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Synthesis, characterization and 11 C‐radiolabeling of aminophenyl benzothiazoles: structural effects on the alkylation of amino group
Author(s) -
Venkatachalam T. K.,
Stimson D. H. R.,
Bhalla R.,
Pierens G. K.,
Reutens D. C.
Publication year - 2014
Publication title -
journal of labelled compounds and radiopharmaceuticals
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.432
H-Index - 47
eISSN - 1099-1344
pISSN - 0362-4803
DOI - 10.1002/jlcr.3216
Subject(s) - chemistry , benzothiazole , steric effects , alkylation , isopropyl , yield (engineering) , thiazole , reactivity (psychology) , ring (chemistry) , stereochemistry , medicinal chemistry , combinatorial chemistry , organic chemistry , catalysis , medicine , materials science , alternative medicine , pathology , metallurgy
Several aminophenyl benzothiazoles were prepared with a view to using them as amyloid binding agents for imaging β‐amyloid in Alzheimer's disease. These precursors were radiolabeled with 11 C‐positron‐emitting radioisotope using an automated synthesizer and selected radiolabeled compounds were further purified by HPLC. Our results demonstrate that changes in structure have a major influence on the radioactive yield and the ease with which the radiolabel can be introduced. Aminophenyl benzothiazoles with an attached isopropyl group resisted dialkylation perhaps due to steric hindrance caused by this group. Straight chain attachment of methyl, ethyl, butyl, and crotyl groups in the structure decreased the radiochemical yield. Notably, the o ‐aminophenyl benzothiazole derivatives were difficult to alkylate despite stringent experimental conditions. This reactivity difference is attributed to the hydrogen bonding characteristics of the o ‐amino group with the nitrogen atom of the thiazole ring.