Approaches to the synthesis of (+/-)-strychnine via the cobalt-mediated [2 + 2 + 2] cycloaddition: rapid assembly of a classic framework.

Five synthetic approaches to racemic strychnine (1), with the cobalt-mediated [2 + 2 + 2] cycloaddition of alkynes to indoles as the key step, are described. These include the generation and attempted cyclization of macrocycle 8 and the synthesis of dihydrocarbazoles 15, 22, and 26 and their elaboration to pentacyclic structures via a conjugate addition, dipolar cycloaddition, and propellane-to-spirofused skeletal rearrangement, respectively. Finally, the successful total synthesis of 1 is discussed. The development of a short, highly convergent route (14 steps in the longest linear sequence) is highlighted by the cyclization of enynoylindole 40 with acetylene and the formal intramolecular 1,8-conjugate addition of amine 49 to form pentacycle 50. Numerous attempts toward the formation of the piperidine ring of 1 from vinyl iodide 56 were made and its successful formation via palladium-, nickel-, and radical-mediated processes is described.

The formal total synthesis of (+/-)-strychnine via a cobalt-mediated [2 + 2 + 2]cycloaddition.

A short, highly convergent total synthesis of racemic isostrychnine, and thus strychnine, has been completed. The route involves 14 steps in the longest linear sequence and is highlighted by a cobalt-mediated [2 + 2 + 2]cycloaddition of an alkynylindole nucleus to acetylene.

Vismione H and structurally related anthranoid compounds of natural and synthetic origin as promising drugs against the human malaria parasite Plasmodium falciparum: structure-activity relationships.

Natural and synthetic anthranoid compounds were subjected to an evaluation against asexual erythrocytic stages of the human malaria parasite Plasmodium falciparum in vitro. Stimulated by the good activities of Vismia guineënsis extracts, a more detailed investigation of the active principles revealed the pre-nylated preanthraquinone vismione H (1) to be a potent antimalarial [50% growth-inhibitory concentration (IC50) 0.088 microg/ml]. On the basis of this finding a series of chemically related phlegmacins (2-5), flavomannins (6-8), and rufoolivacins (9-11) isolated from several species of Cortinarius, a genus of higher fungi, and 5 synthetic vismione-like anthranoids (12-16) were evaluated as well. Although these compounds displayed weaker antiplasmodial effects than did vismione H (1) itself, considerable levels of activity were obtained with phlegmacin B1 (2), flavomannin-6,6'-di-O-methyl ether A1 (6), trans-4-hydroxy-flavomannin-6,6'-di-O-methyl ether A (8), and rufoolivacin B (10). Initial preconditions for activity within the vismiones and related anthranoids were established.