Diospyros maritima BLUME (Ebenaceae) is a shrub growing in Southeast Asia. We previously reported the isolation of nine naphthoquinone derivatives 1-9 from the fruits of this plant.1) In a continuing investigation of the naphthoquinone constituents of this plant, we obtained three new naphthoquinone derivatives 16-18 and six known naphthoquinone derivatives 10-15 from the fruits. This paper reports the isolation and structure elucidation of the new naphthoquinones 16-18 and the biological activities such as ichthyotoxic activity and germination inhibitory activity of quinones 11-18.
Results and DiscussionStructure Elucidation After chromatographic separation, the ethanol extract of the fresh fruits of D. maritima yielded, six known naphthoquinone derivatives, isozeylanone (10), 2) 3,3Ј-biplumbagin (11), 3) chitranone (12), 4,5) methylene-3,3Ј-biplumbagin (13), 5) 2,3-epoxyplumbagin (14), 6) 3,8Ј-biplumbagin (15), 7,8) and three new quinones 16-18, in addition to quinones 1-8, friedelin, b-amyrin, and lupeol.Quinone 14, pale yellow needles, mp 92-93°C, is 2,3-epoxyplumbagin. We have prepared 2,3-epoxyplumbagin by the treatment of plumbagin (4) with sodium perborate.6) This is the first report of quinone 14 as a natural product.Quinone 15, orange plates, mp 204-205°C, is 3,8Ј-biplumbagin. 3,8Ј-Biplumbagin has been obtained as one of the products of the reaction between plumbagin (4) and its hydroquinone by Sankaram et al. 7) This is also the first report of quinone 15 as a natural product.New H-NMR spectrum indicates that quinone 16 is a plumbagin (4) derivative with an 1-ethoxyethyl group (-CH(CH 3 )OCH 2 CH 3 ) substitution. Since one quinonoid proton and one pair of ortho-coupled aromatic protons were observed, the location of the 1-ethoxyethyl group must be at C-6 or C-8. The heteronuclear multiple-bond correlation (HMBC) spectrum (Fig. 1) showed long-range correlations between the methyl protons of the ethylidene group and C-6, and between OH-5 and C-6. This HMBC spectrum indicates that the 1-ethoxyethyl group is located at C-6. Thus quinone 16 is characterized as 6-(1-ethoxyethyl)plumbagin.New (4) linked by an ethylidene bridge. Since no quinonoid proton was observed, the position of the dimeric linkage must be 3-3Ј. The HMBC spectrum (Fig. 1) showed long-range correlations between the methyl protons of the ethylidene group and C-3,3Ј. These HMBC correlations indicate that the ethylidene group is located at C-3 and C-3Ј. On the basis of this evidence, quinone 17 was characterized as ethylidene-3,3Ј-biplumbagin.New , 6-(1-ethoxyethyl)plumbagin (16), ethylidene-3,3-biplumbagin (17), and ethylidene-3,6-biplumbagin (18), were isolated, in addition to six known naphthoquinones, isozeylanone (10), 3,3-biplumbagin (11), chitranone (12), methylene-3,3-biplumbagin (13), 2,3-epoxyplumbagin (14), and 3,8-biplumbagin (15), from the fruits of Diospyros maritima BLUME (Ebenaceae). The structures of the new compounds were established by spectroscopic methods. The eight naphthoquinones 11-18 were examined for ichthyo...