Methods for the synthesis of each of the four stereoisomers of 6-(3propylthio-1,2,5-thiadiazol-4-yl)-1-azabicyclo[3.2.1]octane (10, 11, 12, and 13) and 3-(3-propylthio-1,2,5-thiadiazol-4-yl)-1-azabicyclo[2.2.1]heptane (18, 19, 20, and 21), and the two stereoisomers of 3-(3-propylthio-1,2,5-thiadiazol-4-yl)-1-azabicyclo[2.2.2]octane (27 and 28) were developed. The relative configuration of the compounds was determined on the basis of previously described 1 H NOE experiments, and the absolute configuration of 6-(3-propylthio-1,2,5-thiadiazol-4-yl)-1-azabicyclo[3.2.1]octanes (10, 11, 12, and 13) and 3-(3-propylthio-1,2,5-thiadiazol-4-yl)-1-azabicyclo[2.2.2]octane (27 and 28) was determined by single crystal X-ray crystallography. Optical purity was determined by capillary electrophoresis (CE) using chiral selectors as trimethyl-cyclodextrin and heparin dissolved in the running buffer. All the 3-(3-propylthio-1,2,5thiadiazol-4-yl)-1-azabicycles had low nanomolar affinity for muscarinic receptors as determined by displacement of radiolabelled oxotremorine-M ( 3 H-Oxo-M) and pirenzepine ( 3 H-Pz) from cortical rat brain homogenates. The binding assay discriminated between diastereomers, but only a minor degree of enantioselectivity was observed in the binding assays. Chirality 9: 739-749, 1997.