The synthesis and characterization of manganese (II) complexes of cyclen-based macrocycles such as H4DOTA and DOTAM has been of recent interest due to the insights they can provide into the design of MRI and paraCEST contrast agents. The 1H and 17O relaxivities of Mn(H2DOTA), for example, exhibit a strong pH dependence due to the protonation/deprotonation of the carboxylate pendant arms and decomplexation of the ligand at low pH. In contrast, [Mn(DOTAM)]2+ has considerably greater stability but has a very low pH relaxivity which is nearly pH independent. It is of interest to incorporate features of both of these complexes into one compound. The synthesis of a new mixed-functionality ligand, 1,7-bis(acetate)-4,10-bis(acetamide)-1,4,7,10-tetraazacyclododecane (DO2A2AM), with both carboxylate and amide pendant arms has been achieved. The stability of the Mn(II) complex is pH-dependent as are the 1H and 17O relaxivities. Comparisons of the new complex with Mn(H2DOTA), [Mn(DOTAM)]2+ and complexes of the analogous disubsitituted cyclens (H2DO2A and DO2AM) yield insights into the correlation of structure with relaxivity properties in this series of compounds.

Mn(II) complex of a new mixed pendant arm cyclen-based ligand: A correlation between chemical structure and relaxivity

251st National Meeting (2016)

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