Investigations of acetonitrile solvent cluster formation in supercritical carbon dioxide, and its impact on microscale syntheses of carbon-11-labeledradiotracers for PET

A new strategy has been developed for synthesizing positron emission tomogr aphy (PET) radiotracers using [C-11]methyl iodide. This strategy relies on the ability of organic co-solvents to cluster within mixtures of supercriti cal fluids resulting in localized regions of high density which can serve a s microscopic pockets for reaction. We've shown that acetonitrile will clus ter about dilute solutes when mixtures of this co-solvent with carbon dioxi de are forced to behave as a homogeneous fluid at the critical point. We ap plied this strategy in a systematic investigation of the conditions for opt imized reaction between methyl iodide and L-alpha-methyl-N-2-propynyl phene thylamine (nordeprenyl) to yield L-deprenyl. Variables such as temperature, ultraviolet light exposure, co-solvent concentration, system pressure, and methyl iodide concentration were explored. The synthesis of radioactive [C -11]-L-deprenyl using no carrier added concen trations of [C-11]methyl iodi de was also tested. Results showed that greater than 90% radiochemical yiel d of the desired product could be attained using 40 times less labeling sub strate than in conventional PET tracer syntheses. NUCL MED BIOL 26;4:443-41 54, 1999. (C) 1999 Elsevier Science Inc. All rights reserved.