34 タキソールの不斉全合成研究(口頭発表の部)

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Taxol 1 has attracted much attention because of its promising anti-cancer activities, as well as its complex molecular structure containing the unique tetracyclic skeleton. This report discloses our recent studies toward the asymmetric total synthesis of 1. In our strategies, the following transformations should be very important: 1) construction of the tricyclic carbon framework, 2) introduction of C19 methyl group on taxane skelton, 3) construction of oxetane ring. As for the point 1), we have already reported the highly efficient method for the construction of taxane skeltons, using intramolecular vinylogous aldol reaction. By applying this method, tricyclic compound 12 was easily prepared starting from optically active hydroxy aldehyde 2 (A-ring fragment) and cyclohexadiene 3 (C-ring fragment). (Eq 1) At the next stage (2) introduction of C19 methyl group), we have decided to utilize reductive cleavage of cyclopropylketone, and 20 was prepared as shown in eq 2. Although birch reduction of 20 gave the product having C19 methyl group in excellent yield, it was enol derivative 21 unexpectedly (eq 3). We are now studying about the isomerization of enol-form 21 into keto-form 22. If it is accomplished, the transformation of 22 to 8 should be very easy. We have been also investigating the transformation of synthetic intermediate 8 to taxol 1, which corresponds to the latter half of our total synthesis. The compound 8 was prepared by degradation of 10-deacetylbaccatin III (eq 5). We are currently studying about the conversion of 8 to 1 based on the Holton's procedures (eq 6).
1996-09-02

34 タキソールの不斉全合成研究(口頭発表の部)

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