Modified antibody and radioactive metal-labelled antibody

A compound represented by the following formula (II):

• wherein n is 0 or 1, one of R and R2 represents a hydrogen atom and the other represents a group represented by CO(CH2)mN3 where m is an integer 1 to 10,
• to which a polypeptide to be bound to a target molecule is bound, or a salt thereof, wherein
• the polypeptide is a modified IgG-binding peptide comprising:
• an IgG-binding peptide comprising an amino acid sequence represented by the following formula (I) which consists of 13 to 17 amino acid residues,
• and
• a modification linker represented by the following formula (III) that is bound to the N terminus of the IgG-binding peptide,
• (X1-3)-C-(X2)-H-(Xaa1)-G-(Xaa2)-L-V-W-C-(X1-3) (I) (SEQ ID NO:
• 6),
• wherein
• each X independently represents an amino acid residue other than cysteine,
• C represents a cysteine residue,
• H represents a histidine residue,
• Xaa1 represents a lysine residue, a cysteine residue, an aspartic acid residue, a glutamic acid residue, 2-aminosuberic acid, or diaminopropionic acid,
• G represents a glycine residue,
• Xaa2 represents a glutamic acid residue, a glutamine residue, or an asparagine residue,
• L represents a leucine residue,
• V represents a valine residue, and
• W represents a tryptophan residue, and
• the two cysteine residues may be disulfide-bonded or bound to each other via a linker, and the C terminus may be amidated,
• and
• L1-L2-L3 (III)
• wherein
• L1 represents a polyethylene glycol linker bound to the N terminus of the IgG-binding peptide,
• L2 represents an amino acid sequence consisting of 0 or more and 5 or less amino acid residues, and
• L3 represents a group having a DBCO group at the terminus,
• and
• wherein the compound is bound to the polypeptide by a click reaction between the azide group in the formula (II) and the DBCO group in the formula (III).

A compound represented by the following formula (II):

• wherein n is 0 or 1, one of R1 and R2 represents a hydrogen atom and the other represents a group represented by CO(CH2)mN3 where m is an integer 1 to 10,
• to which a polypeptide to be bound to a target molecule is bound, or a salt thereof, wherein
• the polypeptide is an IgG antibody to which a modified IgG-binding peptide is bound, wherein the modified IgG-binding peptide comprises:
• an IgG-binding peptide comprising an amino acid sequence represented by the following formula (I) which consists of 13 to 17 amino acid residues,
• and
• a modification linker represented by the following formula (III) that is bound to the N terminus of the IgG-binding peptide,
• (X1-3)-C-(X2)-H-(Xaa1)-G-(Xaa2)-L-V-W-C-(X1-3) (I) (SEQ ID NO:
• 6),
• wherein
• each X independently represents an amino acid residue other than cysteine,
• C represents a cysteine residue,
• H represents a histidine residue,
• Xaa1 represents a lysine residue, a cysteine residue, an aspartic acid residue, a glutamic acid residue, 2-aminosuberic acid, or diaminopropionic acid,
• G represents a glycine residue,
• Xaa2 represents a glutamic acid residue, a glutamine residue, or an asparagine residue,
• L represents a leucine residue,
• V represents a valine residue, and
• W represents a tryptophan residue, and
• the two cysteine residues may be disulfide-bonded or bound to each other via a linker, and the C terminus may be amidated,
• and
• L1-L2-L3 (III)
• wherein
• L1 represents a polyethylene glycol linker bound to the N terminus of the IgG-binding peptide,
• L2 represents an amino acid sequence consisting of 0 or more and 5 or less amino acid residues, and
• L3 represents a group having a DBCO group at the terminus,
• and
• wherein the compound is bound to the polypeptide by a click reaction between the azide group in the formula (II) and the DBCO group in the formula (III).