Disclosed are compounds of formula: ##STR00001## and pharmaceutically acceptable salts and esters thereof, useful in treating and/or preventing Alzheimer's disease and other similar diseases, wherein R.sub.N, R.sub.C, R.sub.1, n and R.sub.20 are defined herein. These compounds include inhibitors of the beta-secretase enzyme that are useful in the treatment of Alzheimer's disease and other diseases characterized by deposition of A beta peptide in a mammal. The compounds of the invention are useful in pharmaceutical compositions and methods of treatment to reduce A beta peptide formation.