The invention is directed to a compound of formula I, as defined herein, or a pharmaceutically acceptable salt thereof; a pharmaceutical composition containing a compound of formula I, a method of treatment of a disorder or condition that may be treated by administration of the compound, the method comprising administering to a mammal, especially a human, in need of such treatment a compound of formula I as described above, and a method of treatment of a disorder or condition selected from the group consisting Human African Trypanosomiasis (HAT), Chagas Disease, Malaria, Leishmaniasis, and other infectious diseases transmitted to humans and animals by exposure to parasites, the method comprising administering to a human or mammal in need of such treatment a compound of formula I as described above.