| CPC A61K 49/0032 (2013.01) [A61B 5/201 (2013.01); A61K 49/0039 (2013.01); G01N 33/533 (2013.01); G01N 33/583 (2013.01); G01N 2800/347 (2013.01)] | 10 Claims | 
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               1. A compound of formula I: 
              (X)a—Y—(Z)b  I 
              where: 
              X is selected from: 
              ![]() ![]() ![]() ![]() where R1 represents a biomarker reactive moiety conjugated to a self-immolative moiety 
              ![]() wherein the self-immolative moiety is selected from: 
              ![]() where the heteroatom directly bonded to the aromatic ring represents the point of attachment to Y and the other heteroatoms represent the point of attachment to a biomarker reactive moiety or are H, provided that at least one of the other heteroatoms is attached to a biomarker reactive moiety; 
              R2 represents a point of attachment to Y and R2′ represents another point of attachment to the same Y group or a point of attachment to a second Y group; 
                R3 represents H, SO3H or COOH; 
                Z is selected from: 
              ![]() R4 is selected from: 
              ![]() where the wavy line represents the point of attachment to the rest of the molecule; 
                R4′ represents the point of attachment to Y; 
                each Y is selected from: 
              ![]() where the wavy line represents the point of attachment to X or Z, 
              ![]() where the wavy line represents the point of attachment to X or Z, 
              ![]() where each R5 is independently selected from H, CH2CHOHCH3, CH2CCH, and 
              ![]() where the left-hand wavy line (adjacent to m) represents the point of attachment to X or Z and the right-hand wavy line represents the point of attachment to the rest of the molecule; 
              a is 0 or 1 and b is 1, provided that: 
                at least one of a and b is 1; and 
                when a and b are both 1, Y is selected from: 
              ![]() or pharmaceutically acceptable salts and/or solvates thereof, provided that when X is 
              ![]() then Z is 0. 
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