P-1 フタバガキ科植物のスチルベンオリゴマーの構造回転異性を有するshoreaketoneの構造とスペクトル特性(ポスター発表の部)

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Many natural stilbenoids in Dipterocarpaceae and Vitaceae exist as 'oligomer' in which some stilbenoid molecules are coupled with other at various positions. These oligomeric stilbenoids have been shown to possess a wide range of physiological and biological properties including anticancer, anti-inflammatory, and antiviral activities. The oligomeric stilbenoids in Dipterocarpaceaeous plants have been our main focus of extensive structural investigation for the past decade. Although a detailed structural determination based on NMR spectra is required as a part of ongoing chemical investigation, the difficulties caused by complicated stereochemistry that comprises diastereomer, epimer and enantiomers make the structural determination somewhat difficult to tackle. In the present study, the structural characterization of shoreaketone (1) isolated from three Dipterocarpaceaeous plants is described, because 1 appears different from other resveratrol tetramers with respect to its skeleton and NMR spectral complexity. The heterocyclic ring in 1 is unique and has not been recorded in any other natural product that contains a dense array of functionality and stereochemistry. We have identified a resveratrol tetramer with a chiral axis in 1 for the first time. Our findings demonstrate complex chemical and dynamic behavior in 1. From detailed spectral data analysis to examine the mutual effect of the hindered rotation around the chiral axis, we could demonstrate the presence of two rotamers (1a and 1b). Using edited ROESY, NOESY, and differential NOE experiments, we propose that both rotamers exhibit rotational conformation exchanges. The formation of the symmetrical molecule, isohopeaphenol (2) solves the stereochemical aspect and stereostructure could be confirmed by demethylation after the acid catalyzed skeletal transformation of 1. From theoretical calculations, the barrier to rotation of the chiral axis was found to be around 33.7kcal/mol. Our study signifies a new dimension toward the ongoing research in this field by exploring such type of complex systems bearing a 2,3-diaryl-dihydrobenzofuran ring. The structure of isohopeaphenol (2) was confirmed by spectroscopic evidences and skeletal conversion of 1.
天然有機化合物討論会の論文
2008-09-01

P-1 フタバガキ科植物のスチルベンオリゴマーの構造回転異性を有するshoreaketoneの構造とスペクトル特性(ポスター発表の部)

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