Organization of amino acids using a metallotriazacyclononane template

The metal-binding chelator 1,4,7-triazacyclononane (1) has been alkylated at all three nitrogens with bromoacetylated L-phenylalanine, BrCH2CONHCH(CH(2)Ph)CO(2)Me, to give a new hexadentate ligand (2). This reacts with metal ions (M = Cu2+, Zn2+) to give the coordination complexes M(2)(2+). An X-ray crystal structure of 3a, [Cu(2)][CuCl4], reveals that one copper is chelated to three triazacyclononane nitrogen atoms and three oxygen, rather than nitrogen, amide donor atoms derived from the bromoacetyl substituents. Metal coordination brings all three amino acids together and orientates their main chains in the same direction. Such organization illustrates how N-capping of peptides with a metallotriazacyclononane can assist folding and assembly of peptides, perhaps facilitating association into three helix bundles.