Antimalarial activity of new water-soluble dihydroartemisinin derivatives. 3. Aromatic amine analogues

A series of artemisinin (1) derivatives containing bromo and heterocyclic or aromatic amine functions was prepared in the search for analogues with good water solubility and high antimalarial activity. Treatment of dihydroartemisinin (2a) with boron trifluoride etherate at room temperature gave the key intermediate, 9,10-dehydrodihydroartemisinin (3), which, on reaction with bromine, gave the dibromide 4. The latter was condensed with amines in anhydrous CH2Cl2 at less than -10 degrees C to give the desired products in 25-55% yield. The new derivatives, tested in vitro against Plasmodium falciparum, were found to be more effective against W-2 than D-6 clones and were not cross-resistant with existing antimalarials. Compound 6b, 3-fluoroaniline derivative, was the most active of the series, with the IC50 less than or equal to 0.16 ng/mL, making it several fold more potent than 1. However, no significant in vivo antimalarial activity against Plasmodium berghei was observed in any of the new compounds tested.