Boosting Bismuth(III) Complexation for Targeted α‐Therapy (TAT) Applications with the Mesocyclic Chelating Agent AAZTA**

Targeted α therapy (TAT) is a promising tool in the of cancer. The radionuclide 213BiIII shows favourable physical properties for this application, but fast and stable chelation metal ion remains challenging. Herein, we demonstrate that mesocyclic chelator AAZTA quickly coordinates BiIII at room temperature, leading to robust complex. A comprehensive study structural, thermodynamic kinetic [Bi(AAZTA)]− reported, along with bifunctional [Bi(AAZTA-C4-COO−)]2− targeted agent [Bi(AAZTA-C4-TATE)]−, which incorporates SSR agonist Tyr3-octreotate. An unexpected increase stability inertness chelate was observed derivative maintained peptide conjugate. cyclotron-produced 205/206Bi mixture used as model 213Bi labelling, stability, biodistribution experiments, allowing efficiency [213Bi(AAZTA-C4-TATE)]− be estimated. High accumulation AR42J tumours reduced kidney uptake were respect macrocyclic [213Bi(DOTA-TATE)]−.