A cell-permeable, water-soluble, potent inhibitor of poly(ADP-ribose) polymerase (PARP; EC50 = 20 nM). Shown to be about 10,000 times more potent than the prototypical PARP inhibitor, 3-Aminobenzamide (Cat. No. 165350; EC50 = 200 µM). Does not act as an antioxidant at higher concentrations (1 µM to 10 mM). Exhibits neuroprotection in in vivo and in vitro models of stroke.