Drug targeting

A bioreductive conjugate of the formula II:

• (wherein
• R1 and R2 independently represent hydrogen or halogen atoms, or a group R, OR, SR, NHR, NR2, CO2R or CONHR;
• or, alternatively, R1 and R2 together with the intervening ring carbon atoms form a 5-7 membered carbocyclic or heterocyclic ring itself optionally substituted by one or more halogen atoms, or by one or more groups selected from R, OR, SR, NHR, NR2, CO2R and CONHR;
• Z represents an alkyl, alkenyl, aryl or aralkyl group optionally carrying at least one OH, SH, NH2 or NHR7 group in which R7 is an alkyl group or Z represents a group of the formula —XH where X represents an oxygen or a sulphur atom, or a group of formula NY in which Y represents a hydrogen atom or an alkyl group;
• R3, R4, R5 and R6 independently represent hydrogen atoms or an alkyl or alkenyl group;
• each group R independently represents a hydrogen atom, an alkyl or alkenyl group;
• E represents the residue of a therapeutic agent to be delivered, optionally attached via a linking group L which is an ester, phosphate ester, ether, amine, thiol or thiol ester group or any combination thereof;
• m=0, 1, 2 or 3;
• and
• p=0 or 2;
• with the proviso that when m=1 then p=0)
• or a salt thereof.