A new hexaazamacrobicyclic cage ligand, 1-N-(4-aminobenzyl)- 3,6,10,13,16,19-hexaazabicyclo[6.6.6]eicosane-1,8-diamine (SarAr) has been designed for conjugation to proteins. SarAr was synthesised and characterised by microanalyses, 1 H NMR and electrospray mass spectrometry. The complexation of selected transition metal ions (Cu(), Ni() and Co() at 10 Ϫ6 M) by SarAr was complete within 30 min over pH 6 to 8. The [ 64 Cu(SarAr)] 2ϩ complex was investigated with a view to applications in radioimaging. The [ 64 Cu(sar)] 2ϩ complex was found to be stable in human plasma for at least 174 h and biodistribution studies in mice, showed that the [ 64 Cu(SarAr)] 2ϩ complex was rapidly excreted through the renal system unlike the free 64 Cu 2ϩ . Overall, the simple synthesis, ready complexation behaviour of SarAr, the kinetic inertness of the [Cu(SarAr)] 2ϩ complex to dissociation of 64 Cu and its facile elimination from mice make it an attractive prospect for use in nuclear medicine.

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The synthesis of macrocyclic ligands that contain appended side chains incorporating potentially reactive donor functions has been of recent interest. The bifunctional nature of these ligands, with one site possessing a high affinity for the metal ion and a second site with a chemically reactive group suitable for further elaboration, has found many applications in the attachment of the ligands to polymers and biomolecules.2'18 There are, however,

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The binuclear octahedral MI1 complexes, incorporating the new 10 coordinate pendant arm ligand LH4,t all show an anti-configuration; in contrast the Cull complex [Cu,(LH2)]2+ adopts a syn-configuration incorporating intramolecular H-bonding.