Macrocyclic polyaminocarboxylates based on cyclen and triazacyclononane are ubiquitous chelates for metal ions across the periodic table with applications ranging from quantitative analysis to biological imaging and radiotherapy. This includes late first-row transition metals; however, their cavity size, charge, and high denticity can lead to significant differences in the kinetic stability of these complexes. Recently, we reported the selective N,N-spirocycle of tetraazacyclododecane-1,4,7-triacetic acid (DO3A) using simple dibromo alkyl reagents (DO3AC4H8). This zwitterionic chelator can form neutral CuII species which can serve as models for N-protonated intermediates relevant to Cu-based radiopharmaceuticals. In this talk, we will share the synthesis and characterization of this chelate to late, divalent first-row transition metals (CoII, NiII, CuII, ZnII). These complexes have been characterized by a suite of physical inorganic techniques (SC-XRD, NMR, and EPR spectroscopy), and support distinct coordination and macrocyclic preferences across the series. The impact of charge effects and spirocycle identity will be discussed, and key structure-property relationships with respect to other macrocyclic polyaminocarboxylates will be highlighted.

Cyclen-based N,N-alkylated spirocyclic chelates for late first-row transition metals

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