A compound, or a pharmaceutically acceptable salt or solvate thereof, or conjugates thereof, selected from the group consisting of formula wherein: (a) R10 is H, and R11 is OH, ORA, where RA is saturated 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 S02M, where z is 2 or 3 and M is a monovalent pharmaceutically acceptable cation, or both M together are a divalent pharmaceutically acceptable cation.