in this area and is a heterocyclic compound that does not have a nitrogen atom in its structure. It is taken from a Chinese folk medicine. It is isolated from the plmt Artemisia annua. It is amazing that this compound, which is completely different than the other drugs described in this chapter in terms of structure, exhibits the exact same therapeutic effect. The main interest in quinoghaosu is based on the fact that it is active against resistant forms of malaria caused by P falciparum, and even its cerebral forms. Synonyms of this drug are artemisine, artemisinin, and others. 

The ozonide (176) was prepared as part of a synthetic study towards the antimalarial natural product artemisinin (177) <92JCS(Pl)325l>. It proved stable enough to allow x-ray crystal structure determination (see Section 4.16.3.1). Other, more complex, polycyclic ozonides were prepared in order to investigate possible antimalarial properties. Compounds were evaluated in vitro for antimalarial activity using a multiresistant strain of Plasmodium falciparum. Most were found to be weakly active although a thousand times less active than artemisinin. 

The isolation and structural determination of the naturally occurring potent antimalar-ial sesquiterpene endoperoxides, artemisinin (qinghaosu) (6)28-31.439 recogni-... 

Posner and coworkers have developed versatile methodology for the synthesis of novel 1,2,4-trioxanes that has allowed detailed investigation of their Structure-Activity Relationships (SAR) , while Jefford and coworkers first synthesized fenozan BO-7, so naturally some of their work has centered on its mechanism of action. Avery and coworkers have also contributed significantly to the area by the syntheses and QSAR (Quantitative SAR) studies of many artemisinin analogues. 

They concluded that the parasiticidal action of trioxanes involved reductive cleavage of the peroxide bond by intracellular iron-sulphur redox centres (rather than heme) and subsequent alkylation of the redox centre. This type of redox centre is known to exist in many enzymes and Wu and coworkers proposed that structural differences between those in the parasite and those in mammalian systems could account for the high selective cytotoxicity of artemisinin. 

Since the first series of compounds were poorly soluble in water, the next crucial phase of the project set out to increase the water solubility of the drug candidates in order to increase absorption from the gastrointestinal tract. Further refinements led to a candidate that was not only well absorbed when administered orally to animals, but also had outstanding antimalarial profiles both in vitro and in vivo. In comparison to available semi-synthetic artemisinins, the drug candidate OZ 277 (Scheme 27) exhibits structural simplicity, an economically feasible and scalable synthesis, superior antimalarial activity and an improved pharmaceutical profile. The toxicological profiles are also acceptable and this drug candidate entered first into man studies during 2004. 

Alkyl halides, hydroperoxide synthesis, 327-8 Alkyl hydroperoxides anion ligands, 114-19 covalent radii, 114, 118-19 dihedral angles, 119 geometric parameters, 115-8 tetrahedral distortion, 119 artemisinin formation, 133-4 chlorotriorganosilane reactions, 779-83 crystal structure, 105-14 anomeric effect, 110-11 geometric parameters, 106-9 hydrogen bonding, 103-5, 111-14 tetrahedral distortion, 110 determination, 674... 

Fig. 2. Structure of artemisinin derivatives. (From van Agtmael et al. Trends Pharmacol Sci 1999 20 202, reproduced with permission from Elsevier Science.)...

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