There is provided compounds of formula (I), wherein R1, R2, R3, R4 and R5 have meanings given in the description, and pharmaceutically-acceptable esters, amides, solvates or salts thereof, which compounds are useful in the treatment of diseases in which inhibition of a protein or lipid kinase (e.g. a PI3-K and/or mTOR) is desired and/or required, and particularly in the treatment of cancer or a proliferative disease.