Abstract: This invention relates to certain heterocyclic compounds and their pharmaceutically acceptable salts, which are useful for sensitizing multidrug-resistant tumor cells to anticancer agents and multidrug resistant forms of malaria, tuberculosis, leishmania and amoebic dysentery to chemotherapeutants. The compounds and their pharmaceutically acceptable salts are also inhibitors of the active drug transport capability of P-glycoprotein which is encoded by the human MDR1 gene, as well as of certain other related ATP-binding-cassette transporters from eukaryotic and prokaryotic organisms (e.g., pfmdr from Plasmodium falciprum, and murine mdr1 and mdr3 gene products).

Abstract: The invention relates to compounds of the formula ##STR1## and to pharmaceutically acceptable salts thereof, wherein R.sup.1, R.sup.2, R.sup.3, R.sup.4, n and m are as defined herein. The compounds of formula I are useful in the treatment of hyperproliferative diseases, such as cancer. The invention further relates to processes of making the compounds of formula I and to methods of using such compounds in the treatment of hyperproliferative diseases.