Naphthoquinone Derivatives from <i>Diospyros maritima</i>

Abstract

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...

Contrasting Dihydronaphthoquinone Patterns in Closely Related Drosera (Sundew) Species Enable Taxonomic Distinction and Identification

“…Neither dihydronaphthoquinone has been isolated from Drosera or Drosophyllum before, but dihydroplumbagin ( 5 ) had been previously obtained and characterized from Juglans L. (Juglandaceae) species [ 11 ], and dihydroplumbagin ( 5 ) and dihydroramentaceone ( 6 ) were already known from Diospyros maritima Blume (Ebenaceae) [ 12 ].…”

Potential of Silver Nanoparticles in Overcoming the Intrinsic Resistance of Pseudomonas aeruginosa to Secondary Metabolites from Carnivorous Plants

“…To date, only the hydroplumbagin glucoside has been demonstrated in species of the genus Drosera , not the free dihydroplumbagin [ 5 , 29 ]. However, dihydroplumbagin was isolated from fresh fruits of Diospyros maritima (Ebenaceae) [ 32 ]. Dihydroplumbagin and 3-chloroplumbagin have been identified as minor components of the D. muscipula analysed.…”

Ebenamariosides A–D: Triterpene Glucosides and Megastigmanes from the Leaves of <i>Diospyros maritima</i>

“…The leaves of D. maritima extracted with MeOH and the MeOH extracts were separated by solvent partition according to the polarity of the constituents. The relatively polar 1-BuOH-soluble fraction was separated by various kinds of chromatography to afford four new triterpene saponins (1)(2)(3)(4) and two new megastigmanes (5,6), together with two known flavonol glycosides (7,8). The structures of new triterpene derivatives were elucidated using one-and two-dimensional spectroscopies.…”

“…1) In summer, it bears green sap fruits of 2 to 3 cm in diameter, which then turn to a dark orange colour in autumn. It is known that the fruits contain a toxic naphthoquinone derivative, plumbagin, and their constituents have been extensively investigated by Higa et al [2][3][4] Recently, from the leaves and branches of a related Thai medicinal plant, D. mollis, the isolation of naphthoquinone glycosides was reported. 5) In our continuing work on Okinawan resource plants, the constituents of the leaves of D. maritima were investigated to give eight ent-kaurane-type diterpenoid glycosides, called diosmariosides A-H. 6) Further extensive work resulted in the isolation of four new triterpene saponins, named ebenamariosides A-D (1-4) and two megastigmanes (5,6), along with two known flavonol glycosides, kaempferol 3-O-β-D-(2″,6″-di-O-α-L-rhamonopyranosyl) glucopyranoside (7) 7) and 3-O-β-D-(2″,6″-di-α-L-rhamonopyranosyl) galactopyranoside (8) 8) (Fig.…”