Abstract
A UPLC-PDA-QTOFMS-guided isolation strategy was employed to screen and track potentially new compounds from Garcinia oblongifolia. As a result, two new prenylated xanthones, oblongixanthones D and E (1ā2), six new prenylated benzoylphloroglucinol derivatives, oblongifolins VāZ (3ā7) and oblongifolin AA (8), as well as a known compound oblongifolin L (9), were isolated from the EtOAc-soluble fraction of an acetone extract of the leaves of Garcinia oblongifolia guided by UPLC-PDA-QTOFMS analysis. The structures of the new compounds were elucidated by 1D- and 2D-NMR spectroscopic analysis and mass spectrometry. Experimental and calculated ECD spectra were used to determine the absolute configurations. The results of wound healing and transwell migration assay showed that oblongixanthones D (1), E (2), and oblongifolin L (9) have the ability to inhibit cancer cell migration in lower cytotoxic concentrations. Western blotting results showed that these compounds exhibited an anti-metastasis effect mainly through downregulating RAF protein levels. In addition, 2 and 9 could inhibit phospho-MEK and phospho-ERK at downstream. Moreover, 1, 2, and 9 could inhibit snail protein level, suggesting that they could regulate the EMT pathway.
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Introduction
Garcinia oblongifolia Champ. ex Benth. (Clusiaceae), a tree or medium-sized shrub with edible fruits, is widely distributed in tropical regions of southern mainland China and northern Vietnam. It has been used for many years as a folk medicine in China to treat stomatitis, eczema, and burns1,2. Previous phytochemical studies of this species led to the discovery of many new compounds, including prenylated benzoylphloroglucinols3,4,5,6, xanthones4,5, biphenyls2, and a new bixanthone derivative, garciobioxanthone7, which have been reported to possess a wide range of biological activities, including antitumor1,8,9,10, anti-inflammatory11, and antienteroviral effects3,12.
In our previous study, a series of new prenylated benzoylphloroglucinols, oblongifolins JāU were isolated from the bioacitve petroleum ether-soluble part of the acetone extract of G. oblongifolia leaves by bioassay-guided fractionation, in which two compounds exhibited significant anti-EV71 activity3. In our efforts to identify more new bioactive compounds from Garcinia species, the EtOAc-soluble fraction of the acetone extract of the leaves of G. oblongifolia was found to contain many potentially new compounds by UPLC-PDA-QTOFMS analysis. In follow-up work, UPLC-PDA-QTOFMS-guided fractionation led to the isolation of two new prenylated xanthones, oblongixanthones D and E (1ā2), six new prenylated benzoylphloroglucinol derivatives, oblongifolins VāZ (3ā7) and oblongifolin AA (8), as well as a known compound, oblongifolin L (9) from this fraction (Fig. 1). In this report, the isolation and structural elucidation of these compounds, as well as their migration-inhibitory activity in esophageal cancer are described.
Results and Discussion
The EtOAc-soluble fraction of the acetone extract of the leaves of Garcinia oblongifolia and its subfractions were analyzed by UPLC-PDA-QTOFMS in positive mode to screen and characterize potentially new compounds. As a result, 13 unknowns of interest were detected from this extract and its subfractions by analysis of their UV, MS, and MS/MS spectra (Figures S1āS13, Supplementary information). Compounds 1 and 2 both showed the molecular ion [Mā+āH]+ at m/z 447, corresponding to a molecular formula of C24H30O8. Their UV spectra showed similar absorption bands at approximately 257 and 327 nm, indicating that they might be xanthone derivatives (Figures S1 and S2)13. Compounds 3ā8 and P10āP14 produce the characteristic fragment ion at m/z 165.0182 or 177.0182 in their MS/MS spectra (Figures S3āS13), indicating that they might be polycyclic polyprenylated acylphloroglucinols (PPAPs)14,15,16. Their molecular formulas were obtained by accurate mass measurements for precursor ions. These 13 compounds were searched using the molecular formula and further refined by their skeletons in the SciFinder database. The results indicated that they were potentially new xanthones or PPAPs. Thus, they were selected as the targets of interest to be subjected to further phytochemical isolation. Finally, 8 new compounds (1ā8) were isolated by column chromatography over MCI gel, silica gel, reversed-phase C18 silica gel, Sephadex LH-20, and preparative HPLC guided by UPLC-PDA-QTOFMS analysis. Other five potentially new PPAPs (P10āP14) could not been obtained, which were decomposed or oxidized during the isolation procedure or the NMR experiments. In addition, a known compound was obtained, which could be unambiguously identified as oblongifloin L (9) by comparison of the retention time (RT) and MS/MS data with those of the reference compound. Structural elucidation of the new compounds was achieved by HRMS, 1H NMR, 13C NMR, DEPT, HSQC, HMBC, and NOSEY analyses.
Structural elucidation
Oblongixanthone D (1) was isolated as yellow amorphous powder. In the MS/MS spectrum of 1, the most abundant fragment peak (m/z 373) was due to the successive loss of an H2O and a prenyl unit C4H8 (56 Da). This fragment further dissociated by the loss of an H2O and a prenyl unit C4H8 to produce additional fragment ions at m/z 355 and 287. These fragmentaion characteristics indicated that 1 might contain two hydroxylated prenyl groups. The 13C NMR and DEPT spectra showed 12 aromatic carbons (including five oxygenated), one carbonyl carbon, two oxygenated quaternary carbons, four sp3 methylene carbons, four sp3 methyl groups, and one methoxyl group. The 1H NMR spectrum of 1 showed a chelated hydroxyl proton signal at Ī“H 13.28 (1H, s), a methoxy signal at Ī“H 3.82 (3H, s), two ortho-coupled aromatic proton signals at Ī“H 7.54 (1H, d, Jā=ā8.6āHz) and 6.93 (1H, d, Jā=ā8.6āHz), and two 3-hydroxy-3-methylbutyl moiety singals, one showing a pair of gemdimethyl signals at Ī“H 1.18 (6H, s) and two methylene signals at Ī“H 2.64 (2H, m) and 1.59 (2H, m). The other 3-hydroxy-3-methylbutyl group exhibited a pair of gem-dimethyl signals at Ī“H 1.24 (6H, s) and two methylene signals at Ī“H 2.86 (2H, m) and 1.70 (2H, m). Based on the abovementioned information, compound 1 was proposed as a xanthone bearing a methoxy group and two 3-hydroxy-3-methylbutyl groups. The locations of two 3-hydroxy-3-methylbutyl moieties and a methoxy group were assigned to C-2 (Ī“C 117.3), C-4 (Ī“C 114.1), and C-3 (Ī“C 162.7), respectively, based on the correlations from the methoxy protons at Ī“H 3.82 to C-3, from H-11 (Ī“H 2.64) to C-3, C-4, and C-4a (Ī“C 152.3), as well as from H-16 (Ī“H 2.86) to C-1 (Ī“C 157.8) and C-2 in the HMBC spectrum (Fig. 2). Furthermore, the HMBC correlations from aromatic proton at Ī“H 7.54 to C-6 (Ī“C 146.4), C-10a (Ī“C 152.9), and C-9 (Ī“C 180.8), and from aromatic proton at Ī“H 6.93 to C-5 (Ī“C 132.6) and C-8a (Ī“C 112.5) indicated that the locations of those two ortho-coupled aromatic protons were C-7 (Ī“C 113.4) and C-8 (Ī“C 116.2). Hence, the structure of 1 was assigned as 1,5,6-trihydroxy-3-methoxy-2,4-bis(3-hydroxy-3-methylbutyl)xanth-6-one.
The UV and NMR spectra of oblongixanthone E (2) were similar to those of 1, suggesting that 2 was also a xanthone with one methoxy group and two 3-hydroxy-3-methylbutyl groups (Figures S1, S2, and Table 1). However, the MS/MS spectrum of 2 is different from that of 1 (Figures S1 and S2). Furthermore, comparison of the NMR data of 2 with those of 1 suggested that 2 is a 1,3,4,5,6,8-hexsubstituted xanthone [Ī“H 6.69 (1H, s) and 6.43 (1H, s)], compared to 1,2,3,4,5,6-hexsubstituted ring system of 1 [Ī“H 7.54 (1H, d, Jā=ā8.6āHz) and 6.93 (1H, d, Jā=ā8.6āHz)]. HMBC correlations between 1-OH/C-1, 1-OH/C-2, 1-OH/C-3, H-2/C-1, H-2/C-3, OCH3/C-3, H-11/C-3, H-11/C-4, H-11/C-4a, H-16/C-7, and H-16/C-8 indicated that the locations of two 3-hydroxy-3-methylbutyl moieties, a methoxy group, and two aromatic protons were at C-4 (Ī“C 107.7), C-8 (Ī“C 136.8), C-3 (Ī“C 162.9), C-2 (Ī“C 93.9), and C-7 (Ī“C 114.5), respectively (Fig. 2). Therefore, 2 was determined to be 1,5,6-trihydroxy-3-methoxy-4,8-bis(3-hydroxy-3-methylbutyl)xanth-6-one.
Oblongifolin V (3) was obtained as a pale yellow gum. The molecular formula C27H30O5 was established by HRESIMS analysis and NMR spectroscopic data. The MS/MS spectrum of 3 showed a diagnostic fragment ion at m/z 165.0182 in the positive mode, suggesting that it might be a type B PPAP with no prenyl substituent at C-514 (Figure S3). The 1H NMR spectrum indicated the presence of a monosubstituted benzene ring [Ī“H 7.56 (1H, m), 7.42 (2H, m), and 7.59 (2H, m)], an E-configured carbon-carbon double bond [Ī“H 6.71 (1H, dd, Jā=ā15.7, 7.7āHz) and 6.16 (1H, d, Jā=ā15.7āHz)], a vinyl proton [Ī“H 5.18 (1H, brs)], two methylenes [Ī“H 1.94, 1.89, 2.50, and 2.44], two methines [Ī“H 3.13 (1H, s), 2.67 (1H, m)], and five methyl groups [Ī“H 2.65 (3H, s), 1.72 (3H, s), 1.63 (3H, s), 1.17 (3H, s), and 1.02 (3H, s)]. The 13C NMR and DEPT spectra showed signals pertaining to a nonconjugated ketone (Ī“C 206.8), an enolized 1,3-diketone (Ī“C 196.5, 119.5, and 184.8), two quaternary carbons (Ī“C 64.4 and 44.9), a methylene (Ī“C 41.9), and two methines (Ī“C 69.6 and 45.2), which allowed us to identify the bicyclo[3.3.1] nonane ring system typical of the prenylated benzoylphloroglucinols17. Resonances for six aromatic carbons and a conjugated carbonyl group (Ī“C 198.1) were also observed, revealing the occurrence of a benzoyl group. In the HMBC spectrum, the long range correlations observed from the olefinic H-19 (Ī“H 6.71, dd, Jā=ā15.7, 7.7āHz) signal to C-7 (Ī“C 45.2) and C-8 (Ī“C 41.9), along with correlations from olefinic H-20 (Ī“H 6.16, d, Jā=ā15.7āHz) to the ketone resonance at Ī“C 200.8 (C-21), which was in turn correlated with CH3-22, established a 3-buten-2-one side chain located at C-7. Other key HMBC correlations are shown in the Fig. 3. Based on these data, compound 3 was elucidated as a prenylated benzoylphloroglucinol with a prenyl unit at C-1 (Ī“C 64.4), a 3-buten-2-one side chain at C-7, and no prenyl unit at C-5 (Ī“C 69.6).
The relative configuration of 3 was defined via a NOESY experiment. The correlations between H-19 (Ī“H 6.71)/H-18 (Ī“H 1.02) and H-8a (Ī“H 1.94)/H-18 showed that the orientation of the 3-buten-2-one group at C-7 was Ī² (Fig. 3). Thus, there were two possible isomers: (1R,5R,7R)-3 and (1S,5S,7S)-3. The absolute configuration of 3 was determined by comparison of its experimentally measured electronic circular dichroism (ECD) curve with curves calculated using the TDDFT method. Consequently, the overall pattern of the calculated ECD curve of (1R,5R,7R)-3 was consistent with the experimental ECD spectrum of 3 (Fig. 4). Therefore, the structure of oblongifolin V (3) was established as shown.
Oblongifolin W (4) gave the same molecular formula (C27H30O5) as 3 (m/z 435.2173 [M + H]+ (calcd 435.2166)) by HRESIMS. Comparison of its NMR data (Table 2) with those of 3 revealed these compounds to be closely related, except for differences between C-23 (Ī“C 23.4), C-24 (Ī“C 30.9), C-25 (Ī“C 84.8), C-26 (Ī“C 29.8), and C-27 (Ī“C 26.7) of 4 and C-23 (Ī“C 31.2), C-24 (Ī“C 120.8), C-25 (Ī“C 135.8), C-26 (Ī“C 26.4), and C-27 (Ī“C 18.4) of 3. This finding indicated the presence of a 2,2-dimethyl-pyran moiety in 4 instead of a 3-methylbut-2-enyl side chain in 3. HMBC correlations between H-23/C-1, H-23/C-2, H-23/C-9, H-23/C-25, H-24/C-1, H-24/C-25, H-26/C-25, H-27/C-25, and H-27/C-24 confirmed the presence of the 2,2-dimethyl-pyran moiety fused at C-1 (Ī“C 50.2) and C-2 (Ī“C 174.5). Key HMBC correlations are shown in Fig. 3. The relative configuration of 4 was assigned using NOE correlations, as shown in Fig. 3. Thus, two possible isomers, (1R,5R,7R)-4 and (1S,5S,7S)-4, were considered, and the ECD spectra were calculated. Visual inspection suggested that the (1S,5S,7S)-4 curve was similar to the experimental curve (Fig. 4). Thus, the structure of 4 was designated as shown.
The molecular formula of oblongifolin X (5) was determined to be C27H28O5 by HRESIMS. The 1H and 13C NMR data showed close similarities to those of 4, with the exception of differences at C-23 (5: Ī“C 34.3, CH2; 4: Ī“C 23.4, CH2), C-24 (5: Ī“C 91.1, CH; 4: Ī“C 30.9, CH2), C-25 (5: Ī“C 142.5, C; 4: Ī“C 84.8, C), C-26 (5: Ī“C 114.9, CH2; 4: Ī“C 29.8, CH3), and C-27 (5: Ī“C 17.3, CH3; 4: Ī“C 26.7, CH3). HMBC correlations between H-23/C-1, H-23/C-2, H-23/C-8, H-23/C-9, H-23/C-24, H-24/C-23, H-24/C-25, H-24/C-26, H-24/C-27, H-26/C-24, H-26/C-25, H-27/C-24, H-27/C-25, and H-27/C-26 confirmed the presence of a (2-isopropenyl)dihydrofuran ring moiety fused with the phloroglucinol moiety at C-1 (Ī“C 61.7) and C-2 (Ī“C 178.9) (Figure S14, Supplementary information). These data confirmed that a (2-isopropenyl)dihydrofuran ring moiety at C-1 and C-2 of 5 replaced the 2,2-dimethyl-pyran moiety in 4. The planar structure of 5 was further elucidated by careful interpretation of the 2D NMR experiments. The relative configuration of 5 was determined by a NOESY experiment. Key NOE correlations are shown in Figure S14. Furthermore, the calculated ECD curve (Fig. 4) for 5 led to the absolute structure being determined as shown.
Oblongifolin Y (6) was obtained as a pale yellow gum, and its molecular formula of C25H28O6 was established by the positive HRESIMS ion at m/z 425.1969 [Mā+āH]+ (calcd for C25H29O6, 425.1959). Comparison of the spectroscopic data of 6 with those of 4 showed that 6 is also a benzoylphloroglucinol with a 2,2-dimethyl-pyran moiety fused to the phloroglucinol moiety at C-1 and C-2. The only structural difference between the two compounds was the presence of an acetoxy group (COOHāCH2ā) in 6 instead of the 3-buten-2-one group in 4. The location of the acetoxy group was assigned to C-7 by the HMBC correlations from H-7 (Ī“H 2.74) to C-19 (Ī“C 34.3), as well as H-19 (Ī“H 2.65) to C-20 (Ī“C 173.9). The structure of 6 was confirmed by DEPT, HSQC, HMBC, and NOESY experiments. The key HMBC and NOE correlations are shown in Figure S15 (Supplementary information). Furthermore, an ECD experiment and ECD calculation of 6 were conducted. The experimental ECD spectrum of 6 was consistent with the calculated ECD spectra for (1S,5S,7R)-6 (Fig. 4), thus establishing the assignment of the absolute configuration of 6 as depicted.
Oblongifolin Z (7) was obtained as a pale yellow gum. The molecular formula C33H44O5 for 7 was calculated from the HREIMS of the ion peak [Mā+āNa]+ m/z 543.3083 (calc. 543.3081). The 1H NMR data of this compound were similar to values obtained for the known compound oblongifolin Q3, except for differences between H-30 [Ī“H 1.44 (1H, m) and 1.34 (1H, m)] and H-32 [Ī“H 1.12 (3H, s)] in 7 and H-30 [Ī“H 3.95 (1H, t, Jā=ā6.1āHz)] and H-32 [Ī“H 4.89 (1H, s) and 4.80 (1H, s)] in oblongifolin Q. This information indicated the occurrence of a 3-hydroxy-3-methylbutyl group at C-23 in 7 instead of the 2-hydroxy-3-methylbutenyl group of oblongifolin Q. This conclusion was further confirmed by the 13C NMR data of C-29 (Ī“C 23.5, CH2), C-30 (Ī“C 44.3, CH2), C-31 (Ī“C 71.6, C), and C-33 (Ī“C 29.29, CH3) and HMBC correlations between H-30/C-33, H-32/C-30, H-32/C-31, H-32/C-33, H-33/C-30, H-33/C-31, and H-33/C-32 (Figure S16, Supplementary information). According to the observed NOE correlations (Figure S16), the relative configuration of 7 was deduced to be the same as those of oblongifolin Q. In addition, the experimental ECD spectrum of 7 was consistent with that of 7 (Figure S17), suggesting that the absolute configuration of 7 is the same as that of oblongifolin Q. Thus, the structure of oblongifolin Z (7) was established as shown.
Oblongifolin AA (8) had the same molecular formula as the known compound 9 (C33H44O4), which was deduced from HRESIMS. The MS/MS spectrum of 8 in positive was also in near agreement with that of 9 (Figure S18, Supplementary information). The 1H and 13C NMR data (Table 3) showed close similarities to those of 9, with the exception of significant differences in the chemical shifts at C-7, C-8, C-17, and C-18 due to the opposite configuration of C-7 [Ī“C 45.5, 41.0, 25.4, and 31.5 for 8, respectively, versus Ī“C 42.4, 43.2, 27.6, and 21.2 for oblongifolin L, respectively]. These data indicated that 8 was a C-7 epimer of oblongifolin L. The structure of 8 was confirmed by DEPT, HSQC, HMBC, and NOESY experiments. The absolute configuration of 8 was also assigned by experimental and theoretically calculated ECD methods. As shown in Figure S19, the absolute configuration of 8 was determined as shown.
Compounds 1, 2, and 9 inhibit migration in TE1 cells
Our previous studies showed that compounds isolated from Garcinia species had potent inhibitory effect on esophageal cancer cell metastasis10,18. In addition, the EtOAc-soluble fraction of the actone extract of G. oblongifolia leaves could inhibit TE1 cell migration at concentrations of 12.5, 25 and 50 Ī¼g/ml (Figure S20). Therefore, all isolates were screened by wound healing assay to identify new compounds with anti-metastasis activity in esophageal cancer cells. As shown in Fig. 5, after treatment with various compounds at a concentration of 20 Ī¼M, compared to the positive control sorafenib (SFB), compounds 1, 2, and 9 exhibited the ability to inhibit migration in TE1 cells. The cell cytotoxicity tested by MTT assay showed that all compounds had lower cytotoxicity in TE1, KYSE150, HepG2, A549, and HL7702 cell lines (Table S1, Supplementary information). Moreover, the results indicated that TE1 cells were more sensitive to 1, 2 and 9 than other cells.
Transwell assay was performed to confirm the effect of all isolates on cell migration. After being incubated with these compounds at 10 and 20āĪ¼M for 24āh, TE1 cells were fixed and imaged, and the number of migrated cells was counted. As shown in Fig. 6, the migrated cells were significantly reduced after compounds 1, 2 and 9 treatments. Statistical data also suggested that 1, 2 and 9 could significantly inhibit cell migration. In addition, compounds 3ā8 had no significant effect on cell migration, which was consistent with the results of wound healing assay (Figure S21). A transwell invasion assay was preformed to investigate whether the invasion ability was blocked by 1, 2 and 9. The results suggested that 9 significantly attenuated TE1 cells invasion. Moreover, compounds 1 and 2 did not inhibit cell invasion in the matrigel invasion assay (Figure S22, Supplementary information). All these results suggest that 1, 2 and 9 showed a potential effect on cell metastasis.
Compounds 1, 2, and 9 downregulate RAF-MAPK signaling pathway and snail protein level
The RAFāMEKāERK cascade plays a central role in the regulation of cell metastasis, proliferation and survival. The high frequency of this pathway deregulated in human cancer makes it an attractive target for drug development19. Therefore, we examined whether these compounds with anti-metastasis activity could interfere RAF-MAPK cascades. Western blot showed that the 24āh treatment of 1, 2, and 9 attenuated BRAF and CRAF protein levels at both 10 and 20āĪ¼M (Fig. 7). In addition, compounds 2 and 9 inhibited phospho-MEK and phospho-ERK, suggesting that these two compounds could also interfere downstream signals. No significant changes were detected on RAS, MEK and ERK proteins (Fig. 7), as well as on BRAF and CRAF mRNA levels (Figure S22, Supplementary information).
The epithelial-mesenchymal transition (EMT) is a fundamental process that acts on endowing cells with migratory and invasive properties. Snail is a protein that promotes EMT, acting as an EMT marker20. To illustrate whether these compounds could affect snail protein, we performed a western blot analysis. The results showed that 1, 2, and 9 reduced snail protein (Fig. 7), suggesting that they could regulate the EMT pathway. In conclusion, compounds 1, 2, and 9 could downregulate the RAFāMEKāERK cascades and regulate EMT pathway by decreasing snail protein, indicating that these compounds could inhibit cell migration through multiple signaling pathways.
Experimental Section
General Experimental Procedures
Optical rotations were measured using an Autopol VI polarimeter. Ultraviolet absorption spectra were recorded on a UV-2401 PC spectrophotometer. ECD spectra were recorded on a Chirascan-plus spectrometer (Applied photophysics Ltd., Surrey, United Kingdom). IR spectra were obtained from a Perkin-Elmer 577 spectrometer. NMR spectra were measured on a Bruker AV-600 or AV-400 spectrometer and calibrated by the solvent peak used. Mass spectrometry was performed on a SYNAPT G2-Si HDMS (Waters Corp., Manchester, UK) with an electrospray ion source (Waters, Milford, MA) connected to a lock-mass apparatus, which performed real-time calibration correction. Column chromatography was performed with CHP20P MCI gel (75ā150āĪ¼m, Mitsubishi Chemical Corporation, Japan), silica gel (100ā200, or 200ā300 mesh, Qingdao Haiyang Chemical Co., Ltd.), Sephadex LH-20 (GE Healthcare Bio-Sciences AB, Sweden), and reversed-phase C18 silica gel (50āĪ¼m, YMC, Kyoto, Japan). Precoated TLC sheets of silica gel 60 GF254 (Qingdao Haiyang Chemical Co., Ltd.) were used. A Waters 2535 Series machine equipped with a Xbridge C18 column (4.6āĆā250āmm, 5āĪ¼m) was used for HPLC analysis, and a preparative Xbridge Prep C18 OBD column (19āĆā250āmm, 5āĪ¼m) was used for the sample preparation.
Plant Material
The leaves of G. oblongifolia were collected at Bobai, Guangxi Zhuang Autonomous Region, Peopleās Republic of China in December, 2005. The sample was identified by Dr. Chun-Feng Qiao. A voucher specimen (Herbarium No. 20120843) was deposited at the Engineering Research Centre of Shanghai Colleges for TCM New Drug Discovery, Shanghai University of Traditional Chinese Medicine.
Extraction and Isolation
According to the previous separation process3, the EtOAc-soluble fraction (220āg) of an acetone extract of the leaves of G. oblongifolia has been obtained. A UPLC-PDA-QTOFMS-guided isolation approach was employed to track the potentially new compounds during the entire isolation process. The EtOAc-soluble fraction was subjected to column chromatography (CC) on MCI, and successively eluted with H2O, 30%, 95% EtOH, and EtOAc. The 95% EtOH-eluting fraction was separated by chromatography on a silica gel column using a gradient of petroleum etherāacetone (100:0 to 0:100, v/v) to yield 8 fractions AāK.
Fraction F (2.8āg) was subjected to reversed-phase C18 silica gel CC and eluted in a step gradient manner with MeOH-H2O (60:40 to 100:0) to obtain fifteen subfractions FaāFp. Subfraction Fb was purified by preparative HPLC (MeCN-H2O, 45:55, with 0.1% formic acid in H2O, 20āml/min) to yield compound 3 (12.5āmg). Subfraction Fd was further separated by preparative HPLC (MeCN-H2O, 39:61, with 0.1% formic acid in H2O, 20āmL/min) to give compounds 4 (7.1āmg) and 5 (2.7āmg). Compounds 8 (27.3āmg) and 9 (50āmg) were purified by preparative HPLC (MeCN-H2O, 77:23, with 0.1% formic acid in H2O, 20āml/min) from subfraction Fo. Subfraction H (1.2āg) was subjected to CC on a reversed-phase C18 silica gel eluted with MeOH-H2O in a gradient (40:60 to 100:0) to obtain 10 subfractions (HaāHj). Subfraction Hd was purified by preparative HPLC (MeCN-H2O, 40:60, with 0.1% formic acid in H2O, 20āml/min) to yield compound 7 (8.1āmg). Fraction I (1.2 g) was chromatographed on a Sephadex LH-20 column (MeOH) to obtain 9 subfractions Ia-Ii. Fraction Ib (750āmg) was subjected to reversed-phase C18 silica gel CC and eluted in a step gradient manner with MeOH-H2O (50:50 to 100:0) to obtain subfractions IbaāIbj. Subfractions Ibb, Ibc, and Ibd were purified by preparative HPLC to yield compounds 6 (5.8āmg), 1 (5āmg), and 2 (8.9āmg), respectively.
Oblongixanthone D (1): light yellow powder; UV (MeOH) Ī»max (logĪµ) 256 (3.68), 328 (3.19) nm; IR (KBr) Ī½max 3423, 2965, 2927, 1633, 1590, 1515, 1459, 1432,1301, 1213, 1110, 1037, 755ācmā1; 1H NMR (DMSO-d6, 600āMHz) data, see Table 1; 13C NMR (DMSO-d6, 150āMHz) data, see Table 1; HRESIMS 447.2013 [Mā+āH]+ (calcd for C24H31O8, 447.2013).
Oblongixanthone E (2): light yellow powder; UV (MeOH) Ī»max (logĪµ) 255 (3.77), 330 (3.39) nm; IR (KBr) Ī½max 3428, 2965, 1646, 1523, 1444, 1384, 1321, 1115, 1105ācmā1; 1H NMR (DMSO-d6, 400 MHz) data, see Table 1; 13C NMR (DMSO-d6, 100āMHz) data, see Table 1; HRESIMS 447.2015 [Mā+āH]+ (calcd for C24H31O8, 447.2013).
Oblongifolin V (3): light brown gum; [Ī±]25D 4.3 (c 0.02, MeOH); UV (MeOH) Ī»max (logĪµ) 202 (4.10) nm; ECD (c 4.37āĆā10ā4āM, MeOH) Ī»max nm (ĪĪµ) 220 (+22.98), 250 (ā10.10), 291 (ā4.75), 319 (+4.83); IR (KBr) Ī½max 3359, 2921, 2850, 1722, 1633, 1590, 1573, 1467, 1382, 1280, 1025, 701ācmā1; 1H NMR (CD3OD/0.1% TFA, 600āMHz) data, see Table 2; 13C NMR (CD3OD/0.1% TFA, 150āMHz) data, see Table 2; HRESIMS 435.2169 [Mā+āH]+ (calcd for C27H31O5, 435.2166).
Oblongifolin W (4): light brown gum; [Ī±]25D 20.0 (c 0.03, MeOH); UV (MeOH) Ī»max (logĪµ) 253 (3.51) nm; ECD (c 2.42āĆā10ā4āM, MeOH) Ī»max nm (ĪĪµ) 211 (ā7.03), 273 (+3.87), 315 (+0.76); IR (KBr) Ī½max 3359, 3197, 2956, 2923, 2852, 1733, 1677, 1633, 1596, 1467, 1365, 1233, 1118, 755ācmā1; 1H NMR (CD3OD/0.1% TFA, 600āMHz) data, see Table 2; 13C NMR (CD3OD/0.1% TFA, 150āMHz) data, see Table 2; HRESIMS 435.2173 [Mā+āH]+ (calcd for C27H31O5, 435.2166).
Oblongifolin X (5): light brown gum; [Ī±]25D ā 11.8 (c 0.03, MeOH); UV (MeOH) Ī»max (logĪµ) 253 (3.80) nm; ECD (c 11.76āĆā10ā4āM, MeOH) Ī»max nm (ĪĪµ) 209 (ā6.64), 270 (3.34); IR (KBr) Ī½max 3444, 2929, 1733, 1677, 1623, 1448, 1365, 1288, 1207, 1139, 1027ācmā1; 1H NMR (CD3OD/0.1% TFA, 600āMHz) data, see Table 2; 13C NMR (CD3OD/0.1% TFA, 150āMHz) data, see Table 2; HRESIMS 433.2010 [Mā+āH]+ (calcd for C27H29O5, 433.2009).
Oblongifolin Y (6): light brown gum; [Ī±]25D 24.1 (c 0.06, MeOH); UV (MeOH) Ī»max (logĪµ) 253 (3.40) nm; ECD (c 3.54āĆā10ā4āM, MeOH) Ī»max nm (ĪĪµ) 207 (ā3.78), 272 (3.39); IR (KBr) Ī½max 3444, 2967, 1733, 1644, 1594, 1452, 1375, 1336, 1118ācmā1; 1H NMR (acetone-d6, 600āMHz) data, see Table 2; 13C NMR (acetone-d6, 150āMHz) data, see Table 2; HRESIMS 425.1969 [Mā+āH]+ (calcd for C25H29O6, 425.1959).
Oblongifolin Z (7): light brown gum; [Ī±]25D ā 23.5 (c 0.03, MeOH); UV (MeOH) Ī»max (logĪµ) 244 (3.35), 282 (3.37) nm; ECD (c 2.60āĆā10ā4āM, MeOH) Ī»max nm (ĪĪµ) 215 (4.97), 253 (ā3.74), 319 (1.63); IR (KBr) Ī½max 3444, 2929, 1718, 1670, 1635, 1590, 1573, 1382, 1078ācmā1; 1H NMR (CD3OD/0.1% TFA, 400āMHz) data, see Table 3; 13C NMR (CD3OD/0.1% TFA, 100āMHz) data, see Table 3; HRESIMS 543.3083 [Mā+āNa]+ (calcd for C33H44O5Na, 543.3081).
Oblongifolin AA (8): light brown gum; [Ī±]25D ā 36.2 (c 0.05, MeOH); UV (MeOH) Ī»max (logĪµ) 253 (3.54), 286 (3.56) nm; ECD (c 2.60āĆā10ā4 M, MeOH) Ī»max nm (ĪĪµ) 217 (21.85), 254 (ā12.88), 316 (5.52); IR (KBr) Ī½max 3444, 2962, 2923, 1729, 1673, 1637, 1590, 1573, 1448, 1382, 1286, 1025ācmā1; 1H NMR (CD3OD/0.1% TFA, 400āMHz) data, see Table 3; 13C NMR (CD3OD/0.1% TFA, 100āMHz) data, see Table 3; HRESIMS 503.3164 [Mā+āH]+ (calcd for C33H45O4, 503.3167).
UPLC-PDA-QTOFMS analysis
UPLC was performed using a Waters Acquity UPLC Iclass system (Waters, Milford, MA, USA), equipped with a binary solvent delivery system, an autosampler, and a photodiode-array detection (PDA) system. Chromatography was performed on a Waters ACQUITY BEH C18 column (2.1āmmāĆā100āmm I.D., 1.7āĪ¼m, Waters, Milford, MA, USA). The mobile phase consisted of (A) 0.1% formic acid in water and (B) ACN containing 0.1% formic acid. The 0.1% formic acid was added to both the aqueous solution and ACN. The UPLC eluting conditions were as follows: 32ā42% B (0ā5āmin), 42ā46% B (5ā10āmin), 46ā70% B (10ā23āmin), 70ā95% B (23ā29āmin) and 95ā100% B (29ā32āmin). The flow rate was maintained at 0.4āml/min. The column and autosampler were maintained at 40āĀ°C and 10āĀ°C, respectively.
Mass spectra were obtained using a SYNAPT G2-Si HDMS (Waters Corp., Manchester, UK) equipped with an electrospray ionization source. ESI mass spectra were acquired over the m/z 50ā1200 range. The desolvation gas was set to 800āL hā1 at temperature of 400āĀ°C, the cone gas was set to 50āL hā1, and the source temperature was set to 120āĀ°C. The capillary voltage was set to 2500āV. Spectra were acquired in continuum and positive mode. Argon was employed as the collision gas. The SYNAPT G2-Si HDMS system was calibrated using sodium formate clusters and operated in resolution mode. Leucine enkephalin was used as a lock mass. All fractions were analyzed by UPLC-QTOFMS using the data-dependent acquisition (DDA) mode. The top five ions were selected for MS/MS from a single MS survey scan. The scan time for MS/MS was 0.1ās. The collision energy in the trap cell was ramped from 15 to 40āV. UNIFI 1.8 was used for visualization, processing, and interpretation of MS data.
Cell culture
The human esophageal cancer cell line TE1 and the KYSE150 cells were provided from Fudan University Shanghai Cancer Center. The human cell line HepG2, A549 and HL7702 cells were purchased from the Shanghai Institute of Biochemistry and Cell Biology (Shanghai, China). Cells were grown in RPMI 1640 or DMEM medium (Hyclone, Logan, UT, USA) with 10% fetal bovine serum (FBS), 100 U/ml penicillin and 100 mg/ml streptomycin, cultivated at 37āĀ°C containing 5% CO2.
Cell viability assay
The cell viability was assessed by an MTT assay. Briefly, 5āĆā103 cells were seeded into a 96-well culture plate. After 24āh, cells were incubated with various compounds for 48āh. Approximately 10āĪ¼l of MTT (5āmg/ml) was added and dimethyl sulfoxide was used to dissolve the formazan crystals. The absorbance was measured at 570ānm by a microplate reader.
Wound healing assay
Cell motility was evaluated by wound healing. Briefly, 1āĆā105 cells were seeded into a 24-well culture plate. When the cells grew to 80ā90% confluence, a scratch was created through the cell monolayer by sterile 100āĪ¼l pipette tips, and media containing various dilutions of compounds were added. Cell migration was observed and imaged under an IX83 microscope (Olympus, Tokyo, Japan) after 36āh.
Transwell migration and invasion assay
Cell migration and invasion were estimated using transwell chambers (Corning, NY, USA) with a pore size of 8 Ī¼m. For the migration assay, 5āĆā104 cells were added into the upper chamber in serum-free medium, and in the bottom chamber, 600āĪ¼L of 10% FBS medium was added. After incubating with various concentrations of compounds for 24āh, the cells on the upper surface of the chamber were removed using cotton swabs. The migrated cells on the bottom surface were fixed in 4% paraformaldehyde, stained with 0.1% crystal violet and scored under a light microscope in five random fields. For the transwell invasion assay, the upper chamber membranes were pre-incubated with matrigel (BD Biosciences, Bedford, MA, USA) for 2āhours at 37āĀ°C.
Quantitative Real-time PCR
After treatment, total RNA was extracted from TE1 cells using Trizol (Takara, Shiga, Japan). Then, RNA was reverse transcribed by a PrimeScript RT reagent kit. Quantitative PCR was conducted with forward and reverse primers containing SYBER Green. Then, real-time PCR was performed under a StepOnePlus Real-Time PCR System. The primers for human genes were as follows: for GAPDH, forward primer: 5ā²-TGTTGCCATCAATGACCCCTT-3ā², reverse primer: 5ā²-CTCCACGACGTACTCAGCG-3ā², for B-RAF, forward primer: 5ā²-CATTGGTTTTGATGAGTATATGAAC-3ā², reverse primer: 5ā²-GGAGACACTTTGTAGCAGAG-3ā² and for C-RAF, forward primer: 5ā²-TGAGCACTGTAGCACCAAAGTACCT-3ā², reverse primer: 5ā²-CAGACTCTCGCATACGACGCAT-3ā².
Western blot analysis
TE1 cells were seeded on a 3.5-cm dish, treated with various compounds, and lysed in RIPA buffer. Proteins were separated on SDS polyacrylamide gels and transferred to PVDF membranes (Millipore, Billerica, MA, USA). The membranes were blocked and immunoblotted with primary antibodies at 4āĀ°C overnight, followed by appropriate secondary antibodies. GAPDH was used as the loading control. Membranes were visualized under an Image Quant LAS 4000 mini and processed by Image Quant TL 1D software (General Electric Company).
The primary antibodies C-RAF (Cat.9422), MEK1/2 (Cat.9122), p-MEK (Ser217/221, Cat.9154), ERK (Cat.4695), p-ERK (Tyr202/Tyr204, Cat.4370), GAPDH (Cat.5174) and snail (Cat.3879) were purchased from Cell Signaling Technologies (Danvers, MA, USA). RAS (Cat.ab137739) and B-RAF (Cat.ab33899) were purchased from Abcam (Cambridge, UK).
Additional Information
How to cite this article: Zhang, H. et al. UPLC-PDA-QTOFMS-guided isolation of prenylated xanthones and benzoylphloroglucinols from the leaves of Garcinia oblongifolia and their migration-inhibitory activity. Sci. Rep. 6, 35789; doi: 10.1038/srep35789 (2016).
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Acknowledgements
This work was financially supported by the National Natural Science Foundation of China (Nos 81273403 and 81303188). We are grateful to Dr. Chun-Feng Qiao for collecting the plant material. The authors are grateful to Dr. Shuang Liang and Da-Hai He for fruitful discussions about structural elucidation.
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H.Z. and D.Z. contributed equally to this work. They conducted the main experiments, analyzed the data, and wrote the manuscript. Z.-J.D. and Y.-Z.L. performed the biological assay; H.-S.T. and H.-X.X. edited and polished this manuscript; H.Z. and H.-X.X. designed the experiments and commented the manuscript. All authors reviewed the manuscript.
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Zhang, H., Zheng, D., Ding, ZJ. et al. UPLC-PDA-QTOFMS-guided isolation of prenylated xanthones and benzoylphloroglucinols from the leaves of Garcinia oblongifolia and their migration-inhibitory activity. Sci Rep 6, 35789 (2016). https://doi.org/10.1038/srep35789
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DOI: https://doi.org/10.1038/srep35789
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