The present invention relates to compounds of formula I, wherein A1, A2, A3, R1, R2, R3, R4, R5, R6, L, Ar and Q are each as defined herein. The compounds of the present invention are inhibitors of autotaxin (ATX) enzyme activity. The present invention also relates to processes for the preparation of these compounds, to pharmaceutical compositions comprising them, and to their use in the treatment of proliferative disorders, such as cancer, as well as other diseases or conditions (e.g. fibrosis) in which ATX activity is implicated.