The present invention provides compounds of formula I and pharmaceutically acceptable salts, wherein R1, R2, R3, R4, R5, X and Y have the meanings defined in the specification. The compounds have histone deacetylase (HDAC) inhibitory activity which is useful in cancer treatment. Also provided is a process for making a compound of formula I by reacting a compound of formula III with a compound of formula IV wherein A is a displaceable group and PG is a protecting group.