Reaction mechanisms of d -[18
F]FAC and l -[18
F]FMAU. Syntheses of d-[18F]FAC (top) and l-[18F]FMAU (bottom). Synthesis protocol of the two tracers differs only in the ribose sugar (a vs. d) and base coupling (b vs. e) precursors. During HPLC purification, only the beta form (shown here) are collected as final products (c and f).