Compounds capable of binding to proteins and conjugates obtained from these compounds

A compound of formula (II):

• wherein:
• the attachment head is a compound of formula (I), formula (Ia), or formula (Ib):
• wherein:
• each A is the residue of a pyridyl;
• each X is a halogen;
• each Y is selected from a direct bond, —CO—, and —NH—;
• X1 is
• W is —CONR3R4 or —NR3COR4;
• each Z is independently a direct bond, —CH2—, —O—, —S—, —CO—, —NH—, or —C(═NR1)—;
• and m, n and p are each, independently of one another, an integer in the range from 0 to 8;
• R3 is —H or —(C1-C6)alkyl or —(CH2)u—SO3H;
• R4 is —(CH2CH2O)qR5, —(CRcRd)rR5, —(CRcRd)r—NHCO—(CH2CH2O)q—R5, —(CRcRd)r—CONH—(CH2CH2O)q—R5, —(CH2CH2O)q—(CH2)r—NHCO—(CRcRd)r—R5, —(CH2CH2O)q—(CH2)r—CONH—(CRcRd)r—R5, —CH—[(CRcRd)r—CONH—(CRcRd)r—(OCH2CH2)q—R5]2, —CH—[(CRcRd)r—NHCO—(CRcRd)r—(OCH2CH2)q—R5]2, —CH—[(CRcRd)r—CONH—(CRcRd)rR5]2, or —CH—[(CRcRd)r—NHCO—(CRcRd)r—R5]2;
• R5 is —(CH2)sR6 or —(CH2)sR7;
• R6 is —COOR8, —COSR8, —CONR8R9, or —NR8COR9;
• R7 is selected from:
• Rc is —H;
• each Rd is —H, —SO3H, or —CH2—SO3H;
• R8 is —H or —(C1-C6)alkyl;
• R9 is —H or —(C1-C6)alkyl;
• each q is an integer in the range from 1 to 24;
• each r is an integer in the range from 1 to 8;
• each s is an integer in the range from 0 to 6;
• each u is an integer in the range from 1 to 6;
• the binding arm is a direct bond;
• an amino acid residue;
• or a peptide residue;
• the spacer is a direct bond or a group of formula:
• M is a molecule of interest.