Abstract: The influence of the anomeric effect on bicyclic organophosphates could be shown for the first time by means of X-ray analysis. In the course of our syntheses of bicyclic organophosphates as inhibitors of acetylcholinesterase we have been able to crystallize a series of four isomeric compounds: (±)-7-aza-7-benzyl-3-fluoro-2,4-dioxa-3l5- phosphabicyclo[4.4.0]decan-3-ones (±)-1ax,eq and (±)-2ax,eq, cis- and trans-decaline-type congeners with the Fsubstituent in the axial and equatorial position. The syntheses of the mentioned and of some related compounds as well as their inhibitory effects on acetylcholinesterase are described on a separate Poster A0047