A new Lignan from the bark of Machilus odoratissima Nees
Huu-Nghi Nguyen1, Nguyen Thi Hong Ngoc1, Dang Thai Duong2, Dang Thai Hoa2, Tran Thi Oanh1*
1 Institute for Research and Development of Natural Products, 176 Phung Khoang, Nam Tu Liem Distric, Hanoi city, Vietnam
2 Faculty of Forestry, University of Agriculture and Forestry, Hue University, 102 Phung Hung, Hue City, Vietnam
A new aryltetralone lignan was identified as 8,8′-Dimethyl-3′,4′-dimethoxy-4,5-methylenedioxy-2,7’-cyclolignan-7-one (1) from the bark of Machilus odoratissima Nees. The structure was elucidated by spectrometric analyses and comparison with those reported in literature. To our knowledge, this is the first time, the lignan has been isolated and identified from the genus Machilus.
Key words: Machilus odoratissima Nees, lignan, 4′-O-methylenshicine, NMR.
Machilus odoratissima Nee, a species belongs to the genus Machilus, is a medical herb distributed throughout Vietnam and has been used as folk medicine owing to their antiseptic and anti-inflammation activities. Research have identified about 140 bioactive compounds from this genus which include lignans, butanolides, flavonoids, alkanoids, sesquiterpenes, diterpenes, and others. A mong their bioactive compounds, lignans are the predominant constituents within the genus Machilus. The biological activities of the genus Machilus have been reported such as antibacterial, antioxidant, anticancer, hepatoprotective and neuroprotective activities.
Irrespective to extensive work on identification of compounds from other species of the genus Machilus, few attempts have been made to characterize constituents from M. odoratissima. Among these efforts, several lignans and neolignans with antioxidant and antibacterial activities have been identified and evaluated from M. odoratissima. Owing to potential pharmacological application of M. odoratissima, the present study aimed to identify bioactive lignans from this species. The new lignan (1) was identified from the bark of M. odoratissima. The structure properties were elucidated through high resolution-electrospray ionization-mass spectrometry (HR-ESI-MS) and nuclear magnetic resonance (NMR) based techniques and comparison with the reported spectral data in the literature.
2.1. General experimental procedures
The 13C (125 MHz) and 1H (500 MHz) NMR spectrum were obtained using a Bruker Avance AM 500 FT – NMR spectrometer (Bruker, Germany) using trimethylsilane as an internal standard. The HR-ESI-MS spectra were recorded from AGILENT 1100 LC – MSD with G1946D mass spectrometer (AGILENT, Germany). Separation was performed using silica gel 60 column (0.063 – 0.2 mm, Merk, Germany), thin layer chromatography (TLC) was carried out on Merck TLC plate (Silica gel 60 GF254) and detected by spraying with 10% H2SO4 in 50% EtOH, followed by heating on a hot plate at 110°C.
2.2. Plant material
The air-dried bark of M. Odoratissima was collected from central provinces in Vietnam. A voucher specimen (no. HCTN 2006-6) is deposited in the Laboratory of Chemistry of Natural Product, Faculty of Chemistry, Vietnam National University, Hanoi, Vietnam.
2.3. Extraction and isolation
The air-dried bark of M. Odoratissima (0.8 kg) was powdered and extracted three times (each time for 2 days) with ethanol (EtOH) 70% at room temperature. After concentration by evaporation under reduced pressure, the residue EtOH extract was suspended in EtOH:water (1:1, v/v) and sequentially extracted with ethylacetate. The ethylacetate fraction (40.3 mg) was separated on a silica gel column (0.063-0.2 mm) using various rates of the mixture of dichlomethane:methanol (100:1; 20:1; 15:1; 10:1; 4:1; and 2:1, v/v). Factions were collected on the basis of TLC patterns. Faction 1 (0.58 g) was further purified by silica gel column using n-hexan:acetone (5:1, v/v) to give 1 (10.0 mg).
Compound (1) was collected as a yellow oil. HR-ESI-MS spectra showed molecular ion peak at m/z 355.1546 [M+H]+, which was in accordance with the molecular formula C21H22O5. The 1H-NMR spectrum of (1) (Table 1) showed proton signals of two aromatic rings in which two singlet protons of the A ring at δH 6.44 (1H, s, H-6) and 7.56 (1H, s, H-3), and three proton of the B ring at δH 6.54 (1H, d, J = 1.5 Hz, H-2′), 6.53 (1H, dd, J = 2.0 Hz; 8.0, H-6′), and 6.73 (1H, d, J = 8.0 Hz, H-5′). A methylene signal shifted downfield at δH 5.94 (2H, s), which was O-CH2-O group. The spectrum also showed three methine signals at δH 3.96 (1H, d, J = 5.0 Hz, H-7′), 2.39 (1H, m, H-8), and 2.77 (1H, m, H-8′). Two upfield methyl signals at δH 0.98 (3H, d, J = 7.0 Hz, CH3-9) and 1.12 (3H, d, J = 7.0 Hz, CH3-9′) and two methyl signals of methoxyl groups bonded with the B ring at δH 3.94 (3H, s, OCH3-3′) and 3.79 (3H, s, OCH3-4′).
The 13C-NMR and DEPT spectrum of (1) (Table 1) showed twenty one carbon signals in which a carbonyl signal shifted very downfield at δC 199.8. Twelve carbon signals belong to two aromatic rings at δC 153.8 (C-4), 148.3 (C-3′), 147.9(C-4′), 146.3 (C-5), 138.5 (C-2), 137.6 (C-1′), 125.6 (C-1), 121.9 (C-6′), 111.8 (C-6), 109.0 (C-2′), 108.2 (C-3), and 108.1 (C-5′). A carbon signal of dioxymethylene at δC 101.0 (O-CH2-O), Two methoxyls at δC 55.98 and 55.96 (OCH3), three methines at δC 50.4 (C-7′), 42.6 (C-8), 42.4 (C-8′), and two methyls at δC 15.8 and 11.9 (CH3-9, CH3-9′). The structure of (1) was further clarified on the basis of COSY, and HMBC analyses as summaried in Table 1 and refered to those in the literature. As a results, 1 was identified as 8,8′-Dimethyl-3′,4′-dimethoxy-4,5-methylenedioxy-2,7’-cyclolignan-7-one or 4′-O-methylenshicine and the formular structure was shown in Figure 1. to our knowledge, the new lignan (1) has never been reported from the genus Machilus thus far. Since lignans have been reported with neuroprotective, hepatoprotective, antioxidant, anticancer activities, pharmacological properties of the new lignan are under our further investigation.
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Corresponding author: Tran Thi Oanh
Institute for Research and Development of Natural Products
176 Phung Khoang, Nam Tu Liem District, Hanoi, Vietnam