Synthesis and biological evaluation of novel oxindole derivatives for imaging neurofibrillary tangles in Alzheimer's disease.

This letter describes the synthesis and biological evaluation of a novel series of radioiodinated oxindole (OI) derivatives for detecting neurofibrillary tangles (NFTs) in the brains of patients with Alzheimer's disease (AD). In binding experiments in vitro, 2-oxindole (2-OI) and 3-oxindole (3-OI) derivatives showed affinity for tau aggregates. The 3-OI derivative 14 showed the highest affinity of these derivatives. In biodistribution experiments using normal mice, the OI derivatives displayed good uptake (2.4-2.5%ID/g at 2 min) and clearance from the brain with time (0.6-1.4%ID/g at 30 min). In fluorescence staining experiments using AD brain sections, 14 clearly stained NFTs. 3-OI may serve as a new molecular scaffold for developing novel NFT imaging agents.