Compounds of formula Ic:
or a pharmaceutically acceptable salt thereof, and pharmaceutically acceptable compositions thereof, are useful as modulators of ATP-Binding Cassette ("ABC") transporters or fragments thereof, including Cystic Fibrosis Transmembrane Conductance Regulator ("CFTR"). The present invention also relates to the use of the compounds of the present invention for the preparation of a medicament for treating ABC transporter mediated diseases, like cystic fibrosis.
