Disclosed are compounds of formula I or a stereoisomer, tautomer, or pharmaceutically acceptable salt or solvate thereof, U, W, X, R.sup.1, R.sup.2, R.sup.6, R.sup.7, R.sup.30 and R.sup.31 are as described above in the specification. Also disclosed is the method of inhibiting aspartyl protease, and in particular, the methods of treating cardiovascular diseases, cognitive and neurodegenerative diseases. Also disclosed are methods of treating cognitive or neurodegenerative diseases using the compounds of formula I in combination with a cholinesterase inhibitor or a muscarinic m.sub.1 agonist or m.sub.2 antagonist.