MAPT and Alzheimer disease: In an effort to develop a more potentand effective 4R-tau PET tracer, [18F]5 ([18F]CBD-2115, [18F]OXD-2115) (Figure 1) was developed, but it suffered from lowbrain entry as shown by PET studies in mouse, rat, and nonhuman primate.44 Structural modifications of 5 resultedin the identification of [18F]6 ([18F]OXD-2314), which demonstrated improved brain entry in rat and nonhumanprimate PET imaging studies and high binding affinity in AD, PSP,CBD, and PiD post-mortem brain tissue homogenate assays.45