It was predicted that a covalent inhibitor may need only a short exposure to have a prolonged parasiticidal effect, whilst a non-covalent inhibitor would be less active after a short exposure. To test this notion parasites at ring stage were exposed for 6 hours only with compound 4 (covalent), and TCMDC-135051 (1) (non-covalent). Following compound washout the parasite culture was continued for 66 hours and parasite viability tested. Under these conditions the potency of TCMDC-135051 (1) significantly reduced (pIC50 = 5.91, p = 0.0003, Fig. ) whilst the potency of compound 4 was not reduced following wash out (pIC50 = 7.04, p = 0.9439, Fig. ). These data are consistent with a covalent mechanism of action in parasite cells for chloroacetamide inhibitor 4. Furthermore, the demonstration of a short exposure time resulting in a prolonged parasiticidal effect is a useful finding in the quest for a single-dose cure for malaria. (blue and yellow, respectively), compound medium was exchanged for compound-free medium after 6 hours, and parasites were incubated for a further 66 hours. While TCMDC-135051 (left)