Polyphenolic Constituents of the Pericarp of Mangosteen (Garcinia

May 29, 2015 - The edible aril of the fruit is known as the queen of fruits and food of the gods because of its pleasant taste. The pericarp of the ma...
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Polyphenolic Constituents of the Pericarp of Mangosteen (Garcinia mangostana L.) Morio Yoshimura,† Kana Ninomiya,† Yukari Tagashira,§ Kazuhiro Maejima,§ Takashi Yoshida,† and Yoshiaki Amakura*,† †

College of Pharmaceutical Sciences, Matsuyama University, 4-2 Bunkyo-cho, Matsuyama, Ehime 790-8578, Japan Food Development Laboratory, Nippon Shinyaku Company, Ltd., 14 Nishinosho-monguchi-cho, Kisshoin, Minami-ku, Kyoto 601-8550, Japan

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S Supporting Information *

ABSTRACT: Three new polyphenols, together with 14 known compounds, were isolated from a hot water extract of mangosteen (Garcinia mangostana L.) pericarp, a plant that has been used medicinally in Southeast Asia. The three new polyphenols were characterized as a 4-aryl-2-flavanylbenzopyran derivative (tentatively named GM-1), 1, 3,4,3′,5′-tetrahydroxy-5methoxybenzophenone (GM-2), 2, and 2,3-dihydrochromone derivative (GM-3), 3 on the basis of NMR and MS data. The relative stereostructure of GM-1 was assigned to have 2,3-cis-3,4-trans- and 2″,3″-cis configurations on the basis of the coupling constants of heterocyclic ring protons in the 1H NMR spectrum along with nuclear Overhauser effect correlations. The HPLC analysis indicated that major polyphenolic components in the hot water extract of mangosteen pericarp were epicatechin and procyanidin B2 (epicatechin dimer). KEYWORDS: mangosteen, Garcinia mangostana, pericarp, polyphenols, procyanidin

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INTRODUCTION

the medicinally used decoction of mangosteen pericarp have been less investigated. In the present study, we examined the polar ingredients, especially water-soluble polyphenols, in mangosteen pericarp, thus contributing to the identification of bioactive components in the pericarp.

Garcinia mangostana L. (Hypericaceae), commonly known as mangosteen, is a tropical evergreen tree widely distributed and cultivated in Southeast Asia. The edible aril of the fruit is known as the queen of fruits and food of the gods because of its pleasant taste. The pericarp of the mangosteen contains dark purple to red-purple pigment related to proanthocyanidins and, therefore, has been used for coloring fabrics. Also, the pericarp of mangosteen has been used in Thai folk medicine to treat skin infections, diarrhea, fever, and wounds and was reported to have various bioactivities including anti-inflammatory,1 αglucosidase inhibitory,2 antimicrobial,3,4 and antitumor activities.5,6 Recently, mangosteen extract has been also used as a dietary supplement in the United States for its functional effect. Previous studies have reported bioactivities of several ingredients isolated from the pericarp of mangosteen that are beneficial to health. Some nonpolar compounds such as xanthones (α-, β-, γ-mangostins, garcimangosones A, B, etc.)4,6−9 and prenylated benzophenone derivatives (guttiferones A, E, H, etc.)10 were isolated from the organic solvent extract of the pericarp and bioactive ingredients (e.g., αmangostin; prenylated xanthone, which is a major constituent of ethanol extract of mangosteen pericarp) were used for functional food or as supplements because of their role in promoting health. The polar compounds of polyphenols and condensed tannins such as catechins, procyanidins, and anthocyanidins, which are known as potent antioxidative ingredients were detected in the polar fraction of the pericarp. Moreover, it has also been suggested that mangosteen pericarp is a good source of oligomeric proanthocyanidins with B-type linkages dominant.11 However, bioactive polar ingredients in © XXXX American Chemical Society

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MATERIALS AND METHODS

General. Optical rotations were recorded on a JASCO P-1030 polarimeter (Tokyo, Japan). NMR spectra were recorded on av AVANCE 500 (Bruker Biospin Co., Billerica, MA, USA; 500 MHz for 1 H and 126 MHz for 13C) with chemical shifts given in δ (ppm) values relative to those of the solvent [methanol-d4 (δH 3.30, δC 49.0), acetone-d6 (δH 2.05, δC 29.8)] on a TMS scale. High-resolution electrospray ionization mass spectrometry (HR-ESI-MS) spectra were obtained on a micrOTOF-Q mass spectrometer (Bruker Daltonics, Bremen, Germany). Reversed-phase HPLC was performed on a Shimadzu LC-10Avp system (Kyoto, Japan), using a YMC-pack ODSAQ column (150 mm × 2.0 mm i.d., 5 μm; Kyoto, Japan) at 40 °C with a flow rate of 0.25 mL/min. The analyses were conducted using solvent A (100 μM phosphate buffer, pH 2.6) and solvent B (methanol) at the following gradient: 0−50% B (linear gradient) from 0 to 30 min; 50−60% B (linear gradient) from 30 to 50 min, monitored at 210−400 nm. Column chromatography was carried out on silica gel 60, 75 μm (Nacalai Tesque Inc., Kyoto, Japan), Diaion HP-20, MCI-gel CHP20P (Mitsubishi Chemical Co., Tokyo, Japan), Toyopearl HW-40 (coarse grade) (Tosoh Co., Tokyo, Japan), YMCgel ODSAQ12S50 (YMC Co., Ltd.), and Sephadex LH-20 (GE Special Issue: 27th ICP and 8th Tannin Conference (Nagoya 2014) Received: January 9, 2015 Revised: April 14, 2015 Accepted: April 17, 2015

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DOI: 10.1021/acs.jafc.5b01771 J. Agric. Food Chem. XXXX, XXX, XXX−XXX

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Journal of Agricultural and Food Chemistry

Figure 1. Structures of compounds (1−17) isolated from mangosteen (Garcinia mangostana L.) pericarp. Healthcare Japan, Tokyo, Japan). Each authentic sample [procyanidin B2 (Extrasynthese, Lyon, France), procyanidin C1 (ChromaDex, Inc., Irvin, CA, USA), chlorogenic acid (Tokyo Chemical Industry, Tokyo, Japan), protocatechuic acid (Wako Pure Chemical Industries, Osaka, Japan)] was purchased from the manufacturer. Isolation Procedure of Mangosteen Pericarp. The fruits of mangosteen were harvested in Chanthaburi province (eastern Thailand) and Nakhon Si Thammarat province (southern Thailand). The powdered dried mangosteen pericarps (600 kg) were extracted with hot water (90 °C, 5600 L) for 3 h, and the filtered concentrate was powdered with a spray-dryer after the addition of dextrin (to 25%) as diluent to yield hot water extract (92.1 kg). The hot water extract (100 g) was resuspended in water and subjected to liquid−liquid partition to yield n-hexane (65.5 mg), ethyl acetate (EtOAc) (2.6 g), nbutanol (n-BuOH) (12.5 g), and water extract. A part of the n-BuOH extract (9.0 g/12.5 g) was chromatographed over MCI-gel CHP20 (40 cm × 1.1 cm i.d.) eluted with water to methanol. The water eluate was further purified using YMC-gel ODS-AQ (40 cm × 1.1 cm i.d.) column chromatography to give six known compounds identified as 2furancarboxylic acid, 4 (11.2 mg); chlorogenic acid, 5 (6.5 mg); epicatechin, 6 (12.4 mg); procyanidin B2, 7 (10.5 mg); rhodanthenone B, 8 (14.0 mg); and dihydrodehydrodiconiferyl alcohol 9-Oglucoside, 9 (2.0 mg) (Figure 1). The EtOAc extract (2.6 g) was chromatographed over a YMC-gel ODS-AQ (40 cm × 1.1 cm i.d.) column and eluted in a stepwise gradient mode with water−methanol.

The water and 10% methanol eluate (960.5 mg) was separately chromatographed over Sephadex LH-20 (20 cm × 1.1 cm i.d.) yielding epicatechin, 6 (145.2 mg); procyanidin B2, 7 (28.7 mg); protocatechuic acid, 10 (11.9 mg); and procyanidin C1, 11 (7.4 mg). The 20% methanol eluate (297.4 mg) was further separated by column chromatography over Chromatorex ODS (20 cm × 1.1 cm i.d.) and Sephadex LH-20 (20 cm × 1.1 cm i.d.) to yield GM-3, 3 (1.0 mg); epicatechin, 6 (77.5 mg); dihydrophaseic acid, 12 (5.3 mg); garcimangosone D, 13 (2.7 mg); and 2-O-(3,4-dihydroxybenzoyl)2,4,6-trihydroxyphenylacetic acid, 14 (2.4 mg). The 30% methanol eluate (215.4 mg) was further purified using Sephadex LH-20 (20 cm × 1.1 cm i.d.), Chromatorex ODS (20 cm × 1.1 cm i.d.), and MCI-gel CHP20 (20 cm × 1.1 cm i.d.) column chromatography to give GM-1, 1 (2.2 mg); GM-2, 2 (1.2 mg); garcimangosone D, 13 (2.2 mg); 2-O(3,4-dihydroxybenzoyl)-2,4,6-trihydroxyphenylacetic acid, 14 (2.6 mg); eucryphin, 15 (2.6 mg); 3,4,5,3′-tetrahydroxybenzophenone, 16 (1.2 mg); and 4,6,3′,4′-tetrahydroxy-2-methoxybenzophenone, 17 (1.6 mg). Each structure of known compounds was inferred from the NMR and MS data or from a direct HPLC comparison with an authentic sample. GM-1, 1: pale brown amorphous powder; [α]27D −42.5° (c 0.2, MeOH); 1H NMR (methanol-d4) δ 6.73 (1H, d, J = 8.5 Hz, H-5‴), 6.63 (1H, d, J = 8.0 Hz, H-5′), 6.60 (1H, d, J = 2.0 Hz, H-2‴), 6.59 (1H, d, J = 2.0 Hz, H-2′), 6.43 (1H, dd, J = 2.0, 8.5 Hz, H-6′), 6.16 (1H, dd, J = 2.0, 8.5 Hz, H-6‴), 5.99 (1H, s, H-6″), 5.93 (2H, s, H-6, B

DOI: 10.1021/acs.jafc.5b01771 J. Agric. Food Chem. XXXX, XXX, XXX−XXX

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Journal of Agricultural and Food Chemistry 8), 5.63 (1H, br s, H-2), 4.68 (1H, br s, H-2″), 4.26 (1H, dd, J = 1.0, 2.5 Hz, H-3), 4.15 (1H, d, J = 2.5 Hz, H-4), 4.10 (1H, m, H-3″), 2.87 (1H, dd, J = 5.0, 17.0 Hz, H-4″), 2.70 (1H, dd, J = 1.5, 17.0 Hz, H-4″); 13 C NMR (methanol-d4) δ 158.7 (C-5 or -8), 158.2 (C-7), 158.0 (C5″), 157.8 (C-5 or -8), 157.3 (C-7″), 154.7 (C-8″a), 146.0 (C-3′), 145.7 (C-3‴), 145.3 (C-4‴), 144.4 (C-4′), 136.4 (C-1′), 131.6 (C1‴), 120.9 (C-6′), 119.0 (C-6‴), 116.9 (C-2′), 116.8 (C-5‴), 116.5 (C-5′), 113.8 (C-2‴), 105.2 (C-8″), 102.1 (C-4a), 100.3 (C-4″a), 97.9 (C-6″), 96.8, 95.4 (each 1H, C-6,8), 80.0 (C-2″), 74.4 (C-3), 70.3 (C2), 67.5 (C-3″), 45.7 (C-4), 29.6 (C-4″); HR-ESI-MS m/z 577.1343 [M − H]− (calculated for C30H26O12 − H, 577.1352). GM-2, 2: pale brown amorphous powder; 1H NMR (acetone-d6 + D2O) δ 6.53 (2H, d, J = 2.0 Hz, H-2′, 6′), 6.45 (1H, t, J = 2.0 Hz, H4′), 6.02 (1H, d, J = 2.0 Hz, H-2), 6.01 (1H, d, J = 2.0 Hz, H-6), 3.50 (3H, s, 5-OMe); 13C NMR (acetone-d6 + D2O) δ 198.4 (C-7), 164.4 (C-4), 162.9 (C-3), 162.5 (C-5), 158.8 (2C, C-3′,5′), 143.8 (C-1′), 107.2 (2C, C-2′,6′), 106.9 (C-1), 106.3 (C-4″), 96.4 (C-2), 92.3 (C6), 55.7 (5-OMe); HR-ESI-MS m/z 275.0565 [M − H]− (calculated for C14H12O6 − H, 275.0561). GM-3, 3: [α]27D +30.5° (c 0.2, MeOH); pale brown amorphous powder; 1H NMR (acetone-d6) δ 12.16 (1H, s, 5-OH), 5.94 (1H, d, J = 2.0 Hz, H-8), 5.90 (1H, d, J = 2.0 Hz, H-6), 4.42 (1H, dt, J = 3.5, 3.5, 13.0 Hz), 3.96 (1H, dt, J = 4.0, 4.0, 9.0 Hz, H-1′), 3.79 (2H, m, H-3′), 3.00 (1H, dd, J = 13.0, 17.5 Hz, H-3), 2.55 (1H, dd, J = 3.0, 17.5 Hz, H-3), 1.86 (2H, m, H-2′); 13C NMR (acetone-d6) δ 197.7 (C-4), 167.2 (C-7), 165.2 (C-5), 164.3 (C-8a), 103.2 (C-4a), 96.6 (C-6), 95.7 (C-8), 81.2 (C-2), 70.8 (C-1′), 59.8 (C-3′), 38.6 (C-3), 36.0 (C-2′); HR-ESI-MS m/z 253.0711 [M − H]− (calculated for C12H14O6 − H, 253.0718).

Figure 2. Heteronuclear multiple-bond connectivity (HMBC) correlations and the nuclear Overhauser effect (NOE) correlations of GM-1, 1.

correlations of H-2 and H-2″ to C-8a″ proved that the intermolecular connection was in the 2→8″ position. The relative configuration of 1 was considered to have 2,3-cis-3,4trans configurations on the basis of the nuclear Overhauser effect correlations of H-2 to H-2′, H-6′, and H-3, but no correlation between H-2 and H-4 (Figure 2). Additionally, small coupling constants (J = ca. 2 Hz) of H-2 and H-3 in the 1 H NMR spectrum indicated that the heterocyclic ring in 1 adopted the boat form similar to that of 4-aryl-2-flavanylbenzopyrans produced as the artifact from procyanidins under basic conditions.17 With the co-occurrence of 1 with procyanidins B2 or C-1 taken into consideration, the 2-flavanyl moiety was tentatively assigned as (−)-epicatechin. On the basis of these spectroscopic data, the structure of GM-1 was established as 1 (Figure 1). Although artificial diastereoisomeric analogues of 1 were previously reported,17 this is, to our knowledge, the first report of this type of compound to be isolated from a natural source. GM-2, 2, has the molecular formula C14H12O6, as determined from the HR-ESI-MS data. The 1H NMR spectrum showed three meta-coupled signals [a 2H-doublet (δ 6.53, J = 2.0 Hz), two 1H-doublets (δ 6.01 and 6.02, J = 2.5 Hz), and a 1H-triplet (δ 6.45, J = 2.0 Hz)] in the aromatic region. In the 13C NMR spectrum, equivalent carbon signals assignable to C-2′,6′ (δ 107.2) and C-3′,5′ (δ 158.8) and a carbonyl carbon signal (δ 198.4) indicate that the structure of 2 is a benzophenone derivative. Additionally, the spectra indicated the presence of a methoxy group (δH 3.50, δC 55.7), which was located on a benzene ring (C-5) with nonequivalent protons. HMBC correlations (Figure 3) also supported the proposed structure. From the above spectroscopic data, the structure of 2 was elucidated as 3,4,3′,5′-tetrahydroxy-5-methoxybenzophenone.

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RESULTS AND DISCUSSION A hot water extract of mangosteen (G. mangostana L.) pericarp was successively partitioned with n-hexane, EtOAc, and nBuOH to give respective extracts. The n-BuOH extract was subjected to successive column chromatography over MCI-gel CHP20 and YMC-gel ODS-AQ, yielding six known compounds identified as 2-furancarboxylic acid, 4; chlorogenic acid, 5; epicatechin, 6; procyanidin B2, 7; rhodanthenone B, 8;12 and dihydrodehydrodiconiferyl alcohol 9-O-glucoside, 9.9 The EtOAc extract was similarly separated by successive column chromatography over YMC-gel ODS-AQ, Sephadex LH-20, and Chromatorex ODS, yielding three new compounds (GM-1, -2, and -3), 1−3 along with 10 known compounds, which were characterized by NMR data or direct HPLC comparison with authentic samples as epicatechin, 6; procyanidin B2, 7; protocatechuic acid, 10; procyanidin C1, 11; dihydrophaseic acid, 12; garcimangosone D, 13;9 2-O-(3,4-dihydroxybenzoyl)2,4,6-trihydroxyphenylacetic acid, 14;13 eucryphin, 15;14 3,4,5,3′-tetrahydroxybenzophenone, 16;15 and 4,6,3′,4′-tetrahydroxy-2-methoxybenzophenone, 1716 (Figure 1). Among the known compounds, 4, 8, 9, 11, 14, and 15 were for the first time isolated from mangosteen. Besides the reported xanthones and other low-polarity compounds, we demonstrated that the pericarp of mangosteen contains various types of benzophenones and procyanidins. GM-1, 1, was obtained as a pale brown amorphous powder with an assigned molecular formula of C30H26O12 inferred from the high-resolution (HR)-ESI-MS data. The 1H−1H correlation spectroscopy (COSY) spectrum showed two pairs of ABX signals, two meta-coupled doublets, a singlet in the aromatic region, and three- and four-spin signals in the aliphatic region, thus suggesting 1 to be a dimeric flavonoid. The heteronuclear multiple-bond connectivity (HMBC) correlations (Figure 2) of H-2 to C-7″, -8″, and -8a″ and of H-4 to C-1′ and -4a indicated that 1 has a 4-aryl-2-flavanylbenzopyran skeleton. Furthermore,

Figure 3. HMBC correlations of GM-2, 2, and GM-3, 3 (HMBC: H → C).

GM-3, 3, a pale brown amorphous powder, showed an [M − H]− ion peak at m/z 253.0711 in the HR-ESI-MS and was assigned the molecular formula C12H14O6 (calculated for 253.0718, C12H14O6 − H). The 1H NMR spectrum of 3 showed a 1H-singlet at δ 12.2 (chelated −OH) and two metacoupled 1H-doublets (δ 5.90 and 5.94, J = 2.0 Hz) in the aromatic region. In the aliphatic region, two pairs of methylene C

DOI: 10.1021/acs.jafc.5b01771 J. Agric. Food Chem. XXXX, XXX, XXX−XXX

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Figure 4. High-performance liquid chromatography (HPLC) profiles of hot water extract of mangosteen pericarp. The numbered peaks on the chromatogram correspond to the structure number in Figure 1: 1, GM-1; 2, GM-2; 3, GM-3; 4, 2-furancarboxylic acid; 5, chlorogenic acid; 6, epicatechin; 7, procyanidin B2; 8, rhodanthenone B; 9, dihydrodehydrodiconiferyl alcohol 9-O-glucoside; 10, protocatechuic acid; 11, procyanidin C1; 12, dihydrophaseic acid; 13, garcimangosone D; 14, 2-O-(3,4-dihydroxybenzoyl)-2,4,6-trihydroxyphenylacetic acid; 15, eucryphin; 16, 3,4,5,3′tetrahydroxybenzophenone; 17, 4,6,3′,4′-tetrahydroxy-2-methoxybenzophenone.

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protons [δ 1.86 (2H, m, H-2′), 2.55 (1H, dd, J = 3.5, 17.5 Hz, H-3), and 3.00 (1H, dd, J = 13.0, 17.5 Hz, H-3)], an oxygenbearing methylene [δ 3.79 (2H, m, H-3′)], and two oxygenated methines [δ 3.96 (1H, br dt, J = 4.0, 4.0. 9.0 Hz, H-1′), 4.42 (1H, dt, J = 3.5, 3.5, 13.0 Hz, H-2)] were confirmed from COSY and heteronuclear single-quantum coherence correlations. Furthermore, all of the aliphatic proton signals have relay correlations in 1H−1H COSY, and the location of the side chain was established from HMBC correlations of H-2 to C-8a and H-3 to C-4a (Figure 3). Additionally, 13C NMR data also support this structure. From these results, the planar structure of GM-3 was identified as depicted in Figure 1. Each peak on HPLC of the hot water extract of mangosteen pericarp was assigned by direct comparison with those of individual isolates as shown in Figure 4. Among polyphenolics detected at 280 nm, epicatechin, 6 and procyanidin B2, 7, were major ingredients in the extract. On the other hand, benzophenones (8, 13, and 16) and chlorogenic acid (5) were readily distinguished from other phenolics by monitoring at 315 nm. In the present study, along with 14 known compounds, we isolated 3 new compounds and elucidated their chemical structures. α-Mangostin and other xanthones that were known as representative bioactive components of mangosteen were not observed in the hot water extract of the pericarp because of their low polarity. These prenylated xanthones were effectively extracted with ethanol from the mangosteen pericarp. In traditional medicine, mangosteen pericarp is mainly decocted or macerated in water, thus preserving the bioactive properties of catechin and other polyphenols, which were revealed to be the major polar ingredients of the hot water extract. The componential analysis of water-soluble polar compounds would thus provide valuable information to discuss any function (e.g., antioxidant) of the pericarp arising from bioactive components other than xanthones and benzophenones.

ASSOCIATED CONTENT

S Supporting Information *

NMR spectra (1H, 13C, 1H−1H COSY, HSQC, HMBC, and NOESY) of GM-1, 1, GM-2, 2, and GM-3, 3. The Supporting Information is available free of charge on the ACS Publications website at DOI: 10/1021/acs.jafc.5b01771.

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AUTHOR INFORMATION

Corresponding Author

*(Y.A.) Phone: +81 89 925 7111. Fax: +81 89 926 7162. Email: [email protected]. Notes

The authors declare no competing financial interest.

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REFERENCES

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DOI: 10.1021/acs.jafc.5b01771 J. Agric. Food Chem. XXXX, XXX, XXX−XXX