title: The Double-Bond Configuration of Corynanthean Alkaloids and Its Impact on Monoterpenoid Indole Alkaloid Biosynthesis.
abstract: Experimental evidence is provided for the coherence of the double-bond geometry and the occurrence of "secondary cyclizations" in the biosynthesis of monoterpenoid indole alkaloids. Biosynthetically, akuammiline, C-mavacurine, and Strychnos alkaloids are proposed to be derived from the corynanthean alkaloid geissoschizine, a key intermediate in the biosynthetic pathway of these monoterpenoid indole alkaloids. This process occurs by so-called "secondary cyclizations" from geissoschizine or its derivatives. Although corynanthean alkaloids like geissoschizine incorporate E or Z double bonds located at C19-C20, the alkaloids downstream in the biosynthesis exclusively exhibit the E double bond. This study shows that secondary cyclizations preferentially occur with the E isomer of geissoschizine or its derivatives. This is attributed to the flexibility of the quinolizidine system of the corynanthean alkaloids, which can adopt a cis or trans conformation. For the secondary cyclization to take place, the cis-quinolizidine conformation is required. Experimental evidence supports the hypothesis that the E double bond of geissoschizine induces the cis conformation, whereas the Z double bond induces the trans conformation, which prohibits secondary cyclization of the Z compounds.
authors.affiliation: Institute of Organic Chemistry, Leibniz University of Hannover, Schneiderberg 1b, 30167, Hannover, Germany.
authors.forename: Ruben
authors.initials: R
authors.lastname: Eckermann
authors.affiliation: Department of Organic Chemistry, University of Konstanz, Universitätsstrasse 10, 78464, Konstanz, Germany. tanja.gaich@uni-konstanz.de.
authors.forename: Tanja
authors.initials: T
authors.lastname: Gaich
mesh_terms: D001669:Biochemical Phenomena; D053898:Biosynthetic Pathways; D002243:Carbolines; D003500:Cyclization; D026121:Indole Alkaloids / Q000737:chemistry*; D015394:Molecular Structure; D046948:Secologanin Tryptamine Alkaloids / Q000737:chemistry*; D031451:Strychnos / Q000737:chemistry*
chemical_list: D002243:Carbolines; D026121:Indole Alkaloids; D046948:Secologanin Tryptamine Alkaloids; C000594872:corynanthean; C410326:geissoschizine
keywords: alkaloids; biosynthesis; conformation analysis; indoles; terpenoids