Synthesis and evaluation of novel benzothiazole derivatives based on the bithiophene structure as potential radiotracers for beta-amyloid plaques in Alzheimer's disease.

In this study, six novel benzothiazole derivatives based on the bithiophene structure were developed as potential beta-amyloid probes. In vitro binding studies using Abeta aggregates showed that all of them demonstrated high binding affinities with K(i) values ranged from 0.11 to 4.64nM. In vitro fluorescent staining results showed that these compounds can intensely stained Abeta plaques within brain sections of APP/PS1 transgenic mice, animal model for AD. Two radioiodinated compounds [(125)I]-2-(5'-iodo-2,2'-bithiophen-5-yl)-6-methoxybenzo[d]thiazole [(125)I]10 and [(125)I]-2-(2,2'-bithiophen-5-yl)-6-iodobenzo[d]thiazole [(125)I]13 were successfully prepared through an iododestannylation reaction. Furthermore, in vitro autoradiography of the AD model mice brain sections showed that both [(125)I]10 and [(125)I]13 labeled the Abeta plaques specifically with low background. In vivo biodistribution studies in normal mice indicated that [(125)I]13 exhibited high brain uptake (3.42% ID/g at 2min) and rapid clearance from the brain (0.53% ID/g at 60min), while [(125)I]10 showed lower brain uptake (0.87% ID/g at 2min). In conclusion, these preliminary results of this study suggest that the novel radioiodinated benzothiazole derivative [(125)I]13 may be a candidate as an in vivo imaging agent for detecting beta-amyloid plaques in the brain of AD patients.