The present invention relates to a compound of formula (II) chosen from (IIa)and (IIb) or of formula (VI) chosen from (VIa) and (VIb) of following generalformulae: in which: X1, X2, X3, X4 and X5 represent, independently of oneanother, L-Y in which L represents a C1-C3 alkyl group, preferably (CH2)n withn = 1 to 3, Y represents -CONH2, -CO-NR7R8 or -NR7-CO-R8, or an isomer, anenantiomer or a diastereoisomer of these or their mixtures or apharmaceutically acceptable salt of the compounds of formulae (VIa) and (VIb).It also relates to a complex of these compounds with a paramagnetic metal or aradionuclide and their use in diagnostic methods.
