The invention relates to malonamide derivatives of formula (I), wherein: R1 is one of the following groups (Formulae a), b), c), d)); R2 is lower alkyl, lower alkinyl, -(CH2)n-O-lower alkyl, -(CH2)n-S-lower alkyl, -(CH2)n-CN, -(CR'R')n-CF3, -(CR'R')n-CHF2, -(CR'R')n-CH2F, -(CH2)n-C(O)O-lower alkyl, -(CH2)n-halogen, or is -(CH2)n-cycloalkyl, optionally substituted by one or more substituents, selected from the group consisting of phenyl, halogen or CF3; R',R' are independently from n and from each other hydrogen, lower alkyl, lower alkoxy, halogen or hydroxy; R3, R4 are independently from each other hydrogen, lower alkyl, lower alkoxy, phenyl or halogen; R5 is hydrogen, lower alkyl, -(CH2)n-CF3 or -(CH2)n-cycloalkyl; R6 is hydrogen or halogen; R7 is hydrogen or lower alkyl; R8 is hydrogen, lower alkyl, lower alkinyl, -(CH2)n-CF3,-(CH2)n-cycloalkyl or -(CH2)n-phenyl, optionally substituted by halogen; R9 is hydrogen, lower alkyl, -C(O)H, -C(O)-lower alkyl, -C(O)-CF3,-C(O)-CH2F,-C(O)-CHF2,-C(O)-cycloalkyl,-C(O)-(CH2)n-O-lower alkyl,-C(O)O-(CH2)n-cycloalkyl, -C(O)-phenyl, optionally substituted by one or more substituents selected from the group consisting of halogen or -C(O)O-lower alkyl, or is -S(O)2-lower alkyl, -S(O)2-CF3,-(CH2)n-cycloalkyl or is -(CH2)n-phenyl, optionally substituted by halogen; n is 0, 1, 2, 3 or 4; and to pharmaceutically suitable acid addition salts, optically pure enantiomers, racemates or diastereomeric mixture thereof. These compounds may be used for the treatment of Alzheimer's disease.