From the chloroform extract of the fresh fruits of Diospyros maritima BLUME (Ebenaceae), five new naphthoquinone derivatives, 2,7′-dimethyl-2′,3-bijuglone (27), 2,7′-dimethyl-3,3′-bijuglone (28), 2,7′-dimethyl-6,8′-bijuglone (29), 7,7′-dimethyl-3,3′-ethylidenebijuglone (30), and 2′,7-dimethyl-3,6′-ethylidenebijuglone (31), were isolated, in addition to twenty-one known naphthoquinone derivatives: plumbagin (4), droserone (5), 2,3-epoxyplumbagin (8), 3,3′-biplumbagin (9), chitranone (10), 3,8′-biplumbagin (11), elliptinone (12), maritinone (13), isozeylanone (14), methylene-3,3′-biplumbagin (15), ethylidene-3,3′-biplumbagin (16), ethylidene-3,6′-biplumbagin (17), ethylidene-6,6′-biplumbagin (18), 7-methyl-β-dihydrojuglone (19), 7-methyljuglone (
Key words Diospyros maritima; Ebenaceae; naphthoquinone; bijuglone; ethylidenebijugloneDiospyros maritima BLUME (Ebenaceae) is a shrub that grows in Southeast Asia. We previously reported the isolation of eighteen naphthoquinone derivatives, 1-18, from the ethanol extract of the fruits of this plant 1,2) (Chart 1). The naphthoquinone derivatives isolated to date from the genus Diospyros are commonly assumed to be derived from a precursor equivalent to 4,5-dihydroxy-2-methylnaphthalene or a biogenetic analog.3) 3-Methylplumbagin (3), 3-(2-hydroxyethyl) plumbagin (6), 6-(1-ethoxyethyl) plumbagin (7), methylene-3,3′-biplumbagin (15), ethylidene-3,3′-biplumbagin (16), ethylidene-3,6′-biplumbagin (17), and ethylidene-6,6′-biplumbagin (18) isolated from this plant contain an alkyl group that is not found in the naphthoquinone derivatives isolated from other Diospyros species. Because it is possible to isolate rare and novel quinones using different extraction solvents, we employed chloroform as the extraction solvent instead of ethanol to examine the naphthoquinone derivatives in the chloroform extract of the fresh fruits. Here, we describe the isolation and structure elucidation of five new naphthoquinone derivatives, 27-31, from the chloroform extract; we also discuss the classification of naphthoquinone derivatives obtained only from the ethanol extract of the fresh fruits of this plant, only from the chloroform extract, and from both extracts.
Results and DiscussionStructure Elucidation A chloroform extract of the fresh fruits of D. maritima afforded, after chromatographic separation, eight known naphthoquinone derivatives: 7-methyl-β-dihydrojuglone (19), 7-methyljuglone (20), 2,3-epoxy-7-methyljuglone (21), neodiospyrin (22), mamegakinone (23), ehretione (24), isoxylospyrin (25), β-dihydroplumbagin (26), and five new quinones (27 to 31) (Chart 2), in addition to quinones 4, 5, and 8-18, which were previously isolated from the ethanol extract.The new quinone 27 was obtained as red prisms with a melting point (mp) of 184-185°C. Its molecular formula was determined to be C [δ 7.28 (1H, dd, J=1.0, 8.0 Hz), 7.65 (1H, t, J=8.0 Hz), 7.71 (1H, dd, J=1.0, 7.5 Hz)], and another hydrogen-bonded hydroxyl (δ 11.75, (1H, s)) were attributed to the plumbagin moiety. From these resul...
