Site-specific antibody conjugation and antibody-drug conjugate as specific embodiment thereof

A peptide-compound conjugate having a structure of formula 6-3:

• D-C-A-W-H-(Xa1)′-G-E-L-V—W-C-T (SEQ ID NO:
• 16), [formula 6-3]
• wherein,
• D is an aspartic acid residue, C is a cysteine residue, A is an alanine residue, W is a tryptophan residue, H is a histidine residue, G is a glycine residue, E is a glutamic acid residue, L is a leucine residue, V is a valine residue, and T is a threonine residue, and
• (Xa1)′ is
• wherein
• H1 is a click chemistry functional group selected from the group consisting of a terminal alkyne, an azide, a strained alkyne, a diene, a dienophile, a dibenzocyclooctyne-amine, a trans-cyclooctene, a norbornene, an alkene, a thiol, and a tetrazine,
• D1 is selected from a covalent bond, C1-4alkylene or heteroalkylene, C2-4alkenylene, C2-4alkynylene, and C3-8cycloalkylene,
• X1 is S,
• D2 is selected from C1-7alkylene, C2-7alkenylene, C2-7alkynylene, and C3-8cycloalkylene,
• D3 is a covalent bond, or C1-3alkylene, and
• X3 is NH,
• wherein the peptide exhibits the activity of binding to human immunoglobulin G (IgG), and
• wherein the cysteine residue adjacent to the N-terminus of formula 6-3 and the cysteine residue adjacent to the C-terminus of formula 6-3 are optionally linked.