Targeted pyrrolobenzodiazapine conjugates

A method for preparing a Drug linker compound, or a salt thereof, the method comprising the steps of:

• a) contacting a PBD compound having the formula of:
• wherein —R2 has the formula of:
• wherein A is a C5-7 aryl group and X is *—NH(RN),
• wherein RN is selected from the group consisting of H and C1-4 alkyl;
• the asterisk indicates the point of attachment to Q2, and either:
• (i) Q1 is a single bond and Q2 is a single bond or —Z—(CH2)n—, wherein Z is selected from the group consisting of a single bond, O, S and NH;
• and subscript n is from 1 to 3, or
• (ii) Q1 is —CH═CH— and Q2 is a single bond;
• and
• R12 is a C5-10 aryl group, substituted by a group selected from the group consisting of —OH, —CO2H, and —CO2RO, where RO is C1-4 alkyl;
• R6 and R9 are independently selected from the group consisting of H, R, OH, OR, SH, SR, NH2, NHR, NRR′, nitro, Me3Sn and halo, wherein R and R′ are independently selected from the group consisting of optionally substituted C1-12 alkyl, C3-20 heterocyclyl and C5-20 aryl groups, wherein C3-20 heterocyclyl is a monovalent moiety derived from removing a hydrogen atom of a heterocyclic compound which has 3 to 20 ring atoms, of which 1 to 10 are heteroatoms selected from the group consisting of N, O and S;
• R7 is selected from the group consisting of H, R, OH, OR, SH, SR, NH2, NHR, NRR′, nitro, Me3Sn and halo,
• R″ is a C3-12 alkylene group, which chain is optionally interrupted by one or more heteroatoms selected from the group consisting of O, S, and NRN2, wherein RN2 is H or C1-4 alkyl, and/or by an aromatic ring;
• Y and Y′ are independently selected from the group consisting of O, S, and NH;
• R6′, R7′, R9′ are selected from the same groups as R6, R7 and R9, respectively,
• with a peptide coupling agent and a compound of formula G1-L1, wherein
• L1 is a dipeptide of formula —NH—X1—X2—CO2H, wherein —NH— is the amino group of X1, and CO2H is the carboxylic acid functional group of X2 for peptide coupling by the peptide coupling agent to the nitrogen atom of X of the PBD compound and wherein the peptide is cleavable by the action of an enzyme for release of the PBD compound;
• and
• G1 is a Stretcher Unit for connection to an antibody or antigen-binding fragment thereof, wherein G1 is comprised of a maleimide group for reaction with a reactive thiol functional group provided by the antibody or antigen-binding fragment for said connection, and wherein G1 further comprises the functionality —CO— connected directly to the amino terminus of X1, thereby forming an amide link with —X1—,
• wherein said contacting provides the Drug Linker compound having the formula of G1-L1-D, wherein G1 is the Stretcher Unit and L1 and D correspond in structure to the dipeptide and PBD compound, respectively.