Abstract: Disclosed are compounds of formula I: ##STR1## wherein X is selected from oxygen, sulfur and NR; whereinR is selected from hydrogen, loweralkyl and CH.sub.2 CH.sub.2 COAr.sub.1 ; andZ is hydrogen; straight or branched chain alkyl having 1-6 carbon atoms; or Z and R.sub.1, R.sub.2 or R.sub.3 together represent CH.sub.2 ; CH.sub.2 CH.sub.2 ; CH.sub.2 0; or CH.sub.2 S forming a five or six membered ring and such ring may be optionally substituted with loweralkyl or phenyl;R.sub.24 is hydrogen; loweralkyl, or optionally substituted phenyl;each R.sub.10 is selected from hydrogen and loweralkyl; andAr.sub.1 represents an aryl group or optionally substituted phenyl, thienyl or optionally substituted thienyl; or the pharmaceutically acceptable salts thereof, useful for preventing or decreaseing the production of abnormally phosphorylated paired helical filament (PHF) epitopes associated with Alzheimer's Disease and, therefore, useful for treating Alzheimer's Disease.