This invention relates to novel compounds of the class of succinoyl lactams, such as diazepinee of Formula (Id), or a pharmaceutically acceptable salt thereof, as described above, having drug and bio-affecting properties. These novel compounds inhibit the processing of amyloid precursor protein and, more specifically, inhibit the production of Aβ-peptide, thereby acting to prevent the formation of neurological deposits of amyloid protein. More particularly, the present invention relates to the treatment of Alzheimer's disease.