Studies on the Constituents of Orchidaceous Plants. IX. : Constituents of Spiranthes sinensis (PERS.) AMES var. amoena (M. BIEBERSON) HARA. (2). Structures of Spirantheosol, Spiranthoquinone, Spiranthol-C, and Spirasineol-B, New Isopentenyldihydrophenanthrenes

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Four new dihydrophenanthrene derivatives, spiranthesol, spiranthoquinone, spiranthol-C, and spirasineol-B, were isolated from the roots of Spiranthes sinensis (PERS.) AMES var. amoena (M. BIEBERSON) HARA (Japanese name "nezibana"). The structures 1, 2, 3, and 4 were proposed for these compounds, respectively, on the basis of spectroscopic data obtained by various methods including ¹H-detected heteronuclear multiple-bond multiple-quantum coherence (HMBC) spectroscopy. Chemical conversions of spiranthol-A to spiranthol-C and spiranthoquinone and of spirasineol-A-to spirasineol-B are also described.