Isolation and Synthesis of Melodamide A, a New Anti-inflammatory Phenolic Amide from the Leaves of Melodorum fruticosum

• Introduction
• Materials and Methods
• General experimental procedures
• Plant materials
• Extraction and isolation
• Crystallographic data of 1
• General procedure for the synthesis of compounds 1 and 14a–p
• Preparation of human neutrophils
• Measurement of O2 •− generation
• Measurement of elastase release
• Lactate dehydrogenase (LDH) release
• Western analysis
• Measurement of intracellular calcium concentration ([Ca2+]i)
• Statistical analysis
• Supporting information
• Results and Discussion
• Acknowledgements
• References

Abstract

Together with twelve known compounds (2–13), melodamide A (1), a new phenolic amide possessing p-quinol moiety, was purified and characterized from the methanolic extracts of the leaves of Melodorum fruticosum. The structure of melodamide A (1) was established with a combination of 2D NMR experiments, HR-ESI-MS and X-ray analyses. The other known compounds were identified by comparison of their spectroscopic and physical data with those reported in the literature. Moreover, some isolated compounds were examined for their inhibitory activity towards superoxide anion generation and elastase release in human neutrophils. Among the tested compounds, 1, 3, and 5 exhibited strong inhibition of superoxide anion generation with IC₅₀ values ranging from 5.25 to 8.65 µM. Furthermore, synthesis and biological evaluation of melodamide A (1) and its analogs (14a–p) were described.

Introduction

Inflammation is a complex biological response of vascular tissues to harmful stimuli such as pathogens, damaged cells, or irritants. Inflammation can be classified as either acute or chronic. Although inflammation is a protective attempt by the organism to remove the injurious stimuli, chronic inflammation can also lead to a host of diseases such as hay fever, atherosclerosis, rheumatoid arthritis, and cancer [1], [2], [3]. From the point of view of exploring new lead compounds for the treatment of these diseases, it is valuable to identify the anti-inflammatory principles from the natural sources, and several phytochemical and biological studies on this subject were reported by our group recently [4], [5], [6], [7]. Melodorum fruticosum (Annonaceae) is widely distributed in South-East Asia and commonly known as devil tree, white cheesewood, and lamduan [8]. Its flowers and barks have been reported to have antifungal, antioxidant, and cytotoxic activities [8], [9], [10]. In this study, a new phenolic amide along with twelve known compounds were identified from the leaves of M. fruticosum. Herein we wish to report the isolation, structural elucidation, and biological activity of melodamide A (1) as well as synthesis of 16 counterparts with different substitutions (halide, -NO₂, -OCH₃, -CH₃) on ring A of melodamide A (1).

Materials and Methods

General experimental procedures

Melting point was determined using a Fisher Scientific melting point measuring apparatus without corrections. The UV spectrum was recorded on an Agilent UV-VIS recording spectrophotometer. The IR spectrum was obtained, as KBr discs, on a Bruker type spectrometer. Optical rotation was measured with a Jasco DIP-1000 KUY polarimeter. The electrospray ionization (ESI) mass spectrum was determined using an Agilent 1200 LC-MSD Trap spectrometer, and the HR-ESI-MS was completed with the aid of the Bruker APEX II mass spectrometer. ¹H- and ¹³C-NMR, COSY, NOESY, HMQC, and HMBC spectra were recorded on the Bruker AV-500, Avance-III 400, and Avance 300 NMR spectrometers, using tetramethylsilane (TMS) as the internal standard. X-ray structure analyses were performed on a Bruker APEX DUO diffractometer. Standard pulse sequences and parameters were used for the NMR experiments, and all chemical shifts were reported in parts per million (ppm, δ). All chemicals (reagent grade) used were purchased from Sigma-Aldrich. Column chromatography (CC) was performed on silica gel (Kieselgel 60, 70–230 mesh and 230–400 mesh; E. Merck).

Plant materials

The leaves of Melodorum fruticosum (Annonaceae) were collected from Hue, Vietnam, during May 2009, and the plant materials were identified and authenticated by Dr. Tran Huy Thai, Institute of Ecology and Biological Resources, Vietnamese Academy of Science and Technology. A voucher specimen (20090515) was deposited in the Herbarium of the Institute of Ecology and Biological Resources, Vietnamese Academy of Science and Technology, Hanoi, Vietnam.

Extraction and isolation

The leaves of Melodorum fruticosum (9.8 kg) were powdered and soaked with methanol (40 L × 3) at room temperature, and the combined extracts were concentrated under reduced pressure to give a deep brown syrup (716 g). The crude extract was suspended into water and partitioned with n-hexane, ethyl acetate, and n-butanol, successively to afford n-hexane (38 g), ethyl acetate (267 g), n-butanol (192 g), and water soluble (49 g) fractions, respectively.

The n-hexane soluble (38 g) fraction was chromatographed over a silica gel column (300 g, 120 × 5 cm) by gradient elution with n-hexane and increasing concentrations of acetone (9 : 1, 5 : 1, 3 : 1, 1 : 1, each 2.0 L) to afford eight fractions (fraction 1–6). Fraction 2 (3 g) was further subjected into silica gel column chromatography (100 g, 60 × 3.5 cm) eluted with n-hexane/acetone (19 : 1) to yield β-sitosterol (2) (321 mg). The ethyl acetate soluble fraction (267 g) was chromatographed over a silica gel column (2 kg, 150 × 10 cm) by gradient elution with n-hexane and increasing concentrations of acetone (19 : 1, 12 : 1, 7 : 1, 3 : 1, 1 : 1, each 2.0 L) to afford eight fractions (fraction 1–12). Fraction 6 (14.2 g) was further subjected into silica gel column chromatography (150 g, 80 × 3.5 cm) eluted with n-hexane/acetone (19 : 1) to yield flavokawain-A (3) (52 mg). Silica gel column chromatography (500 g, 110 × 5 cm) of fraction 9 (35.7 g) with step gradient elution of n-hexane/acetone (15 : 1, 10 : 1, 7 : 1, 5 : 1, each 1 L) led to the isolation of melodamide A (1) (99 mg), (−)-7,4′-dihydroxy-5-methoxyflavanone (4) (35 mg), 2′,6′-dihydroxy-4′-methoxychalcone (5) (70 mg), and 2′,4′-dihydroxy-4,6′-dimethoxydihydrochalcone (6) (71 mg), successively. Purification of fraction 10 (15.9 g), by column chromatography with silica gel (150 g, 90 × 4 cm) eluted by n-hexane/acetone (7 : 1), afforded 4′,5-dimethoxy-7-hydroxyflavanone (7) (58 mg). The n-butanol soluble residues (143 g) were subjected to silica gel column chromatography (1.5 kg, 120 × 8 cm) and purified by step gradient elution with chloroform and increasing concentrations of methanol (0 %, 5 %, 10 %, 20 %, 30 %, 50 %, 70 %, 90 %, and 100 %, each 2 L) to afford ten fractions (fraction 1–10). Silica gel column chromatography (80 g, 80 × 2 cm) of fraction 3 (5.0 g) with the eluent mixtures of chloroform-methanol (19 : 1) and step gradient with methanol afforded ponciretin (8) (39 mg) and oxoanolobine (11) (14 mg). Separation of fraction 4 (18.6 g) by silica gel column chromatography (200 g, 100 × 4 cm) with chloroform-methanol (15 : 1) yielded rutinic acid (9) (87 mg) and 3,3′,4-tri-O-methylellagic acid (10) (45 mg), successively. Fraction 6 (30.6 g) was subjected to column chromatography with silica gel (300 g, 80 × 2 cm) using elution mixtures of chloroform-methanol-water (9 : 1 : 0.05) and further purified by repeated silica gel column chromatography to result in β-sitosteroyl-3-O-β-D-glucoside (13) (97 mg). Silica gel column chromatography (80 g, 60 × 3 cm) of fraction 7 (10.4 g) with the eluent mixtures of chloroform-methanol-water (4 : 1 : 0.05) and step gradient with methanol afforded 3-O-β-D-apiofuranosyl-(1 → 2)-O-[α-L-rhamnopyranosyl-(1 → 6)]-β-D-glucopyranoside (12) (12 mg).

Melodamide A (1): Colorless powder; mp 183–185 °C; UV (MeOH) λ _max (log ε) 272 (4.9), 217 (4.8), 204 (4.7) nm; IR (KBr) _max : 3290, 2920, 2851, 1713, 1663, 1620, 1551, 1450, 1227 cm⁻¹; ¹H-NMR (DMSO-d ₆, 500 MHz) δ 8.09 (1H, br t, J = 4.5 Hz, NH), 7.55 (2H, d, J = 8.5 Hz, H-5, H-9), 7.39 (3H, m, H-3, H-6, H-8), 7.39 (1H, d, J = 15.5 Hz, H-3), 6.94 (2H, d, J = 8.5 Hz, H-4′, H-8′), 6.56 (1H, d, J = 15.5 Hz, H-2), 6.09 (2H, d, J = 8.5 Hz, H-5′, H-7′), 5.83 (1H, br s, OH), 3.18 (2H, dd, J = 14.0, 7.0 Hz, H-1′), 1.83 (2H, t, J = 7.0 Hz, H-2′); ¹³C-NMR (DMSO-d ₆,125 MHz) δ 185.2 (C-6′), 164.8 (C-1), 152.8 (C-4′, C-8′), 138.6 (C-3), 134.9 (C-4), 129.4 (C-7), 128.9 (C-6, C-8), 127.5 (C-5, C-9), 126.8 (C-5′, C-7′), 122.1 (C-2), 67.8 (C-3′), 39.0 (C-2′), 34.2 (C-1′). ESI-MS m/z 284 ([M + Na]⁺); HRESI-MS m/z 284.1289 [M + Na]⁺ (calcd. for C₁₇H₁₇NO₃Na, 284.1287).

Crystallographic data of 1

Crystal system monoclinic, space group P121/n 1 a = 8.6116 (3) Å, b = 10.3693 (3) Å, c = 17.8352 (6) Å, V = 1559.44 (9) ų, T = 100 (2) K, Z = 4, Dc = 1.283 mg/m³, absorption coefficient 0.751 mm⁻¹, crystal size 0.18 × 0.15 × 0.12 mm³. 8662 reflections collected, 2619 independent reflections (R _int = 0.0199). Data were 95.8 % complete to 66.38° θ. The final R ₁ values were 0.0320 with I > 2σ (I), and the final wR (F ²) values were 0.0857. Goodness-of-fit on F2 was 1.036. Crystallographic data for 1 (CCDC 872 187) have been deposited with the Cambridge Data Centre.

General procedure for the synthesis of compounds 1 and 14a–p

The general procedure is illustrated immediately below with compound 1 as a specific example. N-(4-hydroxyphenethyl)cinnamamide was prepared by mixing cinnamoyl chloride (1.8 g, 8.0 mmol), tyramine (1.0 g, 7.3 mmol), and triethylamine (2.0 mL) in CH₂Cl₂ at 0 °C under nitrogen. The reaction mixture was stirred for 2 h, extracted by EtOAc and washed with saturated aqueous NaHCO₃. The organic phases were combined and dried over Na₂SO₄. After the solvent was removed under vacuum, the residue was purified by column chromatography eluting with hexanes/EtOAc (1 : 1) to yield N-(4-hydroxyphenethyl)cinnamamide (15) as a colorless crystalline solid (0.675 g, 84 %), identified by mp, UV, IR, ¹H-, ¹³C-NMR, and mass spectral analysis [11]. To a solution of 200 mg (0.748 mmol) of 15 in 2 mL of THF/CH₃CN/H₂O (1 : 1 : 1) was added phenyliodine (III) diacetate 289 mg (0.898 mmol) at 0 °C. After stirring for 1 h, phenyliodine (III) diacetate 121 mg (0.374 mmol) was added at 0 °C and kept for one more hour. The reaction mixture was extracted by EtOAc and washed with saturated aqueous NaHCO₃. The organic phases were combined and dried over Na₂SO₄. After the solvent was removed under vacuum, the crude product was purified by column chromatography eluting with CH₂Cl₂/EtOAc (1 : 1) to yield melodamide A (1) as a colorless solid (47.0 mg, 23 %). The structure was identified by comparison of its spectral and physical data with those of the isolated compound.

Preparation of human neutrophils

Blood was taken from healthy human donors (20 ~ 32 years old) by venipuncture, using a protocol approved by the institutional review board at Chang Gung Memorial Hospital. Neutrophils were isolated using a standard method of dextran sedimentation prior to centrifugation in a Ficoll Hypaque gradient and the hypotonic lysis of erythrocytes. Purified neutrophils that contained > 98 % viable cells, as determined by the trypan blue exclusion method, were resuspended in a calcium (Ca²⁺)-free HBSS buffer at pH 7.4 and maintained at 4 °C before use.

Measurement of O₂ ^•− generation

The assay of O₂ ^•− generation was based on the SOD-inhibitable reduction of ferricytochrome c [12]. In brief, after supplementation with 0.5 mg/mL ferricytochrome c and 1 mM Ca²⁺, neutrophils were incubated with drugs for 5 min at 37 °C. Cells were then activated with 100 nM FMLP for 10 min. Cytochalasin B (CB, 1 µg/mL) was incubated for 3 min before activation by the peptide (FMLP/CB). Changes in absorbance with the reduction of ferricytochrome c at 550 nm were continuously monitored in a double-beam, six-cell positioner spectrophotometer with constant stirring (Hitachi U-3010). Sorafenib tosylate (Selleck Chemicals, purity 99 %) and SB202190 (Sigma, purity > 98 %) were used as the positive control.

Measurement of elastase release

Experiments were performed using MeO-Suc-Ala-Ala-Pro-Val-p-nitroanilide as the elastase substrate [13]. Briefly, after supplementation with MeO-Suc-Ala-Ala-Pro-Val-p-nitroanilide (100 µM), neutrophils (5 × 10⁵/mL) were equilibrated at 37 °C for 2 min and incubated with drugs for 5 min. Cells were activated by 100 nM FMLP and 0.5 µg/mL CB. Changes in absorbance at 405 nm were continuously monitored to assay elastase release.

Lactate dehydrogenase (LDH) release

Cytotoxicity was represented by LDH release in culture medium. The total LDH released was determined by lysing cells with 0.1 % Triton X-100 for 30 min at 37 °C. LDH concentrations were determined according to the manufacturerʼs instructions (Promega).

Western analysis

Neutrophils were incubated with drugs for 5 min at 37 °C before being stimulated with FMLP for 0.5 min. The reaction was stopped by adding 5× Laemmliʼs sample buffer [14]. Samples were centrifuged at 14 000 × g for 20 min at 4 °C to yield whole-cell lysates. Proteins derived from whole-cell lysates were separated by SDS-polyacrylamide gel electrophoresis (PAGE) using 12 % polyacrylamide gels and blotted onto nitrocellulose membranes. Immunoblotting was performed using the indicated antibodies and horseradish peroxidase (HRP)-conjugated secondary anti-rabbit antibodies (Cell Signaling Technology). The immunoreactive bands were visualized by an enhanced chemiluminescence system (ECL; Amersham Biosciences) and detected by UVP imaging.

Measurement of intracellular calcium concentration ([Ca²⁺]_i)

Neutrophils were loaded with 2 µM fluo-3 AM at 37 °C for 45 min. The change in fluorescence was monitored using a Hitachi F-4500 spectrofluorometer in a quartz cuvette with a thermostat (37 °C) and continuous stirring. The excitation wavelength was 488 nm, and the emission wavelength was 520 nm [13].

Statistical analysis

Results were expressed as mean ± SD. Calculation of 50 % inhibitory concentration (IC₅₀) was computer-assisted (PHARM/PCS v.4.2). Statistical comparisons were made between groups using Studentʼs t test. Values of p less than 0.05 were considered to be statistically significant.

Supporting information

The full characterization of compounds 14a–p, 15, and 16a–p are available as Supporting Information.

Results and Discussion

The methanol extract of the leaves of Melodorum fruticosum yielded a new compound, melodamide A (1) ([Fig. 1]), together with 12 known compounds identified as β-sitosterol (2) [15], flavokawain-A (3) [16], (-)-7,4′-dihydroxy-5-methoxyflavanone (4) [17], 2′,6′-dihydroxy-4′-methoxychalcone (5) [18], 2′,4′-dihydroxy-4,6′-dimethoxydihydrochalcone (6) [19], 4′,5-dimethoxy-7-hydroxyflavanone (7) [20], ponciretin (8) [21], rutinic acid (9) [22], 3,3′,4-tri-O-methylellagic acid (10) [23], oxoanolobine (11) [24], kaempferol 3-O-β-D-apiofuranosyl-(1 → 2)-O-[α-L-rhamnopyranosyl-(1 → 6)]-β-D-glucopyranoside (12) [25], and β-sitosteroyl-3-O-β-D-glucoside (13) [26] by comparing their spectroscopic data with those reported in the literature.

Melodamide A (1) was isolated as colorless powder and showed a [M + Na]⁺ ion peak at m/z 284.1289 in its HRESIMS, corresponding to the molecular formula C₁₇H₁₇NO₃Na. The UV spectrum of 1 displayed absorption maxima at 272 and 217 nm, and the IR spectrum exhibited strong absorption peaks for OH (3290 cm⁻¹), a conjugated carbonyl group (1713 cm⁻¹), and amide (1663, 1450 cm⁻¹). In the ¹H-NMR spectrum, there were signals observed for a D₂O exchangeable proton at δ 8.11 (1H, br s, NH), a set of five mutually aromatic protons at δ 7.55 (2H, d, J = 7.5 Hz, H-5 and H-9) and 7.39 (3H, m, H-3, H-4, H-5), trans-olefinic protons at δ 7.39 (1H, d, J = 15.5 Hz, H-3) and δ 6.56 (1H, d, J = 15.5 Hz, H-2), four conjugated olefinic protons at δ 6.94 (2H, d, J = 8.5 Hz, H-4′, H-8′) and 6.09 (2H, d, J = 8.5 Hz, H-5′, H-7′), and upfield signals for four mutually coupled protons at δ 3.18 (2H, dd, J = 14.0, 7.0 Hz, H-8′) and 1.83 (2H, t, J = 7.0 Hz, H-2′). The ¹³C-NMR and DEPT spectra combined with HMQC experiment indicated 17 signals including a conjugated ketone (δ 185.2), a conjugated amide (δ 164.8), two olefinic carbon resonances (δ 138.6, 122.1), two conjugated alkenes (δ 152.8, 152.8, 126.8, 126.8), six aromatic signals (δ 134.9, 129.4, 129.4, 128.9, 127.5, 127.5), an oxygen-bearing quaternary carbon (δ 67.8), and two methylenes (δ 39.0 and 34.2). The HMBC correlations of H-2 (δ 6.56) to C-1 (δ 164.8)/C-4 (δ 134.9) showed the cinnamic amide sequence in the molecule of 1 ([Fig. 2]). In addition, the B-ring possessing a p-quinol moiety was established by the signals of H-5′/H-7′ (δ 6.09) and H-4′/H-8′ (δ 6.94) related with C-3′ (δ 67.8) and C-6′ (δ 185.2), respectively. Furthermore, the cross peaks of H-1′ (δ 3.18) to C-1 (δ 164.8)/C-2′ (δ 39.0)/C-3′ (δ 67.8) and H-2′ (δ 1.83) to C-1′ (δ 34.2)/C-3′ (δ 67.8)/C-4′ (δ 152.8)/C-8′ (δ 152.8) in the HMBC spectrum indicated the conjugated amide and p-quinol B-ring were connected with C-1′ and C-2′, respectively. Besides, the structure of 1 was confirmed by an X-ray diffraction crystallographic study ([Fig. 3]). On the basis of these data, 1 was identified as shown.

The isolated pure compounds 1, 3–5, and 7–10 (purity > 92 %) were evaluated for their inhibitory effects on superoxide anion generation and elastase release by human neutrophils in response to formyl-L-methionyl-L-leucyl-L-phenylalanine/cytochalasin B (FMLP/CB) ([Table 1]). Among them, compound 1 exhibited more potent inhibition in response to FMLP/CB induced superoxide anion generation with IC₅₀ values of 5.25 µM. Culturing with compound 1 (up to 30 µM) did not affect cell viability, as assayed by LDH release (data not shown). Compound 1 at concentrations of up to 30 µM failed to induce DPPH reduction. α-Tocopherol (3, 10, and 30 µM) was used as a positive control in the DPPH assay (data not shown). These results rule out the possibility that the inhibitory effect of compound 1 on superoxide anion generation occur through the direct radical scavenging activity. The action mechanisms of compound 1 were further investigated in this study. The intracellular signaling mechanisms responsible for neutrophil activations are very complex. FMLP activates neutrophils by binding to the GPCR and induces the Ca²⁺ signal via activation of phospholipase C [27]. No significant inhibition of FMLP-induced increase in [Ca²⁺]_i mobilization by compound 1 was observed in human neutrophils ([Fig. 4]), suggesting that compound 1 might not inhibit phospholipase C. In addition, stimulation of human neutrophils by FMLP resulted in the rapid phosphorylation of several proteins, including mitogen-activated protein kinases (MAPKs) and protein kinase B (Akt). Activation of these signal transduction pathways is known to be responsible for various neutrophil activations [13], [27]. Our data showed that the FMLP-induced phosphorylation of p38 MAPK, but not ERK and Akt, was diminished by compound 1 ([Fig. 5]). To investigate whether the activation of p38 MAPK has a significant role on superoxide anion generation and elastase release in FMLP/CB-induced human neutrophils, the effects of SB202190, a selective p38 MAPK inhibitor, in superoxide anion generation and elastase release were assayed. SB202190 diminished FMLP/CB-induced superoxide anion generation with an IC₅₀ value of 6.73 ± 0.65 µM. However, it did not show significant inhibition of elastase release (IC₅₀ value > 10 µM) ([Table 1]). These data suggested that p38 MAPK signaling pathway is a significant component in FMLP/CB-induced superoxide anion generation in human neutrophils. Taken together, our results demonstrate that the suppressive effects of compound 1 are associated with inhibition of p38 MAPK signaling pathway. In addition, p38 MAPK is a component of the oxidant stress-sensitive signaling kinases [28]. Therefore, whether the reduction of oxidant stress involved inhibition of p38 MAPK phosphorylation will need to be further investigated in future studies.

In order to investigate the synthesis of natural products as anti-inflammatory agents, melodamide A (1) was designed and synthesized ([Fig. 6]). To begin with, N-(4-hydroxyphenethyl)cinnamamide (15) was obtained in 84.4 % yield through the nucleophilic reaction of tyramine and cinnamoyl chloride. Oxidation of 15 with phenyliodine (III) diacetate afforded the new compound 1 with p-quinol B-ring (22.5 %). The spectral (¹H-, ¹³C-NMR, and MS) and physical data of the synthetic compound 1 coincided well with those of the natural melodamide A. In addition, the synthesis of different substituents (halide, NO₂, OCH₃, CH₃) on ring A of melodamide A (1) is also presented in [Fig. 6]. IR, ¹H-, ¹³C-NMR, and MS spectra were used for identifying the analogs structures (14a–p). The synthesized compounds (14a–p, purity > 96 %) were evaluated for their inhibitory effects against the release of both O⁻ ₂ and elastase by human neutrophils. As shown in [Table 1], compounds 14a, 14 d, and 14 f displayed inhibitory activity on O⁻ ₂ as well as 1, with IC₅₀ values of 7.49, 5.59, and 5.19 µM, while showing the presence of 2-chloro, 3-fluoro, and 2-bromo substitutions on ring A, respectively. However, all test compounds exhibited no inhibitory activity of elastase release. The results indicated that the substitutions on ring A were not of much benefit to the anti-inflammatory activity.

In summary, a new amide possessing novel p-quinol, melodamide A (1), was isolated from the leaves of M. fruticosum. The structure of 1 was fully elucidated by X-ray and 2D-NMR analyses. Moreover, 1 showed potent inhibitory effect on superoxide anion generation in fMLP/CB-activated human neutrophils via inhibiting p38 MAPK signaling pathway. In addition, melodamide A (1) and the analogs of 1 possessing p-quinol were synthesized and evaluated for their anti-inflammatory activity.

Acknowledgements

The authors would like to thank Dr. Tran Huy Thai, Institute of Ecology and Biological Resources, Vietnam Academy of Science and Technology, for the plant identification. This study was supported by the National Science Council to T. S. Wu (Taiwan) and by NAFOSTED (104.01–2010.27) (Vietnam).

Conflict of Interest

The authors have no conflict of interest to report.

^* These authors provided equal contributions to this work.

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• 18 Freeman P, Murphy S, Nemorin J, Taylor W. The constituents of Australian Pimelea species. II. The isolation of unusual flavones from P. simplex and P. decora . Aust J Chem 1981; 34: 1779-1784
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• 19 Seidel V, Bailleul F, Waterman PG. (Rel)-1β,2α-di-(2,4-dihydroxy-6-methoxybenzoyl)-3β,4α-di-(4-methoxyphenyl)-cyclobutane and other flavonoids from the aerial parts of Goniothalamus gardneri and Goniothalamus thwaitesii . Phytochemistry 2000; 55: 439-446
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• 20 Choudhary MI, Maher S, Begum A, Abbaskhan A, Ali S, Khan A. Shafique-ur-Rehman, Atta-ur-Rahman. Characterization and antiglycation activity of phenolic constituents from Viscum album (European Mistletoe). Chem Pharm Bull 2010; 58: 980-982
  CrossrefPubMedSearch in Google Scholar
• 21 Vasconcelos JMJ, Silva AMS, Cavaleiro JAS. Chromones and flavanones from Artemisia campestris subsp. maritima . Phytochemistry 1998; 49: 1421-1424
  CrossrefPubMedSearch in Google Scholar
• 22 Wu TS, Chan YY. Constituents of leaves of Uncaria hirsuta Haviland. J Chin Chem Soc 1994; 41: 209-212
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• 23 Bai N, He K, Roller M, Zheng B, Chen X, Shao Z, Peng T, Zheng Q. Active compounds from Lagerstroemia speciosa, insulin-like glucose uptake-stimulatory/inhibitory and adipocyte differentiation-inhibitory activities in 3 T3-L1 cells. J Agric Food Chem 2008; 56: 11668-11674
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• 24 Phoebe CH, Schiff PL, Knapp JE, Slatkin DJ. Oxoanolobine, a new oxoaporphine alkaloid from Guatteria melosma . Heterocycles 1980; 14: 1977-1978
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• 25 Piccinelli AL, Veneziano A, Passi S, Simone FD, Rastrelli L. Flavonol glycosides from whole cottonseed by-product. Food Chem 2007; 100: 344-349
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• 26 Basnet P, Kadota S, Shimizu M, Xu HX, Namba T. 2′-Hydroxymatteucinol, a new C-methyl flavanone derivative from Matteccia orientalis – potent hypoglycemic activity in streptozotocin-Induced diabetic rat. Chem Pharm Bull 1993; 41: 1790-1795
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• 27 Selvatici R, Falzarano S, Mollica A, Spisani S. Signal transduction pathways triggered by selective formylpeptide analogues in human neutrophils. Eur J Pharmacol 2006; 534: 1-11
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• 28 Ushio-Fukai M, Alexander RW, Akers M, Griendling KK. p 38 Mitogen-activated protein kinase is a critical component of the redox-sensitive signaling pathways activated by angiotensin II – Role in vascular smooth muscle cell hypertrophy. J Biol Chem 1998; 273: 15022-15029
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Correspondence

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  CrossrefPubMedSearch in Google Scholar
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  CrossrefPubMedSearch in Google Scholar
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  CrossrefPubMedSearch in Google Scholar
• 24 Phoebe CH, Schiff PL, Knapp JE, Slatkin DJ. Oxoanolobine, a new oxoaporphine alkaloid from Guatteria melosma . Heterocycles 1980; 14: 1977-1978
  CrossrefPubMedSearch in Google Scholar
• 25 Piccinelli AL, Veneziano A, Passi S, Simone FD, Rastrelli L. Flavonol glycosides from whole cottonseed by-product. Food Chem 2007; 100: 344-349
  CrossrefPubMedSearch in Google Scholar
• 26 Basnet P, Kadota S, Shimizu M, Xu HX, Namba T. 2′-Hydroxymatteucinol, a new C-methyl flavanone derivative from Matteccia orientalis – potent hypoglycemic activity in streptozotocin-Induced diabetic rat. Chem Pharm Bull 1993; 41: 1790-1795
  CrossrefPubMedSearch in Google Scholar
• 27 Selvatici R, Falzarano S, Mollica A, Spisani S. Signal transduction pathways triggered by selective formylpeptide analogues in human neutrophils. Eur J Pharmacol 2006; 534: 1-11
  CrossrefPubMedSearch in Google Scholar
• 28 Ushio-Fukai M, Alexander RW, Akers M, Griendling KK. p 38 Mitogen-activated protein kinase is a critical component of the redox-sensitive signaling pathways activated by angiotensin II – Role in vascular smooth muscle cell hypertrophy. J Biol Chem 1998; 273: 15022-15029
  CrossrefPubMedSearch in Google Scholar

• Supplementary Material