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Article

New Polyprenylated Phloroglucinol and Other Compounds Isolated from the Fruits of Clusia nemorosa (Clusiaceae)

1
Departamento de Química, Universidade Federal Rural do Rio de Janeiro, 23890-000 Seropédica, Brazil
2
Departamento de Ciências Moleculares, Universidade Federal Rural de Pernambuco, 52171-900 Recife, Brazil
*
Author to whom correspondence should be addressed.
Molecules 2015, 20(8), 14326-14333; https://doi.org/10.3390/molecules200814326
Submission received: 21 May 2015 / Revised: 27 June 2015 / Accepted: 22 July 2015 / Published: 6 August 2015
(This article belongs to the Section Natural Products Chemistry)

Abstract

:
Clusia nemorosa has been widely used in folk medicine to treat various ailments, including headaches and inflammation. Investigation of the fruits of Clusia nemorosa (Clusiaceae) led to the isolation and characterization of a new phloroglucinol derivative, named 6S,8S,28S-nemorosic acid (1), together with seven known compounds: friedelin (2), β-sitosterol (3), stigmasterol (4), β-sitosterol glycoside (5), kaempferol (6), quercetin (7) and dimethyl citrate (8). The structures were determined by extensive 1D- and 2D-NMR, CD and MS spectroscopic analyses.

1. Introduction

The Clusiaceae family, also known Guttiferae, is characterized by the presence of flower resin and latex in most of its species [1]. The genus Clusia presents a notable metabolite diversity, including benzophenones, xanthones and biflavonoids [2,3,4,5].Several species are used in folk medicine all around the world to treat rheumatism, stomach problems and as a purgative [6]. Phytochemical and pharmacological studies of plants belonging to this genus have reported many biological activities, such as antibacterial, antioxidant, antitumour, antimicrobial and anti-inflammatory properties [7]. (–)-Nemorosonol, a prenylated benzophenone, exhibited antimicrobial activity against Escherichia coli, Staphylococcus aureus, Bacillus subtilis, Micrococcus luteus, Aspergillus niger, Trichophyton mentagrophytes and Candida albicans [8]. The biflavonoids GB1-7′′O-glucoside and GB1a-7′′O-glucoside showed promising free radical scavenging capacity in in vitro assays [5]. Phloroglucinol derivatives exhibited chemopreventive properties and inhibited NO production [9]. The Clusia genus thus represents an important source of bioactive compounds.
Clusia nemorosa Mey., popularly known as “pororoca”, is a tree that is widespread in the northeast region of Brazil [10]. This species has been widely used in folk medicine to treat headaches and inflammation [11]. Prior phytochemical studies of the fruits of this species led to the isolation of a polyisoprenylated benzophenone and phloroglucinol derivatives [12,13]. The additional study of this species presented herein allowed us to identify a new phloroglucinol derivative, named nemorosic acid (1), as well as seven known compounds that were identified for the first time in the fruits: friedelin (2), β-sitosterol (3), stigmasterol (4), β-sitosterol glycoside (5), kaempferol (6), quercetin (7) and dimethyl citrate (8).

2. Results and Discussion

The fruit of Clusia nemorosa was extracted with dichloromethane (CH2Cl2) and methanol (MeOH). The fractionation of these extracts and the analysis of the fractions allowed us to obtain seven known compounds—friedelin [14], β-sitosterol [15], stigmasterol [15], β-sitosterol glycoside [16], kaempferol [17], quercetin [17] and dimethyl citrate [18]—as well as a new phloroglucinol derivative, named nemorosic acid (1).
Nemorosic acid (1) was isolated as an optically active ([αD] = −5.34°) yellow gum. The molecular formula was established as C31H44O7 on the basis of negative ESI-MS data (found m/z 527.3220, [M − H], calc. 527.3009). The IR spectrum displayed absorptions of hydroxyl (3435 cm−1) and carbonyl groups (1707 cm−1), as well as other signals. The 1H- and 13C-NMR data (Table 1) suggested that 1 was a phloroglucinol derivative. The structure was defined by the detailed analysis of 2D-NMR (1H-1H COSY, HMQC, NOESY and HMBC) spectra data and comparison with the data of the known compounds nemorosinic acid B [13], adlupulone [19], and garcinenone F [20]. Comparison of the 13C-NMR data of 1 with those of adlupulone, which was isolated from Humulus lupulus L. [19], revealed that 1 contained two enolic C-atoms at δ(C) 170.4 (C(3)) and 191.9 (C(5)), one C=O group at δ(C) 205.5 (C(1)), and three quaternary carbons at δ(C) 103.3 (C(2)), 109.6 (C(4)), and 60.9 (C(6)), which was the same as for adlupulone and garcinenone F. Thus, 1 was characterized as having a cyclohexa-2,4-dien-1-one moiety. Extensive analysis of 1H- and 13C-NMR, together with HMBC spectra, indicated the presence of a 3-methylbut-2-en-1-yl group (δ(H) 2.53 (brd, J = 7.3 Hz, 2H, H-22), 4.77 (m, H-23), 1.51 (s, 3H, H-26), and 1.48 (s, 3H, H-25); δ(C) 42.2 (C(22)), 116.8 (C(23)), 135.6 (C(24)), 25.8 (C(26), and 17.8 (C(25)), an oxidized lavandulyl group (δ(H) 2.26 (brd, 10Hz, H-12a), 2.08 (m, H-12b), 2.14 (m, H-13), 4.51/4.42 (brs, H-15a, 15b), 1.48 (s, 3H, H-16), 2.14 (m, H-17), 6.64–6.68 (m, H-18), and 1.77 (s, 3H, H-21); δ(C) 40.4 (C(12)), 44.4 (C(13)), 145.7 (C(14)), 114.1 (C(15)), 17.6 (C(16)), 33.3 (C(17)), 142.5 (C(18)), 127.5 (C(19)), 172.2 (C(20)), and 12.0 (C(21)) (Figure 1, Table 1), a 2-methylbutanoyl group (δ(H) 3.53 (sextet, 1H, H-28), 1.45 (m, H-29a, 1.75 (m, H-29b), 0.93 (t, 7.3 Hz, 3H, H-30), and 1.18 (d, 6.8Hz, 3H, H-31); δ(C) 196.5 (C(27)), 40.7 (C(28)), 27.4 (C(29)), 11.9 (C(30)), and 17.2 (C(31)), and a 2,3-dioxy-3-methylbutyl moiety (δ(H) 2.87–3.01 (m,H-7a,7b), 4.75–4.83 (m, 1H, H-8), 1.32 (s, 3H, H-10), and 1.26 (s, 3H, H-11)); δ(C) 26.6 (C(7)), 92.4 (C(8)), 71.8 (C(9)), 24.8 (C(10)), and 24.6 (C(11)) (Table 1). The positions of the substituents were deduced by analysis of the HMBC data (Table 1, Figure 1). The HMBC cross-peaks of CH2(22) and CH2(12) with δ(C) 205.5 (C(1), 191.9 (C(5), and 60.9 (C(6), established that a 3-methylbut-2-en-1-yl and lavandulyl group were linked to C(6). The observed signals on the HMBC spectrum of nJHC of CH2(7) with δ(C) 109.3 (C(4)), 170.4 (C(3)), 92.4 (C(8)), and 71.8 (C(9)) allowed to located the 2,3-dihydro-2-(1-hydroxyl-1-methylethyl)-furan moiety at C(3) and C(4), different from those of garcinenone F [20]. Besides other long range coupling signals, the value 191.9 of 1 (with H-22 and H-17) allowed to locate the enolic OH group at C(5), different of C(5) in garcinenone F [20]. The remaining 2-methylbutanoyl group was attached at C(2) based on the 3JHC of H-28 and C(2) (δC 103.5) (Table 1). The chemical shifts of Ha and Hb of C(7), C(17), and C(22) were overlapped in the 1H-NMR (see supplementary material).
Table 1. 1H (500 MHz) and 13C (125 MHz) NMR data of 1 in CDCl3.
Table 1. 1H (500 MHz) and 13C (125 MHz) NMR data of 1 in CDCl3.
PositionδHδCHMBC(2,3JH-C)
1-205.6-
2-103.5-
3-170.4-
4-109.3-
5-191.9-
6-60.9-
72.87–3.01 (m)26.6C-3; C-4; C-5; C-8; C-9
84.75–4.83 (m)92.4C-3; C-4 ;C-10; C-11
9-71.8-
101.32 (s)24.8C-8; C-9; C-11
111.26 (s)24.6C-8; C-9; C-10
122.26 (br d, 10 Hz, H-12a); 2.08 (m, H-12b) a40.4C-1; C-5; C-6; C-13; C-14; C-17
132.14 (m)44.4C-6; C-14; C-15; C-17
14-145.7-
154.51 (brs, H-15a); 4.52 (brs, H-15b) a114.1C-13; C-14; C-16
161.48 (s)17.8C-13; C-14; C-15
172.14 (m)33.3C-12; C-14; C-18; C-19
186.68 (brt, 6.6 Hz)142.5C-13; C-17; C-19; C-20; C-21
19-127.5-
20-172.2-
211.77 (s)12.0C-18; C-19; C-20
222.53 (brd, 7.3 Hz)42.2C-1; C-5; C-6; C-12; C-23; C-24
234.75–4.83 (m)116.8C-22; C-25; C-26
24-135.6-
251.48 (s)17.6C-23; C-24;C-26
261.51 (s)25.7C-23; C-24; C-25
27-196.5-
283.53 (sextet, 6.8 Hz)40.7C-2;C-27; C-29; C-30; C-31
291.45–1.50 (m, H-29a); 1.75 (m, 29b) a27.4C-27; C-28; C-30; C-31
300.93 (t, 7.3 Hz)11.9C-28; C-29
311.18 (d, 6.8 Hz)17.2C-27; C-28; C-29
a Correlation from 1Hx1H-COSY and HMQC spectra.
Figure 1. Structure of compound 1.
Figure 1. Structure of compound 1.
Molecules 20 14326 g001
As described by Monache et al. [13], there is a possibility of epimers at C(28), besides the keto-enolic equilibrium to form tautomeric structures in these kinds of compound. In the case of 1, in addition there exists the possibility of epimers at C(8), and different conformers of the linked groups at C(6). These structural properties justify the additional signals in the 1H- and 13C-NMR spectra. Moreover the proposed structure 1 is the major component which provided the chiral properties discussed below. The detailed MS analysis (Figure 2) was used to confirm the structure of 1. Various polyisoprenylated phloroglucinol derivatives have being isolated from genus Clusia [13]. Most of them belong to a bicyclononane ring system, as in the case of nemorosonol [12], whereas nemorosic acid, having a cyclohexa-2,4-dien-1-one moiety, is similar to nemorosinic acid B, isolated from Clusia nemorosa [13], lupulone, which occur in Humulus lupulus [9], and garcinenone F, isolated from Garcinia xanthochymus [20]. Lupulone derivatives possess one or more stereogenic centres, but these compounds were racemic ([α]D = 0) [9]. However, 1 was optically active ([α]D = −5.34°), and the CD curve is presented in Figure 3. Therefore, the configuration of 1 was proposed as 6S,8S,28S- according to the negative and positive Cotton effect at 340 and 300 nm, respectively (Figure 3), such as (−)-nemorosonol [8] and marmesinin [20], with negative and positive Cotton effect at 250 and 230 nm, containing identical furan system with S configuration [21]. Therefore 1 is a new phloroglucinol derivative whose structure was defined as (–)-6S,8S,28S-6-(lavundolyl-6-carboxy)-6-(3-methylbut-2-en-1-yl)-2-(2-methylbutanoyl)-[2′-hydroxyiso-propyl-2′,3′-dihydrobenzofurane-(2′,3′:3,4)]-5-hydroxycyclohexa-2,4-dienone, named as nemorosic acid. The known compounds were identified by 1D- and 2D-NMR spectroscopic data analysis, and comparison with literature data [14,15,16,17,18].
Figure 2. Proposed fragmentation to justify the principal peaks detected in the mass spectrum.
Figure 2. Proposed fragmentation to justify the principal peaks detected in the mass spectrum.
Molecules 20 14326 g002
Figure 3. Circular dichroism spectrum of 1 in methanol.
Figure 3. Circular dichroism spectrum of 1 in methanol.
Molecules 20 14326 g003

3. Experimental Section

3.1. General Procedures

The melting points were determined with a Mel-temp II apparatus and were uncorrected. IR spectra were obtained with KBr discs and NaCl film using a Vertex-70 spectrophotometer (Bruker Corporation, Billerica, MA, USA). UV spectra were obtained on a Shimadzu UV-mini 1240 UV-VIS spectrophotometer (Quioto, Kansai, Japan). 1H- and 13C-NMR experiments were performed on Bruker Avance III 500 (Billerica, MA, USA) (500 for 1H and 125 MHz for 13C) and Bruker AC-400 (400 for 1H and 100 MHz for 13C) spectrometers using DMSO-d6, methanol-d4, pyridine-d5 or CDCl3 as solvents with TMS as the internal reference. Chemical shifts are in ppm and the J values in Hz. Mass spectra were registered on a microTOFq II–ESI–TOF spectrometer (Bruker Corporation, Billerica, MA, USA) using ESI- in negative mode. Optical rotation was measured with a Jasco P-2000 polarimeter (Easton, MO, USA). The circular dichroism spectrum was realized at DC J-180 Jasco PT4235\190–400 nm. Column chromatography was performed using silica gel (Vetec, Duque de Caxias, RJ, BR and Sigma-Aldrich, St. Louis, MO, USA) (0.05–0.20 mm) and Sephadex™ LH-20 (Sigma-Aldrich, St. Louis, MO, USA). Silica gel F254 G (Vetec) was used for preparative TLC; aluminium-backed Sorbent silica gel plates, w/UV 254, were used for analytical TLC, with visualization under UV (254 and 366 nm), with AlCl3-EtOH (1%), vanillin and iodine vapour.

3.2. Plant Material

The fruits of Clusia nemorosa Mey. were collected in the Campus of Universidade Federal Rural de Pernambuco (UFRPE), Recife, Brazil, in January 2012. A voucher (number 51474) is deposited at the herbarium of Vasconcelos Sobrinho (PEUFR), Universidade Federal Rural de Pernambuco.

3.3. Extraction and Isolation

The dried fruits (130.0 g) were extracted with dichloromethane (2.0 L), followed by extraction with methanol (2.0 L) at room temperature three times. The two extracts were separately concentrated to give 15.0 g of CH2Cl2 extract and 27.0 g of MeOH extract. Part of the dichloromethane extract (11.0 g) was subjected to column chromatography on silica gel with dichloromethane, ethyl acetate (EtOAc) and methanol (MeOH) as eluents to give three fractions (A1–A3). The A2 fraction (3.0 g) was subjected to repeated silica gel chromatography using hexane–CH2Cl2, CH2Cl2–AcOEt and EtOAc–MeOH to furnish the compounds 1 (35.0 mg) and 5 (65.0 mg). The A1 fraction (5.1 g) was further fractionated through silica gel column chromatography using hexane–EtOAc and EtOAc–MeOH to furnish compounds 2 (20.0 mg) and the mixture of 3 and 4 (10.0 mg). Meanwhile, the dry MeOH extract (20.0 g) was suspended in H2O and was partitioned with chloroform (3 × 200 mL), ethyl acetate (3 × 200 mL) and n-butanol (3 × 200 mL). The EtOAc fraction (3.5 g) was subjected to Sephadex LH-20 column chromatography and eluted with MeOH to give five fractions. Fraction 4 was rechromatographed on Sephadex LH-20 and eluted with MeOH to give 6 (5.0 mg) and 7 (5.0 mg). Fraction 5 was rechromatographed over a silica gel column using CHCl3-MeOH (0%–100% methanol) as eluents to give 8 (35.0 mg).
Nemorosic acid (1). Yellow gum; [α]D –5.34 (MeOH; c 0.16); CD: Δɛ (nm): −2.8 (340), +2.6 (300), −3.2 (270), +3.7 (230); UV (MeOH) λmax (nm): 257 and 327; IR: νKBr (cm−1): 3435, 1707, and 1638, besides other signals; 1H-NMR (500 MHz, CDCl3) and 13C-NMR (125 MHz, CDCl3), see Table 1; TOF-MS/MS (negative mode) m/z (rel. int.): 527.3 (70), 509.3 (2), 483.3 (10), 361.2 (15), 305.2 (100) and 247.1 (20), Figure 2.

4. Conclusions

Eight compounds, including the novel compound 1, were isolated from the fruits of C. nemorosa. The discovery of this new compound from the genus Clusia provides more spectroscopic data to characterize the components of its isolates, as well as contribute to the understanding of the taxonomy and evolution of the genus Clusia.

Supplementary Materials

Supplementary materials can be accessed at: https://www.mdpi.com/1420-3049/20/08/14326/s1.

Acknowledgments

The authors are grateful to Fundação Carlos Chagas Filho de Amparo a Pesquisa do Estado do Rio de Janeiro (FAPERJ), Fundação de Amparo à Ciência e Tecnologia do Estado de Pernambuco (FACEPE- PRONEM APQ-0741-1.06/14), Coordenação de Aperfeiçoamento de Pessoal de Ensino Superior (CAPES), and to Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) for scholarships and financial support.

Author Contributions

Rafaela Oliveira Ferreira designed the whole experiment and wrote the manuscript; Tania Maria Sarmento da Silva and Mario Geraldo de Carvalho analysed results and revised the manuscript.

Conflicts of Interest

The authors declare no conflict of interest.

References

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  • Sample Availability: Samples of the compounds are not available from the authors.

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MDPI and ACS Style

Ferreira, R.O.; Da Silva, T.M.S.; De Carvalho, M.G. New Polyprenylated Phloroglucinol and Other Compounds Isolated from the Fruits of Clusia nemorosa (Clusiaceae). Molecules 2015, 20, 14326-14333. https://doi.org/10.3390/molecules200814326

AMA Style

Ferreira RO, Da Silva TMS, De Carvalho MG. New Polyprenylated Phloroglucinol and Other Compounds Isolated from the Fruits of Clusia nemorosa (Clusiaceae). Molecules. 2015; 20(8):14326-14333. https://doi.org/10.3390/molecules200814326

Chicago/Turabian Style

Ferreira, Rafaela Oliveira, Tania Maria Sarmento Da Silva, and Mário Geraldo De Carvalho. 2015. "New Polyprenylated Phloroglucinol and Other Compounds Isolated from the Fruits of Clusia nemorosa (Clusiaceae)" Molecules 20, no. 8: 14326-14333. https://doi.org/10.3390/molecules200814326

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