The invention concerns compounds of Formula I, or a pharmaceutically acceptable salt thereof,
where R
1
, n, R
2
, R
3
, and R
4
are as defined in the description. The present invention also relates to processes for the preparation of such compounds, pharmaceutical compositions containing them and their use in the manufacture of a medicament for use as an antiproliferative agent in the prevention or treatment of tumours or other proliferative conditions which are sensitive to the inhibition of EphB4 kinases.