Patent ID: 8475768

Claim:
Compound of formula (I): wherein R 1 is H, NO 2 , NH 2 or NHC(═O)R 2 , wherein R 2 is C 1 -C 6 -alkyl, C 6 -C 15 -aryl, C 7 -C 22 -arylalkyl, O—C 1 -C 6 -alkyl, O—C 7 -C 22 -arylalkyl, (CH 2 ) n —(C 6 H 4 )—NCS, (CH 2 ) m —C≡CH or (CH 2 ) m —N 3 wherein n is 0 to 6 and m is 1 to 6; W and the bonds represented as dotted lines are present or absent and when present, W is N; and wherein when W is not present, R 1 is NHC(O)R 2 , wherein R 2 is C 7 -C 22 -arylalkyl, O—C 1 -C 6 -alkyl, O—C 7 -C 22 -arylalkyl, (CH 2 ) n —(C 6 H 4 )—NCS, (CH 2 ) m —C≡CH or (CH 2 ) m —N 3 ; X is a chelator moiety X consisting of a 6-membered aromatic or partially saturated ring system containing up to three heteroatoms selected from nitrogen and oxygen and having a hydroxyl group as a first substituent bound to a first atom in said ring system, and a hydroxyl group or an oxygen atom doubly bound to a second atom in said ring system wherein said first and second atom are adjacent atoms and wherein said first and second substituents are in ring positions such that X is capable of forming a complex with a paramagnetic metal ion; and wherein X is optionally substituted by up to three additional substituents, R, where each R is independently a hydrophilic group which renders the compound of formula (I) soluble in aqueous solutions.