Biomimetic Synthesis of Nitraria Alkaloids, based on Tetrahydropyridine Synthons

Amsterdam Institute of Molecular Studies, Laboratory of Organic Chemistry, University of Amsterdam, Nieuwe Achtergracht 129, 1 018 WS Amsterdam, The Netherlands

Manuscript received 8 September 1997

Many of the alkaloids found in Nitraria and Lupine species can be envisaged to arise from two simple building blocks, namely, tryptamine and tetrahydropyridine. In particular in the Nitraria species, the alkaloids occur as racemates in some cases, despite the presence of many stereocenters. We assume that racemic alkaloids might be formed without interference of enzymes via spontaneous reactions of highly reactive intermediates. By carrying out a biomimetic approach many of these alkaloids were obtained by us via chemical synthesis, based on this concept of reactive precursors. The paper discusses the preparation of racemic lupinine, spartein, and nitraramine from tryptamine and the trimer oftetrahydropyridine, based on imine-enamine chemistry.