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A new 1,2-ethanedione benzofurane derivative from Tephrosia purpurea a

b

c

d

d

Yan Peng , Yinning Chen , Chenghai Gao , Tao Yan , Wenhao Cao be

& Riming Huang a

Life Science & Technology School, Zhanjiang Normal University, Zhanjiang, 524-048, P.R. China b

Key Laboratory of Plant Resources Conservation and Sustainable Utilization, South China Botanical Garden, Chinese Academy of Sciences, Guangzhou, 510-650, P.R. China c

Guangxi Key Laboratory of Marine Environmental Science, Guangxi Academy of Sciences, Nanning, 530-007, P.R. China d

South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou, 510-301, P.R. China e

Department of Pharmacy and Pharmacology, University of Bath, Bath, BA2 7AY, UK Published online: 12 Aug 2014.

To cite this article: Yan Peng, Yinning Chen, Chenghai Gao, Tao Yan, Wenhao Cao & Riming Huang (2014) A new 1,2-ethanedione benzofurane derivative from Tephrosia purpurea, Natural Product Research: Formerly Natural Product Letters, 28:20, 1705-1708, DOI: 10.1080/14786419.2014.940587 To link to this article: http://dx.doi.org/10.1080/14786419.2014.940587

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Natural Product Research, 2014 Vol. 28, No. 20, 1705–1708, http://dx.doi.org/10.1080/14786419.2014.940587

A new 1,2-ethanedione benzofurane derivative from Tephrosia purpurea

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Yan Penga, Yinning Chenb, Chenghai Gaoc, Tao Yand, Wenhao Caod and Riming Huangbe* a Life Science & Technology School, Zhanjiang Normal University, Zhanjiang 524-048, P.R. China; bKey Laboratory of Plant Resources Conservation and Sustainable Utilization, South China Botanical Garden, Chinese Academy of Sciences, Guangzhou 510-650, P.R. China; cGuangxi Key Laboratory of Marine Environmental Science, Guangxi Academy of Sciences, Nanning 530-007, P.R. China; dSouth China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou 510-301, P.R. China; eDepartment of Pharmacy and Pharmacology, University of Bath, Bath BA2 7AY, UK

(Received 2 June 2014; final version received 28 June 2014) A new 1,2-ethanedione benzofurane derivative, purpdione (1), was isolated from Tephrosia purpurea, together with seven known flavonoids, purpurenone (2), pongamol (3), ovalitenin A (4), karanjin (5), lanceolatin B (6), tachrosin (7) and villosinol (8). The new structure was elucidated based on the analysis of its spectroscopic data. The structures of the known compounds were identified by comparing their spectroscopic data with those reported in the literature. The isolates exhibited marginal ability to inhibit the settlement of barnacle (Balanus reticulatus). Keywords: 1, 2-ethanedione benzofurane derivative; flavonoids; purpdione; Tephrosia purpurea

1. Introduction The genus Tephrosia belonging to the Leguminosae family is a large pantropical genus of more than 350 species, many of which have important traditional uses (Hegazy et al. 2011; Stevenson et al. 2012). Plants of the genus are known as common sources of structurally unique and biologically active natural products, some of which possessed various biological activities (Chen et al. 2014). In our study of bioactive compounds from plants of Tephrosia purpurea collected from Zhanjiang city, a new 1,2-ethanedione benzofurane derivative, purpdione (1), as well as seven known flavonoids (2– 8), namely purpurenone (2) (Rao & Raju 1984), pongamol (3) (Chang et al. 1997), ovalitenin A (4) (Gupta & Krishnamurti 1977), karanjin (5) (Magalhaes et al. 2000), lanceolatin B (6) (Magalhaes et al. 2000), tachrosin (7) (Smalberg et al. 1971) and villosinol (8) (Sarma et al. 1976), were obtained. All the isolates exhibited marginal ability to inhibit the settlement of barnacle (Balanus reticulatus).

2. Results and discussion Compound 1, white solid, was assigned as C17H12O4 on the basis of its HR-ESI-MS ([M þ H]þ at m/z: 281.0810, calcd for C17H13O4, 281.0808; [M þ Na]þ at m/z: 303.0632, calcd for C17H12NaO4, 303.0628) and NMR data, implying 12 double bond equivalents. The 1H, 13C NMR and HMQC spectra of 1 indicated the presence of one methyl, nine sp2 methines and seven sp2 quaternary carbons. Analysis of the 1H NMR data revealed the presence of an AB system signals at dH 8.05 (1H, d, J ¼ 8.7 Hz, H-60 ) and 7.37 (1H, d, J ¼ 8.7 Hz, H-50 ) for an 1,2,3,4*Corresponding author. Email: [email protected] q 2014 Taylor & Francis

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tetrasubstituted-phenyl moiety; signals at dH 7.96 (2H, d, J ¼ 7.7 Hz, H-2/6), 7.71 (1H, d, J ¼ 7.7 Hz, H-4) and 7.51 (2H, t, J ¼ 7.7 Hz, H-3/5) which indicated that another phenyl moiety in compound 1 is not substituted; two cis-olefinic protons as AB-type typical signals at dH 7.65 (1H, d, J ¼ 2.2 Hz, H-80 ) and 7.26 (1H, d, J ¼ 2.2 Hz, H-70 ); as well as a methoxyl group (dH 3.80, s). Furthermore, together with the analysis of its molecular formula, the NMR spectra of it established that 1 possessed 20 -methoxy-(30 ,40 ,70 ,80 )-furano-phenyl skeleton, which indicated that 1 was similar to those of 1-(4-methoxy-5-benzofuranyl)-2-phenyl-ketone (Kawase et al. 1958), indicating that 1 and 1-(4-methoxy-5-benzofuranyl)-2-phenyl-ketone are structurally related. A careful comparison of the 1H and 13C NMR spectra of 1 with those of 1-(4-methoxy-5benzofuranyl)-2-phenyl-ketone revealed that C-7 in 1 is a keto group. HMBC correlations (Figure S1) were used to establish the molecular skeleton of 1. The key HMBC correlations from H-80 to C-30 and C-40 , CH3 to C-20 , and H-70 to C-20 and C-40 , indicated the presence of a 20 -methoxy-(30 ,40 ,70 ,80 )-furano-phenyl moiety in 1 (Sinha et al. 1982). Moreover, the HMBC correlations from H-60 to C-8 and from H-6 to C-2, as well as analysis of the molecular formula, indicated the presence of 1,2-ethanedione moiety in 1. The gross structure was further established by the aid of HMQC and HMBC experiments (Figure S1). Thus, the structure of 1 was elucidated to be 1-(20 -methoxy-30 ,40 -benzofuranyl)-2-phenyl-1,2ethanedione and named as purpdione. The structures of known compounds 2 –8 were confirmed by detailed NMR data comparison with those in the literature (Smalberg et al. 1971; Sarma et al. 1976; Gupta & Krishnamurti 1977; Rao & Raju 1984; Chang et al. 1997; Magalhaes et al. 2000). To the best of our knowledge, compound 1 is the first example of 1,2-ethanedione benzofurane isolated from natural resource (Figure 1). The compounds 1 –8 were evaluated for their ability to inhibit the settlement of barnacle (B. reticulatus) (Harder et al. 2001; Ortlepp et al. 2007; Zhou et al. 2009). These isolates exhibited marginal ability to inhibit the settlement of barnacle (B. reticulatus) with the inhibition ratio of less than 10% at 100 mg/cm2. 3. Experimental 3.1. General experimental procedures UV spectra were recorded in MeOH on a Perkin-Elmer Lambda 35 UV – Vis spectrophotometer. The IR spectra were measured in KBr on a WQF-410 FT-IR spectrophotometer. NMR spectra

8′

7′

O

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OMe O 7

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OMe

1-(4-methoxy-5-benzofuranyl)-2phenyl-ketone

Figure 1. Structures of compounds 1 – 8 and 1-(4-methoxy-5-benzofuranyl)-2-phenyl-ketone.

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were recorded on a Bruker AV500 NMR spectrometer with TMS as an internal standard. HRESI-MS data were obtained from Bruker Maxis mass spectrometer. The silica gel GF254 used for TLC was supplied by the Qingdao Marine Chemical Factory (Qingdao, China). Spots were detected on TLC under UV light or by heating after spraying with 5% H2SO4 in EtOH. All solvent ratios were measured in v/v.

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3.2. Plant material The plants of T. purpurea were collected from Zhanjiang city, Guangdong province, China, in April 2011. The specimen was identified by Dr Pang Wang from the South China Botanical Garden, Chinese Academy of Sciences. A voucher specimen (No. 2011001) has been deposited in the Key Laboratory of Plant Resources Conservation and Sustainable Utilization, Chinese Academy of Sciences, China. 3.3. Extraction and isolation The dry powdered stem of T. purpurea (35 kg) was extracted with 95% ethanol (50 L £ 3) at room temperature, for 3 days each time. After evaporation of the solvent in vacuo, the combined crude ethanolic extract (2 kg) was suspended in H2O to produce an aqueous solution, then partitioned with petroleum ether and EtOAc to afford petroleum ether fraction (450 g) and EtOAc fraction (570 g). The petroleum ether fraction was subjected to a silica gel column chromatography eluted with petroleum ether/EtOAc mixtures with increasing polarities (98:2 to 10:90) to yield six fractions (1 – 6). Fraction 4 (57.6 g) was further separated by polyamide CC eluting with petroleum ether– acetone (70:30 to 100:0) to afford three sub-fractions (4a –4c). Sub-fraction 4a (13.8 g) was subjected to silica gel CC using petroleum ether/EtOAc (90:10 to 60:40) to afford 1 (7 mg) and 2 (12 mg). The EtOAc-soluble extract was subjected to a silica gel column chromatography eluted with CHCl3/MeOH mixtures with increasing polarities (98:2 to 10:90) to yield six fractions (E1 – E6). Fraction 2 (87.6 g) was further separated by polyamide CC eluting with MeOH –H2O (70:30 to 100:0) to afford three sub-fractions (E2a – E2c). Sub-fraction E2a (13.8 g) was subjected to silica gel CC using petroleum ether/EtOAc (90:10 to 60:40) to afford 5 (20.5 mg). Sub-fraction E2b (4.3 g) was purified by recrystallisation with MeOH to yield 3 (20 mg) and 4 (15 mg), respectively. Fraction E2c (3.1 g) was further separated by Sephadex LH-20 using MeOH to yield 7 (15 mg). Fraction E3 (65.4 g) was subjected to silica gel CC using petroleum ether/acetone (80:20 to 50:50) to afford three sub-fractions (E3a – E3c). Sub-fraction E3a (7.5 g) was subjected to silica gel CC using CHCl3/MeOH (90:10 to 50:50) to yield 6 (30 mg) and 8 (20 mg). Purpdione (1), yellow oil; UV (MeOH) lmax (log e max) 210 (4.45), 287 (4.31) nm; IR (KBr) nmax 1642 and 1053 cm21; HR-ESI-MS: m/z 281.0810 ([M þ H]þ, calcd for C17H13O4, 281.0808), [M þ Na]þ at m/z: 303.0632, calcd for C17H12NaO4, 303.0628; 1H NMR (500 MHz, CDCl3) dH: 8.05 (1H, d, J ¼ 8.7 Hz, H-60 ), 7.96 (2H, t, J ¼ 7.7 Hz, H-2/6), 7.71 (1H, d, J ¼ 7.7 Hz, H-4), 7.65 (1H, d, J ¼ 2.2, H-80 ), 7.51 (2H, t, J ¼ 7.7 Hz, H-3/5), 7.37 (1H, d, J ¼ 8.7 Hz, H -50 ), 7.26 (1H, d, J ¼ 2.2 Hz, H -70 ), 3.80 (3H, s, 30 -OMe); 13C NMR (125 MHz, CDCl3) dC: 194.3 (C-8), 193.5 (C-7), 160.8 (C-40 ), 156.3 (C-20 ), 145.8 (C-80 ), 133.8 (C-4), 133.2 (C-1), 129.4 (C-2/6), 128.8 (C-3/5), 126.5 (C-60 ), 120.2 (C-10 ), 118.0 (C-30 ), 107.7 (C-50 ), 105.5 (C-70 ) and 59.8 (30 -OMe). 3.4. Antifouling assay Following the methods reported earlier (Harder et al. 2001; Ortlepp et al. 2007; Zhou et al. 2009), the antifouling activity was carried out.

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4. Conclusion Our investigation on the chemical constituents of T. purpurea led to the identification of a new 1,2ethanedione benzofurane derivative, purpdione (1) and seven known flavonoids (2–8). To determine whether they could serve as non-toxic or less damaging alternative antifouling agents, the compounds 1–8 were evaluated for their ability to inhibit the settlement of barnacle (B. reticulatus), and the isolates exhibited marginal ability to inhibit the settlement of barnacle (B. reticulatus).

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Supplementary material Experimental details relating to this article are available online along with Figures S1 –S6. Acknowledgements R.-M.H. acknowledges a CAS Academic Visitor Fellowship and thanks Dr Ian S Blagbrough, University of Bath, for helpful discussions.

Funding This study was supported by grants from the National Natural Science Foundation of China [grant no. 31100260], the Natural Science Foundation of Zhanjiang Normal University [grant no. 2L1312], the Program of Guangzhou City [grant no. 12C14061559], the Zhanjiang City-Science and Technology Program [grant no. 2013A01024] and the Foundation of Key Laboratory of Plant Resources Conservation and Sustainable Utilization, South China Botanical Garden, Chinese Academy of Sciences [grant no. 201210ZS]. Riming Huang acknowledges a CAS Academic Visitor Fellowship and thanks Ian S. Blagbrough, University of Bath, for many helpful discussions.

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A new 1,2-ethanedione benzofurane derivative from Tephrosia purpurea.

A new 1,2-ethanedione benzofurane derivative, purpdione (1), was isolated from Tephrosia purpurea, together with seven known flavonoids, purpurenone (...
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