93 NMRを有効に利用した天然物の構造解析 : ヒトリシズカのセスキテルペン二、三量体について(ポスター発表の部)

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In the course of our continuing search for sesquiterpenoids of the Chloranthaceae, ten lindenane dimers, shizukaols A-I(1-9) and cycloshizukaol A(10), and one trimer, trishizukaol A(11), have been isolated from the ether extracts of Chloranthus japonicus Sieb. Their structures were elucidated mainly through the combined use of various NMR techniques as follows. Compounds 2, 6, 7 and 8 carry a unique pendent macrocyclic lactone ring containing a C_5 hydroxylic acid (γ-hydroxytiglic or γ-hydroxysenecioic acid) and a C_4 dicarboxylic acid (succinic or malic acid) as the ester units. Connectivities between the oxymethine and the neighboring carbonyl in the malic ester residue in 7 and 8 were efficiently determined by selective INEPT. On the other hand, assignments of the two methylenes in the succinic ester residue in 2 and 6 were problematic because of the close similarity of the ^<2J>CH and ^<3J>CH values. The use of heteronuclear NOE could overcome these difficulties and the simultaneous selective inversion of two non-equivalent methylene proton signals by a double DANTE pulse train yielded clear NOE enhancements at the neighboring carbonyl carbons. The stereostructure of a C_2 symmetric molecule, 10, was unambiguously determined by detecting NOEs between equivalent protons using 2D ^<13>C-coupled HMQC-NOESY. Finally, the complex structure of the trimer, 11, was elucidated by utilizing spin decoupling difference experiments as well as the other ^<LRJ>CH detection methods.
天然有機化合物討論会の論文
1993-09-10

93 NMRを有効に利用した天然物の構造解析 : ヒトリシズカのセスキテルペン二、三量体について(ポスター発表の部)

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