The bioactivity of isolated compounds against intracellular T. cruzi amastigotes grown in rat L6 cardiomyocytes is presented in Table . Only tephrosin showed activity in the nanomolar range (IC 50 of 0.04 μM) comparable to that of deguelin (39, 0,02 μM) and rotenone (37, 0.01 μM). Interestingly, the eight other rotenoids tested (compounds 29 to 36) were not active against T. cruzi, demonstrating that the activity is very specific even for compounds of the same chemical class. Rotenone and deguelin are known to be strong mitochondrial complex I (also known as NADH:ubiquinone oxidoreductase) inhibitors , while different activities between closely related rotenoids (rotenone, 5'-α-epirotenone, and 5'-β-epirotenone)