1. The Mode of Action and Possible Target of Artemisinin
Mike Van Linn
Chemistry 496
23 April 2004

2. Outline Introduction Rationale for Research Modes of Action
Malaria
Artemisinin
Rationale for Research
Modes of Action
Iron-Oxo route
Epoxidation reactions
Alkylation reactions
The Target of Artemisinin

3. Introduction Malaria Four species of Plasmodium
Infects 200 million people annually
1 million lethal
Resistance to current drugs

4. Introduction Artemisinin
Natural product extracted from sweet wormwood, Artemisia annua
Used by Chinese for over 2000 years
A. absinthium used to make absinthe

5. Rationale for Research
Anti-malarial Activity of Artemisinin
Artemisinin Derivatives
Used currently for life threatening cases

6. Rationale for Research
Anti-malarial Activity of Artemisinin
Artemisinin Derivatives
Used currently for life threatening cases
Drug Resistance of Plasmodium
Malaria spreading
Synthesis of new drugs

7. Possible Modes of Action
Iron-Oxo Route
Epoxidation Reactions
Alkylation Reactions

8. Iron-Oxo Route Donation of Oxygen from Peroxide Bridge to Iron
Generate Fe(IV)=O
No Support from Raman Resonance Data
Signal/Noise < 2
Should be ~10 or 20

9. Epoxidation Reactions
MnIITPP or FeCl2
NO EPOXIDE FORMATION +
ARTEMISININ OR
MnIITPP or FeCl2 +
Na+ -OCl
EPOXIDE FORMATION

10. Robert, et al

11. Cazelles, et al

12. Cazelles, et al

13. 1,5 H Shift Possible??? Critical Distance Calculated to be 2.1Å
Exceeded in Stable Conformation
Boat-like Conformation (High energy state)
Houk

14. Comparing Route 1 and 2 Route 1 Dominant to Route 2
90/10 ratio from isolated products
Artemisinin + MnIITPP
1,5 H shift?
Route 1 Biologically Active
Route 2 Inactive
Stereochemistry Effecting Alkylation

15. Robert, et al
Cazelles, et al

16. Mode of Action Route 1 Dominant Derivatives Used
Alkyl radical formation from reduction of peroxide bridge
Derivatives Used
Observe correlation of alkylating ability to drug activity
Alkylate MnIITPP
Pharm. active

17. The Target Alkylation of Heme within Infected Erythrocytes (RBC’s)
Free heme in food vacuole of erythrocyte
Cleavage of peroxide bond
Alkylation of heme or specific parasite proteins can occur
Too General…

18. The Target, More Specifically
Sarco/Endoplasmic Reticulum Ca2+-ATPase (SERCA) Enzyme
PfATP6 gene sequence
Testing the hypothesis
Heme Not Required?
Free heme blocked with Ro protease inhibitor
Localized in the Food Vacuole?
Fluorescent labeled artemisinin

20. Conclusions Malaria Remains as a Problem
Resistant strains
Anti-malarial Activity of Artemisinin
Mode of Action is Now Understood
Alkylation via route 1
A Specific Target Found
PfATP6 gene sequence of the SERCA enzyme
Fe2+ is required
Activity not localized in the food vacuole

21. References
Robert, Anne, et al. “From Mechanistic Studies on Artemisinin Derivatives to New Modular Antimalarial Drugs.” Accounts of Chemical Research, 2002, Vol. 35, pp
Cazelles, Jerome, et al. “Alkylating Capacity and Reaction Products of Antimalarial Trioxanes after Activation by a Heme Model.” The Journal of Organic Chemistry, 2002, Vol. 67, Number 3, pp
Wu, Wen-Min, et al. “Unified Mechanistic Framework for the Fe(II)-Induced Cleavage of Qinghaosu and Derivatives/Analogues. The First Spin-Trapping Evidence for the Previously Postulated Secondary C-4 Radical.” J. Am. Chem. Soc., 1998, Vol. 120, pp
Biot, Christophe, et al. “Synthesis and Antimalarial Activity in Vitro and in Vivo of a New Ferrocene-Chloroquine Analogue.” J. of Medicinal Chemistry, 1997, Vol. 40, pp
Yarnell, Amanda; “Rethinking How Artemisinin Kills,” Chemical and Engineering News, Aug. 25, 2003, Vol. 81 (24), pp. 6.
Eckstein-Ludwig, Ursula, et al. “Artemisinins Target the SERCA of Plasmodium falciparum,” Nature, 2003, Vol. 424, pp.957.

22. Questions