The Mode of Action and Possible Target of Artemisinin

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The Mode of Action and Possible Targetof
Artemisinin

• Mike Van Linn
• Chemistry 496
• 23 April 2004

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Outline

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

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Introduction

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

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Introduction

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

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Rationale for Research

• Anti-malarial Activity of Artemisinin
• Artemisinin Derivatives
• Used currently for life threatening cases

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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

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Possible Modes of Action

• Iron-Oxo Route
• Epoxidation Reactions
• Alkylation Reactions

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Iron-Oxo Route

• Donation of Oxygen from Peroxide Bridge to Iron
• Generate Fe(IV)O
• No Support from Raman Resonance Data
• Signal/Noise lt 2
• Should be 10 or 20

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Epoxidation Reactions
MnIITPP or FeCl2
NO EPOXIDE FORMATION

ARTEMISININ
OR
MnIITPP or FeCl2

EPOXIDE FORMATION
Na -OCl
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Robert, et al
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Cazelles, et al
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Cazelles, et al
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1,5 H Shift Possible???

• Critical Distance Calculated to be 2.1Å
• Exceeded in Stable Conformation
• Boat-like Conformation (High energy state)
• Houk

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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

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Robert, et al
Cazelles, et al
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Mode of Action

• Route 1 Dominant
• Alkyl radical formation from reduction of
  peroxide bridge
• Derivatives Used
• Observe correlation of alkylating ability to drug
  activity
• Alkylate MnIITPP

Pharm. active
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The Target

• Alkylation of Heme within Infected Erythrocytes
  (RBCs)
• Free heme in food vacuole of erythrocyte
• Cleavage of peroxide bond
• Alkylation of heme or specific parasite proteins
  can occur
• Too General

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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 40-4388 protease
  inhibitor
• Localized in the Food Vacuole?
• Fluorescent labeled artemisinin

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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

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References

1. Robert, Anne, et al. From Mechanistic Studies
   on Artemisinin Derivatives to New Modular
   Antimalarial Drugs. Accounts of Chemical
   Research, 2002, Vol. 35, pp. 167-174.
2. 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. 609-619.
3. 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. 3316-3325.
4. 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.
   3715-3718.
5. Yarnell, Amanda Rethinking How Artemisinin
   Kills, Chemical and Engineering News, Aug. 25,
   2003, Vol. 81 (24), pp. 6.
6. Eckstein-Ludwig, Ursula, et al. Artemisinins
   Target the SERCA of Plasmodium falciparum,
   Nature, 2003, Vol. 424, pp.957.

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Questions