The present invention relates to compounds of the Formula ##STR00001## wherein R.sup.1, R.sup.1a, R.sup.1b, R.sup.2, R.sup.3, R.sup.4, R.sup.5, R.sup.6, R.sup.7, R.sup.8, R.sup.9, R.sup.10, R.sup.11, R.sup.12, X, Y, Z and n are as defined. Compounds of the Formula I have activity inhibiting production of A.beta.-peptide. This invention also relates to pharmaceutical compositions and methods of treating diseases, for example, neurodegenerative diseases, e.g., Alzheimer's disease, in a mammal comprising compounds of the Formula I.