The condensation of 2-bromo-N,N-bis(benzyloxycarbonylmethyl)acetamide (I) with N,N'-bis(2-hydroxyethyl)ethylene-1,2-diamine (II) by means of TEA in DMF gives the corresponding bis-adduct (III). The monoacylation of (III) with butyryl chloride (IV) and DMAP in THF yields the monobutyrate (V), which is acylated with acetyl chloride (VI) and DMAP in THF affording the mixed diester monoacetate monobutyrate (VII). The deprotection of (VII) by hydrogenation with H2 over Pd/C in ethanol provides the tetraacetic acid (VIII), which is finally treated with gadolinium trichloride and NaOH to furnish the target compound.