A compound with the formula I: wherein: R2 is of formula II: where A is a C5-7 aryl group, X is selected from the group comprising: NHNH2, CONHNH2, formula III, formula IV, and either: (i) Q1 is a single bond, and Q2 is selected from a single bond and -Z-(CH2)n-, where Z is selected from a single bond, O, S and NH and n is from 1 to 3； or (ii) Q1 is -CH=CH-, and Q2 is a single bond； R12 is a C5-10 aryl group, optionally substituted by one or more substituents selected from the group comprising: halo, nitro, cyano, ether, C1-7 alkyl, C3-7 heterocyclyl and bis-oxy-C1-3 alkylene； R6 and R9 are independently selected from H, R, OH, OR, SH, SR, NH2, NHR, NRR', nitro, Me3Sn and halo； where R and R' are independently selected from optionally substituted C1-12 alkyl, C3-20 heterocyclyl and C5-20 aryl groups； R7 is selected from H, R, OH, OR, SH, SR, NH2, NHR, NHRR', nitro, Me3Sn and halo； either: (a) R10 is H, and R11 is OH, ORA, where RA is C1-4 alkyl； (b) R10 and R11 form a nitrogen-carbon double bond between the nitrogen and carbon atoms to which they are bound； or (c) R10 is H and R11 is SOzM, where z is 2 or 3 and M is a monovalent pharmaceutically acceptable cation； R" is a C3-12 alkylene group, which chain may be interrupted by one or more heteroatoms, and/or aromatic rings； Y and Y' are selected from O, S, or NH； R6', R7', R9' are selected from the same groups as R6, R7 and R9 respectively and R10' and R11' are the same as R10 and R11, wherein if R11 and R11' are SOzM, M may represent a divalent pharmaceutically acceptable cation.
