The invention provides compounds of Formula I: ##STR00001## wherein R.sup.1, R.sup.2, R.sup.3, R.sup.4, R.sup.6, R.sup.7, R.sup.8, and A are as defined. Compounds of formula I have activity inhibiting production of A.beta.-peptide. The invention also provides pharmaceutical compositions and methods for treating diseases, for example Alzheimer's disease, in mammals comprising compounds of Formula I.