The new optically based sibirine with [α]D-22.5° (c 0.81; chloroform), M+ 183, has been isolated from the epigeal part of the Nitraria sibirica by column chromatography. On the basis of the results of chemical transformations (acetylation, oxidation), analysis of spectral characteristics (UV, IR, mass, PMR, ORD), and also a comparison of the alkaloid with the N-methyl derivatives of nitramine and isonitramine, the structure of sibirine has been established as methyl-2-azaspiro[5.5] undecan-7-o1. © 1983 Plenum Publishing Corporation.