The antiplasmodial activity of a series of spirotetrahydro β-carbolines is described. Racemic spiroazepineindole (1) was identified from a phenotypic screen on wild type Plasmodium falciparum with an in vitro IC50 of 90 nM. Structure− activity relationships for the optimization of 1 to compound 20a (IC50= 0.2 nM) including the identification of the active 1 R, 3 S enantiomer and elimination of metabolic liabilities is presented. Improvement of the ...