Preparation of Macrobicyclic Cryptands for Radiometal Complexation

Macrobicyclic cryptands and especially derivatives with functionalized side arms (picolinate, pyrimidine carboxylate, and bipyridine carboxylate) are able to complex metal ions effectively. In this regard, four new functionalized cryptands were prepared in a convenient two-step synthesis procedure starting from basic compound 4,10,16,22,27-pentaoxa-1,7,13,19-tetraazabicyclo[11.11.5]nonacosane and fully characterized. Their complexation behavior was tested via ¹H NMR titration with Ba²⁺, Sc³⁺, La³⁺, Lu³⁺, In³⁺, and Pb²⁺ pointing out log K values between 1.4 and 4.0. Radiolabeling with selected cations of radiopharmaceutical relevance (¹³¹Ba, ²²⁵Ac, and ¹³³La) was performed.