The design, synthesis and evaluation of 3-methylene-substituted indolinones as falcipain inhibitors and antiplasmodial agents are described. These compounds react readily with thiols via an addition-elimination mechanism, indicating their potential as cysteine protease inhibitors. Several indolinones containing a Leu-i-amyl recognition moiety were found to be moderate inhibitors of the Plasmodium falciparum cysteine protease falcipain-2, but not of the related protease falcipain-3, and displayed antiplasmodial activity against the chloroquine-resistant P. falciparum W2 strain in the low micromolar range. Coupling a 7-chloroquinoline moiety to the 3-methylene-substituted indolinone scaffold led to a significant improvement in antiplasmodial activity.
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