Z-(-,-)-[⁷⁶Br]BrQNP: A high affinity PET radiotracer for central and cardiac muscarinic receptors

Racemic E-1-azabicyclo[2.2.2]oct-3-yl α-(1-bromo-1-1-propen-3-yl)-α-hydroxy-α-phenylacetate (BrQNP) was prepared and evaluated in vivo as a potential candidate for imaging muscarinic acetylcholinergic receptors by Positron Emission Tomography. Initial in vivo blocking studies utilizing Z-(-,-)-[¹²⁵I]IQNP as a radiolabelled muscarinic probe demonstrated that a preinjection of cold E-BrQNP effectively blocks the uptake of the radiolabelled probe in the brain and heart, by 71% and 86% respectively. Z-(-,-)-[⁷⁶Br]BrQNP was prepared by electrophilic substitution from a tributylstannyl precursor. Peracetic acid and chloramine T were evaluated as oxidizing agents. After purification by SPE and RP-HPLC, radiolabelling yields of 85% and 95% were obtained with peracetic acid and chloramine T, respectively. The final radiochemical yield was 70% for both oxidizing agents.