56(P1-4) ゲルセミウム属アルカロイド及びその関連化合物のバイオミメティックな合成研究(ポスター発表の部)  [in Japanese] 56(P1-4) STUDIES ON THE BIOMIMETIC SYNTHESIS OF SOME GELSEMIUM ALKALOIDS AND THE RELATED NATURAL PRODUCTS  [in Japanese]

We have recently investigated the alkaloidal constituents of Gelsemium elegans, a toxic medicinal plant from Thailand and proposed the biogenetic route of these alkaloids having novel polycyclic systems. In order to support the biogenetic speculation and to develop the efficient synthetic method of these alkaloids including the minor constituents, we designed the biomimetic partial synthesis of some gelsemium alkaloids from easily obtainable compounds. Koumidine (4) is a plausible biogenetic precursor of the new alkaloid, 19-(Z)-taberpsychine (5) and its structure was revised. Both to provide support for the spectroscopic analysis and to determine the absolute configuration of these compounds, we have synthesized them from ajmaline (16). Koumidine (4) was also prepared from gardnerine (22) by the demethoxylation from indole nucleus and the inverting the configuration of the ethylidene side chain with palladium catalyst. Along the biogenetic speculation, a principal gelsemium alkaloid, koumine (6) was synthesized from 18-hydroxygardnutine (28) by the demethoxylation from indole ring and palladium-catalyzed cyclization between C_7 and C_<20> of biogenetic intermediate (27). A synthetic intermediate (45), which was corresponding to the biogenetic intermediate (12) for gelsedine (13), was prepared from ajmaline (16) in 21 steps via the deformylation (C_<21>) and the construction of five-membered D-ring having an α-ethyl group on C_<20>. Talcarpine (49), one of the macroline-type pleiocarpa alkaloid, was synthesized from (16) in 10 steps and the configuration at C_<19> was determined to be (R) by the analysis of 2D-NMR spectra.