The complete tetracyclic core structure of plicamine, a novel Amaryllidaceae-type alkaloid, was expeditously prepared by a Ugi four-component condensation reaction, followed by a one-pot sequential phenolic oxidation and intramolecular coupling process. The employment of this strategy resulted in a rapid, formal synthesis of (±)-plicamine.
Flavones were directly alkylated at the C-3 position in moderate yields using a xanthate-based oxidative radical addition procedure. This methodology is a suitable synthetic tool for the direct substitution of the vinylic and unactivated C-H bond of the C ring of the flavone by an alkyl functionality under neutral conditions.
The addition of a nicotinate–xanthate derivative to N‐allylindoles and N‐allylpyrroles resulted in polycyclic heterocycle‐fused pyridonaphthyridines through a tandem radical intermolecular/intramolecular oxidative addition reaction sequence that created three new C–C bonds and two new rings in a single event. Such polyheterocycles showcase the matrine alkaloid framework and are similar to indole–monoterpenoid natural products.
Several species from the Apocynaceae family, such as Tabernanthe iboga, Voacanga africana, and many Tabernaemontana species, produce ibogan type alkaloids, some of which present antiaddictive properties. In this study, we used gas chromatography/mass spectrometry (GC/MS) to examine the efficiency of methanol, acetone, ethyl acetate, dichloromethane, chloroform, and hydrochloric acid in extracting the antiaddictive compounds coronaridine, ibogamine, voacangine, and ibogaine (altogether the CIVI‐complex) from the root barks of Tabernaemontana alba and Tabernaemontana arborea. These Mexican species have recently shown great potential as alternative natural sources of the aforementioned substances. Methanol proved to be the most suitable solvent. Furthermore, the crude methanolic extracts could be engaged in a one‐step demethoxycarbonylation process that converted coronaridine and voacangine directly into its non‐carboxylic counterparts ibogamine and ibogaine, respectively, without the intermediacy of their carboxylic acids. The established protocol straightforwardly simplifies the alkaloid mixture from four to two majority compounds. In summary, our findings facilitate and improve both the qualitative and quantitative analysis of CIVI‐complex‐containing plant material, as well as outlining a viable method for the bulk production of these scientifically and pharmaceutically important substances from Mexican Tabernaemontana species.
Five Aspidosperma alkaloids within three structurally diverse topologies were synthesized from a single key intermediate, which could be selectively driven through three reaction paths: N(1)- vs. C(3)-indole cyclization vs. over-reduction, via the incorporation of conformational and electronic constraints that influence the reactivity of its derived iminium ion 7.
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