Main Alkaloids of Securinega suffruticosa. Nitrogen Atom Inversion in Securinine

The main alkaloids such as securinine (1), allosecurinine (2), and securitinine (3) are isolated from the Securinega suffruticosa plant and identified by spectral techniques. The spatial structure of 3 is determined by single crystal XRD. The inversion of the pyramidal-tetrahedral nitrogen atom of compound 1 in the crystal and the solution is analyzed based on single crystal XRD and NMR spectroscopy data. By the computational methods and NMR spectroscopy it is shown that the configuration of the nitrogen atom in securinine is related to the alkaloid salt formation rather than the crystal field effect (packing factor).