Helical peptidomimetic compounds as inhibitors of beta-amyloid production are provided. These inhibitors have sequences with lengths from 11 to 16 amino acids, inclusive. These inhibitors potently inhibit intramembrane proteases, notably aspartyl secretases involved in the enzymatic cleavage of amyloid precursor protein (APP) to yield amyloid-.beta.-peptide. Methods are provided for making a medicament containing the compounds and for administering the compounds to treat .beta.-amyloid-associated diseases, notably Alzheimer's disease.