There is provided a series of novel substituted gamma-lactams of Formula (I)
or a stereoisomer; or a pharmaceutically acceptable salt thereof, wherein R
1
, R
2
, R
4
, R
5
and R
6
as defined herein, their pharmaceutical compositions and methods of use. These novel compounds inhibit the processing of amyloid precursor protein (APP) by β-secretase and, more specifically, inhibit the production of Aβ-peptide. The present disclosure is directed to compounds useful in the treatment of neurological disorders related to β-amyloid production, such as Alzheimer's disease and other conditions affected by anti-amyloid activity.