Sulfonamide-containing linkage systems for drug conjugates

A conjugate having the following structure (I):

• [(P)o-(L)]m-(T) (Ia)
• wherein:
• (L) is a linker;
• (T) is a targeting moiety that specifically binds to a target antigen;
• m is between 1 and 10;
• o is between 1 and 20, and
• (P) is a compound of Formula XId:
• wherein:
• R2 is —R″—NH—;
• R″ is selected from optionally substituted alkyl, optionally substituted alkylamino, optionally substituted cycloalkyl, optionally substituted aryl, optionally substituted heterocyclyl and optionally substituted heteroaryl, and
• R4 and R5 are each independently selected from:
• H and C1-C6 alkyl.

A conjugate having the following structure (I):

• [(P)o-(L)]m-(T) (Ia)
• wherein:
• (L) is a linker;
• (T) is an antibody or antigen-binding antibody fragment;
• m is between 1 and 10;
• o is between 1 and 20;
• (P) is a compound of Formula XId:
• wherein:
• R2 is —R″—NH—;
• R″ is selected from optionally substituted alkyl, optionally substituted cycloalkyl or optionally substituted aryl;
• R4 and R5 are each methyl, and
• (L)-(T) has structure (III):
• wherein:
• each AA is independently an amino acid;
• (AA)1-(AA)x is a dipeptide, a tripeptide, a tetrapeptide or a pentapeptide;
• (L′) is the remaining portion of linker (L),
• the —NH— group bonded to R″ in —R″—NH— forms a junction peptide bond (JPB) with (AA)1 in structure (III), and
• wherein (AA)1-(AA)x taken together comprises an amino acid sequence that facilitates cleavage of the JPB.