A conjugate of formula (A): ** Formula ** and salts and solvates thereof, where: D represents the group D1 or D2: ** Formula ** the dotted line indicates the optional presence of a double bond between C2 and C3； when a double bond is present between C2 and C3, R2 is selected from the group consisting of: (ia) C5-10 aryl group, optionally substituted with one or more substituents selected from the group comprising: halo, nitro, cyano, ether , carboxy, ester, C1-7 alkyl, C3-7 heterocyclyl and C1-3 bis-oxy-alkylene； (ib) saturated aliphatic C1-5 alkyl； (ic) saturated C3-6 cycloalkyl； ** Formula **, where each of R31, R32 and R33 are independently selected from H, saturated C1-3 alkyl, C2-3 alkenyl, alkynyl and C2-3 cyclopropyl, where the Total number of carbon atoms in group R2 is not more than 5； ** Formula **, where one of R35a and R35b is H and the other is selected from: phenyl, said phenyl is optionally substituted with a group selected from halo, methyl, methoxy； pyridyl and thiophenyl and ** Formula ** where R34 is selected from: H； saturated C1-3 alkyl； C2-3 alkenyl； C2-3 alkynyl； cyclopropyl； phenyl, said phenyl is optionally substituted with a group selected from halo, methyl, methoxy； pyridyl and thiophenyl； (ig) halo； when a single bond is present between C2 and C3, R2 is ** Formula ** where R36a and R36b are independently selected from H, F, saturated C1-4 alkyl, C2-3 alkenyl, whose alkyl and alkenyl groups are optionally substituted with a group selected from C 1-4 alkylamido and C 1-4 alkyl ester； or, when one of R36a and R36b is H, the other is selected from nitrile and a C1-4 alkyl ester； R6 and R9 are independently selected from H, R, OH, OR, SH, SR, NH2, NHR, NRR ', NO2, SnMe3 and halo； or (a) R10 is H and R11 is OH or ORA, where RA is C1-4 alkyl or (b) R10 and R11 form a nitrogen-carbon double bond between the nitrogen and carbon atoms to which they are attached or (c ) R10 is H and R11 is OSOzM, where z is 2 or 3 and M is a pharmaceutically accepta
