Inhibitors of amyloid beta-protein production

A method of protecting a warm-blooded mammal from the progression of Alzheimer's disease, which comprises administering an effective amount of a compound of general formula. I in which: R1 represents an optionally substituted aromatic or heteroaromatic group; L1 and L2 each independently represents a bond or an unbranched (1-4C) alkylene group, which alkylene group may optionally bear a (1-4C) alkyl, phenyl or phenyl (1-2C) alkyl substituent; one of Y1 and Y2 represents NR3 and the other represents O, S or NR3, in which R3 represent hydrogen, hydroxyl, (1-4C) alkoxy, (1-4C) alkyl or di (1-4C) alkylamino; Z represents O or S; and R2 represents (3-8C) cycloalkyl, heterocyclyl, and optionally substituted aromatic or heteroaromatic group, or together with L2, (1-10C) alkyl; or a pharmaceutically acceptable salt thereof.