Disclosed are substituted heterocyclic compounds of formula (I) and pharmaceutically acceptable salts thereof, which may be suitable for imaging tau aggregates, b-sheet aggregates, beta-
amyloid aggregates or alpha-
synuclein aggregates, and hence are useful in binding and imaging tau aggregates in Alzheimer's patients. More specifically, this invention relates to a method of using the compounds of formula (I) as tracers in
positron emission
tomography (PET) imaging to study tau deposits in brain
in vivo to allow diagnosis of Alzheimer's
disease and other neurodegenerative diseases characterized by
tau pathology. The disclosure further relates to a method of measuring
clinical efficacy of therapeutic agents for Alzheimer's
disease and other neurodegenerative diseases characterized by
tau pathology.