A compound of formula (I) where one of A1, A2 or A3 is N, and the others are independently selected from CH or N; ring B is a fused 5 or 6-membered carbocyclic or heterocyclic ring which is optionally substituted as defined in the specification, and R1, R2, R3, R4, and n are as defined in the specification. The compounds are inhibitors of EphB4 or EphA2 and therefore may be useful in pharmaceutical compositions for the treatment of conditions such as cancer.