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Eight new bibenzyl derivatives from Dendrobium candidum abc

Yan Li

a

c

, Chun-Lan Wang , Hai-Jun Zhao & Shun-Xing Guo

a

a

Institute of Medicinal Plant Development, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing 100193, China b

School of Chemistry and Pharmaceutical Engineering, Qilu University of Technology, Jinan 250353, China c

College of Basic Medical Sciences, Shandong University of Traditional Chinese Medicine, Jinan 250355, China Published online: 30 Oct 2014.

To cite this article: Yan Li, Chun-Lan Wang, Hai-Jun Zhao & Shun-Xing Guo (2014) Eight new bibenzyl derivatives from Dendrobium candidum, Journal of Asian Natural Products Research, 16:11, 1035-1043, DOI: 10.1080/10286020.2014.967230 To link to this article: http://dx.doi.org/10.1080/10286020.2014.967230

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Journal of Asian Natural Products Research, 2014 Vol. 16, No. 11, 1035–1043, http://dx.doi.org/10.1080/10286020.2014.967230

Eight new bibenzyl derivatives from Dendrobium candidum Yan Liabc, Chun-Lan Wanga, Hai-Jun Zhaoc and Shun-Xing Guoa* a

Institute of Medicinal Plant Development, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing 100193, China; bSchool of Chemistry and Pharmaceutical Engineering, Qilu University of Technology, Jinan 250353, China; cCollege of Basic Medical Sciences, Shandong University of Traditional Chinese Medicine, Jinan 250355, China

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(Received 30 April 2014; final version received 15 September 2014) Eight bibenzyl derivatives, namely dendrocandins J –Q (1 – 8), were isolated from the stems of Dendrobium candidum. Their structures were elucidated by 1D and 2D NMR experiments and mass spectrometry. Compounds 1 – 8 were examined for antioxidant activity by 1,1-diphenyl-2-picrylhydrazyl free radical scavenging assay, and the IC50 values were 36.8, 70.2, 45.0, 60.5, 87.6, 50.4, 22.3, and 30.3 mM, respectively. Keywords: Dendrobium candidum; bibenzyl derivatives; dendrocandins J – Q; antioxidant activity

1. Introduction The genus Dendrobium (Orchidaceae) includes about 1100 species in the world, 74 species and 2 variations of which are distributed in China, and several of them are used as traditional Chinese medicine “Shi Hu” [1]. In our previous study, some antioxidant bibenzyl derivatives have been isolated [2 –4]. The further research led to the isolation of eight new compounds, dendrocandins J– Q (1– 8). The structural elucidation and the evaluation of antioxidant activities of these compounds are reported in this contribution. 2. Results and discussion The molecular formula of dendrocandin J (1) was deduced as C31H30O8 due to the appearance of an [M 2 H]2 ion at m/z 529.1880 in the HR-ESI-MS. Furthermore, compound 1 and dendrocandin F have similar 1H and 13C NMR spectroscopic data, except for the absence of a methoxyl group signal [4]. The HMBC correlations [1-OMe (dH 3.82)/C-1, 12-OMe (dH 3.64)/

C-12 and 10 -OMe (dH 3.75)/C-10 ] and the molecular formula of 1 suggested that the methoxyl group at C-120 in dendrocandin F is replaced by a hydroxyl group in compound 1. Thus, the structure of 1 was determined as showed in Figure 1. Dendrocandin K (2) exhibited an [M 2 H] 2 ion at m/z 515.1729 (C30H27O8) in the HR-ESI-MS. The NMR spectroscopic data of 2 were similar to those of 1, except for the lack of a methoxyl group signal. The HMBC correlations [1-OMe (dH 3.83)/C-1 and 10 -OMe (dH 3.75)/C-10 ] and the molecular formula of 2 indicated that the methoxyl group at C-12 in compound 1 is replaced by a hydroxyl group in compound 2. Dendrocandin L (3) was determined to have a molecular formula C30H22O8 by HR-ESI-MS at m/z 509.1251 [M 2 H]2, which is 16 mass units less than that of dendrocandin H [4]. The NMR spectroscopic data of compound 3 were similar to those of dendrocandin H, indicating that they were structurally related analogs, and the difference is likely the lack of one

*Corresponding author. Email: [email protected] q 2014 Taylor & Francis

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Y. Li et al. H3CO R1

HO

OH

13

12

10

9

5 7

8

11'

R2

3'

5 7

6

3' 4'

2' 1'

OH 12'

OCH3

O

6' 7' 8'

9' 14'

13'

OCH3

O

5' 11' 10'

1'

14'

Dendrocandin F

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2'

6' 13'

8

O

5'

9' 8'

9

O

7'

12'

10

OCH3

1

4

6

4' 10'

14

1

OH 3 2

11

3 2 14 4

11

HO

13

12

R

HO

R1= R2=OCH3

Dendrocandin H R=OH 1 R1=OCH3; R2=OH 3 R=H 2 R1= R2=OH

1

H

HOH2C H HO

10

H3CO

9'

O

8'

6

2

7

12 14

OH

OCH3 6

13

4

3

5'

11

9

5

7'

4'

8

H3CO

6'

11

R1

OCH3

2'

2

8 7

9'

O

CH2OH

8' 7'

5

9

12

1' 3'

10

1

4

3

5'

6'

OCH3

1'

O

2'

14

4'

13

OH

3'

OH

R2 4

Dendrocandin B

R1= R2=OCH3 5 R1= OH; R2=H

11' 10'

OCH3 1 6

2

O

8'

9'

5 7

4 14

8

3

7'

O

10 11

R2

6 R1= R2=OH

13' 14' 6'

1'

OCH3

2' 4'

13

9

5'

12'

12

R1

Dendrocandin I

3'

OH

OH

H-7', 8': trans R1=R2=OCH3 7 H-7', 8': cis

R1=R2=OH

8 H-7', 8': trans R1=R2=OH

Figure 1. Compounds 1 – 8 isolated from D. candidum

hydroxyl group. This was supported by the corresponding doublets in the 1H NMR spectrum of 3 at dH 7.91 (d, J ¼ 8.4 Hz, H-80 ) and 7.98 (d, J ¼ 8.4 Hz, H-70 ), while

in dendrocandin H the signal of H-70 appeared as a single at dH 7.29 [4] (Table 1). Additionally, comparison of the chemical shifts of C-70 , C-80 , and C-90 with those of

4 6 7 8 10 11 13 14 40 60 70 80 100 110 120 130 140 MeO-1 MeO-12 MeO-10

No.

Table 1.

6.03 s

2 6.37 s

3

7

6.40 d (1.8) 6.29 d (1.8) 3.92 t (6.0) 3.91 t (6.6) 4.33 t (4.8) 2.70– 2.75 m 2.59 dd (13.2, 7.2) and 2.65 – 2.68 m 2.57 dd (13.2, 7.2) and 2.64 – 2.68 m 2.85 dd (13.2, 4.8) and 2.95 dd (13.2, 5.4) 2.70– 2.75 m 6.43 d (8.4) 6.35 d (8.4) 6.57 d (9.0) 6.93 d (8.4) 6.57 d (8.4) 6.44 d (8.4) 6.53 d (9.0) 6.63 d (8.4) 6.57 d (8.4) 6.44 d (8.4) 6.53 d (9.0) 6.63 d (8.4) 6.43 d (8.4) 6.35 d (8.4) 6.57 d (9.0) 6.93 d (8.4) 6.25 d (1.8) 6.46 s 6.45 s 6.06 d (1.8) 2.65– 2.68 m and 2.80– 2.82 m 2.63– 2.68 m and 2.81– 2.83 m 7.98 d (8.4) 4.65 s 2.70– 2.72 m 2.70– 2.72 m 7.91 d (8.4) 4.65 s 6.90 d (8.4) 6.91 d (8.4) 6.90 d (8.4) 6.61 d (8.4) 6.61 d (8.4) 9.33 d (9.6) 6.61 d (8.4) 7.24 dd (9.6, 2.4) 6.61 d (8.4) 6.61 d (8.4) 6.61 d (8.4) 6.90 d (8.4) 6.91 d (8.4) 7.13 d (2.4) 6.90 d (8.4) 3.82 s 3.83 s 3.78 s 3.70 s 3.64 s 3.58 s 3.75 s 3.75 s 3.60 s

1

H NMR spectral data for compounds 1 –3 and 7 and 8 (600 MHz, CD3OD, d ppm, J in Hz).

6.03 s

1

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3.60 s

6.61 d (8.4) 6.88 d (8.4) 3.71 s

6.39 d (1.8) 6.29 d (1.8) 2.70 – 2.75 m 2.70 – 2.75 m 6.93 d (8.4) 6.63 d (8.4) 6.63 d (8.4) 6.93 d (8.4) 6.28 d (1.8) 6.08 d (1.8) 4.61 d (8.4) 4.69 d (8.4) 6.88 d (8.4) 6.61 d (8.4)

8

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Y. Li et al.

dendrocandin H showed that they shifted from dC 104.3, 158.7, and 131.5 to dC 122.9, 133.5, and 141.0, respectively. These data showed that the difference between 3 and dendrocandin H is due to the lack of the hydroxyl group at C-80 in 3. Dendrocandin M (4) was isolated as a yellow syrup and showed an [M 2 H]2 ion at m/z 469.1870 (C26H29O8) in the HRESI-MS. The 1H NMR spectrum of 4 exhibited resonances for nine aromatic protons, appearing as a pair of o-coupled doublets at dH 6.61 (2H, d, J ¼ 8.4 Hz) and 6.89 (2H, d, J ¼ 8.4 Hz), an ABX spin system at dH 6.69 (1H, d, J ¼ 8.4 Hz), 6.72 (1H, dd, J ¼ 8.4 and 1.8 Hz), and 6.92 (1H, d, J ¼ 1.8 Hz), and a singlet signal at dH 6.37 (2H, s). The 13C NMR and HMQC spectra revealed the presence of 26 carbon resonances, including 3 methoxyl, 3 methylene, 11 methine, and 9 quaternary carbons. These NMR spectroscopic date indicated the presence of one 1,4-disubstituted, one 1,3,4-trisubstituted, and one 1,3,4,5-tetrasubstituted aromatic ring units in the molecule. The NMR spectra of 4 also showed three methoxyl groups at dH 3.70 (6H, s) and 3.78 (3H, s); two methylene groups at dH 2.75 (4H, s); one oxygenated methylene group at dH 3.46 (1H, dd, J ¼ 12.0 and 3.0 Hz) and 3.82 (1H, dd, J ¼ 12.0 and 5.4 Hz); and two oxygenated methine groups at dH 4.08– 4.10 (1H, m) and 4.84 (1H, d, J ¼ 4.8 Hz). In the HMBC spectrum, the correlations found at H-4, 6/C-1, 2, 3, 7 and H7, 8/C-4, 5, 6, 9, 10 indicated the presence of a bibenzyl unit; and the correlations (H40 /C-20 , 60 , 70 , H-70 /C-40 , 50 , 60 , 80 , and H-90 / C-80 ) showed the presence of a phenylpropane unit. Based on the molecular formula and unsaturation degrees of 4, the two units were linked through an oxygen bridge. The location was determined at C2/C-80 via an oxygen atom, which was deduced from the chemical shifts. In the phenylpropane unit, the chemical shift of the C-80 (dC 87.5) shifted about 10 ppm to low field compared to the analogs which

the hydrogen of OH group was unsubstituted [5]. Thus, the linked point of this unit was determined at C-80 . Comparison of the chemical shifts of the bibenzyl unit with those of 4,4 0 -dihydroxy-3,5dimethoxybibenzyl showed that the chemical shifts of C-1, 3 (dC 154.2) shifted about 5 ppm to low field, which suggested that the linked point of this unit was at C-2 [2]. In the EI-MS, the fragment ion peak at m/z 107 [C7H7O]þ supported the above deduction. The relative stereochemistry between C-70 and C-80 was concluded to be erythro, based on the small coupling constant (J ¼ 4.8 Hz) [6], which was further confirmed by the observance of cross peaks of H-70 $ H-80 and H-60 $ H-90 , and nonobservance of correlation between H-80 and aromatic protons H-40 and H-60 in ROESY spectrum. The absolute configurations of chiral centers were established as (70 S, 80 R) on the basis of the negative value of optical rotation [7]. The complete assignments of the 1H and 13C NMR spectroscopic data of 4 were therefore fully achieved by HMQC spectroscopy. Dendrocandin N (5) showed an [M 2 H] 2 ion at m/z 437.1604 (C25H25O7) in the HR-ESI-MS. The NMR spectroscopic data of compound 5 were similar to those of dendrocandin B, indicating that the structures of both compounds were related [3]. In the NMR spectra, the phenylpropane unit of 5 lacked one methoxyl signals with respect to dendrocandin B, and the three aromatic protons appeared as an ABX spin system at dH 6.77 (1H, d, J ¼ 8.4 Hz), 6.82 (1H, dd, J ¼ 8.4 and 1.8 Hz), and 6.92 (1H, d, J ¼ 1.8 Hz) (Table 2), which indicated that the H-30 was not been replaced by the methoxyl group. The HMBC correlations [1-OMe (dH 3.73)/C-1 and 10 -OMe (dH 3.81)/C-10 ] and the molecular formula of 5 indicated that the methoxyl group at C-12 in dendrocandin B is replaced by an hydroxyl group in compound 5. The relative configurations of the chiral centers

Journal of Asian Natural Products Research Table 2.

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No. 4 6 7 8 10 11 13 14 30 40 60 70 80 90 MeO-1 MeO-3 MeO-10

1

1039

H NMR spectral data for compounds 4 –6 (600 MHz, CD3OD, d ppm, J in Hz). 4

5

6

6.37 s 6.33 d (1.8) 6.33 d (1.2) 6.37 s 6.27 d (1.8) 6.27 d (1.2) 2.75 s 2.67 – 2.73 m 2.67 –2.73 m 2.75 s 2.67 – 2.73 m 2.67 –2.73 m 6.89 d (8.4) 6.90 d (8.4) 6.91 d (8.4) 6.61 d (8.4) 6.61 d (8.4) 6.61 d (8.4) 6.61 d (8.4) 6.61 d (8.4) 6.61 d (8.4) 6.89 d (8.4) 6.90 d (8.4) 6.91 d (8.4) 6.69 d (8.4) 6.77 d (8.4) 6.72 dd (8.4, 1.8) 6.82 dd (8.4, 1.8) 6.51 d (1.2) 6.92 d (1.8) 6.92 d (1.8) 6.49 d (1.2) 4.84 d (4.8) 4.78 d (7.8) 4.71 d (7.8) 4.08 – 4.10 m 3.91 – 3.94 m 3.88 –3.90 m 3.46 dd (12.0, 3.0) and 3.82 3.43 dd (12.6, 4.8) and 3.62 3.44 dd (12.6, 4.8) and 3.62 dd (12.0, 5.4) dd (12.6, 2.4) dd (12.6, 2.4) 3.70 s 3.73 s 3.73 s 3.70 s 3.78 s 3.81 s 3.79 s

of 5 were confirmed as trans from the ROESY cross peak H-60 $ H-80 and the coupling constant (J 70 ,80 ¼ 7.8 Hz) 0 0 between H-7 and H-8 [8 –10]. The molecular formula of dendrocandin O (6) was established as C25H26O8 based on HR-ESI-MS at m/z 453.1556 [M 2 H]2, which is 16 mass units more than that of 5. The spectroscopic data of compound 6 were very similar to those of 5, indicating that they were structurally related analogs, and the only difference is likely the presence of one more hydroxyl group. In the 1H NMR spectrum, the two aromatic protons for phenylpropane unit of 6 appeared as a pair of m-coupled doublets at dH 6.49 (1H, d, J ¼ 1.2 Hz) and 6.51 (1H, d, J ¼ 1.2 Hz), supporting the above deduction. The relative configurations of the chiral centers of 6 were confirmed as trans from the ROESY cross peak H-60 $ H-80 and the coupling constant (J70 ,80 ¼ 7.8 Hz) between H-70 and H-80 [8– 10]. The HR-ESI-MS of dendrocandin P (7) exhibited a pseudomolecular ion peak at m/z 515.1743 [M 2 H]2, ascribable to a molecular formula of C30H28O8. The NMR spectroscopic data of compound 7 resembled those of dendrocandin I, except

for the absence of two methoxyl group signals [4]. The HMBC correlations [1-OMe (dH 3.70)/C-1 and 10 -OMe (dH 3.60)/C-10 ] and the molecular formula of 7 indicated that the methoxyl groups at C-12 and C-120 in dendrocandin I are replaced by two hydroxyl groups in compound 7. The relative configurations of the chiral centers of 7 were confirmed as cis from the coupling constant (J70 ,80 ¼ 0 Hz) between H-70 and H-80 [8 –10]. Dendrocandin Q (8) was a stereoisomer of 7. The relative configurations of the chiral centers of 8 were confirmed as trans from the ROESY cross peak H-60 $ H-80 , H-70 $ H-100 , and the coupling constant (J70 ,80 ¼ 8.4 Hz) between H-70 and H-80 [8 –10]. The biosynthetic origin of compounds 5 – 8 is hypothesized as illustrated in Figure 2, 2-methoxy-4-(3-hydroxyprop-1en-1-yl)-phenol (i), 2-hydroxy-3-methoxy5-(3-hydroxyprop-1-en-1-yl)-phenol (ii), 2-hydroxy-3-methoxy-5-[2-(4-hydroxyphenyl)ethyl]phenol (iii), and 2-hydroxy3-methoxy-5-[2-(4-hydroxyphenyl)ethenyl]phenol (iv) are oxidized with NADPH/ O2 to afford the radicals (v), (vi), (vii), and (viii), respectively. Radical coupling

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Y. Li et al. OCH3

OCH3 HOH2C

HO OH

OH i: R=H ii: R=OH

R

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OH OH

OH iii

NADPH/O2 One-electron oxidation –H, –e

iv

NADPH/O2 One-electron oxidation –H, –e

OCH3 HOH2C

NADPH/O2 One-electron oxidation –H, –e

OCH3

OCH3 HO

HO O

v: R=H vi: R=OH

OCH3 HO

O

O OH

R

OH

vii

viii

oxidative coupling

oxidative coupling OH

OCH3

OCH3 O

O

CH2OH OCH3

OH HO

OCH3

OH

O

O OH

R

OH

7, 8

5: R=H 6: R=OH

Figure 2. Suggested biosynthetic process for 5– 8.

reaction between (v) and (vii) yields the precursor of 5, between (vi) and (vii) yields the precursor of 6, and between (vii) and (viii) yields the precursors of 7 and 8, which are then afford 5– 8, respectively [11]. The antioxidant activity of compounds 1– 8 was evaluated by 1,1-diphenyl-2picrylhydrazyl (DPPH) free radical scavenging assay, and vitamin C was used as positive control with IC 50 23.2 mM. Among the tested compounds, 7 showed significant scavenging activity

with IC50 value of 22.3 mM, while 1 –6 and 8 exhibited moderate potent antioxidant activities with IC50 36.8, 70.2, 45.0, 60.5, 87.6, 50.4, and 30.3 mM, respectively. 3. 3.1

Experimental General experimental procedures

Optical rotations were measured using a Perkin-Elmer 341 digital polarimeter (Wellesley, MA, USA). UV spectra were measured with a UV-2550 UV – VIS

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Journal of Asian Natural Products Research recording spectrometer (Shimadzu, Kyoto, Japan) and IR spectra were measured with a FTIR-8400S infrared spectrometer (Shimadzu). NMR spectra were obtained on a Varian Unity 600 instrument (Varian, Inc., Palo Alto, CA, USA). Chemical shifts are given in d values (ppm) relative to tetramethylsilane as an internal standard. The HR-ESI-MS was recorded on a LTQ Orbitrap XL instrument (Thermo Fisher Scientific, Waltham, MA, USA) in the negative-ion mode. Silica gel (300–400 mesh, Qingdao Marine Chemical Factory, Qingdao, China) and Sephadex LH-20 (Pharmazia, Uppsala, Sweden) were used for column chromatography, and silica gel GF254 plates (Yantai Marine Chemical Co., Ltd, Yantai, China) were used for thin-layer chromatography. The analytical HPLC was performed on a Waters HPLC system equipped with a PAD-2996 detector using a Symmetry C18 column (3.9 mm £ 150 mm, Waters, Milford, MA, USA). The preparative HPLC was carried out on a Waters HPLC system with DAD-2487 detector using a SymmetryPrep C18 column (7.8 mm £ 300 mm, Waters).

3.2

Plant material

The stems of Dendrobium candidum were collected in October 2006 in Yiwu City, Zhejiang Province, China, and identified by Prof. Shun-Xing Guo of the Institute of Medicinal Plant Development, Peking Union Medical College. A voucher specimen (TPSH-2006) was deposited in the herbarium of the Institute of Medicinal Plant Development.

3.3

Extraction and isolation

The powdered air-dried stems of D. candidum (2.6 kg) were refluxed with EtOAc for three times to get the EtOAc extract (57 g). The EtOAc extract was subjected to column chromatography on silica gel (200 –300 mesh, 1000 g) and

1041

eluted with petroleum –EtOAc (100:0 to 0:100) to yield 13 fractions (1 – 13). Fraction 8 (2 g) was further separated by column chromatography on silica gel and eluted with CHCl3 –MeOH (10:0 to 7:3) to yield six subfractions. Subfraction 2 (60 mg) was passed over a Sephadex LH-20 column with CHCl3 –MeOH (1:1) as eluent and then purified by preparative HPLC (60% MeOH, 3.0 ml/min) to yield compounds 7 (2.79 mg, tR 9.4 min) and 8 (1.32 mg, tR 10.6 min). Fraction 9 (2 g) was subjected to column chromatography on silica gel and eluted with petroleum – acetone (9:1 to 5:5) to yield six subfractions. Subfraction 4 (20 mg) was purified by preparative HPLC (70% MeOH, 10.0 ml/min) to yield compound 3 (2.11 mg, tR 11.1 min). Fraction 10 (0.5 g) was subjected to column chromatography on silica gel and eluted with CHCl3 –MeOH (10:0 to 6:4) to yield seven subfractions. Subfraction 3 (20 mg) was purified by preparative HPLC (70% MeOH, 10.0 ml/min) to yield compound 1 (2.60 mg, tR 14.0 min). Fraction 11 (45 mg) was passed over a Sephadex LH-20 column with CHCl3 – MeOH (1:1) as eluent to yield two subfractions. Subfraction 1 (25 mg) was purified by preparative HPLC (63% MeOH, 3.0 ml/min) to yield compounds 4 (1.90 mg, tR 18.1 min) and 5 (2.80 mg, tR 27.1 min). Subfraction 2 (15 mg) was purified by preparative HPLC (60% MeOH, 3.0 ml/min) to yield compound 2 (1.69 mg, tR 8.4 min). Fraction 12 (50 mg) was passed over a Sephadex LH-20 column with CHCl3 – MeOH (1:1) as eluent to yield two subfractions. Subfraction 2 (20 mg) was purified by preparative HPLC (60% MeOH, 3.0 ml/min) to yield compound 6 (2.09 mg, tR 28.1 min). 3.3.1

Dendrocandin J (1)

Reddish-yellow syrup; ½a20 2 3.1 D (c ¼ 0.13, MeOH); UV lmax (MeOH, log 1): 279.5 (3.7) nm; for 1H NMR (CD3OD, 600 MHz) and 13 C NMR (CD 3OD,

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150 MHz) spectral data, see Tables 1 and 3; HR-ESI-MS: m/z 529.1880 [M 2 H]2 (calcd for C31H29O8, 529.1862).

3396, 3007, 2937, 2839, 1650, 1618, 1586, 1510, 1475, 1375, 1327,1229, 1130, 1030, 947, 835; UV lmax (MeOH, log 1): 227 (4.4), 296 (3.9), 390 (3.4) nm; for 1H NMR (CD 3OD, 600 MHz) and 13 C NMR (CD3OD, 150 MHz) spectral data, see Tables 1 and 3; HR-ESI-MS: m/z 509.1251 [M 2 H] 2 (calcd for C30H21O8, 509.1236).

3.3.2 Dendrocandin K (2) Reddish-yellow syrup; ½a20 2 4.7 D (c ¼ 0.08, MeOH); UV lmax (MeOH, log 1): 279.5 (3.8) nm; for 1H NMR (CD3OD, 600 MHz) and 13C NMR (CD 3OD, 150 MHz) spectral data, see Tables 1 and 3; HR-ESI-MS: m/z 515.1729 [M 2 H]2 (calcd for C30H27O8, 515.1706). 3.3.3

3.3.4 Dendrocandin M (4) Yellow syrup; ½a20 D 2 18.9 (c ¼ 0.10, MeOH); UV lmax (MeOH, log 1): 279 (3.6) nm; for 1H NMR (CD3OD, 600 MHz) and 13C NMR (CD3OD, 150 MHz) spectral data, see Tables 2 and 3; HR-ESI-MS:

Dendrocandin L (3)

Red amorphous powder; ½a20 ^0 D (c ¼ 0.10, MeOH); IR (KBr, cm21): nmax Table 3. No. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 10 20 30 40 50 60 70 80 90 100 110 120 130 140 MeO-1 MeO-3 MeO-12 MeO-10

13

C NMR spectral data for compounds 1 – 8 (150 MHz, CD3OD, d ppm). 1

2

3

4

5

6

7

8

137.3 138.2 142.2 110.2 117.8 140.4 40.1 45.7 131.8 131.6 114.1 159.6 114.1 131.6 147.8 133.9 143.0 119.0 130.3 109.0 35.1 38.2 134.0 130.5 116.1 156.5 116.1 130.5 61.7

137.3 138.2 142.2 110.2 117.9 140.4 40.2 45.8 130.7 131.7 115.5 156.5 115.5 131.7 147.8 134.0 143.0 119.1 130.3 109.0 35.1 38.2 134.0 130.5 116.1 156.7 116.1 130.5 61.7

137.9 138.4 144.8 109.8 123.5 138.9 36.1 43.8 130.9 131.7 114.3 159.9 114.3 131.7 180.1 151.3 114.9 188.6 129.0 129.6 122.9 133.5 141.0 125.6 131.3 123.3 159.2 110.8 61.9

154.2 134.8 154.2 107.1 139.7 107.1 39.7 38.2 133.8 130.6 116.0 156.6 116.0 130.6 148.7 146.8 115.7 120.5 133.8 111.4 74.0 87.5 61.4

149.7 132.5 145.5 110.7 135.6 106.4 39.2 38.3 133.9 130.5 116.0 156.5 116.0 130.5 149.2 148.3 116.2 121.7 129.6 112.0 77.6 79.9 62.2

149.7 132.5 145.5 110.6 135.6 106.4 39.2 38.3 133.9 130.5 116.0 156.5 116.0 130.5 149.8 135.8 146.8 104.0 128.8 109.3 77.8 80.0 62.2

56.6 56.6

56.6

56.6

149.9 133.3 145.6 110.6 135.7 106.5 39.3 38.3 134.0 130.5 115.9 156.5 115.9 130.5 149.2 135.3 146.3 109.6 128.8 104.5 82.1 81.9 129.2 130.3 116.0 158.7 116.0 130.3 56.6

149.9 133.2 145.7 110.6 135.7 106.5 39.3 38.3 134.0 130.5 115.9 156.5 115.9 130.5 149.2 135.3 146.3 109.5 128.7 104.6 82.1 81.8 129.2 130.1 116.0 158.7 116.0 130.1 56.6

55.5 56.7

56.7

56.3

56.4

56.6

56.5

56.6

55.5

Journal of Asian Natural Products Research

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m/z 469.1870 [M 2 H]2 (calcd for C26H29O8, 469.1862).

3.3.5 Dendrocandin N (5) Yellow syrup; ½a20 ^ 0 (c ¼ 0.16, D MeOH); UV lmax (MeOH, log 1): 279 (3.7) nm; for 1H NMR (CD3OD, 600 MHz) and 13C NMR (CD3OD, 150 MHz) spectral data, see Tables 2 and 3; HR-ESI-MS: m/z 437.1604 [M 2 H]2 (calcd for C25H25O7, 437.1600).

1043

3.4 Measurement of DPPH free radical scavenging capacity The DPPH free radical scavenging assay was performed as the procedure reported in our previous report [3]. Acknowledgments This research work was financially supported by the National Natural Sciences Foundation of China (No. 31170016), PIRTI-IT1302, and Doctor Station Fund for Priority Development Field (20131106130002).

References 3.3.6 Dendrocandin O (6) Yellow syrup; ½a20 ^ 0 (c ¼ 0.10, D MeOH); UV lmax (MeOH, log 1): 279.5 (3.6) nm; for 1H NMR (CD3OD, 600 MHz) and 13C NMR (CD3OD, 150 MHz) spectral data, see Tables 2 and 3; HR-ESI-MS: m/z 453.1556 [M 2 H]2 (calcd for C25H25O8, 453.1549).

3.3.7

Dendrocandin P (7)

Yellow syrup; ½a20 ^ 0 (c ¼ 0.14, D MeOH); UV lmax (MeOH, log 1): 275 (3.6) nm; for 1H NMR (CD3OD, 600 MHz) and 13C NMR (CD3OD, 150 MHz) spectral data, see Tables 1 and 3; HR-ESI-MS: m/z 515.1743 [M 2 H]2 (calcd for C30H27O8, 515.1706).

3.3.8

Dendrocandin P (8)

Yellow syrup; ½a20 D 2 10.6 (c ¼ 0.07, MeOH); UV lmax (MeOH, log 1): 275 (3.5) nm; for 1H NMR (CD3OD, 600 MHz) and 13C NMR (CD3OD, 150 MHz) spectral data, see Tables 1 and 3; HR-ESI-MS: m/z 515.1708 [M 2 H]2 (calcd for C30H27O8, 515.1706).

[1] Jiangsu New Medical College, Dictionary of Chinese Herb Medicines (Shanghai Scientific and Technologic Press, Shanghai, 1986). [2] Y. Li, C.L. Wang, S.X. Guo, J.S. Yang, and P.G. Xiao, Chem. Pharm. Bull. 56, 1477 (2008). [3] Y. Li, C.L. Wang, Y.J. Wang, S.X. Guo, J.S. Yang, X.M. Chen, and P.G. Xiao, Chem. Pharm. Bull. 57, 218 (2009). [4] Y. Li, C.L. Wang, Y.J. Wang, F.F. Wang, S.X. Guo, J.S. Yang, and P.G. Xiao, Chem. Pharm. Bull. 57, 997 (2009). [5] H. Kijima, T. Ide, H. Otsuka, C. Ogimi, E. Hirata, A. Takushi, and Y. Takeda, Phytochemistry 44, 1551 (1997). [6] Z. Yuan and X. Li, Chin. J. Magn. Reson. 20, 307 (2003). [7] Z. Yuan, B.Y. Zhou, and X. Li, Chin. J. Magn. Reson. 19, 309 (2002). [8] C.Y. Ma, H.J. Zhang, G.T. Tan, N.V. Hung, N.M. Cuong, D.D. Soejarto, and H.H. S. Fong, J. Nat. Prod. 69, 346 (2006). [9] T.H. Kim, H. Ito, K. Hayashi, T. Hasegawa, T. Machiguchi, and T. Yoshida, Chem. Pharm. Bull. 53, 641 (2005). [10] M.G. Banwell, A. Bezos, S. Chand, G. Dannhardt, W. Kiefer, U. Nowe, C.R. Parish, G.P. Savage, and H. Ulbrich, Org. Biomol. Chem. 1, 2427 (2003). [11] K. Baba, T. Kido, M. Taniguchi, and M. Kozawa, Phytochemistry 36, 1509 (1994).

Eight new bibenzyl derivatives from Dendrobium candidum.

Eight bibenzyl derivatives, namely dendrocandins J-Q (1-8), were isolated from the stems of Dendrobium candidum. Their structures were elucidated by 1...
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