Facile access to 12‐membered macrocyclic ligand PCTA and novel derivatives including carboxylate, amide and phosphinate ligating functionalities.

Claude Picard; Morgane Enel; Nadine Leygue; Nathalie Saffon; Chantal Galaup

Index: 10.1002/ejoc.201800066

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Abstract

We describe a convenient synthetic pathway for the access of the 12‐membered PCTA macrocycle, a polyaminocarboxylate ligand whose M2+ and M3+ complexes are commonly associated with applications in biomedical diagnostic and radiotherapy. The synthetic pathway is based on the use of a linear tri‐N‐alkylated triamine synthon incorporating masked acetate arms and an efficient sodium template ion effect for the crucial macrocyclization step (87 % macrocyclization yield). This approach was then successfully applied to the access of three new PCTA[12] derivatives containing either a 4‐pyridol unit either amide or phosphinate coordinating functions in the central side arm. In all cases macrocyclization reactions are controlled by a sodium template ion effect and display macrocyclization yields in the range 60 ‐ 75 %. The luminescence or relaxometric properties behaviour of Eu(III), Tb(III) or Gd(III) complexes derived from mixed coordinating arms PCTA derivatives are also investigated, making these complexes as possible alternative candidates for PCTA[12]‐Ln(III) complexes.