The genus Gelsemium (Loganiaceae) consists of three species of plants: Gelsemium sempervirens Ait., Gelsemium elegans Benth., and Gelsemium rankinii Small. Alkaloids derived from these plants comprise an important class of compounds which show great promise as medicinal agents. Extensive isolation and characterization studies have been performed on alkaloids derived from the first two species. These compounds have a long history of use as analgesics in the treatment of neuralgia and migraine. There is also potential for application of these compounds to the treatment of cardiovascular and respiratory diseases. Consequently it is desirable to have synthetic routes to these systems which allow for structural modification and preparation of analogues for testing. A total synthesis of the Gelsemium alkaloid koumine is proposed. Koumine is the major alkaloid constituent of the Chinese medicinal plant kou-wen. It is reported to exhibit physiological activity similar to gelsemine, a compound with a long history of medical application in this country. The synthesis plan employs a novel intramolecular addition of a B- ketoester enolate to an azoene (1,2-diazabutadiene) for construction of the bicyclononane skeleton. New methods are outlined for preparation of the acid labile 11alkyl4ketotetrahydrocarbazole starting material. Also, several potentially valuable Bketoester equivalents are described which can be introduced into the molecule using alkylation procedures. The bicyclononadione derived from azoene alkylation is expected to provide koumine following 1) stereocontrolled introduction of a methylamine substituent 2) ring formation via intramolecular alkylation of an imimium by allyl silane 3) intramolecular etherification by S/N2' displacement of an alkoxide on an N-tosyl enamine.
