The invention provides compounds of the formula (1): or salts or tautomers thereof； wherein X1 is N or N+(O&minus；)； X2 is N or CH； Q is a C1-3 alkylene group； R1 is selected from hydrogen, C1-4 hydrocarbyl and hydroxy-C2-4 hydrocarbyl； R2, R3 and R4 are the same or different and each is selected from hydrogen, fluorine, chlorine and methyl； Ar1 is an optionally substituted monocyclic 5 or 6-membered aryl or heteroaryl ring containing 0, 1 or 2 heteroatom ring members selected from O, N and S, or a naphthyl ring and Ar2 is an optionally substituted monocyclic 5 or 6-membered heteroaryl ring containing 1, 2 or 3 heteroatom ring members selected from O, N and S. The compounds of formula (1) are inhibitors of p70S6 kinase and are useful in the treatment of proliferative diseases.
