Still more preferably, A and B are C.sub.1-C.sub.4 alkyl and D is H or methylDisclosed is a method of treating a patient who has, or in preventing a patient from getting, a disease or condition selected from the group consisting of Alzheimer's disease, for helping prevent or delay the onset of Alzheimer's disease, fortreating patients with mild cognitive impairment (MCI) and/or preventing or delay