Biologically active O-substituted azabicyclo oximes having the Z configuration may be isolated simply, without chromatographic separation, and in high yield and Z/E purity through the coupling of a 1-azabicyclo-3-one with an O-substituted hydroxylamine in acidic aqueous solution and conversion of E-configured isomer to Z-isomer without requiring purification or separation. Neutralization and subsequent isolation of the free base followed by precipitation of the salt allows separation of the Z-isomer with high Z/E purity.