The Influence of Amino Group Position on Aryl Moiety of SarAr on Metal Complexation and Protein Labelling

New hexaazamacrobicyclic cage bi-functional chelators (BFCs), 1-N-(3-aminobenzyl)-3,6,10,13,16,19-hexaazabicyclo[6.6.6]eicosane-1,8-diamine (m-SarAr) and 1-N-(2-aminobenzyl)-3,6,10,13,16,19-hexaazabicyclo[6.6.6] eicosane-1,8diamine (o-SarAr), were synthesised. Their complexation with selected transitions metal ions i.e. Cu-II, Co-II, and Cd-II was investigated over a range of pH at micromolar concentrations. Cu-II was complexed by m-SarAr and o-SarAr rapidly within 5 min in pH range of 5-9 at ambient temperature. In contrast, the complexation of Co-II and Cd-II by these ligands was slower. The conjugation efficiencies of p-SarAr, m-SarAr, and o-SarAr to bovine serum albumin (BSA) were compared under various reactions. Conditions were optimised to a molar ratio of BSA/N-(3-dimethylaminopropyl)-N'-ethylcarbodiimide (EDC)/BFC of 1 : 250 : 50 in pH 5 buffer for 30 min at ambient temperature. Under these conditions, the average number of p-SarAr, m-SarAr, or o-SarAr attached to BSA were determined to be 2.21 +/- 0.16, 4.90 x 10(-1) +/- 2.48 x 10(-2), and 2.67 x 10(-2) +/- 2.67 x 10(-3), respectively. This fundamental study clearly demonstrates that the position of the amine on the phenyl ring has a significant effect on the metal complexation and conjugation reactions with BSA.