39 アスコフラノンの合成

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Ascofuranone (1) is an antitumor hypolipidemic antibiotic isolated from the mycelium of Ascochyta viciae Libert and recently found to have an antitumor protective effect also. The structure of ascofuranone is characterized by a fully substituted benzene ring and a sesquiterpenoid side chain having 4, 5-dihydro-3(2H)-furanone moiety. Our synthetic approach consists of (1) construction of the hexa-substituted benzene 6 (or 7), (2) synthesis of the terpenoid side chain precursor 15, (3) coupling of the two segments, and (4) regeneration of the phenolic hydroxyls. Feasibility of the strategy was first tested by the synthesis of model compounds, colletochlorin B (2a) and colletochlorin D (2b). Bromobenzene 6 (or 7) was prepared from dimethyl malonate and 3-penten-2-one through 3 and 4 and metallated to give a mixed cuprate which was allowed to react with geranyl bromide to give 8 (or 9). This was transformed into 10 (or 11). Deprotection of the phenolic hydroxyls of 10 with EtSNa gave colletochlorin B (2a) which was also afforded by treatment of 11 with Bu_4NF. Colletochlorin D (2b) was prepared similarly, starting with 10 and 1-bromo-3-methyl-2-butene. The bromide 15, synthesized by transformation of the aldehyde 12 to 13 followed by silver(I)-mediated dihydrofuranone formation, deprotection of the primary alcohol, and bromination with CBr_4 and (octyl)_3P, was connected with 6 (or 7) and the resulting 16(or 17 or 18) was successfully transformed to 19(or 20) in a like manner as above. Though neither EtSNa nor Bu_4NF was proved to be ineffective to yield ascofuranone from 19(or 20), P_2I_4, when applied to 20, gave rise to the target compound, ascofuranone (1).
天然有機化合物討論会の論文
1985-09-07

39 アスコフラノンの合成

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