97(P16) タキサジエンの合成研究(ポスター発表の部)

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In the biosynthesis of Taxol^[○!R] (1), the initial step is the cyclization of geranylgeranyl diphosphate (3) to taxa-4(5),11(12)-diene (2). But the nature of the subsequent oxidation process from 2 to 1 has not been reported. In preparation for tracer experiments with ^<13>C-labeled compounds, we examine the synthesis of 2 and its oxidative products. The carboxylic acid 4 (A ring unit) was prepared from the Wieland-Miesher ketone (5) via Beckmann fragmentation of the oxime 8. The B ring was constructed by means of the lactam-sulfoxide ring contraction reported by Oishi. Cyclization of 12, derived from the carboxylic acid 4 and the o-thioaniline derivative 10 as a spacer, to the lactam-sulfide 13a was achieved under a high dilution condition. The ring contraction of the 12-membered ring lactam-sulfoxide 15b proceeded smoothly to afford the 8-membered ring ketone. In contrast, the isomer 15a was not contracted. Removal of the spacer moiety in 15b gave the AB ring unit 17. Construction of the C ring was performed as follows. Aldol condensation of 17 afforded the diastereomer mixture 18a-b, having the same 19β-methyl as natural taxadienes. Construction of the C ring was achieved via intramolecular pinacol coupling of the keto-aldehyde 19 by treatment with SmI_2 at 66℃ to give the diol 20, having the tricyclic taxadiene skeleton. The stereochemistry of 20 was B/C-trans and 3,4-syn-diol. Thus, the synthesis of the tricyclic skeleton of taxadienes was achieved by means of lactam-sulfoxide ring contraction and intramolecular pinacol coupling with SmI_2.
天然有機化合物討論会の論文
1998-08-31

97(P16) タキサジエンの合成研究(ポスター発表の部)

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