A pharmaceutical preparation comprising {circle around (−)}A2-73 substantially free of ⊕A2-73. This invention further includes a method treating Alzeheimer's disease in a subject in need of such treatment by the method of administering a therapeutically effective amount of {circle around (−)}A2-73 substantially free of ⊕A2-73.This invention yet further includes a method of classifying cells as to sigma receptor type by the method of exposing said cells to a detectable amount of {circle around (−)}A2-73 substantially free of ⊕A2-73 and determining the level of sigma receptor binding
