Kristina JENETT-SIEMS-1, Macki KALOGA-1, Eckart EICH-1, Karsten
SIEMS-2, Ludger WITTE-3, and Thomas HARTMANN-3
1- Institut für Pharmazie II (Pharmazeutische Biologie), Freie
Universität Berlin. Königin-Luise-Straße 2+4, D-14195 Berlin;
2- AnalytiCon AG, Gustav-Meyer-Allee 25, D-13355 Berlin;
3- Institut für Pharmazeutische Biologie, Technische Universität
Braunschweig, Mendelssohnstraße 1, D-38106 Braunschweig
The tropical bindweed Ipomoea hederifolia L. (syn.: I. angulata Lamk.) has turned out to be the first member of the convolvulaceous family containing pyrrolizidine alkaloids [1]. Two pairs of isomeric alkaloids -the ipangulines and isoipangulines could be isolated. Further investigations on different parts of I. hederifolia by capillary gas chromatography-mass spectroscopy now revealed the occurrence of additional 63 pyrrolizidine alkaloids. During this work we reinvestigated the stereochemistry of the alkaloids. Originally the ipangulines were thought to be turneforcidinediesters, esterified with the erythro- or threo-form of 2,3-dihydroxy-2methylbutyric acid and phenylacetic acid or salicylic acid, respectively.
New evidence now prompted us to correct this suggestion. Semi-synthesis of (-)-platynecine and comparison of its spectroscopic properties with those of the necine moiety of the ipangulines showed that both compounds were identical. So the ipangulines have to be esters of platynecine and not of turneforcidine. All novel alkaloids apparently represent also derivatives of platynecine (diesters and even monoesters) differing only in the necic acids.
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