Sesquiterpenoids from the barks and roots of Michelia alba collected in Xuan Mai town, Hanoi City, Viet Nam

Cite this paper: Vietnam J. Chem., 2021, 59(1), 120-126 Article DOI: 10.1002/vjch.202000199 120 Wiley Online Library © 2021 Vietnam Academy of Science and Technology, Hanoi & Wiley-VCH GmbH Sesquiterpenoids from the barks and roots of Michelia alba collected in Xuan Mai town, Hanoi City, Viet Nam Ly Thi Thu Hoai1,3, Nguyen The Anh2, Nguyen Thi Luu2, Ngo Van Hieu1,3, Pham Thi Ninh2,3, Tran Van Loc2,3, Nguyen Linh Chi2,3, Nguyen Xuan Nam4, Tran Thi Phuong Thao2,3* 1Quang Binh University, 312 Ly Thuogn Kiet, Bac Ly, Dong Hoi City, Quang Binh 47000, Viet Nam 2Institute of Chemistry, Vietnam Academy of Science and Technology, 18 Hoang Quoc Viet, Cau Giay, Hanoi 10000, Viet Nam 3Graduate Academy of Science and Technology, Vietnam Academy of Science and Technology, 18 Hoang Quoc Viet, Cau Giay, Hanoi 10000, Viet Nam 4Vietnam National University of Forestry, 21 Highway, Xuan Mai Town, Chuong My, Hanoi 10000, Viet Nam Submitted December 9, 2020; Accepted December 24, 2020 Abstract Eight sesquiterpenoids including costunolide (1), parthenolide (2), 11α,13-dihydroparthenolide (3), 9β-hydroxy- dihydroparthenolide (4), (-)-bisparthenolidine (5), 11α,13-dihydro-β-cyclocostunolide (6), α-cadinol (7), magnograndiolide (8) were isolated from the barks and roots of Michelia alba. The structures of these compounds were elucidated by spectroscopic methods (MS, 1D and 2D NMR) and comparison with the reported data. Compounds 5-8 have been isolated for the first time from Michelia alba. Keywords. Michelia alba, sesquiterpenoids, costunolide, parthenolide, dihydroparthenolide, bisparthenolidine, dihydro- β-cyclocostunolide, α-cadinol, magnograndiolide. 1. INTRODUCTION Michelia alba D.C, (Vietnamese name: Ngoc lan hoa trang) is a species of Magnoliaceae family. This plant is native in Vietnam, South and Southeast Asia.[1] Due to its pleasant fragrance, M. alba flowers are utilized for worship and flavor in tea, dessert and cosmetic.[2] Its roots are used in folk medicine for the treatment of urethritis, purulent dermatitis, boils, and menstrual irregularities.[1] Its barks are used to reduce fever and to treat gonorrhoea and syphilis diseases.[3] The flowers of Michelia alba are used for the treatment of bronchitis, pertussis, headache, dizziness, chest pain, prostatitis, while the leaves can cure chronic bronchitis and prostatitis.[1-3] Phytochemical study of M. alba showed a diversity of chemical constituents of this plant such as alkaloids,[4-6] lignan,[4-6] phenols,[4-6] sesquiterpenes,[5] amides,[5-6] triterpenoids,[6] etc. In this paper, we present the isolation and characterization of eight sesquiterpenoids from the roots and barks of Michelia alba, including costunolide (1), parthenolide (2), dihydroparthenolide (3), 9β- hydroxy-dihydroparthenolide (4), (-)- bisparthenolidine (5), 11α,13-dihydro-β- cyclocostunolide (6), α-cadinol (7), magnograndiolide (8). Compounds 5-8 have been isolated for the first time from Michelia alba. 2. MATERIALS AND METHODS 2.1. Plant materials The barks and roots of Michellia alba were collected in Xuan Mai town, Chuong My district, Ha Noi, Vietnam in July 2018. The plant was authenticated by Dr. Nguyen Quoc Binh (Vietnam National Museum of Nature, VAST). The specimen (NLT01) was kept in Institute of Chemistry, VAST, 18 Hoang Quoc Viet Road, Cau Giay, Hanoi, Viet Nam. 2.2. General experiment procedures ESI-MS experiments were conducted on an Agilent 1100 mass spectrometer (USA). HR-ESIMS data Vietnam Journal of Chemistry Tran Thi Phuong Thao et al. © 2021 Vietnam Academy of Science and Technology, Hanoi & Wiley-VCH Verlag GmbH www.vjc.wiley-vch.de 121 were obtained by using a FT-ICR-MS Varian (USA). NMR spectra were recorded at 500 MHz for 1H and 125 MHz for 13C on a Bruker Avance III spectrometer (Switzerland), using TMS as an internal standard. Column chromatography was carried out on silica gel (Kieselgel 60, 230-400 mesh, Merck), RP-18 resins (30-50 μm, Fujisilisa Chemical Ltd.). TLC plates (silica gel 60 F254, 0.25 mm, Merck) were visualized under UV light (365 and 254 nm) and acid solution (H2SO4/vanillin). 2.3. Extraction and isolation The dried powder of the roots and barks of Michelia alba (5 kg) was extracted with EtOH/H2O (9:1, 3x24hx8L) at room temperature. The combined extract was suspended with water and partitioned sequentially with n-hexane, EtOAc and BuOH to give the corresponding extract (18.6, 94.0 and 70.0 g, respectively). The n-hexane extract (18.6 g) was chromatographed on a silica gel column (n- hexane/EtOAc 98:2, 95:5to 50:50) to obtain seventeen subfractions (Fr.1-Fr.17). Subfraction Fr.2 (426.4 mg) was subjected to column chromatography on silica gel (n-hexane/EtOAc 95:5) to afford compound 1 (6.5 mg). Subfraction Fr.4 (397.1 mg) was purified over a silica gel column with an elution of DCM/EtOAc (100:0.1) to obtain compound 7 (12.0 mg). Subfraction Fr.5 (374.2 mg) appeared as white solid which was washed with n-hexane to give compound 6 (5.6 mg). Subfraction Fr.13 (2.66 g) was chromatographed on a silica gel column (n-hexane/DCM/MeOH 5:5:0.1) to obtained five fractions (Fr.13.1-Fr.13.5). The solid appeared in fraction Fr.13.2 (200.0 mg) was washed with n-hexane to obtain compound 3 (6.0 mg). The EtOAc extract (94.0 g) was separated on a diaion column (MeOH/H2O 0:100, 50:50, 100:0) to obtain fifteen subfractions (Fr.1-Fr.15). Subfraction Fr.4 (1.1 g) was applied to a silica gel column (n- hexane/EtOAc/NH4OH 7:3:0.1) to obtain twenty two fractions (Fr.4.1-Fr.4.22). Fraction Fr.4.10 (96 mg) was subjected to a Sephadex column (MeOH 100 %), following by a RP column (Acetone/H2O 7:3) to give compound 5 (8.0 mg). The solid appeared in fraction Fr.6 (8.0 mg) was washed with n-hexane to give compound 2 (5.5 mg). Fraction Fr.10 (77.0 mg) was separated over a Sephadex column (n- hexane/DCM/MeOH 1/1/2) to give compound 4 (6.7 mg). Fraction Fr.13 (380.0 mg) was repeatedly chromatographed on silica gel columns (n- hexane/EtOAc/MeOH 2:8:0.1) to obtain compound 8 (8.0 mg). Figure 1: Sesquiterpenoids isolated from the roots and barks of Michelia alba Costunolide (1): Colourless needles, C15H20O2; ESI-MS (m/z): 232.9 [M+H]+; 214.9 [M-H2O+H]+ ; 1H NMR (CDCl3, 500 MHz), δH (ppm), J (Hz): 6.26 (1H, d, J = 3.5, H-13b), 5.52 (1H, d, J = 3.5, H-13a), 4.84 (1H, ddd, J = 11.0, 4.0, 1.5, H-1), 4.73 (1H, d, J = 10, H-5), 4.56 (1H, dd, J = 10.0, 9.0, H-6), 2.56 (1H, dddt, J = 9.5, 8.0, 4.0, 2.0, H-7), 2.45 (1H, dd, J = 13.5, 6.0, H-9b), 2.35-2.00 (6H, m, H-2, H-3, H-8a, H-9a), 1.68 (1H, m, H-8b), 1.70 (3H, s, H-15), 1.42 (3H, s, H-14),; 13C NMR (CDCl3, 125 MHz): 170.43 (C-12), 141.43 (C-4), 140.14 (C-11), 136.92 (C-10), 127.32 (C-5), 127.09 (C-1), 119.58 (C-13), 81.91 (C- Vietnam Journal of Chemistry Sesquiterpenoids from the barks and roots © 2021 Vietnam Academy of Science and Technology, Hanoi & Wiley-VCH Verlag GmbH www.vjc.wiley-vch.de 122 6), 50.45 (C-7), 41.02 (C-9), 39.48 (C-3), 28.09 (C-8), 26.19 (C-2), 17.32 (C-15), 16.09 (C-14). Table 1: 1H NMR spectra of compounds 2-5 (δH (ppm), J (Hz)) Position 2a Parthenolideb 3a 11α,13- Dihydro- parthenolideb 4a 9β -hydroxy- dihydro- partheno- lidea 5a (-)-bis- parthenolidineb 1 5.21 dd (14.0, 2.5) 5.21 brdd (12.5, 2.8) 5.17 d (11.5) 5.15 dd (11.9, 2.3) 5.37 dd (12.0, 1.5) 5.37 (br, dd,12.3, 1.2) 5.28 dd (12.5, 2.5) 5.27 dd (9.8, 2.2) 2 2.11-2.21 m 2.35-2.44 m 2.11-2.22 m 2.35-2.46 m 2.08 m 2.38 m 2.11 dddd (2.3, 6.0, 13.0, 13.3) 2.37 dddd (5.0, 11.9, 13.0, 13.3) 2.22 m 2.48 dddd (13.5, 12.0, 5.5, 5.0) 2.14 (m) 2.46 (dddd, 13.4, 12.2, 5.4, 4.5) 2.17 d (12.0) 2.31 - 2.42 m 2.26 dd (12.1, 6.0) 2.40 m 3 1.24 dt (15.0, 6.0) 2.11-2.21 m 1.24 brdt (13.3, 6.1) 2.11-2.22 m 1.21 dd (13.0, 6.0) 2.15 m 1.21ddd (6.0, 13.0, 13.3) 2.16 m 1.20 ddd (13.0, 6.0, 5.5) 2.14 m 1.12 (ddd, 13.0, 5.6, 5.5) 2.14 m 1.21 dd (13.0, 5.5) 2.10, dd (14.5, 5.5) 1.23 td (13.9, 5.9) 1.88 dd (14.6, 5.9) 4 - - - - - - - - 5 2.78 d (8.5) 2.78 d (8.9) 2.69 d (9.0) 2.69 d (9.0) 2.61 d (8.5) 2.60 d (8.9) 2. 75 d (9.0) 2.74 d (8.8) 6 3.86 t (8.5) 3.86 t (8.6) 3.80 dd (9.0, 9.5) 3.80 dd (8.4, 9.0) 3.80 t (8.5) 3.8 t (8.6) 3.86 t (8.0) 3.86 t (8.8) 7 2.78 dt (8.5, 1.0) 2.780 dtt (8.6, 3.5, 1.4) 2.29 m 2.28 m 1.98 m 1.96 m 2.42 m 2.40 m 8 2.11-2.21 m 1.72 dddd (15.0, 13.0, 7.5, 2.0) 2.11-2.22 m 1.72 dddd (15.3, 12.5, 8.5, 2.0) 2.29 m 1.88 m 2.28 m 1.80 m 1.98 m 1.95 m 1.96 m 1.86 m 1.88 dd (14.5, 5.5) 1.69 m 2.18 m 1.70 m 9 2.11-2.21 m 2.35-2.44 m 2.11-2.22 m 2.35-2.46 m 1.88 m 2.15 m 1.80 m 2.25 m 4.17 dd (8.5, 4.0) - 4.16 m 2.26 (13.5, 6.5) 2.17 m 2.l0-2.18 m 2.l0 – 2.18 m 10 - - - - - - - - 11 - - 1.62 m 2.27 dq (6.8, 10.3) 2.32 m 2.29 m 2.37 2.40 m 12 - - - - - - - - 13 5.62 d (3.0)/ 6.33 d (3.5) 5.62 d (3.2)/ 6.33 d (3.7) 1.24 d (7.0) 1.25 d (6.8) 1.31 d (7.0) 1.30 d (7.0) 3.15 dd (13.0, 3.0)/2.93 dd (13.0, 4.0) 3.15 dd (13.1, 2.8)/2.92 dd (13.1, 2.8) 14 1.71 s 1.71 d (1.1) 1.71 s 1.68 s 1.74 s 1.73 s 1.69 s 1.67 s 15 1.30 s 1.30 d (1.0) 1.30 s 1.27 s 1.32 s 1.31 s 1.30 s 1.30 s NH 5.29 s - aCDCl3, 500 MHz, bCDCl3, 400 MHz. Parthenolide (2): Colourless powder, C15H20O3; ESI-MS (m/z): 270.8 [M+Na]+; 519.0 [2M+Na]+; 1H (CDCl3, 500 MHz) and 13C (CDCl3, 125 MHz) NMR, see tables 1 and 2. Vietnam Journal of Chemistry Tran Thi Phuong Thao et al. © 2021 Vietnam Academy of Science and Technology, Hanoi & Wiley-VCH Verlag GmbH www.vjc.wiley-vch.de 123 11α,13-Dihydroparthenolide (3): Colourless powder, C15H22O3; ESI-MS (m/z): 248.8 [M-H]-, 232.8 [M+H-H2O]+ ; 1H (CDCl3, 500 MHz) and 13C NMR (CDCl3, 125 MHz), see tables 1 and 2. 9β-hydroxy-dihydroparthenolide (4): Colourless powder, C15H22O4; ESI-MS (m/z): 266.9 [M+H]+, 248.8 [M+H-H2O]+ ; 1H NMR (CDCl3, 500 MHz) and 13C NMR (CDCl3, 125 MHz), see tables 1 and 2. (-)-bisparthenolidine (5): White solid, C30H43NO6; ESI-MS (m/z): 514.0 [M+H]+; HR- ESIMS (m/z): 514.3163, calcd. for C30H44NO6 : 514.3169 [M+H]+; 1H (CDCl3, 500 MHz) and 13C NMR (CDCl3, 125 MHz), see tables 1 and 2. 11α,13-Dihydro-β-cyclocostunolide (6): Colourless needles, C15H22O2; ESI-MS (m/z): 234.9 [M+H] +, 216.8 [M+H-H2O]+ ; 1H NMR (CDCl3, 500 MHz), δH (ppm), J (Hz): 4.91 (1H, d, J = 1.5, H- 15a), 4.75 (1H, d, J = 1.5, H-15b), 3.97 (1H, t, J = 11.0, H-6), 2.32 (2H, m, H-3a, H-7), 2.11 (1H, d, J = 11.0, H-5), 2.00 (1H, ddd, J = 18.0, 14.5, 7.0, H-3b), 1.82 (1H, m, H-11), 1.70-1.30 (8H, m, H-1, H-2, H- 8, H-9), 1.21 (3H, d, J = 6.5, H-13), 0.86 (3H, s, H- 14); 13C NMR (CDCl3, 125 MHz): 179.50 (C-12), 144.76 (C-4), 108.85 (C-15), 79.82 (C-6), 54.51 (C- 5), 52.73 (C-7), 41.84 (C-1), 41.25 (C-11), 40.02 (C- 9), 38.55 (C-10), 36.00 (C-3), 23.27 (C-8), 22.89 (C- 2), 18.05 (C-14), 12.50 (C-13). Table 2: 13C NMR spectra of compounds 2-5 aCDCl3, 125 MHz, bCDCl3, 100 MHz. α-cadinol (7): White solid, C15H26O; ESI-MS (m/z) : 222.5 [M+H] +; 1H NMR (CDCl3, 500 MHz), δH (ppm), J (Hz): 5.48 (1H, s, H-5), 2.12 (1H, m, H- 9), 1.95-1.89 (4H, m, H-7, H-4a, H-8A), 1.67 (1H, m, H-2a), 1.60 (3H, s, H-12), 1.41-1.25 (4H, m, H- 2b, H-3, H-8b), 1.15 (3H, s, H-13), 1.01 (1H, m, H- 8B), 0.93 (1H, m, H-4), 0.85 (3H, d, J = 7.0, H-11), 0.72 (3H, d, J = 7.0, H-10); 13C NMR (CDCl3, 125 MHz): 134.34 (C-6), 122.68 (C-5), 70.67 (C-1), 47.98 (C-8a), 46.70 (C-4), 40.34 (C-2), 37.76 (C- 4a), 30.92 (C-7), 28.46 (C-13), 26.19 (C-9), 23.74 (C-12), 22.61 (C-8), 21.40 (C-11), 19.84 (C-3), 15.21 (C-10). Magnograndiolide (8): Colourless powder, C15H22O4; ESI-MS (m/z): 554.5 [2M+Na] +; 1H NMR (CDCl3, 500 MHz), δH (ppm), J (Hz): 6.24 (1H, d, J = 3.5, H-13a), 5.54 (1H, d, J = 3.5, H-13b), 4.24 (1H, dd, J = 12.0, 10.0, H-6), 2.69 (1H, m, H-7), 2.63 (1H, m, H-1), 2.38 (1H, t, J = 12.0, H-5), 2.14 (1H, dddd, J = 14.5, 11.0, 4.5, 3.5, H-8a), 2.08 (2H, s, OH), 2.00 (1H, m, H-9b), 1.97 (1H, m, H-2a), 1.84 (1H, ddd, J = 12.0, 7.0, 5.0, H-3a), 1.81 (1H, ddd, J = 12.0, 7.0, 5.0, H-3b), 1.70 (1H, ddd, J = 13.0, 4.0, 5.0, H-9a), 1.61 (1H, m, H-2b), 1.47 (1H, m, H-8b), 1.35 (3H, s, H-14), 1.24 (3H, s, H-15); 13C NMR (CDCl3, 125 MHz): 169.46 (C-12), 138.55 (C- 11), 120.48 (C-13), 82.82 (C-6), 79.94 (C-4), 74.80 (C-10), 55.42 (C-5), 49.86 (C-1), 47.31 (C-7), 43.86 (C-9), 39.39 (C-3), 25.38 (C-2), 25.07 (C-8), 24.29 (C-14), 23.55 (C-15). Position 2a Parthenolideb 3a 11α,13- Dihydro- parthenolideb 4a 9β-hydroxy- dihydro- parthenolidea 5a (-)-bis- parthenolidineb δC (ppm) 1 125.34 125.3 125.22 125.1 126.38 126.6 125.37 125.3 2 24.17 24.2 24.09 24.0 23.79 24.2 24.17 24.2 3 36.42 36.4 36.70 36.6 36.40 36.8 36.59 36.5 4 61.52 61.5 61.44 61.4 61.32 61.8 61.63 61.6 5 66.45 66.4 66.41 66.3 66.12 66.5 66.46 66.1 6 82.48 82.5 82.18 82.1 81.30 81.7 82.62 82.3 7 47.74 47.7 52.00 51.9 48.61 48.9 49.00 49.0 8 30.70 30.7 29.82 29.7 37.84 38.2 30.24 30.2 9 41.26 41.3 41.20 41.1 79.65 80.0 40.93 40.9 10 134.61 134.6 134.44 134.4 136.49 136.9 134.37 134.3 11 139.31 139.3 42.52 42.4 42.17 42.5 45.77 45.5 12 169.24 169.3 177.30 179.6 176.90 177.4 176.69 176.7 13 121.21 121.3 13.28 13.2 13.27 13.6 46.35 46.2 14 16.97 17.0 17.19 17.1 17.32 17.7 17.28 17.2 15 17.32 17.3 16.89 16.8 10.89 11.3 16.88 16.8 Vietnam Journal of Chemistry Sesquiterpenoids from the barks and roots © 2021 Vietnam Academy of Science and Technology, Hanoi & Wiley-VCH Verlag GmbH www.vjc.wiley-vch.de 124 3. RESULTS AND DISCUSSION Compound 1 was isolated as colorless needles, with a molecular ion peak at m/z 232.9 [M+H]+ in ESI- MS spectrum. The NMR data suggested the feature of a sesquiterpene lactone structure in compound 1. The 13C NMR spectra indicated fifteen carbons, including one carbonyl lactone at δC 170.42 (C-12), six olefin carbons at δC 141.43-119.58 (C-1, C-4, C- 5, C-10, C-11 and C-13), one oxygenated methine carbon at δC 81.91 (C-6), 4 methylenes at δC 26.19 (C-2), 39.48 (C-3), 28.09 (C-8), 41.02 (C-9), one methine at δC 50.45 (C-7), and 2 methyls at δC 17.32 (C-15), 16.09 (C-14). Its 1H-NMR spectrum displayed the signals corresponding with 13C NMR spectra, dedicating by the appearance of four olefin protons at δH 5.52 and 6.26 (each 1H, d, J = 3.5, H- 13a and H-13b), 4.84 (1H, ddd, J = 11.0, 4.0, 1.5, H- 1) and 4.73 (1H, d, J = 10.0, H-5). The oximethine proton was resonated at δH 4.56 (1H, dd, J = 10.0, 9.0, H-6). Two methyl singlets at δH 1.70 and 1.42 were assigned to H-14 and H-15, respectively. The other methylene protons were observed at δH 2.45- 1.68. Based on the above analysis and comparison with the reported data,[7] 1 was determined as costunolide. This compound was isolated from the barks and the roots of Michelia alba.[8,9] Compound 2 was obtained as a colourless powder. Its ESI-MS displayed a molecular ion peak at m/z 270.8 [M+Na]+. The NMR data of 2 showed the signals similar to those of 1, suggesting that 2 is a serquiterpene lactone. The only difference was the appearance of an epoxy group at carbon atoms C-4 and C-5 in compound 2, instead of a double bond in compound 1. This was confirmed by the appearance of a tertiary oxygenated carbon at C-4 (δC 61.52) and an oximethine carbon/proton at C-5/H-5 (δC/δH 66.45/82.48). The structure of 2 was unambiguously assigned by 2D NMR (COSY, HSQC, HMBC, NOESY) spectral data. The HMBC correlation between H-14 (δH 1.71) with C-1 (δC 125.34), C-9 (δC 41.26), C-10 (δC 134.61) as well as H-15 (δH 1.30) with C-3 (δC 36.42), C-4 (δC 61.52) and C-5 (δC 66.45) confirmed the location of the methyl groups in 2. Besides, the correlations between H-13a (δH 5.62)/C-12 (δC 169.24), C-7 (δC 47.74) and H- 13b (δH 6.33)/C-11 (δC 139.31), C-12 (δC 169.24), C- 7 (δC 47.74) further determined the structure of the lactone ring. The relative configuration of 2 was deduced based on the NOESY corrleations between H-5 (δH 2.78)/H-7 (δH 2.78), H-6 (δH 3.86)/H-14 (δH 1.71), H-15 (δH 1.30). By comparison of NMR data of 2 with the literature,[10] this compound was identified as parthenolide. It was reported that parthenolide showed antiflammatory and anticancer activity.[13] Compound 3 was obtained as a colourless powder. The ESI-MS spectrum of 3 indicated a molecular ion peak at m/z 248.8 [M-H]-. The NMR spectral data of 3 indicated the signals similar to those of 2, except the signals at C-11 and C-13. In the structure of 3, a methyl group was located at C- 11, instead of a double bond in 2. This was confirmed by the appearance of the signals at H-11 (δH 1.62, m)/C-11 (δC 42.52) and H-13 (δH 1.24, d, J = 7.0)/C-13 (δC 13.28) in NMR spectral data of 3. With the above evidences and comparison with the literature,[10] compound 3 was identified as 11α,13- dihydroparthenolide which was isolated from the barks of Michelia alba.[9] Compound 4 was yielded as a colourless powder. Its ESI-MS indicated a molecular ion peak at m/z 266.9 [M+H]+. The NMR spectral data of 4 showed the signals similar to 3, except the presence of an additional hydroxyl group at C-9/H-9 [δC/δH 79.65/4.17 (1H, dd, J = 8.5, 4.00)]. Futhermore, due to the substitution of hydroxyl group at C-9, the signal of carbon C-8 shifted to much downfield chemical shift (δC 37.84), comparing with those in compound 3 (δC 29.82). From the above evidences and by comparison with the literature,[14] compound 4 was elucidated to be as 9β-hydroxy- dihydroparthenolide. It was reported that 9β- hydroxy-dihydroparthenolide was isolated from the roots of Michelia alba.[8] Compound 5 was isolated as a white solid. Its molecular formula was established from a molecular ion peak at m/z 514.3163, calcd. for C30H44NO6 514.3169 [M+H]+. The NMR and HR- ESIMS data suggested that compound 5 is a dimer of 11α,13-dihydroparthenolide, of which each monomer linked to each other by secondary amine bond (-NH). The 1H and 13C NMR exhibited a half total of protons and carbons calculating by spectral data, due to the symmetry of the structure feature of this compound. The NMR data of 5 indicated the signals similar to those of 3, except the location of a methylene group at C-11 resonated at much downfield chemical schift [δC/δH 46.35 (C-13)/3.15 (H-13a, 1H, dd, J = 13.0 and 3.0) and 2.93 (H-13b, 1H, dd, J = 13.0, 4.0)], comparing with those in 3 [δC/δH 13.28/1.24 (3H, d, J = 7.0)]. This was due to the effect of the amine neighbor group (-NH). Thus, the structure of 5 was determined as (-)- bispathenolidine by comparing its spectral data with those in the literature.[11] Compound 5 is an unusual germacranolide alkaloid which was isolated for the first time from M. alba. Vietnam Journal of Chemistry Tran Thi Phuong Thao et al. © 2021 Vietnam Academy of Science and Technology, Hanoi & Wiley-VCH Verlag GmbH www.vjc.wiley-vch.de 125 Compound 6 was obtained as colorless needles. A molecular ion peak at m/z 234.9 [M+H]+ was displayed in its ESI-MS spectrum. Its 13C NMR spectra displayed 15 carbons, including one carbonyl lactone at δC 179.50 (C-12), one oxygenated methine carbon at δC 79.82 (C-6), two olefin carbons [δC 144.76 (C-4) and 108.85 (C-15)], five methylene, two methyl, three methine and one tertiary carbons at δC 54.51-12.50. The 1H NMR spectral data showed an exo-methylene group at δH 4.91 (1H, d, J = 1.5, H-15a) and 4.75 (1H, d, J = 1.5, H-15b), one