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Chemical Constituents from Maca (Lepidium meyenii).

Byline: Zhen Zang, Meng Jia Li, Ze Lei, Li Ma, Feng Yi Liu, Dan Li Li, Xiang Hua Wu and Yong Zhao

Summary: Two new natural products, tetrahydro-2-benzyl-1H-pyrrolo-[1,2-C] imidazole-1,3(2H) -dione (1) and (1S,4R,4aR,9aS)-4a-methyl-1,4,4a,9a- tetrahydro-1,4-methano-anthracene-9,10-dione (2), together with eleven known compounds (3-13) were isolated from the petroleum ether fraction of the 95% ethanol extract from the tubers of Lepidium meyenii. Among them, compounds 1 and 2 were new natural products, compounds 3, 4, 7-11, and 13 were isolated from L. meyenii for the first time. In addition, the spectroscopic data of compound 1 were firstly reported. Their structures were elucidated by 1D and 2D NMR spectroscopic analysis along with comparison with literature reports.

Keywords: Lepidium meyenii, Tubers, Imidazole derivative, Macamides, Tetrahydroanthraquinone, Phenylacetonitrile.

Introduction

Maca (Lepidium meyenii Walp.), belonging to the Cruciferae family, has been cultivated in the Peruvian Andes as a staple food crops for the indigenous people [1]. The reputation of Maca as a libido and fertility enhancer has made it popular in the USA and other Western countries. Besides these properties, Maca has also been used traditionally for the treatment of rheumatism, premenstrual, and menopausal symptoms [2]. Previous phytochemical studies have demonstrated the presence of some alkaloids, glucosinolates, fatty acids, and macamides in this plant [3-6]. Furthermore, the research results of McCollom and W. W. Jin revealed the constituents for Maca were different with the change of planting area [7, 8]. To our best of knowledge, there have not been reports on the constituents isolated from Maca cultivated in Yunnan Province, China.

In the course of searching for more bioactive constituents from Maca collected in Qujing Prefecture, Yunnan Province, Republic of China, two new natural products, tetrahydro-2- benzyl-1H-pyrrolo [1,2-C] imidazole-1,3 (2H)-dione (1) and (1S,4R,4aR,9aS)-4a-methyl-1,4,4a,9a- tetrahydro-1,4-methanoanthracene-9,10-dione (2) [9], along with eleven known compounds dibenzylurea (3) [10], N-benzylformamide (4) [11], N-benzylocta decanamide (5) [7], N-(3-methoxy benzyl)-hexadecanamide (6) [7], 1-O-b-D-gluco pyranosyl (2S,3R,4E,8Z)-2-N-(2'-hydroxy palmitoyl) octadecasphinga-4,8-dienine (7) [12], 3-hydroxy phenyl acetonitrile (8) [13], 3-methoxyphenyl acetonitrile (9) [14], 4-hydroxylphenylacetonitrile (10) [15], phenylacetonitrile (11) [16], ursolic acid (12) [17], and cycloeucalenol (13) [18] (Fig. 1) were isolated and identified by 1D and 2D NMR spectroscopic analysis.

Among them, compounds 3, 4, 7-11, and 13 were isolated from L. meyenii for the first time, and derivatives of phenylacetonitrile and tetrahydro anthraquinone were the first examples from this plant. The spectroscopic data of 1 were also provided firstly in this paper.

Experimental

General Experimental

Optical rotations were recorded in MeOH using a JASCO P-1020 Polarimeter (Jasco Corp., Japan). UV spectra were acquired in MeOH with a Shimadzu UV-2401PC UV-VIS spectrophotometer (Shimadzu Corp., Japan). IR spectrum was recorded on a Bruker Tensor 27 FTIR Spectrometer with KBr pellet (Bruker Corp., Germany). 1D and 2D NMR spectra were measured on a Bruker DRX-500 instrument with TMS as internal standard (Bruker Corp., Switzerland). ESI-MS spectra were recorded using a Waters Xevo TQ-S Ultrahigh Pressure Liquid Chromatography Triple Quadrupole Mass Spectrometer (Waters Corp., UK). Column chromatography was performed on silica gel (200-300 mesh; Qingdao Marine Chemical Inc.), Lichroprep RP-18 gel (40-63 um, Merck, Darmstadt, Germany). Semipreparative HPLC was performed on an Agilent 1100 liquid chromatograph with a Zorbax SB-C18, 9.4 mm 25 cm, column.

Column chromatography was performed using silica gel (100-200 mesh and 200-300 mesh, Qingdao Marine Chemical Inc., China), silica gel 60 RP-18 (EMD Chemicals Inc., Germany) and Sephadex LH-20 (25-100 um, Pharmacia Biotech Ltd., Sweden). Thin-layer chromatography (TLC) was carried out on silica gel 60 F254 on glass plates (Qingdao Marine Chemical Inc.) using various solvent systems.

Plant Material

The tubers of Lepidium meyenii Walp. were collected in the Qujing prefecture, Yunnan Province, People's Republic of China, in September 2012. A voucher specimen (YTCM 20120902) was deposited at the College of Yunnan Traditional Chinese Medical, and was identified by Prof. Yao-Wen Yang.

Isolation

Dry tubers of L. meyenii (4.0 kg) were percolated with 95% ethanol (3 10 L) at room temperature overnight. The crude extract was evaporated under reduced pressure to yield a dark brown residue (254 g). The residue was suspended in H2O and then partitioned with petroleum ether. The petroleum ether concentrated solution (80 g) was chromatographed over silica gel, eluting with a gradient of increasing EtOAc in petroleum ether, to give fractions A1-A7. Fraction A2 (3.5 g) was further separated by normal-phase silica gel, using petroleum ether-EtOAc (20:1), to yield compound 11 (15 mg, 0.0038). Fraction A3 was subjected to Sephadex LH-20 column (MeOH) to afford seven subfractions A3-1-A3-7. Subfraction A3-6 was further purified by RP-18, eluting with 60% MeOH-H2O, followed by normal-phase silica gel using petroleum ether-EtOAc (15:1), to yield compounds 2 (10 mg, 0.0025) and 12 (3 mg, 0.0008).

Fraction A5 was separated by RP-18 (CH3OH-H2O 1:5-0:1) to give ten subfractions A5-1-A5-10. Compounds 8 (10 mg, 0.0025) and 9 (30 mg, 0.0075) were afforded from A5-2 by a further purification on silica gel CC, eluting with petroleum ether-EtOAc (10:3 and 2:1, respectively). Compound 13 (3 mg, 0.0008) was obtained from A5-8 by PTLC, eluting with petroleum ether-EtOAc (10:1). Fraction A6 (3.8 g) was divided into eight subfractions (A6-1-A6-8) by silica gel CC eluting with petroleum ether-EtOAc (5:1).

Subfraction A6-3 afforded compound 10 (30 mg, 0.0075) by RP-18, eluting with 20% MeOH-H2O. Compound 1 (8 mg, 0.0020) was obtained from A6-4 by RP-18, eluting with 40% MeOH-H2O. Compounds 5 (10 mg, 0.0025) and 6 (1.8 mg, 0.0005) were yielded by semipreparative HPLC (MeOH-H2O 72:28) from subfraction A6-5. Compound 3 (3 mg, 0.0008) was gotten from the A6-8 by recrystallization in MeOH. Fraction A7 was applied to a silica gel flash column and eluted with petroleum ether-acetone (2:1-1:9) to give five subfractions A7-1-A7-5, Fraction A7-2 was further separated by CHCl3-MeOH (35:1-10:1), followed by Sephadex LH-20 to give compound 4 (30 mg, 0.0075). Compound 7 (20 mg, 0.0050) was purified from the A7-5 by recrystallization in MeOH.

Results and Discussion

Compound 1, a white powder, exposed an [M+H]+ at m/z 231.1129 (calcd. 231.1128), corresponding to the molecular formula C13H14N2O2 in the positive ion HR-ESI-MS, revealing eight degrees of unsaturation. The IR spectrum showed absorption bands at 1713 and 1772 cm-1 (carbonyl group), and a single substituted phenyl at 1638, 751, and 701 cm-1, which was supported by the characteristic signals of five methine protons at dH 7.37 (2H, m), 7.32 (2H, m), and 7.28 (1H, m) in the 1H NMR spectrum and carbon signals at dC 136.2, 128.9, 128.9, 128.7, 128.7, and 128.1 in the 13C NMR spectrum (Table-1). In addition, two diagnostic carbonyl for imidazole derivatives at dC 173.8 and 160.7 were observed in 13C NMR spectrum [19]. Moreover, another two rings to meet eight degrees of unsaturation were in agreement with the imidazole derivatives. The proton sequence, observed in the 1H-1H COSY spectrum, showed the presence of a framework of -CHCH2CH2CH2- (Fig. 2).

Moreover, the HMBC correlations from H-4 (dH 4.09) and H-7 (dH 3.69, 3.25) to carbonyl carbon at C-1 (dC 160.7) and from H-4 (dH 4.09) and H-5 (dH 2.25, 1.67) to carbonyl carbon at C-3 (dC 173.8) proved 1 to be an imidazole derivative. Observation of the correlations of H-1' (dH 4.62) with C-1, C-3, C-2', and C-3'(C-7') in its HMBC experiment allowed the phenyl moiety to be located at N-2 as shown in Fig 2. Consequently, compound 1 was assigned as tetrahydro-2-benzyl- 1H-pyrrolo [1,2-C] imidazole-1,3 (2H)-dione.

Table 1: 1H and 13C NMR data of compounds 1 and 2 (d ppm)

###1###2

###C###dC a,b###dH a,c###C###dC a,d###dH a,e

###1###160.7 s###1###49.5 d###3.57 (br s, 1H)

###2###2###134.9 d###5.92 (dd, 1H, J = 5.7, 2.9 Hz)

###3###173.8 s###3###138.4 d###6.11 (dd, 1H, J = 5.7, 3.0 Hz)

###4###63.6 d###4.09 (dd, 1H, J = 9.1, 7.5 Hz) 4###54.4 d###3.24 (br s, 1H)

###5###27.7 t###2.25 (m, 1H)###5###126.8 d###8.04 (m, 1H)

###1.67 (m, 1H)###6###133.7 d###7.72 (m, 1H)

###6###27.2 t###2.07 (m, 2H)###7###134.0 d###7.72 (m, 1H)

###7###45.7 t###3.69 (m, 1H)###8###127.5 d###8.04 (m, 1H)

###3.25 (m, 1H)###9###198.4 s

###1'###42.7 t###4.62 (s, 2H)###10###201.5 s

###2'###136.2 s###11###46.7 t###1.79 (dd, 1H, J = 9.0 Hz)

###3'###128.7 d###7.32 (m, 1H)###1.59 (overlapped, 1H)

###4'###128.9 d###7.37 (m, 1H)###12###26.9 q###1.58 (s, 3H)

###5'###128.1 d###7.28 (m, 1H)###4a###53.7 s

###6'###128.9 d###7.37 (m, 1H)###5a###135.7 s

###7'###128.7 d###7.32 (m, 1H)###8a###135.7 s

###9a###58.0 d###3.08 (d, 1H, J = 4.0 Hz)

Compound 2, obtained as a colorless oil, showed an [M-H]- at m/z 237.0915 (calcd. 237.0921), suggesting the molecular formula of C16H14O2 in the HR-ESI-MS, corresponding to ten degrees of unsaturation. The IR spectrum revealed absorption bands due to ketone (1734 cm-1), double band (1679 cm-1), and an aromatic ring (3065 and 1594 cm-1). The presence of an o-disubstituted phenyl was supported by the characteristic signals of four methine protons at dH 8.04 (2H, m) and 7.72 (2H, m) in the 1H NMR spectrum and carbon signals (dC 135.7, 135.7, 134.0, 133.7, 127.5, and 126.8) in the 13C NMR spectrum (Table 1). The 1H and 13C NMR spectra showed the presence of two olefinic methines (dH 6.11 dd, 1H, J = 5.7, 3.0 Hz, dC 138.4; 5.92 dd, 1H, J = 5.7, 2.9 Hz, dC 134.9) in 2. In addition, two conjugated carbonyl (dC 201.5, 198.4) were observed in 13C NMR spectrum.

Hence, there should be three more rings to meet ten degrees of unsaturation. The presence of a framework for -CHCH(CH2)CH=CH CHCH2- was observed in the 1H-1H COSY spectrum (Fig 2). Careful comparison of 1D NMR data of 2 showed to be identical with those reported for the known synthetic compound 4a-methyl-1,4,4a,9a-tetrahydro-1,4-methano-anthracene-9,10-dione [9] thus confirming its identity.

The HMBC correlations from H-5 (dH 8.04) and Me-12 (dH 1.58) to carbonyl carbon at C-10 (dC 201.5), from H-8 (dH 8.04) to carbonyl carbon at C-9 (dC 198.4), from Me-12 (dH 1.58) to C-4 (dC 54.4), from H-2 (dH 5.92) to C-9a (dC 58.0), and from H-3 (dH 6.11) to C-4a (dC 53.7), demonstrated the structure of compound 2 as shown in Fig. 1.

The relative congurations of 2 were determined by the ROESY correlations (Fig. 2) of H2-11(dH 1.79 and 1.59) with Me-12 (dH 1.58) and H-9a (dH 3.08), which was consistent with the 3D structure of 2 obtained using a molecular modeling program with MM2 force-field calculations for energy minimization. Accordingly, compound 2 was elucidated as (1S,4R,4aR,9aS)-4a-methyl-1,4,4a,9a- tetrahydro-1,4-methanoanthracene-9,10-dione.

The other known compounds (3-13) were identified on the basis of NMR and MS spectra as well as comparison with values from the literature.

Tetrahydro-2-benzyl-1H-pyrrolo [1,2-C] imidazole- 1,3 (2H)-dione (1)

White powder (CHCl -CH OH, 1:1). [a]21.9 -67.66 (c 0.02, MeOH); UV (MeOH) lmax ( log e): 205 (3.23) nm; IR (KBr) max (cm-1): 3456, 2924, 1772, 1713, 1638, 1437, 1413, 751,701; HR-ESI-MS m/z: 231.1129 [M+H]+ (C13 H14N2O2+H, calcd. 231.1128); 1H-NMR (CDCl3, 600 MHz) and 13C-NMR (CDCl3, 150 MHz) see the Table 1.

(1S,4R,4aR,9aS)-4a-methyl-1,4,4a,9a-tetrahydro-1,4 - methano-anthracene-9,10-dione (2)

Colorless oil (CHCl -CH OH, 1:1). [a]22.7 -8.11 (c 0.07, MeOH); UV (MeOH) lmax ( log e): 225 (3.71) nm; IR (KBr) max (cm-1): 3440, 3065, 2979, 2966, 1734, 1679, 1594, 1452, 1268, 989, 706; HR-ESI-MS m/z: 237.0915 [M-H]- (C16H14O2-H, calcd. 237.0921); 1H-NMR (CDCl3, 500 MHz) and 13C-NMR (CDCl3, 125 MHz) see the Table 1.

dibenzylurea (3)

White powder (CHCl -CH OH, 1:1). [a]22.9 -2.35 (c 0.10, MeOH); UV (MeOH) lmax (log e): 203 (3.55) nm; HR-ESI-MS m/z: 241.1338 [M+H]+ (C15H16N2O+H, calcd. 241.1335); 1H-NMR (DMSO, 500 MHz) d: 7.31 (4H, t, J = 7.6 Hz, H-3,3',5,5'), 7.23 (6H, m H-2,2',4,4',6,6'), 6.46 (2H, m, NH), 4.22 (4H, d, J = 6.0 Hz, H-7,7'); 13C-NMR (DMSO, 125 MHz) d: 158.2 (C=O), 140.1 (C-1,1'), 128.3 (C-3,3',5,5'), 127.1 (C-2,2',6,6'), 126.7 (C-4,4'), 43.1 (C-7,7').

N-benzylformamide (4)

White powder (CH3OH). ESI-MS m/z: 158 [M+Na]+ (C8H9NO+Na); 1H-NMR (CD3OD, 500 MHz) d: 8.14 (1H, s CHO), 7.30 (5H, m, H-2-H-6), 4.40 (2H, s, H-7); 13C-NMR (CD3OD, 125 MHz) d: 163.6 (CHO), 139.4 (C-1), 129.7 (C-3), 129.6 (C-5), 128.6 (C-2), 128.4 (C-6), 128.2 (C-4), 42.7 (C-7).

N-benzyloctadecanamide (5)

White amorphous powder (CH3OH). ESI-MS m/z: 374 [M+H]+ (C25H43NO+H); 1H-NMR (CD3OD, 600 MHz) d: 7.36 (2H, m, H-4',6'), 7.30 (3H, m, H-3',5',7'), 5.75 (1H, br s, NH), 4.46 (2H, d, J = 6.8 Hz, H-1'), 2.23 (2H, t, J = 9.2 Hz, H-2), 1.67 (2H, m, H-3), 1.34-1.28 (28H, m, H-4-H-17), 0.91 (3H, t, J = 8.3 Hz, H-18); 13C-NMR (CD3OD, 150 MHz) d: 173.0 (C-1), 138.5 (C-2'), 128.7 (C-4',6'), 127.8 (C-3',7'), 127.5 (C-5'), 43.6 (C-1'), 36.8 (C-2), 31.9 (C-16), 29.7-29.3 (C-4-15), 25.8 (C-3), 22.7 (C-17), 14.1 (C-18).

N-(3-methoxybenzyl)-hexadecanamide (6)

White amorphous powder (CH3OH). ESI-MS m/z: 376 [M+H]+ (C24H41NO2+H); 1H-NMR (CD3OD, 500 MHz) d: 7.27-7.23 (1H, m, H-6'), 6.85 (1H, d, J = 7.7 Hz, H-7'), 6.82 (2H, m, H-3',5'), 5.76 (1H, br s, NH), 4.41 (2H, d, J = 5.7 Hz, H-1'), 3.80 (3H, s, OCH3), 2.21 (2H, t, J = 7.7 Hz, H-2), 1.65 (2H, m, H-3), 1.32-1.27 (24H, m, H-4-H-15), 0.88 (3H, t, J = 6.7 Hz, H-16); 13C-NMR (CD3OD, 125 MHz) d: 173.0 (C-1), 159.9 (C-4'), 140.0 (C-2'), 129.8 (C-6'), 120.0 (C-7'), 113.4 (C-5'), 113.0 (C-3'), 55.2 (OCH3), 43.5 (C-1'), 36.9 (C-2), 32.0 (C-14), 29.7-29.4 (C-4-13), 25.8 (C-3), 22.7 (C-15), 14.1 (C-16).

1-O-b-D-glucopyranosyl-(2S,3R,4E,8Z)-2-N-(2'- hydroxypalmitoyl) octadecasphinga-4,8-dienine (7)

White amorphous powder (CH3OH). ESI-MS m/z: 712 [M-H]- (C40H75NO9-H); 1H-NMR (CD3OD, 500 MHz) d: 5.75 (1H, br d, J = 15.3 Hz, H-5), 5.49 (1H, dd, J = 15.3, 7.4 Hz, H-4), 5.45 (2H, m, H-8,9), 4.29 (1H, d, J = 7.9 Hz, H-1'), 4.15 (2H, m, H-2,3), 4.01 (2H, dd, J = 7.8, 3.8 Hz, H-1), 3.89 (1H, br d, J = 7.0 Hz, H-2'), 3.73 (1H, dd, J = 10.4, 3.6 Hz, H-6a'), 3.69 (1H, m, H-6b'), 3.37 (1H, br s, H-3'), 3.30 (2H, m, H-2',4'), 3.21 (1H, t, J = 9.0 Hz, H-5'); 13C-NMR (CD3OD, 125 MHz) d: 175.8 (C-1'), 133.0 (C-5), 130.6 (C-9), 129.8 (C-8), 129.3 (C-4), 103.3 (C-1'), 76.6 (C-5'), 76.5 (C-3'), 73.6 (C-2'), 71.7 (C-2'), 71.5 (C-3), 70.2 (C-4'), 68.3 (C-1), 61.3 (C-6'), 53.2 (C-2), 34.5 (C-3'), 32.3 (C-6), 32.2 (C-4'), 31.9 (C-11), 31.7 (C-16,14'), 29.0 (C-10), 28.9 (C-7), 29.4, 29.3, 29.1, 24.7 (C-12-15, C-5'-14'), 22.3 (C-17,15'), 13.0 (CH3).

3-hydroxyphenylacetonitrile (8)

Colorless Oil (CHCl3-CH3OH, 1:1). ESI-MS m/z: 132 [M-H]- (C8H7NO-H); 1H-NMR (CDCl3, 600 MHz) d: 7.26 (1H, t, J = 7.9 Hz, H-5), 6.87 (3H, m, H-2,4,6), 3.75 (2H, s, H-7); 13C-NMR (CDCl3, 150 MHz) d: 156.6 (C-3), 131.2 (C-1), 130.5 (C-5), 120.1 (C-6), 118.0 (CN), 115.4 (C-4), 114.9 (C-2), 23.5 (C-7).

3-methoxyphenylacetonitrile (9)

Colorless Oil (CHCl3-CH3OH, 1:1). ESI-MS m/z: 170 [M+Na]+ (C9H9NO+Na); 1H-NMR (CDCl3, 600 MHz) d: 7.28 (1H, m, H-5), 6.90 (1H, d, J = 7.0 Hz, H-6), 6.86 (2H, m, H-2,4), 3.82 (3H, s, OCH3), 3.73 (2H, s, H-7); 13C-NMR (CDCl3, 150 MHz) d: 160.2 (C-3), 131.4 (C-1), 130.3 (C-5), 120.3 (C-6), 117.9 (CN), 113.7 (C-4), 113.7 (C-2), 55.4 (OCH3), 23.7 (C-7).

4-hydroxyphenylacetonitrile (10)

White powder (CHCl3-CH3OH, 1:1). ESI-MS m/z: 132 [M-H]- (C8H7NO-H); 1H-NMR (CDCl3, 600 MHz) d: 7.17 (2H, d, J = 8.5 Hz, H-2,6), 6.84 (2H, d, J = 8.5 Hz, H-3,5), 3.69 (2H, s, H-7); 13C-NMR (CDCl3, 150 MHz) d: 156.7 (C-4), 130.4 (C-2,6), 122.6 (C-1), 119.5 (CN), 117.1 (C-3,5), 23.9 (C-7).

phenylacetonitrile (11)

Colorless Oil (CHCl3-CH3OH, 1:1). ESI-MS m/z: 118 [M+H]+ (C8H7N+H); 1H-NMR (CDCl3, 600 MHz) d: 7.41 (2H, m, H-3,5), 7.37 (3H, m, H-2,4,6), 3.78 (2H, s, H-7); 13C-NMR (CDCl3, 150 MHz) d: 129.9 (C-1), 129.2 (C-3,5), 128.2 (C-4), 128.0 (C-2,6), 118.0 (CN), 23.6 (C-7).

ursolic acid (12)

White powder (CHCl3-CH3OH, 1:1). 1H-NMR (DMSO, 500 MHz) d: 5.12 (1H, br s, H-12), 4.32 (1H, d, J = 5.2 Hz, H-3), 1.03, 0.91, 0.89, 0.86, 0.74, 0.67 (each 3H, s, Me-23-Me-29), 0.80 (1H, d, J = 6.4 Hz, Me-30); 13C-NMR (DMSO, 125 MHz) d: 178.4 (C-28), 138.2 (C-13), 124.6 (C-12), 76.9 (C-3), 54.8 (C-5), 52.4 (C-18), 47.0 (C-17), 46.9 (C-9), 41.7 (C-14), 40.0 (C-8), 38.6 (C-19), 38.5 (C-20), 38.4 (C-4), 38.3 (C-1), 36.6 (C-10), 36.4 (C-22), 32.7 (C-7), 30.2 (C-21), 28.3 (C-23), 27.6 (C-15), 27.0 (C-2), 23.8 (C-16), 23.3 (C-27), 22.9 (C-11), 21.2 (C-30), 18.0 (C-6), 17.0 (C-26), 17.0 (C-29), 16.2 (C-25), 15.3 (C-24).

cyloeucalenol (13)

White powder (CHCl3-CH3OH, 1:1). 1H-NMR (CDCl3, 500 MHz) d: 4.71 (1H, br s, H-31a), 4.66 (1H, br s, H-31b), 3.28 (1H, m, H-3), 1.03 (3H, d, J = 3.6 Hz, Me-26), 1.02 (3H, d, J = 3.6 Hz, Me-27), 0.96, 0.96, 0.89, 0.89, 0.81, (each 3H, s, Me-18, 21, 28-30); 13C-NMR (CDCl3, 125 MHz) d: 157.0 (C-24), 105.8 (C-31), 78.8 (C-3), 52.3 (C-17), 48.8 (C-14), 48.0 (C-8), 47.1 (C-5), 45.4 (C-13), 40.4 (C-4), 36.1 (C-20), 35.6 (C-12), 35.0 (C-22), 33.8 (C-25), 32.9 (C-15), 32.0 (C-1), 31.3 (C-23), 30.4 (C-2), 30.0 (C-19), 29.7 (C-10), 28.2 (C-7), 26.5 (C-16), 26.0 (C-11), 25.4 (C-30), 22.0 (C-26), 21.9 (C-27), 21.1 (C-6), 19.9 (C-9), 19.3 (C-28), 18.3 (C-21), 18.1 (C-18), 14.0 (C-29).

Acknowledgments

This work was financially supported by The National Natural Science Foundation of China (No.21162044) and Mid-aged and Young Academic and Technical Leader Raising Foundation of Yunnan Province (No. 2010CI040).

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Author:Zang, Zhen; Li, Meng Jia; Lei, Ze; Ma, Li; Liu, Feng Yi; Li, Dan Li; Wu, Xiang Hua; Zhao, Yong
Publication:Journal of the Chemical Society of Pakistan
Article Type:Report
Geographic Code:9PAKI
Date:Jun 30, 2016
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