MAPT and Alzheimer disease: Based on previous studies in which the phenyldiazenyl benzothiazole (PDB) derivative 4-[2-(5-methoxy-2-benzothiazolyl)diazenyl]-N,N-dimethyl-benzenamine (33) (Figure 26) had a good ability to distinguish tau aggregates from Aβ aggregates [45], Matsumura et al. reported the synthesis and biological evaluation of novel PDB derivatives (33a–c) (Figure 26) as probes for imaging NFTs in patients with AD [46].