Alkanolammonium Protic Ionic Liquids for Low Temperature 68 Ga‐Radiolabeling of DOTA‐Functionalized Compounds

Nowadays, the radiolabeling of small biomolecules with isotope 68 Ga is one of the important directions in the field of Positron‐Emission Tomography (PET). The right choice of buffer for reaction helps to achieve optimal conditions for higher yields. Earlier, we found that protic ionic liquids based on tris(2‐hydroxyethyl)ammonium and tris(hydroxymethyl)methyl ammonium salts are suitable buffers for the chelation of the 68 Ga to the PSMA‐HBED‐CC (a peptide with an acyclic chelator). Herein we describe the labeling of p ‐SCN‐Bn‐DOTA (DOTA=1,4,7,10‐tetraazacyclododecane‐1,4,7,10‐tetraacetic acid) chelator and peptides (DOTA‐NOC, DOTA‐TATE, and PSMA‐617) with gallium‐68 isotope in media of alkanolammonium buffers based on tris(2‐hydroxyethyl)ammonium (TEA), tris(hydroxymethyl)methyl ammonium (TRIS) and N‐phenyl‐bis(2‐hydroxyethyl)ammonium (PDA) salts. Besides, for the first time, we present results of low‐temperature 68 Ga‐complexation in the presence of organic solvents additives. An essential consequence of this study is that for the series of alkanolammonium buffers, high radiochemical conversions were achieved upon incubation of reaction media under 37 °C.