Über die Alkaloide aus der Rinde von Strychnos melinoniana Baillon. 25. Mitteilung über Calebassen‐Alkaloide

Abstract

Aus der Rinde von Strychnos melinoniana Baillon wurden ausser den von E. Schlittler & J. Hohl früher dargestellten Melinoninen A und B 12 weitere Alkaloide isoliert: Melinonine E, F, G, H, I, K, L, M, Mavacurin, Fluorocurin sowie l‐Narcotin und Thebaïn. Die beiden letzteren Pflanzenbasen stammen sehr wahrscheinlich nicht aus der Rinde, sondern sind während deren Aufarbeitung künstlich eingeschleppt worden.

Catalytic Aza-Wacker Annulation: Tuning Mechanism by the Activation Mode of Amide and Enantioselective Syntheses of Melinonine-E and Strychnoxanthine

“…However, the cyclization of 12 and dehydrogenation in “one-pot” delivered melinonine-E as a yellow solid in 65% yield. The spectra of the synthetic melinonine-E (chloride salt) was identical to the literature data (chloride salt) and confirmed the absolute configuration of this β-carbolinium alkaloid (synthetic: [α] D −11.1 (c 0.86 in MeOH); natural: [α] D −13.9 (c 1.02 in MeOH)). The stereochemical confirmation validated the biogenetic relevance of melinonine-E and matadine. , Moreover, the circular dichroism (CD) spectrum of the synthetic strychnoxanthine (chloride salt) showed a positive Cotton effect (Δε + 3.0) at 360 nm, which reconciles the reported data and thus can assign the absolute configuration as (15 R ,17 R ,20 R ).…”

“…Having accessed the aza-Wacker cyclization to construct bridged lactams, our attention was drawn toward two morphan-core-embedded alkaloids. Melinonine-E ( 5 ) was first isolated in 1957 by Bächli et al from the bark of Strychnos melinoniana Baillon (Loganiaceae), a plant used as an African folk medicine for the treatment of malaria . The plain structure was later revised by Hesse et al as a pentacyclic skeleton of a 2-azabicyclo[3.3.1]­nonane-fused β-carbolinium cation, which is unprecedented in this category of alkaloids .…”

A Bridge to Alkaloid Synthesis

“…The profound effect of the substituents on nitrogen provides flexibility for future diverted synthesis by tuning the activation mode of the aza-Wacker reaction. [33]…”

Salient features of the aza-Wacker cyclization reaction

“…African folk medicine for malarial therapy. 33 A related natural product, strychnoxanthine, was isolated by Angenot and coworkers from Strychnos gossweileri Exell (Loganiaceae); 34 importantly, strychnoxanthine was found to inhibit Plasmodium falciparum (IC 50 ¼ 8.4 mm). 35 Both melinonine-E and strychnoxanthine are pentacycles with a b-carbolinium motif fused to a 2-azabicyclo[3.3.1]nonane skeleton.…”