2-Hydro­xy­benzoic acid salt of physostigmine

Physostigmine, C₁₅H₂₂N₃O₂, is the major alkaloid found in the seeds of Calabar beans. It was the first anticholinesterase used in the treatment of Alzheimer's disease and is still used in the treatment of glaucoma. The structure of its 2-hydroxy­benzoate salt, viz. 5-carbamoyl­oxy-1,2,3,3a,8,8a-hexa­hydro-1,3a,8-tri­methyl­pyrrolo­[2,3-b]­indol-1-ium benzoate, C₁₅H₂₂N₃O₂⁺·C₇H₅O₃⁻, is reported.