Pyrrolobenzodiazepines and targeted conjugates

A conjugate of formula I:

• L-(LU-D)p, (I)
• or a pharmaceutically acceptable salt thereof, wherein
• L is a Ligand Unit selected from the group consisting of an antibody, an antigen-binding fragment of an antibody and an Fc fusion protein;
• LU is a Linker Unit of formula 1a:
• -A1-L1- (1a)
• wherein:
• L1 is an amino acid sequence comprising a dipeptide of formula —NH—X1—X2—CO—, wherein —NH— is the amino group of X1, and CO is the carbonyl group of X2, and wherein the peptide is cleavable by the action of an enzyme to release D as a free drug, wherein the enzyme is a cathepsin;
• A1 is a Stretcher Unit, wherein A1 comprises the functionality —CO— connected directly to the amino group of X1, thereby forming an amide link with —X1—, and wherein A1 is further comprised of the structure of:
• wherein
• S is a sulfur atom derived from the Ligand Unit;
• the wavy line indicates the point of attachment to the Ligand Unit;
• and the asterisk indicates the point of attachment to the remaining portion of A1;
• subscript p is from 1 to 20;
• and
• D is a Drug Unit, wherein the Drug Unit is a PBD dimer having the structure selected from the group consisting of D1-D6:
• wherein the asterisk indicates the point of attachment to LU;
• and
• either:
• (a) R10 is H, and R11 is OH or ORA, wherein 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 bound, or
• (c) R10 is H and R11 is SOzM, wherein subscript z is 2 or 3 and M is a pharmaceutically acceptable cation;
• and
• R10′ and R11′ are the same as R10 and R11, wherein if R11 and R11′ are each SOzM, then each M is an independently selected pharmaceutically acceptable monovalent cation or both M together is a pharmaceutically acceptable divalent cation.