PE859 is a novel, orally active tau aggregation inhibitor that inhibits the heparin-induced aggregation of both 3RMBD and full length tau with IC50 of 0.81 uM and 2.23 uM, respectively; also inhibits amyloid β (Aβ) aggregation with IC50 of 1.2 uM; significantly reduces sarkosyl-insoluble aggregated tau along with the prevention of onset and progression of the motor dysfunction in JNPL3 P301L-mutated human tau transgenic mice.