Abstract: The present invention relates to compounds of formula I, or pharmaceutically acceptable salt thereof, wherein: Z is CR10 or N; one of R1 and R2 is selected from (CH2)mR11, (CH2)mR12, (CH2)mNR12R13, (CH2)mOR12, (CH2)mNR13CO(CH2)nR11, (CH2)mNR13COR12, (CH2)mCONR13(CH2)nR11, (CH2)mCONR12R13, (CH2)mCO(CH2)nR11 and (CH2)mCOR12; where m is 0, 1, 2, 3 or 4 and n is 1, 2, 3 or 4; the other of R1 and R2 is H or R11; R3 and R5 are both H; R4 is H or R11; R6is H or (CH2)pR11, where p is 0 or 1; R7, R9 and R10 are each independently H or R11; R8 is selected from H, halogen, NO2, CN, OR13, NR13R14, NHCOR13, CF3, COR13, R13, CONR13R15, SO2NR13R14, SO2R13, NR13SO2R14, OCH2CH2OH, OCH2CH2OMe, morpholine, piperidine, and piperazine; each R11 is independently halogen, NO2, CN, (CH2)qOR13(CH2)rNR13R14, NHCOR13, CF3, COR13, R13, CONR13R14, SO2NR13R14, SO2R13, OR12, NR13SO2R14, OCH2CH2OH, OCH2CH2OMe, NR13SO2R12, (CH2)sNR12R13, morpholine, piperidine or piperazine, where q, r and s are each independently 0, 1, 2, 3 or