Three of the six compounds were found to be active (<1 µM) or moderately active (1-2.5 µM) in in vitro growth assays with asexual blood-stage P. falciparum (3D7) parasites, representing a hit rate of 50% on a small sample size. Up to this point a total of 398 compounds had been made and evaluated for in vitro activity in OSM Series 4, with the design of these compounds driven entirely by the intuition of medicinal chemists. By setting a potency cut-off of 2.5 µM (the upper limit of reasonable activity), the tally of active compounds discovered in this series stands at 165, representing a comparable human intuition-derived hit rate of 41% on a larger sample size. Most of the compounds were tested (blind) for their ability to disrupt Na + regulation in isolated asexual blood-stage parasites, which confirmed an unchanged mechanism of action: two of the compounds found to be active in in vitro growth assays disrupted Na + regulation whereas the three compounds inactive in growth assays did not, at the concentrations tested (Fig. ).