1. A method for reducing cerebral amyloid load and toxic Ab dimer level in a subject in need thereof, comprising orally administering to said subject a therapeutically effective amount of a compound of the formula wherein, R 1 , R 2 , and R 3 are independently selected from substituted or unsubstituted alkyl and substituted or unsubstituted heteroalkyl; and R 4 is substituted or unsubstituted aryl or substituted or unsubstituted heteroaryl, wherein R 4 is other than adenine joined to the remainder of the compound through an endocyclic nitrogen atom of said adenine, wherein said therapeutically effective amount is sufficient to achieve therapeutic brain concentration of said compound and reduce cerebral amyloid load and toxic Aβ dimer level, and said compound protects MC65 neuroblastoma cells from death caused by Aβ in a medium-throughput cell-based MC65 protection assay.