The present invention relates to compounds for use as therapeutic agents, particularly in the treatment and/or prevention of proliferative disorders, such as cancer, especially brain cancers/tumours, wherein the compounds are generally defined by the formula I: wherein A is an aryl or heteroaryl ring system and R1 to R4 are various possible substituent groups, provided that at least one of an R2 group, the R3 group, or an R4 group is or comprises a hydroxy, amino, NH(Rx), or mercapto group.
