Compound for treating Alzheimer's disease

A method of improving cognitive function in Alzheimer's disease or Down's syndrome, or slowing the progression of Alzheimer's disease or Down's syndrome, comprising administering an effective amount of a compound of formula I or a pharmaceutically acceptable salt thereof:

• wherein,
• X is independently selected from O or NH;
• each A ring and B ring is independently a benzene ring;
• R1 is independently selected from a hydrogen, deuterium, halogen, cyano, (C1-C6)alkyl, (C1-C6)alkyl substituted with one or more substituents selected from halogen, nitro, amino, or hydroxy, (C1-C6)alkoxy, or (C1-C6)alkoxy substituted with one or more substituents selected from halogen, nitro, amino, or hydroxy;
• m is 0, 1, 2, 3, 4 or 5;
• R2 is independently selected from a hydrogen, halogen, (C1-C6)alkyl, (C1-C6)alkyl substituted with one or more substituents selected from halogen, nitro, amino, or hydroxy, (C2-C6)alkenyl, (C2-C6)alkenyl substituted with one or more substituents selected from halogen, nitro, amino, or hydroxy, (C2-C6)alkynyl, (C2-C6)alkynyl substituted with one or more substituents selected from halogen, nitro, amino, or hydroxy, (C1-C6)alkoxy, or (C1-C6)alkoxy substituted with one or more substituents selected from halogen, nitro, amino, or hydroxy;
• n is 1 or 2;
• R3 is a formyl (—CHO) group, alkanoyl (R—C(O)—) group,
• wherein each R3a, R3b, R3c is independently selected from a hydrogen, (C1-C6)alkyl, (C1-C6)alkyl substituted with one or more substituents selected from halogen, nitro, amino, or hydroxy, (C2-C6)alkenyl, (C2-C6)alkenyl substituted with one or more substituents selected from halogen, nitro, amino, or hydroxy, (C2-C6)alkynyl, (C2-C6)alkynyl substituted with one or more substituents selected from halogen, nitro, amino, or hydroxy, or
• and p is an integer of 1-3.