Vol. 281, Issue 2, 895-904, 1997

Pyrrolopyrimidines: Novel Brain-Penetrating Antioxidants with Neuroprotective Activity in Brain Injury and Ischemia Models

E. D. Hall, P. K. Andrus, S. L. Smith, T. J. Fleck, H. M. Scherch, B. S. Lutzke, G. A. Sawada, J. S. Althaus, P. F. Vonvoigtlander, G. E. Padbury, P.G. Larson, J. R. Palmer and G. L. Bundy

CNS Diseases Research (E.D.H., P.K.A., S.L.S., T.J.F., H.M.S., B.S.L., J.S.A., P.F.V.), Drug Delivery Systems Research (G.A.S.), Drug Metabolism Research (G.E.P., P.G.L.) and Medicinal Chemistry Research (J.R.P., G.L.B.), Pharmacia & Upjohn, Inc., Kalamazoo, Michigan

A novel group of antioxidant compounds, the pyrrolopyrimidines, has been discovered recently. Many of these possess significantly improved oral bioavailability (56-70% in rats), increased efficacy and potency in protecting cultured neurons against iron-induced lipid peroxidative injury and as much as a 5-fold increase in brain uptake compared with the 21-aminosteroid antioxidant compound, tirilazad mesylate (U-74006F), described earlier. They appear to quench lipid peroxidation reactions by electron-donating and/or radical-trapping mechanisms. Several compounds in the series, such as U-101033E and U-104067F, demonstrate greater ability than tirilazad to protect the hippocampal CA1 region in the gerbil transient (5-min) forebrain ischemia model. Delaying treatment until 4 hr after the ischemic insult still results in significant CA1 neuronal protection. U-101033E is still effective in salvaging a portion of the CA1 neuronal population when the ischemic duration is extended to 10 min. In addition, U-101033E has been found to be protective in the context of focal cerebral ischemia, reducing infarct size in the mouse permanent middle cerebral artery occlusion model, in contrast to tirilazad which is minimally effective. These results suggest that antioxidant compounds with improved brain parenchymal penetration are better able to limit certain types of ischemic brain damage than those which are localized in the cerebral microvasculature. However, the activity of U-101033E in improving early post-traumatic recovery in mice subjected to severe concussive head injury is similar to that of tirilazad. Last, the oral bioavailability of many pyrrolopyrimidines suggests that they may be useful for certain chronic neurodegenerative disorders in which lipid peroxidation plays a role.