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 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 of Human African Trypanosomiasis (HAT), Chagas disease, Leishmaniasis and malaria, the method comprising administering to a mammal, including a human, in need of such treatment a compound of formula I as described above.