# Preparation of Macrobicyclic Cryptands for Radiometal Complexation: Preparation of Macropa‐Based Cryptands for Efficient Complexation of Radiometals

## TL;DR

Researchers synthesized new macrobicyclic cryptands and tested their ability to bind radiometals, which could be useful in radiopharmaceutical applications.

## Contribution

The development of a two-step synthesis for functionalized macrobicyclic cryptands and their evaluation for radiometal complexation.

## Key findings

- Four new macrobicyclic cryptands were synthesized and characterized.
- The cryptands showed log K complexation values between 1.4 and 4.0 with various metal ions.
- Successful radiolabeling with radiopharmaceutically relevant cations was achieved.

## Abstract

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.

Four macrobicyclic cryptands with pendant side arms were synthesized und their ability to coordinate (radio)metals of interest was tested by 1H NMR and radiolabeling.