Compounds useful for lowering beta amyloid levels are provided. The compounds have the structure of formula Ia: wherein, R1 is lower alkyl, substituted lower alkyl, phenyl, substituted phenyl, benzyl, substituted benzyl, benzyloxy, substituted benzyloxy, or SO2R5; R5 is phenyl, substituted phenyl, heterocycle, substituted heterocycle, alkyl, or substituted alkyl; R2 is lower alkyl, substituted lower alkyl, CF3, alkenyl, substituted alkenyl, alkynyl, substituted alkynyl, phenyl, substituted phenyl, or cycloalkyl; R3 is hydrogen, lower alkyl, or substituted lower alkyl; R4 is phenyl, substituted phenyl, heterocycle, substituted heterocycle, thiophene, or substituted thiophene; R6 is hydrogen, lower alkyl, substituted lower alkyl, CF3, alkenyl, substituted alkenyl, alkynyl, substituted alkynyl, phenyl, substituted phenyl, cycloalkyl, or substituted cycloalkyl; W, X and Y are independently CR7 or N; and R7 is hydrogen, halogen, lower alkyl, or substituted lower alkyl.