Multiflorumisides AâG, Dimeric Stilbene Glucosides with Rare

Article Cite This: J. Nat. Prod. 2018, 81, 254−263

pubs.acs.org/jnp

Multiflorumisides A−G, Dimeric Stilbene Glucosides with Rare Coupling Patterns from the Roots of Polygonum multif lorum Shuo-Guo Li,†,‡,§,⊥ Xiao-Jun Huang,†,‡,§,⊥ Man-Mei Li,‡ Qing Liu,†,‡,§ Hui Liu,†,‡,§ Ying Wang,*,†,‡,§ and Wen-Cai Ye*,†,‡,§ †

Institute of Traditional Chinese Medicine & Natural Products, ‡Guangdong Province Key Laboratory of Pharmacodynamic Constituents of Traditional Chinese Medicine and New Drugs Research, and §JNU-HKUST Joint Laboratory for Neuroscience & Innovative Drug Research, Jinan University, Guangzhou 510632, People’s Republic of China S Supporting Information *

ABSTRACT: Multiflorumisides A−G (1−7), seven new dimeric stilbene glucosides with two rare coupling patterns, were isolated from the roots of Polygonum multif lorum. The structures of these new dimeric stilbene glucosides were elucidated through comprehensive spectroscopic and chemical analyses. The absolute configurations of 3 and 5−7 were established by comparing their experimental and quantum-chemical ECD data. Putative biosynthetic pathways toward the dimers and their suppressive effects against nitric oxide production in lipopolysaccharide-stimulated RAW264.7 cells are also discussed.

■

S

RESULTS AND DISCUSSION Multiflorumiside A (1) was isolated as an amorphous powder. The molecular formula was assigned as C40H44O18 based on its HR-ESIMS (m/z 835.2414 [M + Na]+; calculated for C40H44O18Na: 835.2420) and 13C NMR data. The UV spectrum exhibited absorption maxima at 206 and 282 nm. The IR spectrum showed absorptions attributed to aromatic (1618, 1512, and 1467 cm−1) and hydroxy (3411 cm−1) functionalities. The 1H NMR spectrum of 1 revealed signals for two para-disubstituted benzene moieties [δH 7.09 (2H, d, J = 8.4 Hz), 7.04 (2H, d, J = 8.4 Hz), 6.59 (2H, d, J = 8.4 Hz), and 6.54 (2H, d, J = 8.4 Hz)], two tetrasubstituted benzene moieties [δH 6.47 (1H, d, J = 2.8 Hz), 6.33 (1H, d, J = 2.8 Hz), 6.10 (1H, d, J = 2.8 Hz), and 6.07 (1H, d, J = 2.8 Hz)], and four methines [δH 5.17 (1H, dd, J = 9.6, 8.8 Hz), 4.93 (1H, dd, J = 9.6, 7.2 Hz), 4.40 (1H, overlapped), and 4.13 (1H, dd, J = 10.0, 7.6 Hz)]. In addition, signals corresponding to two anomeric protons [δH 4.43 (1H, d, J = 8.0 Hz) and 4.36 (1H, d, J = 8.0 Hz)] were also evident in the 1H NMR spectrum. Through acid hydrolysis and subsequent HPLC analysis of the monosaccharide derivative, the sugar units of 1 were both identified as D-glucose.19 The β-configuration of the D-glucose moiety was deduced from the 3J1,2 value of the anomeric protons. The 13C NMR spectrum of 1 in conjunction with the

tilbenes are members of a class of plant polyphenols with complex structures and various biological activities. Based on 1,2-diphenylethylene core skeletons, stilbenes exhibit significant structural diversity via the inclusion of various functional groups and oligomerization. More than 450 oligomeric stilbenes have been reported from natural sources with different degrees of polymerization and diverse coupling patterns.1−10 In addition to their intricate structures, many stilbene oligomers have been shown to have diverse bioactivities, such as cytotoxic, antioxidant, antimicrobial, and anti-inflammatory activities.11−16 Their intriguing structural features and interesting biological effects have made stilbene oligomers an attractive research topic for chemists and pharmacologists. In an ongoing investigation on structurally unique and bioactive metabolites from traditional Chinese medicines, a series of new stilbene glucosides and an unusual flavonostilbene glucoside were identified from the roots of Polygonum multif lorum (Polygonaceae).17,18 In the current investigation, the new dimeric stilbene glucosides multiflorumisides A−G (1−7) (Figure 1), along with their putative biosynthetic precursors, (E)-2,3,5,4′-tetrahydroxystilbene 2-O-β-D-glucopyranoside (8) and (Z)-2,3,5,4′-tetrahydroxystilbene 2-O-β-Dglucopyranoside (9),17 were identified from the same plant species. Herein, the isolation, structural elucidation, and putative biosynthetic pathways of these dimeric stilbene glucosides, as well as their in vitro anti-inflammatory activities, are discussed. © 2018 American Chemical Society and American Society of Pharmacognosy

Received: June 23, 2017 Published: January 23, 2018 254

DOI: 10.1021/acs.jnatprod.7b00540 J. Nat. Prod. 2018, 81, 254−263

Journal of Natural Products

Article

Figure 1. Structures of compounds 1−7.

The relative configuration of 1 was defined via the ROESY spectrum. The ROESY correlations of H-6 (δH 6.47) with H-8 (δH 4.40)/H-7′ (δH 4.93) and H-10′ (δH 7.09) with H-8 (δH 4.40)/H-7′ (δH 4.93) revealed cis relationships between H-8 and H-7′ and H-7 and H-8′ and trans relationships between H7 and H-8 and H-7′ and H-8′, respectively. In addition, the ROESY correlations of H-6′ (δH 6.33) with H-8′ (δH 4.13)/H7 (δH 5.17) and H-10 (δH 7.04) with H-8′ (δH 4.13)/H-7 (δH 5.17) further confirmed the relative configuration of 1 (Figure 3). The 2D structure of 1 was therefore established as shown in Figure 1. Notably, the aglycone part of 1 is centrosymmetric and thus an achiral scaffold. However, the presence of the β-Dglucopyranosyl moieties renders 1 chiral, and its structure was consistent with the presence of two sets of NMR signals for the two stilbene glucoside constituent units. Multiflorumiside B (2) was isolated as a crystalline powder with the same molecular formula as 1 based on its HR-ESIMS data (m/z 835.2421 [M + Na]+; calculated for C40H44O18Na: 835.2420). The characteristic UV and IR absorptions of 2 were similar to those of 1. Unlike 1, only 20 carbon signals including 12 aromatic carbons (δC 156.8, 156.1, 151.6, 138.5, 138.3, 134.5, 130.0 × 2, 116.0 × 2, 106.2, and 102.7), two sp3 methines (δC 54.9 and 45.1), and a sugar moiety (δC 107.8,

DEPT-135 spectrum showed the presence of 40 carbon signals, which could be classified into 24 aromatic carbons, four sp3 methines, and the carbons of two β-D-glucopyranosyl moieties. The above spectroscopic features combined with the molecular formula indicated that 1 was a dimeric stilbene glucoside. The full assignment of all proton and carbon signals of 1 was accomplished based on comprehensive analysis of the 2D NMR spectra (Table 1). A spin system (H-7↔H-8′↔H-7′↔H-8↔H-7) in 1 could be constructed based on the correlations in its 1H−1H COSY spectrum, which linked the four methines into a cyclobutane moiety (Figure 2). Based on the HMBC correlations of H-6 (δH 6.47) with C-7 (δC 42.5), H-10 (δH 7.04) with C-8 (δC 46.0), H-6′ (δH 6.33) with C-7′ (δC 42.3), and H-10′ (δH 7.09) with C-8′ (δC 48.0), the four phenyl rings could be linked to the cyclobutane ring. The locations of the two β- Dglucopyranosyl moieties were determined by the HMBC correlations of Glc1-H-1 (δH 4.36) with C-2 (δC 138.8) and Glc2-H-1 (δH 4.43) with C-2′ (δC 138.6). Therefore, the 2D structure of 1 was established as shown in Figure 2 and comprised a dimeric cycloadduct of the accompanying stilbene glucoside monomer 8 (Scheme 1) in a head-to-tail linkage. 255



Article

Table 1. 1H and 13C NMR Data of 1 and 3 (Methanol-d4, J in Hz) 1 no.

a

δCb

3

δHa,c

1 2 3 4 5 6 7

137.5 138.8 150.9 102.3 155.2 107.0 42.5

6.10, d (2.8)

8 9 10/14 11/13 12 Glc1 1 2 3 4 5 6

no.

δ Cb

6.47, d (2.8) 5.17, dd (9.6, 8.8)

1′ 2′ 3′ 4′ 5′ 6′ 7′

137.6 138.6 150.8 102.3 155.1 107.4 42.3

46.0

4.40

8′

48.0

133.7 130.2 115.4 155.9

7.04, d (8.4) 6.59, d (8.4)

9′ 10′/14′ 11′/13′ 12′ Glc2 1 2 3 4 5 6

133.8 130.7 115.3 156.0

108.1 75.4 78.0 70.6 78.2 61.9

4.36, d (8.0) 3.59 3.46, t (9.0) 3.57 3.37, m 3.89, dd (12.0, 4.0) 3.80 b

107.8 75.4 78.0 70.6 78.1 62.1

δHa,c

no.

6.07, d (2.8) 6.33, d (2.8) 4.93, dd (9.6, 7.2) 4.13, dd (10.0, 7.6) 7.09, d (8.4) 6.54, d (8.4)

4.43, d (8.0) 3.58 3.49, t (9.0) 3.57 3.17, td (9.6, 2.8) 3.96, dd (12.0, 2.8) 3.78

δCb

1 2 3 4 5 6 7

135.9 137.1 151.5 102.7 155.6 108.3 41.7

8

47.9

9 10/14 11/13 12 Glc1 1 2 3 4 5 6

133.0 131.0 115.6 156.4 107.4 74.7 77.1 70.7 78.3 61.9

δHa,c

6.10, d (2.8) 6.51, d (2.8) 4.94, dd (10.0, 8.4) 4.29, dd (10.0, 8.4) 7.02, d (8.4) 6.57, d (8.4)

4.39, d (7.6) 3.68 3.45, t (9.2) 3.54, t (9.2) 3.15, m 3.75, dd (12.0, 2.4) 3.67

no.

δ Cb

δHa,c

1′ 2′ 3′ 4′ 5′ 6′ 7′

136.7 138.3 151.3 102.9 155.3 107.7 41.4

8′

48.2

9′ 10′/14′ 11′/13′ 12′ Glc2 1 2 3 4 5 6

133.0 130.7 115.6 156.2

7.02, d (8.4) 6.56, d (8.4)

108.1 75.5 77.4 70.8 78.1 61.9

4.40, d (7.6) 3.58 3.65 3.59 3.10, td (9.6, 2.8) 3.72

6.13, d (2.8) 6.50, d (2.8) 5.05, dd (10.0, 6.8) 4.13, dd (10.0, 6.8)

3.69

c

Recorded at 400 MHz. Recorded at 100 MHz. Overlapped signals are reported without designating multiplicity.

Figure 2. Key 1H−1H COSY and HMBC correlations of 1 and 5.

77.8, 77.6, 75.4, 70.5, and 61.7) were observed in the 13C NMR spectrum of 2. These spectroscopic data combined with the molecular formula indicated that this compound might be a symmetrical stilbene glucoside dimer. Analysis of the 1D and 2D spectra of 2 allowed the assignment of all proton and carbon resonances (Table 2). The C-7 (C-7′) to C-8 (C-8′) spin system was revealed by the 1H−1H COSY correlations of 2. The HMBC correlations between H-6/H-6′ (δH 6.70) and C-7/C-7′ (δC 45.1), between H-10/H-10′ (δH 7.19) and C-8/C-8′ (δC 54.9), and between Glc1-H-1/Glc2-H-1 (δH 4.11) and C-2/C-2′ (δC 138.3) established the partial structure of 2. Similar to 1, compound 2 was also a dimeric stilbene glucoside linked through a cyclobutane ring. However, due to the structural symmetry of 2, the dimerization pattern (head-to-tail or head-to-head) between the monomers could not be established from the NMR data. According to literature reports,20,21 fragment ions at

m/z 243, 405, 487, and 649 should be observed in the mass spectrum of a stilbenoid cycloadduct linked head-to-tail. In addition to the aforementioned fragment ions, fragment ions at m/z 275 and/or 437 are typically present in the mass spectra of cycloadducts joined head-to-head, and these fragments should be absent from the mass spectrum of a head-to-tail cycloadduct. In the HR-ESIMS data of 2, only the fragment ions at m/z 243.0662, 405.1197, 487.1390, and 649.1961 were observed (Figure 4), indicating that 2 was a dimeric cycloadduct connected in a head-to-tail manner. In the ROESY spectrum of 2, the correlations of H-7/H-7′ (δH 4.36) with H-10/H-10′ (δH 7.19) and H-8/H-8′ (δH 3.35) with H-6/H-6′ (δH 6.70) established the trans relationships of H-7 and H-8 and H-7′ and H-8′. However, the stereochemical relationships between H-7′ and H-8 and between H-8′ and H-7 in 2 could not be determined from the ROESY spectrum due to the symmetry of the structure. According to the spectroscopic 256



Article

Scheme 1. Putative Biosynthetic Pathways toward the Formation of 1−7

Table 2. 1H and 13C NMR Data of 2 and 4 (Methanol-d4, J in Hz) 2

Figure 3. Key ROESY correlations of 1−4.

data, 2 possessed the same 2D structure as 1. However, the significant difference in the spectroscopic data of the two compounds suggested the 3D structure of 2 was different from that of 1. Thus, the trans relationships of H-7′ and H-8 and H8′ and H-7 were indirectly established. Multiflorumiside C (3) was found to have the same molecular formula as 1 and 2 established from its HR-ESIMS data (m/z 835.2420 [M + Na]+; calculated for C40H44O18Na: 835.2420). The NMR spectra of 3 exhibited signals analogous to those of 1 (Table 1), which indicated that 3 was also a dimeric stilbene glucoside. The four methines were linked as a cyclobutane ring based on the 1H−1H COSY correlations of H-

no.

δC

1, 1′ 2, 2′ 3, 3′ 4, 4′ 5, 5′ 6, 6′ 7, 7′ 8, 8′ 9, 9′ 10/14, 10′/14′ 11/13, 11′/13′ 12, 12′ Glc1, Glc2 1 2 3 4 5 6

138.5 138.3 151.6 102.7 156.1 106.2 45.1 54.9 134.5 130.0 116.0 156.8

b

107.8 75.4 77.6 70.5 77.8 61.7

4 δH

a,c

6.22, d (2.8) 6.70, br s 4.36, t (10.0) 3.35, t (10.0) 7.19, d (8.0) 6.69, d (8.0)

4.11, d (7.6) 3.38 3.25, t (9.2) 3.46, t (9.2) 2.78, td (9.6, 2.8) 3.63, dd (11.6, 4.0) 3.56, dd (11.6, 2.4)

δC

b

138.0 138.0 151.4 102.7 155.6 107.8 47.1 52.0 135.4 129.3 116.1 156.9 107.7 75.2 77.6 70.7 77.6 62.1

δHa,c

6.20, d (2.8) 6.72, br s 4.19, br d (9.6) 3.46, br d (9.6) 7.15, d (8.4) 6.71, d (8.4)

4.06, d (7.6) 3.19 3.17 3.42 2.89, td (9.6, 2.8) 3.75, dd (11.6, 4.0) 3.67, dd (11.6, 2.4)

a

Recorded at 400 MHz. bRecorded at 100 MHz. cOverlapped signals are reported without designating multiplicity.

7 with H-7′, H-7′ with H-8′, H-8′ with H-8, and H-8 with H-7. The four phenyl groups were connected to the cyclobutane ring based on the HMBC correlations of H-7 (δH 4.94) with C-6 (δC 108.3), H-7′ (δH 5.05) with C-6′ (δC 107.7), H-8 (δH 4.29) with C-10 (δC 131.0), and H-8′ (δH 4.13) with C-10′ (δC 130.7). Moreover, the HMBC correlations of Glc1-H-1 (δH 257



Article

Figure 4. Fragment ions observed in the HR-ESIMS/MS spectrum of 2.

Figure 5. Calculated and experimental ECD spectra of 3 and 5−7.

4.39) with C-2 (δC 137.1) and Glc2-H-1 (δH 4.40) with C-2′ (δC 138.3) established the positions of the two β-Dglucopyranosyl moieties. Therefore, the 2D structure of 3 was established to be a dimeric cycloadduct of (E)-2,3,5,4′tetrahydroxystilbene 2-O-β-D-glucopyranoside (8) (Scheme 1) joined in a head-to-head manner. The correlation of H-6 (δH 6.51) with H-8 (δH 4.29) in the ROESY spectrum of 3 suggested that H-7 was trans to H-8. Similarly, the ROESY correlation of H-6′ (δH 6.50) with H-8′ (δH 4.13) indicated that H-7′ was trans to H-8′. Nevertheless, no correlations between H-7 (δH 4.94) and H-7′ (δH 5.05) and between H-8 (δH 4.29) and H-8′ (δH 4.13) were observed, which indicated H-7 and H-7′ and H-8 and H-8′ were

presumably in a trans configuration. This relative configuration of 3 suggested the presence of a C2 symmetry axis in the molecule. Quantum-chemical electronic circular dichroism (ECD) calculations were used to establish the absolute configuration of 3.22,23 The calculated ECD curve of (7R,8S,7′R,8′S)-3 matched the measured spectrum well (Figure 5). Thus, the structure and absolute configuration of 3 were established and shown in Figure 1. Multiflorumiside D (4) was found to have the same molecular formula as 1−3 based on its HR-ESIMS data. The 1 H and 13C NMR spectra of 4 exhibited signals similar to those of 2, except for the slight shift in the signals of C-7/C-7′ and C8/C-8′ (Table 2). These spectroscopic features in conjunction 258



Article

Figure 6. Fragment ions observed in the HR-ESIMS/MS spectrum of 4.

overlapped); δC 28.9]. In addition, the signals from two sugar moieties [δH 4.65 (1H, d, J = 7.5 Hz) and 3.32 (1H, overlapped); δC 108.4, 105.8, 78.1, 78.0, 77.9, 77.5, 75.3, 75.2, 70.9, 70.8, 62.2, and 61.2] were also present in the 1D NMR spectra of 5. The sugar moieties were both identified as Dglucose using the same method as was used for 1, and its βconfiguration was determined by the 3J1,2 values. The above spectroscopic data together with the molecular formula suggested that 5 was also a dimeric stilbene glucoside. All the proton and carbon signals of 5 were assigned based on analysis of its 2D NMR spectra (Table 3). A C-7 to C-8′ spin system (Figure 2) was revealed by the 1 H−1H COSY correlations. The HMBC correlations of H-8′ (δH 4.29) with C-5 (δC 154.1)/C-1 (δC 134.7) and H-7a (δH 3.37) with C-1 (δC 134.7) suggested the presence of a substituted tetralin system in 5. Furthermore, the HMBC correlations of H-10 (δH 6.57) with C-8 (δC 38.8), H-6′ (δH 6.16) with C-7′ (δC 44.9), and H-10′ (δH 7.00) with C-8′ (δC 45.9) suggested the remaining three phenyl groups were linked at C-8, C-7′, and C-8′ of the tetralin moiety. In addition, the two β-D-glucopyranosyl moieties were connected at C-2 and C2′ based on the HMBC correlations of Glc1-H-1 (δH 4.65) with C-2 (δC 137.9) and Glc2-H-1(δH 3.32) with C-2′ (δC 137.9). Thus, the 2D structure of 5 was established as shown in Figure 2. The correlations between H-7a (δH 3.37) and H-10 (δH 6.57)/H-6′ (δH 6.16) and between H-8 (δH 3.19) and H-7′ (δH 4.09) in the ROESY spectrum of 5 indicated that H-8 and H-7′ were cofacial. Moreover, the ROESY correlations between H-8′ (δH 4.29) and H-6′ (δH 6.16) and between H-7′ (δH 4.09) and H-10′ (δH 7.00) suggested that H-7′ was trans to H-8′ (Figure 7). The relative configuration of 5 was further confirmed by the

with the molecular formula suggested that 4 was also a symmetrical stilbene glucoside dimer linked via a cyclobutane ring. Unlike 2, the two characteristic fragment ion peaks at m/z 275.0580 and 437.1115 were present in the HR-ESIMS/MS spectrum of 4 (Figure 6), indicating the two stilbene glucoside monomers in 4 were linked in a head-to-head manner. The correlations of H-7/H-7′ (δH 4.19) with H-10/H-10′ (δH 7.15) and H-8/H-8′ (δH 3.46) with H-6/H-6′ (δH 6.72) in the ROESY spectrum of 4 suggested that H-7 and H-8 and H7′ and H-8′ were in trans configurations. Considering that 4 has the same 2D structure as 3 but with different NMR spectroscopic data, the relationship between H-7 and H-7′ and H-8 and H-8′ in 4 could be assigned as cis. Multiflorumiside E (5) was obtained as an amorphous powder. The molecular formula of 5 was established as C40H44O18 by its HR-ESIMS data (m/z 835.2420 [M + Na]+; calculated for C40H44O18Na: 835.2420). The UV spectrum exhibited absorption maxima at 206 and 282 nm. The IR spectrum of 5 showed absorptions from aromatic (1618, 1517, and 1460 cm−1) and hydroxy (3431 cm−1) functionalities. The 1D NMR spectra of 5 indicated the presence of two paradisubstituted benzene moieties [δH 7.00 (2H, d, J = 8.5 Hz), 6.69 (2H, d, J = 8.5 Hz), 6.57 (2H, d, J = 8.5 Hz), and 6.50 (2H, d, J = 8.5 Hz); δC 156.4, 156.0, 139.7, 136.9, 130.9 × 2, 130.7 × 2, 115.6 × 2, and 115.5 × 2], a pentasubstituted benzene moiety [δH 6.30 (1H, s); δC 154.1, 149.2, 137.9, 134.7, 118.0, and 102.5], a tetrasubstituted benzene ring [δH 6.19 (1H, d, J = 3.0 Hz) and 6.16 (1H, d, J = 3.0 Hz); δC 155.0, 151.2, 139.2, 137.9, 108.0, and 102.7], three aliphatic sp3 methines [δH 4.29 (1H, d, J = 1.5 Hz), 4.09 (1H, dd, J = 3.5, 2.5 Hz), and 3.19 (1H, overlapped); δC 45.9, 44.9, and 38.8], and a methylene [δH 3.37 (1H, overlapped) and 3.18 (1H, 259



Article

Table 3. 1H and 13C NMR Data of 5−7 (Methanol-d4, J in Hz) 5 no. 1 2 3 4 5 6 7

134.7 137.9 149.2 102.5 154.1 118.0 28.9

8 9 10/14 11/13 12 1′ 2′ 3′ 4′ 5′ 6′ 7′ 8′ 9′ 10′/14′ 11′/13′ 12′ Glc1 1 2 3 4 5 6

38.8 136.9 130.9 115.6 156.4 139.2 137.9 151.2 102.7 155.0 108.0 44.9 45.9 139.7 130.7 115.5 156.0

Glc2 1 2 3 4 5 6 a

δ Cd

6 δHa,c

6.30, s

a 3.37 b 3.18 3.19 6.57, d (8.5) 6.50, d (8.5)

6.19, d (3.0) 6.16, d (3.0) 4.09, dd (3.5, 1.5) 4.29, d (1.5) 7.00, d (8.5) 6.69, d (8.5)

δ Cd

7 δHb,c

135.4 136.6 149.2 102.5 153.6 119.6 32.6

6.21, s

a 3.62 b 2.95 2.94

48.1 137.1 130.7 115.6 156.3 139.3 138.2 151.2 102.4 155.7 106.8 50.4 50.7 141.9 129.8 115.6 155.9

7.03, d (8.4) 6.55, d (8.4)

6.10, d (2.8) 6.38, d (2.4) 3.87, dd (11.2, 7.6) 4.25, d (7.6) 6.70, d (8.8) 6.56, d (8.8)

δCd 134.4 137.7 149.3 102.6 153.9 119.6 31.7 41.8 135.8 131.1 115.4 156.4 138.9 138.4 151.3 102.5 154.6 108.8 46.2 44.5 139.7 130.8 115.4 155.8

δHa,c

6.23, s

a 3.52 b 3.27 3.25 6.56, d (8.5) 6.48, d (8.5)

6.12, d (2.5) 5.84, d (3.0) 4.20 4.17 6.87, d (8.5) 6.56, d (8.5)

108.4 75.3 78.1 70.9 77.5 62.2

4.65, d (7.5) 3.49, t (9.0) 3.37 3.51 3.18 3.80 3.78

107.7 75..3 78.2 71.0 77.9 62.3

4.60, d (6.8) 3.47 3.31 3.45 3.44 3.72 3.68

108.0 75.4 78.0 70.8 77.5 62.7

4.58, d (8.0) 3.48 3.43 3.42 3.28 3.91, dd (12.0, 2.0) 3.76, dd (12.0, 4.0)

105.8 75.2 78.0 70.8 77.9 62.1

3.32 3.25, t (9.0) 3.45, t (9.0) 3.37 2.88, td (10.0, 3.0) 3.74 3.72

106.4 75.4 77.3 70.8 77.8 61.9

3.46 3.31, t (8.0) 3.28 3.34 2.87, td (9.6, 3.2) 3.65 3.63

107.3 75.2 78.4 71.4 77.8 62.0

3.64, d (7.5) 3.35 3.37 3.39 2.92, td (10.0, 3.0) 3.65, d (3.5)

Recorded at 500 MHz. bRecorded at 400 MHz. cOverlapped signals are reported without designating multiplicity. dRecorded at 100 MHz.

established by the coupling constants of H-7′ with H-8 (J = 11.2 Hz) and H-8′ (J = 7.6 Hz), which further confirmed the relative configuration of 6.25 Multiflorumiside G (7) was found to possess the same molecular formula as 5 and 6 based on its HR-ESIMS data. The similarities between the 1H and 13C NMR data of 7 and those of 5 and 6 indicated that the three compounds had identical 2D structures (Table 3), which was corroborated via analysis of the 2D NMR data of 7. The ROESY correlations of H-6′ (δH 5.84) with H-8 (δH 3.25) as well as H-7′ (δH 4.20) with H-10 (δH 6.56) suggested that H-8 was trans to H-7′. The ROESY correlation of H-6′ (δH 5.84) with H-10′ (δH 6.87) revealed that H-7′ and H-8′ were cofacial. Additionally, the absolute configurations of 5−7 were determined by comparing their calculated and experimental ECD spectra. The predicted ECD spectra for (8R,7′R,8′R)-5,

coupling constants of H-7′ (J = 3.5, 1.5 Hz) and H-8′ (J = 1.5 Hz).24 The molecular formula of 6 was identical to that of 5, which was assigned based on its HR-ESIMS data (m/z 835.2419 [M + Na]+; calculated for C40H44O18Na: 835.2420). The 1H and 13C NMR spectroscopic data of 6 (Table 3) closely resembled those of 5, suggesting that 6 was a stereoisomer of 5. Further analysis of the 2D NMR data revealed that 6 possessed the same 2D structure as 5. The ROESY spectrum of 6 showed correlations between H-8 (δH 2.94) and H-6′ (δH 6.38) as well as between H-10 (δH 7.03) and H-7′ (δH 3.87), suggesting that H-8 was trans to H7′. Similarly, the ROESY correlations of H-8′ (δH 4.25) with H6′ (δH 6.38) as well as H-7′ (δH 3.87) with H-10′ (δH 6.70) indicated that H-7′ and H-8′ were also trans-related. Additionally, the axial orientations of H-8, H-7′, and H-8′ were 260



Article

Figure 7. Lowest-energy conformers and key ROESY correlations of 5−7.

of the plant that were not exposed to light (roots), the biosyntheses of 1−4 cannot be regarded as a simple photodimerization of two monomeric stilbene glucosides. Although no [2 + 2]-ase has been identified to date, enzymatic promotion of [2 + 2] cycloaddition reactions has been shown in the dimerization steps of some cyclobutane-containing natural products.27 Compounds 5 and 6 could be produced from two molecules of 8 via the corresponding [4 + 2] cycloaddition reaction and a subsequent [1,3]-hydrogen shift if a phenyl ring is involved in the cycloaddition step. Compound 7 could be generated from 8 and 9 by the same mechanism by which 5 and 6 were formed. The in vitro anti-inflammatory activities of 1−7 were tested against the suppression of nitric oxide (NO) secretion in lipopolysaccharide (LPS)-stimulated RAW264.7 cells. The inhibition rate of dexamethasone, which was used as a positive control, was 60.9 ± 2.5%. Compounds 1−4 exhibited moderate inhibitory activity against NO production with inhibition rates of 22.4 ± 3.8%, 16.7 ± 4.4%, 22.0 ± 6.0%, and 16.8 ± 5.0%, respectively, at 20 μM. Seven new dimeric stilbene glucosides (1−7) were identified by phytochemical investigation of the roots of P. multif lorum. Compounds 1−4 presumably were generated through a [2 + 2] cycloaddition reaction of two monomeric stilbenes to form a cyclobutane ring, which are rare in natural oligomeric stilbenes. The four stereogenic centers of the cyclobutane ring in 1−4 permitted stereochemical diversity. Compound 1 possessed a centrosymmetric aglycone, 2 and 4 appeared to have planes of symmetry, and 3 had a 2-fold (C2) symmetry axis. Compounds 5−7 possessed identical carbon skeletons but with different configurations; all three compounds were generated from two monomeric stilbene moieties coupled to form a tetralin system. Glycosides of stilbene oligomers are rarely reported due to their instability during isolation and the difficulty of their

(8R,7′S,8′S)-6, and (8S,7′R,8′S)-7 resembled the experimental spectra for 5, 6, and 7, respectively (Figure 7). Thus, the absolute configurations of 5, 6, and 7 were determined as shown in Figure 1. Putative biosynthetic pathways toward the formation of 1−7 were proposed as shown in Scheme 1. The two co-occurring monomeric stilbene glucosides, (E)-2,3,5,4′-tetrahydroxystilbene 2-O-β-D-glucopyranoside (8) and (Z)-2,3,5,4′-tetrahydroxystilbene 2-O-β-D-glucopyranoside (9), were considered as the biosynthetic precursors to 1−7. Compounds 1−4 could be formed from two molecules of 8 by [2 + 2] cycloaddition reactions; 1 could also be derived from 9 via the same reaction. In principle,26 [2 + 2] cycloaddition reactions of monomeric stilbene glucosides (8 and 9) may occur in trans−trans, trans− cis, and cis−cis modes. All four cyclobutane-containing dimers (1−4) were obtained in trans−trans form (if stilbene glucoside 9 is considered to be the precursor, compound 1 could also be generated from cycloaddition in the cis−cis orientation). In view of the absolute configurations, [2 + 2] cycloaddition reactions between two molecules of monomeric stilbene in the trans−trans orientation can generate five possible isomers including two enantiomers. Interestingly, all expected isomers (1−4) were obtained in this study except the isomer possessing the enantiomeric aglycone of 3. Moreover, the n-butanolsoluble fraction of the extract of fresh P. multif lorum roots was analyzed by UPLC-QTOF/MS (Figures S67−S80, Supporting Information). As a result, 1−4 were detected in the fresh roots, but the fifth possible stereoisomer was still absent, which suggested that the cycloaddition reaction in this plant showed a certain degree of stereoselectivity. Additionally, water and MeOH solutions of 8 were exposed to sunlight for 4 weeks, and the solutions were then analyzed by UPLC-QTOF/MS. No dimers were detected in either solution. Based on the above result and the identification of 1−4 from the extract of the parts 261



Article

identification. Compounds 5−7 are the first examples of oligomeric stilbene glycosides coupled through a cyclohexene ring, and compounds 1−4 are the second group of oligomeric stilbene glycosides reported to be coupled through cyclobutane rings.28 Furthermore, based on their experimental and calculated ECD spectra, the absolute configurations of 3 and 5−7 were established. In addition, 1−4 moderately inhibit NO secretion of LPS-activated RAW264.7 cells.

■

Multiflorumiside B (2): crystalline powder (MeOH), mp 223−224 °C; [α]20D +16 (c 0.5, MeOH); HR-ESIMS m/z 835.2421 [M + Na]+ (calcd for C40H44O18Na, 835.2420); UV (MeOH) λmax (log ε) 208 (4.59), 232 (sh), 282 (3.73) nm; IR (KBr) νmax 3402, 1621, 1516, 1066 cm−1; NMR data in Table 2. Multiflorumiside C (3): amorphous powder; [α]20D −9 (c 0.5, MeOH); HR-ESIMS m/z 835.2420 [M + Na] + (calcd for C40H44O18Na, 835.2420); UV (MeOH) λmax (log ε) 208 (4.62), 226 (sh), 282 (3.68) nm; IR (KBr) νmax 3398, 1613, 1512, 1456, 1062 cm−1; ECD (MeOH, Δε) λmax 225.2 (−8.52), 245.6 (−6.48) nm; NMR data in Table 1. Multiflorumiside D (4): amorphous powder; [α]20D +14 (c 0.5, MeOH); HR-ESIMS m/z 835.2420 [M + Na] + (calcd for C40H44O18Na, 835.2420); UV (MeOH) λmax (log ε) 208 (4.61), 226 (sh), 282 (3.72) nm; IR (KBr) νmax 3411, 1618, 1516, 1455, 1054 cm−1; NMR data in Table 2. Multiflorumiside E (5): amorphous powder; [α]20D −10 (c 0.5, MeOH); HR-ESIMS m/z 835.2419 [M + Na] + (calcd for C40H44O18Na, 835.2420); UV (MeOH) λmax (log ε) 206 (4.65), 224 (sh), 282 (3.72) nm; IR (KBr) νmax 3431, 1618, 1517, 1460, 1071 cm−1; ECD (MeOH, Δε) λmax 232 (−33.36) nm; NMR data in Table 3. Multiflorumiside F (6): amorphous powder; [α]20D +71 (c 0.5, MeOH); HR-ESIMS m/z 835.2419 [M + Na] + (calcd for C40H44O18Na, 835.2420); UV (MeOH) λmax (log ε) 206 (4.55), 226 (sh), 282 (3.69) nm; IR (KBr) νmax 3395, 1618, 1511, 1001 cm−1; ECD (MeOH, Δε) λmax 208.8 (+9.69), 233.0 (+16.80), 278.0 (−3.74) nm; NMR data in Table 3. Multiflorumiside G (7): amorphous powder, [α]20D −19 (c 0.5, MeOH); HR-ESIMS m/z 835.2421 [M + Na] + (calcd for C40H44O18Na, 835.2420); UV (MeOH) λmax (log ε) 208 (4.45), 228 (sh), 282 (3.60) nm; IR (KBr) νmax 3407, 1618, 1511, 1459, 1071 cm−1; ECD (MeOH, Δε) λmax 212.2 (−43.64), 235.0 (+15.85), 287.4 (−5.91) nm; NMR data in Table 3. Sugar Identification. Samples of compounds 1−7 (3 mg) were separately dissolved in HCl (2 mol/L, 5 mL) and refluxed at 80 °C for 2 h. The residues were obtained by removing the solvent. Each residue was dissolved in pyridine (2 mL), and L-cysteine methyl ester hydrochloride (3 mg) was added to each. The solutions were heated at 60 °C for 1 h. Then, O-tolyl isothiocyanate (3 mg) was added to each mixture, and the solutions were heated at 60 °C for an additional 1 h. The reaction mixtures were analyzed using HPLC (column: Cosmosil 5C18-MS-II, 250 mm × 4.6 mm, 5 μm; detector: G1315D photodiode array; mobile phase: CH3CN−0.05% HOAc (25:75); flow rate: 1.0 mL/min; test wavelength: 250 nm). The sugar moieties of 1−7 were determined to be D-glucose by comparison of the retention times of the monosaccharide derivatives (tR = 16.36 min) to the derivatives of authentic D-glucose (tR = 16.36 min) and L-glucose (tR = 14.86 min).19 Computational Methods. The systematic random conformational analysis was accomplished using the MMFF94s molecular force field and random search approach within the SYBYL 8.1 software. The energy cutoff window was 10 kcal mol−1. Each conformer was optimized using the DFT/B3LYP/6-31+G(d) level of theory in the gas phase by using the Gaussian 09 suite of programs.29 The ECD spectrum of each conformer after optimization was simulated with a time-dependent DFT method using the B3LYP functional and 631+G(d) basis set, and the first 50 excitations were considered. The total ECD spectra of each compound were averaged by a Boltzmann weighting approach with a half-bandwidth of 0.3 eV within SpecDis 1.6 software.23,30 Bioactivity Assay. The nitrite concentration in the medium and the viability of RAW 264.7 cells were assayed to evaluate the in vitro anti-inflammatory activity of the compounds.18 First, 4 × 104 cells per well were seeded into 96-well plates and incubated in a humidified atmosphere of 5% CO2 at 37 °C for 2 h. The cells were treated with 200 ng/mL LPS and serially diluted samples of the test compounds for 48 h at 37 °C. Each supernatant (100 μL) was harvested and mixed with Griess reagent (100 μL). The absorbance of each sample was read with a microplate reader (Thermo, USA) at 540 nm after 15 min of incubation. The viability of the cells was determined by the MTT

EXPERIMENTAL SECTION

General Experimental Procedures. Melting points were measured on an X-5 micro melting point apparatus and are uncorrected (Fukai instrument, Beijing, China). Optical rotations were measured in MeOH on a JASCO P-1020 digital polarimeter with a 0.1-dm-long cell (Jasco, Tokyo, Japan). UV spectra were obtained on a JASCO-V-550 UV/vis spectrophotometer (Jasco, Tokyo, Japan). ECD spectra were acquired on a Jasco J-810 spectropolarimeter (Jasco, Tokyo, Japan). IR spectra were obtained with a JASCO FT/IR-480 Plus infrared spectrometer (Jasco, Tokyo, Japan). NMR spectra were recorded on Bruker AV-400 and Bruker AV-500 spectrometers using tetramethylsilane as an internal standard (Bruker, Fällanden, Switzerland). HR-ESIMS data were collected on an Agilent 6210 ESI/TOF (Agilent Technologies, CA, USA) and a Waters Xevo-G2 Q TOF mass spectrometer (Waters MS Technologies, Manchester, UK). HPLC preparation and HPLC-PDA analysis were carried out on an Agilent 1260 series system with Cosmosil C18 reversed-phase columns of different sizes (250 × 20 mm, 250 × 4.6 mm, 5 μm; Nacalai Tesque Inc., Kyoto, Japan). Column chromatography was performed on Sephadex LH-20 (Pharmacia Fine Chemical, Uppsala, Sweden), macroporous resin (Diaion HP-20, Mitsubishi Chemical Corp., Tokyo, Japan), and silica gel (300−400 mesh; Qingdao Marine Chemical Co. Ltd., China). Plant Material. The roots of P. multif lorum were collected in Deqing County of Guangdong Province, People’s Republic of China, in October of 2010. The plant material was identified by Prof. GuangXiong Zhou (Institute of Traditional Chinese Medicine & Natural Products, College of Pharmacy, Jinan University), and a voucher specimen (No. 20101003) was deposited at the Institute. Extraction and Isolation. The roots of P. multif lorum (14.5 kg) were dried, crushed, and extracted using 95% EtOH under reflux (25 L, 2 h × 2). A residue (1.2 kg) was obtained by removing the solvent under reduced pressure. The residue was sequentially partitioned into petroleum ether (bp 60−90 °C), EtOAc, and n-BuOH. The n-BuOH fraction (144 g) was chromatographed on a macroporous resin column eluting successively with H2O, 30% EtOH, 50% EtOH, 70% EtOH, and 95% EtOH. The 30% EtOH portion (14 g) was chromatographed on a Sephadex LH-20 column eluting with gradient mixtures of MeOH−H2O (7:3 → 10:0) to give eight main fractions (1−8). Fractions 4 and 5 were separated on silica gel columns using gradient mixtures of CHCl3−MeOH (9:1, 8.5:1.5, 8:2, 7.5:2.5, and 7:3) as eluent to yield five subfractions (4a−4e and 5a−5e, respectively). Subfraction 4b was further separated using preparative RP-HPLC (30% MeOH, 6 mL/min) to obtain 1 (99.7 mg). Subfraction 5e was also purified by preparative RP-HPLC (22% MeOH, 6 mL/min) and afforded 5 (28.2 mg), 6 (86.0 mg), and 7 (8.4 mg). Fraction 7 was separated by silica gel column chromatography, eluting with a CHCl3−MeOH mixture (9:1), to yield four subfractions (7a−7d). Subfractions 7b and 7c were further purified using preparative RP-HPLC (35% MeOH, 6 mL/min) to afford 2 (28.4 mg), 3 (105.2 mg), and 4 (7.2 mg), respectively. Fraction 8 was chromatographed on a Sephadex LH-20 column using MeOH as the eluent to give 8 (235.0 mg) and four subfractions (8a−8d). Subfraction 8b was further purified by preparative RP-HPLC (38% MeOH, 6 mL/min) to afford 9 (22.0 mg). Multiflorumiside A (1): amorphous powder; [α]20D +6 (c 0.5, MeOH); HR-ESIMS m/z 835.2414 [M + Na] + (calcd for C40H44O18Na, 835.2420); UV (MeOH) λmax (log ε) 206 (4.59), 226 (sh), 282 (3.73) nm; IR (KBr) νmax 3411, 1618, 1512, 1467, 1066 cm−1; NMR data in Table 1. 262



Article

method. None of the test compounds showed cytotoxicity at their effective concentration for the inhibition of NO production.

■

(15) Mattivi, F.; Vrhovsek, U.; Malacarne, G.; Masuero, D.; Zulini, L.; Stefanini, M.; Moser, C.; Velasco, R.; Guella, G. J. Agric. Food Chem. 2011, 59, 5364−5375. (16) Yamada, M.; Hayashi, K.-I.; Ikeda, S.; Tsutsui, K.; Tsutsui, K.; Ito, T.; Iinuma, M.; Nozak, H. Biol. Pharm. Bull. 2006, 29, 1504−1507. (17) Li, S. G.; Chen, L. L.; Huang, X. J.; Zhao, B. X.; Wang, Y.; Ye, W. C. J. Asian Nat. Prod. Res. 2013, 15, 1145−1151. (18) Chen, L. L.; Huang, X. J.; Li, M. M.; Ou, G. M.; Zhao, B. X.; Chen, M. F.; Zhang, Q. W.; Wang, Y.; Ye, W. C. Phytochem. Lett. 2012, 5, 756−760. (19) Li, S. G.; Huang, X. J.; Li, M. M.; Wang, M.; Feng, R. B.; Zhang, W.; Li, Y. L.; Wang, Y.; Ye, W. C. Chem. Pharm. Bull. 2014, 62, 35−44. (20) Zhang, X. J.; Li, L. Y.; Wang, S. S.; Que, S.; Yang, W. Z.; Zhang, F. Y.; Gong, N. B.; Cheng, W.; Liang, H.; Ye, M.; Jia, Y. X.; Zhang, Q. Y. Tetrahedron 2013, 69, 11074−11079. (21) Yang, C. S.; Wang, X. B.; Wang, J. S.; Luo, J. G.; Luo, J.; Kong, L. Y. Org. Lett. 2011, 13, 3380−3383. (22) Li, X. C.; Ferreira, D.; Ding, Y. Q. Curr. Org. Chem. 2010, 14, 1678−1697. (23) Jian, Y. Q.; Huang, X. J.; Zhang, D. M.; Jiang, R. W.; Chen, M. F.; Zhao, B. X.; Wang, Y.; Ye, W. C. Chem. - Eur. J. 2015, 21, 1−7. (24) Li, X. M.; Huang, K. S.; Lin, M.; Zhou, L. X. Tetrahedron 2003, 59, 4405−4413. (25) Royer, M.; Herbette, G.; Eparvier, V.; Beauchȇne, J.; Thibaut, B. Phytochemistry 2010, 71, 1708−1713. (26) Ma, G. L.; Xiong, J.; Yang, G. X.; Pan, L. L.; Hu, C. L.; Wang, W.; Fan, H.; Zhao, Q. H.; Zhang, H. Y.; Hu, J. F. J. Nat. Prod. 2016, 79, 1354−1364. (27) Stout, E. P.; Wang, Y. G.; Romo, D.; Molinski, T. F. Angew. Chem., Int. Ed. 2012, 51, 4877−4881. (28) Xiao, K.; Xuan, L. J.; Xu, Y.; Bai, D. L.; Zhong, D. X.; Wu, H. M.; Wang, Z. H.; Zhang, N. X. Eur. J. Org. Chem. 2002, 3, 564−568. (29) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Scalmani, G.; Barone, V.; Mennucci, B.; Petersson, G. A.; Nakatsuji, H.; Caricato, M.; Li, X.; Hratchian, H.; Izmaylov, A. F.; Bloino, J.; Zheng, G.; Sonnenberg, J. L.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Vreven, T.; Montgomery, J. A., Jr.; Peralta, J. E.; Ogliaro, F.; Bearpark, M.; Heyd, J. J.; Brothers, E.; Kudin, K. N.; Staroverov, V. N.; Kobayashi, R.; Normand, J.; Raghavachari, K.; Rendell, A.; Burant, J. C.; Iyengar, S. S.; Tomasi, J.; Cossi, M.; Rega, N.; Millam, J. M.; Klene, M.; Knox, J. E.; Cross, J. B.; Bakken, V.; Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.; Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Martin, R. L.; Morokuma, K.; Zakrzewski, V. G.; Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Dapprich, S.; Daniels, A. D.; Farkas, O.; Foresman, J. B.; Ortiz, J. V.; Cioslowski, J.; Fox, D. J. Gaussian 09, Revision A.02; Gaussian, Inc.: Wallingford, CT, 2009. (30) Bruhn, T.; Schaumlöffel, A.; Hemberger, Y.; Bringmann, G. SpecDis version 1.60; University of Wuerzburg: Germany, 2012.

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.jnatprod.7b00540. UV, IR, NMR, and HR-ESIMS spectra of compounds 1− 7, HR-ESIMS/MS spectra of 2 and 4, UPLC-QTOF/MS analysis of the n-butanol fraction of the extract of fresh roots of P. multif lorum, and related ECD calculated data of 3 and 5−7 (PDF)

■

AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected]. *E-mail: [email protected]. ORCID

Ying Wang: 0000-0003-4524-1812 Wen-Cai Ye: 0000-0002-2810-1001 Author Contributions ⊥

S.-G. Li and X.-J. Huang contributed equally.

Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS The National Natural Science Foundation of China (Nos. 81502940, 81622045, 81502939, and 81673670) and the Postdoctoral Science Foundation of China (No. 2015M572415) financially supported this work.

■

REFERENCES

(1) Sotheeswaran, S.; Pasupathy, V. Phytochemistry 1993, 32, 1083− 1092. (2) Li, N.; Li, X. M.; Huang, K. S.; Lin, M. Acta Pharm. Sinica 2001, 36, 944−950. (3) Shen, T.; Wang, X. N.; Luo, H. X. Nat. Prod. Rep. 2009, 26, 916− 935. (4) Wan, X.; Wang, X. B.; Yang, M. H.; Wang, J. S.; Kong, L. Y. Bioorg. Med. Chem. 2011, 19, 5085−5092. (5) Niesen, D. B.; Hessler, C.; Seeram, N. P. J. Berry Res. 2013, 3, 181−196. (6) Yan, S. L.; Su, Y. F.; Que, M.; Gao, X. M.; Chang, J. B. J. Nat. Prod. 2014, 77, 397−401. (7) Papastamoulis, Y.; Richard, T.; Nassra, M.; Badoc, A.; Krisa, S.; Harakat, D.; Monti, J.-P.; Mérillon, J.-M.; Waffo-Teguo, P. J. Nat. Prod. 2014, 77, 213−217. (8) Wu, X. K.; Zhang, J. R.; Gu, B. B.; He, S.; Zhang, J. Y. Rec. Nat. Prod 2016, 10, 349−354. (9) Yang, Y. N.; Li, F. S.; Liu, F.; Feng, Z. M.; Jiang, J. S.; Zhang, P. C. RSC Adv. 2016, 6, 60741−60748. (10) Yang, J. B.; Tian, J. Y.; Dai, Z.; Ye, F.; Ma, S. C.; Wang, A. G. Fitoterapia 2017, 117, 65−70. (11) Chung, E. Y.; Kim, B. H.; Lee, M. K.; Yun, Y.-P.; Lee, S. H.; Min, K. R.; Kim, Y. S. Planta Med. 2003, 69, 710−714. (12) Ito, T.; Endo, H.; Shinohara, H.; Oyama, M.; Akao, Y.; Iinuma, M. Fitoterapia 2012, 83, 1420−1429. (13) He, S.; Wu, B.; Pan, Y. J.; Jiang, L. Y. J. Org. Chem. 2008, 73, 5233−5241. (14) Bala, A. E. A.; Ducrot, K. P.-H.; Majira, A.; Kerhoas, L.; Leroux, P.; Delorme, R.; Einhorn, J. J. Phytopathol. 2000, 148, 29−32. 263


Multiflorumisides AâG, Dimeric Stilbene Glucosides with Rare

Recommend Documents

Multiflorumisides AâG, Dimeric Stilbene Glucosides with Rare