The present invention relates to compounds of formula I: wherein R1 and R2 are as defined herein, or a pharmaceutically acceptable salt or solvate thereof. The compounds of formula I are inhibitors of aurora kinase and/or FLT3. 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 in which aurora kinase and/or FLT3 activity is implicated.