Concise and high-yield synthesis of T808 and T808P for radiosynthesis of [18F]-T808, a PET tau tracer for Alzheimer's disease

The authentic standard T808 and its corresponding mesylate precursor T808P were synthesized in six steps using ethyl vinyl ether and trichlorocetyl chloride as starting materials. The overall chemical yields of T808 and T808P were 35% and 52%, respectively. [18F]-T808 was synthesized from T808P by the nucleophilic substitution with K[18F]F/Kryptofix 2.2.2 and isolated by HPLC combined with solid-phase extraction (SPE) purification in 35-45% radiochemical yield with 37-370 GBq/μmol specific activity at end of bombardment (EOB).