The present invention relates to the use of a compound of formula (I), or a pharmaceutically acceptable salt thereof, in therapy. Preferably, the compound may be used for treating a patient suffering from leukaemia, cancer or other proliferative disorder. A further embodiment relates to the use of a compound of formula (I) in an assay for detecting the phosphorylation and acetylation state of cellular substrates. The present invention also relates to novel compounds of formula (Ia). ##STR1##