The present invention relates to compounds of formula (I): wherein R1 is NH2 or NHMe； R2 is halo； and one of R3 or R4 is hydrogen and the other is selected from SO2NH2, -SO2NHMe or SO2NMe2, -SO2NHEt, or -SO2NEt2； or a pharmaceutically acceptable salt or solvate thereof. The compounds of formula (I) are inhibitors of protein kinases, especially cyclic dependent kinases (CDKs) such as CDK9. 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 protein kinase/CDK activity is implicated.
