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Chemical constituents from the root bark of Dictamnus dasycarpus Turcz. (Rutaceae) and their chemotaxonomic significance
Biochemical Systematics and Ecology 86 (2019) 103931
Contents lists available at ScienceDirect
Biochemical Systematics and Ecology journal homepage: www.elsevier.com/locate/biochemsyseco
Chemical constituents from the root bark of Dictamnus dasycarpus Turcz. (Rutaceae) and their chemotaxonomic significance
T
Jin-Ling Zhanga, Shang-Chun Songb, Ji-Cheng Liua, Peng-Hui Nia, Lei Liua, Yu-Kun Maa, Yu Suna, Qi Liua, Li-Na Guoa,∗ a b
Research Institute of Medicine & Pharmacy, Qiqihar Medical University, Qiqihar, 161006, PR China Harbin University of Commerce, Harbin, 150028, PR China
ARTICLE INFO
ABSTRACT
Keywords: Rutaceae Dictamnus dasycarpus Chemotaxonomy Glycosides
This work described the isolation and characterization of seven compounds from Dictamnus dasycarpus Turcz., including one new ester, (2R)-4-(2,2-dimethyl-5-oxotetrahydrofuran-3-yl)-2-hydroxypent-3-anoic acid ethyl ester (1); and six known glycosides (2–7). The structure of compound 1 was elucidated on the basis of extensive spectral analyses, including IR, HR-ESIMS, 1D and 2D NMR (NOESY, HMBC and HSQC). All these compounds were described here for the first time from the genus Dictamnus. Moreover, the results provide further information about the diversity of compounds in the genus Dictamnus.
1. Subject and source The genus Dictamnus (Rutaceae), consists of five species that are distributed throughout Europe and North Asia but only two species are widely distributed in China. One is Dictamnus dasycarpus Turcz., which has been recorded in the Chinese Pharmacopoeia (Lv et al., 2015). The other is Dictamnus angustifolius G. Don ex Sweet, which is distributed in Xinjiang province. It is used as a traditional medicinal herb and has similar medicinal efficacy as Dictamnus dasycarpus in the treatment of many diseases, such as skin problem, rheumatism, jaundice, and cough (Zhao et al., 2006). Dictamnus dasycarpus also been reported to have anti-inflammatory (Kim et al., 2016), antifungal (Zhao et al., 1998), anti-atherosclerosis (Qin et al., 2010), hemostasis (Hui et al., 1996), anticancer (Park et al., 2015), neuroprotective (Jeong et al., 2010), as well as antioxidation activities (Guo et al., 2016 and Zhang et al., 2017). In present study, the root bark of Dictamnus dasycarpus was obtained from the city of Zalantun in Inner Mongolia China, in October 2009. The material was identified by Professor Jin-Cai Lu (Department of Traditional Chinese Materia Medica, Shenyang Pharmaceutical University). A voucher specimen (No. P-003) has been deposited in Qiqihar Medical University, Qiqihar, China. 2. Previous work Extensive studies of the genus Dictamnus led to the identification of
∗
more than 100 compounds, such as alkaloids, limonoids (Zhao et al., 1998 and Yang et al., 2011), flavonoids, sesquiterpenoids and their glycosides (Takeuchi et al., 1993 and Yang et al., 2018) and coumarins (Komissarenko et al., 1984). Alkaloids and limonoids have been reported as chemical markers of this genus (Gao et al., 2011). 3. Present study The air-dried root bark of Dictamnus dasycarpus (50 kg) were extracted three times with 95% EtOH. Solvent was removed under reduced pressure to afford a crude residue (3 kg), which was resuspended in H2O, and then partitioned sequentially with petroleum ether (PE), dichloromethane (CH2Cl2), ethyl acetate (EtOAc), and n-butanol (nBuOH). The EtOAc extract (100 g) was fractionated by silica gel open column chromatography (CC) eluted with a gradient system of CH2Cl2–MeOH (100:1 to 0:100) to yield twenty-four fractions (1–24). Fraction 16 (300 mg) was divided into five parts 16–1 to 16–5 over silica gel CC using PE-acetone (100:1 to 0:100) and the third fraction via Sephadex LH-20 CC using CH2Cl2–MeOH (1:1, v/v) as the mobile phase to obtain four fractions (16-3-1–16-3-4). Subsequently, fraction 16-3-2 was purified by semi-preparative HPLC (ODS, MeOH–H2O, 45:55; λ 210 nm; 3 mL/min) to yield compound 1 (15 mg, 44 min). Fraction 18 (425 mg) was subjected to silica gel CC and eluted with CH2Cl2–MeOH (100:1 to 0:100) to obtain nine subfractions (18-1–189). Subfraction 18–9 was subjected to Sephadex LH-20 CC (CH2Cl2–MeOH, 1:1, v/v) followed by semi-preparative HPLC (ODS,
Corresponding author. E-mail address: [email protected] (L.-N. Guo).
https://doi.org/10.1016/j.bse.2019.103931 Received 11 June 2019; Received in revised form 30 July 2019; Accepted 10 August 2019 Available online 20 August 2019 0305-1978/ © 2019 Elsevier Ltd. All rights reserved.
Biochemical Systematics and Ecology 86 (2019) 103931
J.-L. Zhang, et al.
Table 1 NMR spectra data for compound 1. No. 1 2 3 4 5 7 8 9α
1
H NMRa,b
4.04 1.30 1.78 0.92
(br d, 10.5) (m), 1.53 (m) (m) (d, 6.5)
2.06 (m) 2.40 (dd, 17.3, 8.4)
13
C NMRa,c
175.1 67.7 39.2 29.9 17.8 87.0 50.9 34.2
No.
1
H NMRa,b
9β 10 11 12 13 14 -OH
2.60 (dd, 17.3, 8.4) 1.26 1.42 4.09 1.19 5.34
(s) (s) (dd, 7.1, 3.4) (t, 7.1) (brs)
13
C NMRa,c
34.2 175.3 21.9 29.5 60.6 14.6
a Measured in DMSO‑d6, tetramethylsilane (TMS) was used as internal standard. b 600MHz. c 150MHz.
MeOH–H2O, 20:80; λ 210, 254 nm; 3 mL/min) to afford compound 3 (3.2 mg, 64.4 min). Fraction 22 (350 mg) was purified in the same way to gain compounds 2 (4 mg) and 4 (26 mg). Fraction 23 (428 mg) was loaded over a silica gel CC and eluted with CH2Cl2–MeOH (100:1 to 0:100) to obtain ten subfractions (23-1–23-10). Subfraction 23–10 was purified by semi-preparative HPLC (ODS, MeOH–H2O, 30:70; λ 210, 254 nm; 3 mL/min) to give compound 5 (4.2 mg, 45.5 min). Similarly, separation of fraction 24 (340 mg) yielded compounds 6 (2.8 mg) and 7 (27 mg). Compound 1 was obtained as a light yellow oil with [α]20 D+0.53 (c 0.25, MeOH). The HR-ESIMS displayed a quasi-molecular ion at m/z 281.1362 [M+Na]+ (calcd 281.1365) consistent with a molecular formula of C13H22O5. The IR spectrum displayed absorption bands characteristic of hydroxyl (3525 cm−1) and carbonyl (1761 cm−1). In the 1H NMR (DMSO‑d6, 600 MHz) (Table 1) spectrum, signals in the highfield region showed four methyl groups at δH 0.92 (3H, d, J = 6.5 Hz, H-5), 1.19 (3H, t, J = 7.1 Hz, H-14), 1.26 (3H, s, H-11) and 1.42 (3H, s, H-12). In addition, it also exhibited six aliphatic protons at δH 1.30–2.54 [1.30 (1H, m, H-7), 1.53 (1H, m, H-7), 1.78 (1H, m, H-4), 2.06 (1H, m, H-8), 2.40 (1H, dd, J = 17.3, 8.4 Hz, H-9α) and 2.54 (1H, dd, J = 17.3, 8.4 Hz, H-9β)], three alkoxy protons at δH 4.04 (1H, d, J = 10.5 Hz, H-2) and 4.09 (2H, dd, J = 7.1, 3.4 Hz, H-13). The 13C NMR spectrum exhibited thirteen carbon signals, including two carbonyl groups at δC 175.3 (C-10) and 175.1 (C-1), three oxygenated carbons at δC 87.0 (C-7), 67.7 (C-2) and 60.6 (C-13), four triplets at δC 50.9 (C-8), 39.2 (C-3), 34.2 (C-9) and 29.9 (C-4), and four methyl carbons at δC 29.5 (C-12), 21.9 (C-11), 17.8 (C-5) and 14.6 (C-14). The 1 H–1H COSY spectrum showed the correlations between H-2, H-3, H-4, H-5, H-8 and H-9, and H-13 and H-14 (Fig. 2). In the HMBC spectrum (Fig. 2), the correlations between H-9 and C-8, C-10; H-8 and C-11, C12, C-9, C-7 and correlations between the methyl at H-11 and C-12, C-7, C-8 established the structure of 2,2-dimethylbutanolide (Nishimura et al., 1986). Furthermore, the correlations between the methyl at H-14 and C-13; H-13 and C-1 suggested the presence of an ethyl ester moiety. Correlations between the methyl at H-5 and C-4 and C-3, correlations between H-3 and C-5, C-4 and C-2, and correlations between H-2 and C4 and C-3, confirmed the methyl was connected with the trisubstituted propyl moiety. Besides, one hydroxyl group was deduced to exist in the structure due to the above NMR spectra and mass spectrometry data. It was further demonstrated to located at C-2 based on the highfield chemical shifts of C-2 (δC 67.7). Thus, the 4-methyl-2-hydroxybutyric acid ethyl ester substituent could be deduced (Fig. 2). The correlations, particularly from H-5 to C-8 and H-9 to C-4, supported the linkage between C-4 and C-8 (Fig. 2). The asymmetric carbon center at C-2 of 1, comparison of the CD spectrum confirmed the C-2 being R configuration, based on the negative Cotton effect at 211.5 nm (Valeria et al., 1997). Moreover, in the NOESY experiment, the cross-peaks between H-9β and H-8, and H-8 and H-12 confirmed that H-9β, H-8 and H-12 were in the same face.
Fig. 1. Chemical structures of compounds 1–7.
Fig. 2. Key HMBC and 1H–1H COSY correlations of compound 1.
Thus, the structure of compound 1 was deduced as (2R)-4-(2,2-dimethyl-5-oxotetrahydrofuran-3-yl)-2-hydroxypent-3-anoic acid ethyl ester, named as dasycarpusester C. The six known compounds 2–7 were determined to be adenosine (2) (Zuo et al., 2007), benzyl-O-β-D-glucopyranoside (3) (Jin et al., 2017), haploperoside A (4) (Liu et al., 2016), lyoniresinol-3α-O-β-D-glucopyranoside (5) (Han et al., 2002), 4-O-α-L-rhamnopyranosyl(1 → 6)-βD-glucopyranosyl acetophenone (6) (Wu et al., 2008), and paeoniflorin (7) (Shu et al., 2014), respectively, by comparison of their NMR data with those in the literature. 4. Chemotaxonomic significance The EA fraction from the ethanol extract of the root bark of Dictamnus dasycarpus was fractionated using several chromatographic methods and afforded seven natural products (Fig. 1), including one ester and six glycosides, representing new chemotaxonomic information for the genus Dictamnus. Compounds 1–7 could be served as potential chemotaxonomic makers to differentiate Dictamnus dasycarpus from other species of Dictamnus, in view of the fact that they have not been isolated from the other species of this genus so far. In addition, compounds 1, 3 and 5–7 were obtained from the family Rutaceae for the first time. Compound 1 ((2R)-4-(2,2-dimethyl-5-oxotetrahydrofuran-3-yl)-2hydroxypent-3- anoic acid ethyl ester) has a similar structure to previously reported dasycarpusester B (Guo et al., 2012), but it has no methyl group at C-13 and is substituted by ethyl. This is the first report of this character. Previously, compound 2 was reported from the genus Tetradium (Wu et al., 1995) also from the family Rutaceae and may indicate a close relationship between the two genera. Compounds 3–7 are glycosides which possess benzyl and glycosyl as their main skeletons. To date, compound 4 was only isolated from Clausena (Rutaceae) (Liu et al., 2016) and Haplophyllum (Rutaceae) (Yuldashev et al., 1985), and none of the other coumarin glycosides has 2
Biochemical Systematics and Ecology 86 (2019) 103931
J.-L. Zhang, et al.
been reported from Dictamnus dasycarpus. This study extends the chemical knowledge about the constituents of family Rutaceae. Compounds 3 and 5–7 were obtained from the family Rutaceae for the first time, they have been reported from unrelated families. For instance, compounds 3 and 6 have been reported from Acanthaceae (Huo et al., 2006 and Zhang et al., 2015) and Compositae (Zhou et al., 2007; Wu et al., 2008; Huang et al., 2009; Zhang et al., 2012), and compound 7 from Paeoniaceae (Wang et al., 2005 and Shu et al., 2014), which suggests a close chemotaxonomic relationship between these family.
31, 2052–2054. Huang, M.F., Li, N., Ni, H., Jia, X.G., Li, X., 2009. J. Shenyang Pharm. Univ. 26, 257–259. Jeong, G.S., Byun, E., Li, B., Lee, D.S., An, R.B., Kim, Y.C., 2010. Arch Pharm. Res. (Seoul) 33, 1269–1275. Jin, Y., Sun, Y., Wu, Y.N., Zhang, C.Y., 2017. Chin. Pharmaceut. J. 52, 1223–1226. Kim, H., Kim, M., Kim, H., Lee, G.S., An, W.G., Cho, S.I., 2016. J. Mol. Med. 38 S74-S74. Komissarenko, N.F., Levashova, I.G., Akhmedov, U.A., 1984. Chem. Nat. Compd. 20, 229–230. Lv, M.Y., Xu, P., Tian, Y., Liang, J.Y., Gao, Y.Q., Xu, F.G., Zhang, Z.J., Sun, J.B., 2015. J. Ethnopharmacol. 171, 247–263. Liu, J., Li, C.J., Yang, J.Z., Ma, J., Zhang, D.M., 2016. J. Pharm. Res. 35, 125–128. Nishimura, K., Eiichi, M., Oshio, T.I., Akira, U., Tadataka, N., Masanori, K., Seigo, F., 1986. Phytochemistry 25, 2375–2379. Park, H.S., Hong, N.R., Ahn, T.S., Kim, H., Jung, M.H., Kim, B.J., 2015. Pharmacogn. Mag. 11, S329–S336. Qin, M., Guo, H.B., Xu, Y., 2010. Acta Lab. Anim. Sci. Sin. 18, 191–195. Shu, X.K., Duan, W.J., Liu, W., Geng, Y.L., Wang, X., 2014. J. Chin. Med. Mater. 37, 66–69. Takeuchi, N., Fujita, T., Goto, K., Morisaki, N., Osone, N., Tobinaga, S., 1993. Chem. Pharm. Bull. 41, 923–925. Valeria, C., Ernesto, F., Alfonso, M., Massimo, D.R., 1997. J. Am. Chem. Soc. 119, 12465–12470. Wu, Z.J., Ouyang, M.A., Wang, S.B., 2008. Nat. Prod. Res. 22, 483–488. Wang, R., Chou, G.X., Zhu, E.Y., Wang, Z.T., Bi, K.S., 2005. Chin. J. Nat. Med. 3, 25–27. Wu, T.S., Chang, F.C., Wu, P.L., Kuoh, C.S., Chen, I.S., 1995. J. Chin. Chem. Soc. 42, 929–934. Yang, S.C., Li, Z., Wang, J.L., Ruan, J.Y., Zheng, C., Huang, P.J., Han, L.F., Zhang, Y., Wang, T., 2018. Molecules 23, 642. Yang, J.L., Liu, L.L., Shi, Y.P., 2011. Plant. Med. 77, 271–276. Yuldashev, M.P., Batirov, E.Kh, Bdovin, A.D., Malikov, V.M., Yagudaev, M.R., 1985. Chem. Nat. Compd. 21, 25–32. Zhao, G.P., Dai, S., Cheng, R.T., 2006. Dictionary of Chinese Traditional Medicine. pp. 1018–1019. Zhao, W.M., Wolfender, J.L., Hostettmann, K., Xu, R.S., Qin, G.W., 1998. Phytochemistry 47, 7–11. Zhang, H.,W., Zhou, L.,H., Deng, C., Feng, G.,L., 2017. China Pharm 28, 4401–4404. Zuo, L., Li, J.B., Xu, J., Yang, J.Z., Zhang, D.M., Tong, Y.,L., 2007. China J. Chin. Mater. Med. 32, 688–691. Zhou, Y.Z., Chen, H., Qiao, L., Hao, D.F., Hua, H.M., Pei, Y.H., 2007. Chin. J. Med. Chem. 17, 380–382. Zhang, Y.M., Cai, Y., Dong, C., Huang, J.M., Li, Y., Yang, M., Zhang, P.Z., 2015. Chin. Tradit. Herb. Drugs 46, 3314–3317. Zhang, T., Ma, L., Wu, F., Chen, R.Y., 2012. China J. Chin. Mater. Med. 37, 1232–1236.
Acknowledgements This work was supported by the Heilongjiang Province Nature Science Foundation (LH2019H126) of PR China, the Project of Qiqihar Medical University Doctor Foundation (QY2016B-30) and Qiqihar Nature Science Foundation (SFGG-201763) of PR China. We kindly thank Mrs. Y. Sun, Mr. Q. Liu, Mr. W.B. Wang and Mr. L. Liu of Qiqihar Medical University for recording HR-ESIMS and NMR spectra. Appendix A. Supplementary data Supplementary data to this article can be found online at https:// doi.org/10.1016/j.bse.2019.103931. References Guo, L.N., Pei, Y.H., Xie, F.X., Liu, L., Cong, H., Cui, H.,X., Wang, X.L., Li, W.J., Jian, B.Y., Liu, J.C., 2016. Chin. J. Nat. Med. 14, 876–880. Gao, X., Zhao, P.H., Hu, J.F., 2011. Chem. Biodivers. 8, 1234–1244. Guo, L.N., Pei, Y.H., Chen, G., Lu, X., Xu, H., Liu, J.C., 2012. J. Asian Nat. Prod. Res. 14, 210–215. Hui, D.Y., Yu, X.F., Lv, Z.Z., Li, S.H., Ji, Y.H., 1996. J. Norman Bethune Univ. Med. Sci. 22, 608–609. Han, S.H., Lee, H.H., Lee, I.S., 2002. Arch Pharm. Res. (Seoul) 25, 433–437. Huo, C.H., Wang, B., Liang, H., Zhao, Y.Y., Lin, W.H., 2006. China J. Chin. Mater. Med.
3
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Chemical constituents from the root bark of Dictamnus dasycarpus Turcz. (Rutaceae) and their chemotaxonomic significance
T
Jin-Ling Zhanga, Shang-Chun Songb, Ji-Cheng Liua, Peng-Hui Nia, Lei Liua, Yu-Kun Maa, Yu Suna, Qi Liua, Li-Na Guoa,∗ a b
Research Institute of Medicine & Pharmacy, Qiqihar Medical University, Qiqihar, 161006, PR China Harbin University of Commerce, Harbin, 150028, PR China
ARTICLE INFO
ABSTRACT
Keywords: Rutaceae Dictamnus dasycarpus Chemotaxonomy Glycosides
This work described the isolation and characterization of seven compounds from Dictamnus dasycarpus Turcz., including one new ester, (2R)-4-(2,2-dimethyl-5-oxotetrahydrofuran-3-yl)-2-hydroxypent-3-anoic acid ethyl ester (1); and six known glycosides (2–7). The structure of compound 1 was elucidated on the basis of extensive spectral analyses, including IR, HR-ESIMS, 1D and 2D NMR (NOESY, HMBC and HSQC). All these compounds were described here for the first time from the genus Dictamnus. Moreover, the results provide further information about the diversity of compounds in the genus Dictamnus.
1. Subject and source The genus Dictamnus (Rutaceae), consists of five species that are distributed throughout Europe and North Asia but only two species are widely distributed in China. One is Dictamnus dasycarpus Turcz., which has been recorded in the Chinese Pharmacopoeia (Lv et al., 2015). The other is Dictamnus angustifolius G. Don ex Sweet, which is distributed in Xinjiang province. It is used as a traditional medicinal herb and has similar medicinal efficacy as Dictamnus dasycarpus in the treatment of many diseases, such as skin problem, rheumatism, jaundice, and cough (Zhao et al., 2006). Dictamnus dasycarpus also been reported to have anti-inflammatory (Kim et al., 2016), antifungal (Zhao et al., 1998), anti-atherosclerosis (Qin et al., 2010), hemostasis (Hui et al., 1996), anticancer (Park et al., 2015), neuroprotective (Jeong et al., 2010), as well as antioxidation activities (Guo et al., 2016 and Zhang et al., 2017). In present study, the root bark of Dictamnus dasycarpus was obtained from the city of Zalantun in Inner Mongolia China, in October 2009. The material was identified by Professor Jin-Cai Lu (Department of Traditional Chinese Materia Medica, Shenyang Pharmaceutical University). A voucher specimen (No. P-003) has been deposited in Qiqihar Medical University, Qiqihar, China. 2. Previous work Extensive studies of the genus Dictamnus led to the identification of
∗
more than 100 compounds, such as alkaloids, limonoids (Zhao et al., 1998 and Yang et al., 2011), flavonoids, sesquiterpenoids and their glycosides (Takeuchi et al., 1993 and Yang et al., 2018) and coumarins (Komissarenko et al., 1984). Alkaloids and limonoids have been reported as chemical markers of this genus (Gao et al., 2011). 3. Present study The air-dried root bark of Dictamnus dasycarpus (50 kg) were extracted three times with 95% EtOH. Solvent was removed under reduced pressure to afford a crude residue (3 kg), which was resuspended in H2O, and then partitioned sequentially with petroleum ether (PE), dichloromethane (CH2Cl2), ethyl acetate (EtOAc), and n-butanol (nBuOH). The EtOAc extract (100 g) was fractionated by silica gel open column chromatography (CC) eluted with a gradient system of CH2Cl2–MeOH (100:1 to 0:100) to yield twenty-four fractions (1–24). Fraction 16 (300 mg) was divided into five parts 16–1 to 16–5 over silica gel CC using PE-acetone (100:1 to 0:100) and the third fraction via Sephadex LH-20 CC using CH2Cl2–MeOH (1:1, v/v) as the mobile phase to obtain four fractions (16-3-1–16-3-4). Subsequently, fraction 16-3-2 was purified by semi-preparative HPLC (ODS, MeOH–H2O, 45:55; λ 210 nm; 3 mL/min) to yield compound 1 (15 mg, 44 min). Fraction 18 (425 mg) was subjected to silica gel CC and eluted with CH2Cl2–MeOH (100:1 to 0:100) to obtain nine subfractions (18-1–189). Subfraction 18–9 was subjected to Sephadex LH-20 CC (CH2Cl2–MeOH, 1:1, v/v) followed by semi-preparative HPLC (ODS,
Corresponding author. E-mail address: [email protected] (L.-N. Guo).
https://doi.org/10.1016/j.bse.2019.103931 Received 11 June 2019; Received in revised form 30 July 2019; Accepted 10 August 2019 Available online 20 August 2019 0305-1978/ © 2019 Elsevier Ltd. All rights reserved.
Biochemical Systematics and Ecology 86 (2019) 103931
J.-L. Zhang, et al.
Table 1 NMR spectra data for compound 1. No. 1 2 3 4 5 7 8 9α
1
H NMRa,b
4.04 1.30 1.78 0.92
(br d, 10.5) (m), 1.53 (m) (m) (d, 6.5)
2.06 (m) 2.40 (dd, 17.3, 8.4)
13
C NMRa,c
175.1 67.7 39.2 29.9 17.8 87.0 50.9 34.2
No.
1
H NMRa,b
9β 10 11 12 13 14 -OH
2.60 (dd, 17.3, 8.4) 1.26 1.42 4.09 1.19 5.34
(s) (s) (dd, 7.1, 3.4) (t, 7.1) (brs)
13
C NMRa,c
34.2 175.3 21.9 29.5 60.6 14.6
a Measured in DMSO‑d6, tetramethylsilane (TMS) was used as internal standard. b 600MHz. c 150MHz.
MeOH–H2O, 20:80; λ 210, 254 nm; 3 mL/min) to afford compound 3 (3.2 mg, 64.4 min). Fraction 22 (350 mg) was purified in the same way to gain compounds 2 (4 mg) and 4 (26 mg). Fraction 23 (428 mg) was loaded over a silica gel CC and eluted with CH2Cl2–MeOH (100:1 to 0:100) to obtain ten subfractions (23-1–23-10). Subfraction 23–10 was purified by semi-preparative HPLC (ODS, MeOH–H2O, 30:70; λ 210, 254 nm; 3 mL/min) to give compound 5 (4.2 mg, 45.5 min). Similarly, separation of fraction 24 (340 mg) yielded compounds 6 (2.8 mg) and 7 (27 mg). Compound 1 was obtained as a light yellow oil with [α]20 D+0.53 (c 0.25, MeOH). The HR-ESIMS displayed a quasi-molecular ion at m/z 281.1362 [M+Na]+ (calcd 281.1365) consistent with a molecular formula of C13H22O5. The IR spectrum displayed absorption bands characteristic of hydroxyl (3525 cm−1) and carbonyl (1761 cm−1). In the 1H NMR (DMSO‑d6, 600 MHz) (Table 1) spectrum, signals in the highfield region showed four methyl groups at δH 0.92 (3H, d, J = 6.5 Hz, H-5), 1.19 (3H, t, J = 7.1 Hz, H-14), 1.26 (3H, s, H-11) and 1.42 (3H, s, H-12). In addition, it also exhibited six aliphatic protons at δH 1.30–2.54 [1.30 (1H, m, H-7), 1.53 (1H, m, H-7), 1.78 (1H, m, H-4), 2.06 (1H, m, H-8), 2.40 (1H, dd, J = 17.3, 8.4 Hz, H-9α) and 2.54 (1H, dd, J = 17.3, 8.4 Hz, H-9β)], three alkoxy protons at δH 4.04 (1H, d, J = 10.5 Hz, H-2) and 4.09 (2H, dd, J = 7.1, 3.4 Hz, H-13). The 13C NMR spectrum exhibited thirteen carbon signals, including two carbonyl groups at δC 175.3 (C-10) and 175.1 (C-1), three oxygenated carbons at δC 87.0 (C-7), 67.7 (C-2) and 60.6 (C-13), four triplets at δC 50.9 (C-8), 39.2 (C-3), 34.2 (C-9) and 29.9 (C-4), and four methyl carbons at δC 29.5 (C-12), 21.9 (C-11), 17.8 (C-5) and 14.6 (C-14). The 1 H–1H COSY spectrum showed the correlations between H-2, H-3, H-4, H-5, H-8 and H-9, and H-13 and H-14 (Fig. 2). In the HMBC spectrum (Fig. 2), the correlations between H-9 and C-8, C-10; H-8 and C-11, C12, C-9, C-7 and correlations between the methyl at H-11 and C-12, C-7, C-8 established the structure of 2,2-dimethylbutanolide (Nishimura et al., 1986). Furthermore, the correlations between the methyl at H-14 and C-13; H-13 and C-1 suggested the presence of an ethyl ester moiety. Correlations between the methyl at H-5 and C-4 and C-3, correlations between H-3 and C-5, C-4 and C-2, and correlations between H-2 and C4 and C-3, confirmed the methyl was connected with the trisubstituted propyl moiety. Besides, one hydroxyl group was deduced to exist in the structure due to the above NMR spectra and mass spectrometry data. It was further demonstrated to located at C-2 based on the highfield chemical shifts of C-2 (δC 67.7). Thus, the 4-methyl-2-hydroxybutyric acid ethyl ester substituent could be deduced (Fig. 2). The correlations, particularly from H-5 to C-8 and H-9 to C-4, supported the linkage between C-4 and C-8 (Fig. 2). The asymmetric carbon center at C-2 of 1, comparison of the CD spectrum confirmed the C-2 being R configuration, based on the negative Cotton effect at 211.5 nm (Valeria et al., 1997). Moreover, in the NOESY experiment, the cross-peaks between H-9β and H-8, and H-8 and H-12 confirmed that H-9β, H-8 and H-12 were in the same face.
Fig. 1. Chemical structures of compounds 1–7.
Fig. 2. Key HMBC and 1H–1H COSY correlations of compound 1.
Thus, the structure of compound 1 was deduced as (2R)-4-(2,2-dimethyl-5-oxotetrahydrofuran-3-yl)-2-hydroxypent-3-anoic acid ethyl ester, named as dasycarpusester C. The six known compounds 2–7 were determined to be adenosine (2) (Zuo et al., 2007), benzyl-O-β-D-glucopyranoside (3) (Jin et al., 2017), haploperoside A (4) (Liu et al., 2016), lyoniresinol-3α-O-β-D-glucopyranoside (5) (Han et al., 2002), 4-O-α-L-rhamnopyranosyl(1 → 6)-βD-glucopyranosyl acetophenone (6) (Wu et al., 2008), and paeoniflorin (7) (Shu et al., 2014), respectively, by comparison of their NMR data with those in the literature. 4. Chemotaxonomic significance The EA fraction from the ethanol extract of the root bark of Dictamnus dasycarpus was fractionated using several chromatographic methods and afforded seven natural products (Fig. 1), including one ester and six glycosides, representing new chemotaxonomic information for the genus Dictamnus. Compounds 1–7 could be served as potential chemotaxonomic makers to differentiate Dictamnus dasycarpus from other species of Dictamnus, in view of the fact that they have not been isolated from the other species of this genus so far. In addition, compounds 1, 3 and 5–7 were obtained from the family Rutaceae for the first time. Compound 1 ((2R)-4-(2,2-dimethyl-5-oxotetrahydrofuran-3-yl)-2hydroxypent-3- anoic acid ethyl ester) has a similar structure to previously reported dasycarpusester B (Guo et al., 2012), but it has no methyl group at C-13 and is substituted by ethyl. This is the first report of this character. Previously, compound 2 was reported from the genus Tetradium (Wu et al., 1995) also from the family Rutaceae and may indicate a close relationship between the two genera. Compounds 3–7 are glycosides which possess benzyl and glycosyl as their main skeletons. To date, compound 4 was only isolated from Clausena (Rutaceae) (Liu et al., 2016) and Haplophyllum (Rutaceae) (Yuldashev et al., 1985), and none of the other coumarin glycosides has 2
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been reported from Dictamnus dasycarpus. This study extends the chemical knowledge about the constituents of family Rutaceae. Compounds 3 and 5–7 were obtained from the family Rutaceae for the first time, they have been reported from unrelated families. For instance, compounds 3 and 6 have been reported from Acanthaceae (Huo et al., 2006 and Zhang et al., 2015) and Compositae (Zhou et al., 2007; Wu et al., 2008; Huang et al., 2009; Zhang et al., 2012), and compound 7 from Paeoniaceae (Wang et al., 2005 and Shu et al., 2014), which suggests a close chemotaxonomic relationship between these family.
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Acknowledgements This work was supported by the Heilongjiang Province Nature Science Foundation (LH2019H126) of PR China, the Project of Qiqihar Medical University Doctor Foundation (QY2016B-30) and Qiqihar Nature Science Foundation (SFGG-201763) of PR China. We kindly thank Mrs. Y. Sun, Mr. Q. Liu, Mr. W.B. Wang and Mr. L. Liu of Qiqihar Medical University for recording HR-ESIMS and NMR spectra. Appendix A. Supplementary data Supplementary data to this article can be found online at https:// doi.org/10.1016/j.bse.2019.103931. References Guo, L.N., Pei, Y.H., Xie, F.X., Liu, L., Cong, H., Cui, H.,X., Wang, X.L., Li, W.J., Jian, B.Y., Liu, J.C., 2016. Chin. J. Nat. Med. 14, 876–880. Gao, X., Zhao, P.H., Hu, J.F., 2011. Chem. Biodivers. 8, 1234–1244. Guo, L.N., Pei, Y.H., Chen, G., Lu, X., Xu, H., Liu, J.C., 2012. J. Asian Nat. Prod. Res. 14, 210–215. Hui, D.Y., Yu, X.F., Lv, Z.Z., Li, S.H., Ji, Y.H., 1996. J. Norman Bethune Univ. Med. Sci. 22, 608–609. Han, S.H., Lee, H.H., Lee, I.S., 2002. Arch Pharm. Res. (Seoul) 25, 433–437. Huo, C.H., Wang, B., Liang, H., Zhao, Y.Y., Lin, W.H., 2006. China J. Chin. Mater. Med.
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