Abstract: Disclosed are CEST paramagnetic agents comprising a substrate (SH) containing mobile protons bonded to a para-magnetic chelate (SR) containing a metal selected from iron (11) (high-spin configuration), iron (111), cobalt (11), rhodium (11), copper (11), nickel (11), cerium (111), praseodymium (111), neodymium (111), dysprosium (111), erbium (111), terbium (111), holmium (111), thulium (III), ytterbium (III) and europium (111).

Abstract: Compounds of general formula (I): in which: R1 through R5 are as defined in the specification FG, which can be the same or different, are carboxy, —PO3H2 or —RP(O)OH groups, wherein R is hydrogen, or an optionally substituted group selected from C1-C20 alkyl, C3-C10 cycloalkyl, C4-C20 cycloalkylalkyl, aryl, arylalkyl, a group bearing an acidic moiety, and a group bearing an amino moiety, each of which may be further optionally substituted with functional groups which allow conjugation with a suitable molecule able to interact with physiological systems; and their chelates with bi-trivalent ions of the metal elements having atomic number ranging between 20 and 31, 39, 42, 43, 44, 49, and between 57 and 83, and radioisotopes chosen among 203Pb, 67Ga, 68Ga, 72As, 111In, 113In, 90Y, 97Ru, 62Cu, 64Cu, 52Fe, 52mMn, 140La, 175Yb, 153Sm, 166Ho, 149Pm, 177Lu, 142Pr, 159Gd, 212Bi, 47Sc, 149Pm, 67Cu, 111Ag, 199Au, 161Tb, 51Cr, 167Tm, 141Ce, 168Yb, 88Y, 165Dy, 166Dy, 97Ru, 103Ru, 186Re, 188Re, 99mTc, 211Bi, 212Bi,