Abstract: A compound of formula (I) and salts and solvates thereof, wherein: R10 is a nitrogen protecting group and R11 is either OH or O—R12, wherein R12 is an oxygen protecting group, or R10 and R11 together form a double bond between N10 and C11; and R10? and R11? are selected from the same options as R10 and R11 respectively.

Abstract: Compounds of the formula: (I) or solvate thereof, wherein: R2 is an optionally substituted C5-20 aryl group; 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; R? is a C3-12 alkylene group, which chain may be interrupted by one or more heteroatoms and/or aromatic rings; X is selected from O, S, or NH; z is 2 or 3; M is a monovalent pharmaceutically acceptable cation; R2?, R6?, R7?, R9?, X? and M? are selected from the same groups as R2, R6, R7, R9, X and M respectively, or M and M? may together represent a divalent pharmaceutically acceptable cation.