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A New fatty acid and some triterpenoids from propolis of Nkambe (North-West Region, Cameroon) and evaluation of the antiradical scavenging activity of their extracts

  • Abakar Ali Mahamat , Jean Noël Nyemb EMAIL logo , Isaac Silvère Gade , Alfred Tamfu Ngenge , Emmanuel Talla , Henoumont Céline , Laurent Sophie and Joseph Tanyi Mbafor
Published/Copyright: April 2, 2020
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Open Chemistry
From the journal Open Chemistry Volume 18 Issue 1

Abstract

The aim of this work was to evaluate in vitro antiradical scavenging activity of propolis from Nkambe (North-West, Cameroon). The polyphenol content of the acetone extract was evaluated using the Folin-Ciocalteu reagent as 0.166±0.008 gGAE/100 gRM. Antiradical scavenging activity of hexane and acetone extracts was carried out on DPPH using ascorbic acid as standard. The results showed that the extracts possess antiradical activity with IC50 of 141 μg/mL and 267 μg/mL for acetone and hexane extracts, respectively. The column chromatography separation on silica gel of the hexane fractionyielded compounds 1 to 3. The structures of these compounds were elucidated by NMR and mass spectrometry data as Lupenone (1), a mixture of α and ß-Amyrin (2) and lastly Hexatriacontanoic acid (3) which was described for the first time from propolis.

Keywords: Propolis; antiradical activity on DPPH; polyphenol content; hexatriacontanoic acid

1 Introduction

Propolis is a resinous, sticky and balsamic substance of viscous consistency, produced by bees principally collected from resin of buds and exudates of plants and their secretions [1]. This substance has important pharmacological activities such as antiplasmodial [2], analgesic [3], antimicrobial [4,5], vasodilatory [1], anti-inflammatory [6], antifugal [7], antioxidant [8], anti-ulcer [9], ostrogenic [10], antiviral, antiprotozoal, antiparastic, antitumor, hepatoprotective and cardioprotective properties [11]. In Cameroun, propolis is used locally to treat illnesses such as dysentery, stomachache, asthma, infertility, ulcers, tooth aches, fever, burns and different forms of inflammation [3,9]. Many studies on different samples show that propolis chemical composition is difficult to standardize because it is highly dependent on a number of factors such as local flora and environmental conditions of the site of collection of resin from plants for production of propolis. This is why propolis from areas not yet studied seems to be a promising source of new bioactive molecules [12]. From different botanical and geographical origins of the world, more than 300 compounds including volatile organic compounds, flavonoid aglycones, phenolic acids and their esters, phenolic aldehydes, alcohols and ketones, sesquiterpenes, quinones, coumarins, steroids, amino acids were reported to have been isolated from propolis [8, 13]. Amongst these compounds, 241 of them were reported for the first time from the year 2000 to 2012 [14]. Despite the chemical variability of propolis, it always possesses promising and considerable biological activities [15].

This present study consisted of evaluating the in vitro antiradical activity of the hexane and acetone extracts of propolis from Nkambe and to purify the hexane extract in order to obtain pure compounds which will be identified based on their spectroscopic data (1H NMR, 13C NMR and MS).

2 Materials and Methods

The propolis sample under investigation was harvested during the month of April 2014 by a bee farmer in Njap village, Nkambe central subdivision, Donga-Mantung division, the North-West Region of Cameroon.

2.1 Extraction and isolation

To extract secondary metabolites, 1 kg of propolis was extracted with 5 L of acetone by maceration with intermittent stirring at intervals of 3 hours during 72 hours after which it was filtered on a N°1 Whatman filter paper and evaporated using a rotary evaporator to near dryness to obtain a crude acetone extract. This process was repeated three times in order to optimize the extraction process. The acetone extract obtained was partitioned using liquid-liquid extraction with hexane to obtain the hexane extract. 60 g of this hexane extract was subjected to column chromatography on 360 g of silica gel with the gradient eluting system hexane (Hex)-dichloromethane (CH2Cl2) (100:0 → 0:100) followed by CH2Cl2-methanol (MeOH) (100:0 → 70:30). Fractions of 100 mL where collected regularly and concentrated on a rotavapor. This process yielded three compounds: Lupenone (1, 200 mg) [16], a mixture of α-amyrin (2a) and β-amyrin (2b) (85 mg) [17] and hexatriacontanoic acid (3, 25 mg).

Lupenone (C30H48O) (1): White crystals; 13C NMR (CDCl3, 150 MHz) δ (ppm): 38.7 (C-1); 27.4 (C-2); 218.2 (C-3); 38.8 (C-4); 54.9 (C-5); 19.7 (C-6); 34.2 (C-7); 40.8 (C-8); 49.7 (C-9); 37.1 (C-10); 20.9 (C-11); 25.1 (C-12); 30.1 (C-13); 42.8 (C-14); 27.4 (C-15); 35.5(C-16); 43.1 (C-17); 48.2 (C-18); 47.9 (C-19); 150.9 (C-20); 29.8 (C-21); 40.0 (C-22); 26.6 (C-23); 21.1 (C-24); 15.9 (C-25); 15.8 (C-26); 14.4 (C-27); 18.1 (C-28); 109.4 (C-29) and 19.3 (C-30). 1H NMR (CDCl3, 500 MHz) δ (ppm): 4.58 (1H, d, H-29a); 4.72 (1H, d, H-29b); 2.55 (1H, m, H-2a); 2.40 (1H, m, H-2b); 1.10 (3H, s, H-23); 1.08 (3H, s, H-24); 1.06 (3H, s, H-26); 0.96 (3H, s, H-25); 0.98 (3H, s, H-27); 0.80 (3H, s, H-28) and 1.72 (3H, s, H-30) [16].

α-amyrin (C30H50O) (2a): White powder; 13C NMR (CDCl3, 150 MHz) δ (ppm): 38.7 (C-1); 27.4 (C-2); 79.1 (C-3); 38.8 (C-4); 55.3 (C-5); 18.4 (C-6); 32.8 (C-7); 40.8 (C-8); 49.7 (C-9); 36.9 (C-10); 23.3 (C-11); 121.7 (C-12); 145.2 (C-13); 42.1 (C-14); 28.4 (C-15); 26.6 (C-16); 33.8 (C-17); 59.1 (C-18); 39.8 (C-19); 40.1 (C-20); 31.3 (C-21); 41.6 (C-22); 28.6 (C-23); 15.4 (C-24); 15.6 (C-25); 16.8 (C-26); 23.1 (C-27); 28.4 (C-28); 17.4 (C-29) and 21.3 (C-30). 1H NMR (CDCl3, 500 MHz) δ (ppm): 3.15 (1H, dd, H-3); 5.15 (1H, t, H-12); 0.84 (3H, d, J=5.6 Hz, H-29); 0.90 (3H, d, J=7.6 Hz, H-30); 0.72 (3H, s); 0.78 (3H, s); 0.93 (3H, s); 0.95 (3H, s); 0.99 (3H, s) and 1.07 (3H, s) [17].

β-amyrin (C30H50O) (2b): White powder; 13C NMR (CDCl3, 150 MHz) δ (ppm): 38.7 (C-1); 27.4 (C-2); 79.1 (C-3); 38.8 (C-4); 55.3 (C-5); 18.4 (C-6); 32.8 (C-7); 40.8 (C-8); 49.7 (C-9); 36.9 (C-10); 23.3 (C-11); 121.7 (C-12); 145.2 (C-13); 42.1 (C-14); 28.4 (C-15); 26.6 (C-16); 33.8 (C-17); 59.1 (C-18); 39.8 (C-19); 40.1 (C-20); 31.3 (C-21); 37.2 (C-22); 28.6 (C-23); 15.4 (C-24); 15.6 (C-25); 16.8 (C-26); 26.0 (C-27); 28.4 (C-28); 33.6 (C-29) and 23.7 (C-30). 1H NMR (CDCl3, 500 MHz) δ (ppm): 3.15 (1H, dd, H-3); 5.15 (1H, t, H-12); 0.72 (3H, s); 0.78 (3H, s); 0.84 (3H, s); 0.90 (3H, s); 0.93 (3H, s); 0.95 (3H, s); 0.99 (3H, s) and 1.07 (3H, s) [17].

Hexatriacontanoic acid (C36H72O2) (3): White powder: ESI TOF-MS: [M+H]+m/z 537.3, Key fragment ions m/z = 185.0; 227.1; 409.2; 445.3 and 532.3 (see figure 2). 13C NMR (CDCl3, 150 MHz) δ (ppm): 178.8 (C-1); 33.8 (C-2); 24.7 (C-3); 31.9 (C-34); 22.7 (C-35); 14.1 (C-36) and 29.4 (C-4 → C-33); 1H NMR (CDCl3, 500 MHz) δ (ppm): 0.80 (3H, t, 3H-36); 1.50 (2H, m, 2H-3); 2.30 (2H, t, 2H-2); 1.20-1.32 [(CH2)32, brs] and 10.70 (1H, s, OH).

Figure 1 Structures of the compounds isolated.
Figure 1

Structures of the compounds isolated.

Figure 2 Proposed fragmentation pattern of compound 3.
Figure 2

Proposed fragmentation pattern of compound 3.

2.2 Total polyphenol content

This was done according to the method described elsewhere [18]. A 100 µL of extract (200 μg/mL) were added to 200 µL of Folin-Ciocalteu followed by addition of 2000 µL of distilled water. The mixture was agitated for 3 minutes. After this, 1000 µL Na2CO3 (20%) was added to the mixture and incubated in a dark cupboard at room temperature for 1 hour. The absorbance of the resulting solution was then measured at 760 nm on a spectrophotometer, with a methanol solution used as negative control. The preparation of the positive control, gallic acid (200 μg/mL) was subjected to the same treatment as the test sample. The results were expressed in term of gram equivalent of gallic acid per 100 g of raw matter (gGAE/100 gRM). The quantification of polyphenolic compounds was done with respect to a linear standardization curve obtained at different concentrations (20 to 120 μg/mL) of gallic acid in the form y=2.428x+0.033 whose correlation coefficient R was 0.994.

2.3 Evaluation of DPPH antiradical scavenging activity

The DPPH (1,1-diphenyl-2-picrylhydrazyl) antiradical scavenging activity of the extracts was done according to the method described elsewhere [12] with slight modifications. To 2 mL of the solution of the test sample prepared at different concentrations, 1 mL of a methanol solution of DPPH (100 μg/mL) was added. The mixture obtained was then stored at room temperature for 1 hour after which the absorbance was then measured at 517 nm against a negative control (6 mL of MeOH and 1 mL of DPPH solution) on a spectrophotometer. The positive control was ascorbic acid. A mother solution of sample at the concentration of 120 μg/mL was prepared by dissolving 5000 μg of extract 41.6 mL of MeOH. From this, five other solution concentrations were obtained from the mother solution making a total of six solutions at six concentrations: 120, 100, 80, 60, 40 and 20 μg/mL. The test at each concentration was done in triplicates, the absorbance was mesured and the percentage inhibition calculated according to the following equation [12].

%inhibition=At0−At1At0×100

Where At0 = absorbance of negative control (without any anti-oxidant substance); At1 = absorbance of tested samples.

Ethical approval: The conducted research is not related to either human or animal use.

3 Results and Discussion

3.1 Isolation and structural elucidation of compounds

The Hexane fraction of propolis of Nkambe was separated by column chromatography of silica gel yielded four compounds (1-3) among which one new compound (3). The structures of known compounds Lupenone (1), α-Amyrin (2a), and β-Amyrin (2b) were elucidated by comparison of their spectral data with those described in the literature [16, 17].

Compound 3 was obtained has a white powder from the Hex/CH2Cl2 9:1 fraction. Its molecular formula was established as C36H72O2 by TOF-MS-ESI+ analysis which showed a quasi-molecular ion peak at m/z 537.3 [M+H]+. In its 1H NMR spectrum a signal of three protons triplet at δH 0.80 (3H, t, J = 6.0 Hz) indicates the presence of a terminal methyl group. A signal at δH 1.20-1.32 (6H, brs, -(CH2)32-) indicated the presence of a straight chain of 32 carbon atoms. The spectrum displayed a signal at δH 2.30 (2H, t, -CH2-COOH) for methylene protons attached to a carboxylic group. On the basis of the NMR spectra it was inferred that compound 3 is an aliphatic acid. The 13C NMR spectrum of compound 3 confirmed this suggestion by exhibiting important signals for carboxylic carbon at δC 180.1 and methyl carbon at δC 14.3 (C-36). The remaining methylene carbon resonated between δC 34.1-29.0. Mass spectral studies offered further support to the above assignment. The molecular ion peak at m/z 537.3 gave the molecular formula C 36H 72O2. The peak at m/z 532.3 was due to the loss of two H2 from molecular ion. The loss of an C9H19 radical from the parent ion gave an ion which appeared at m/z 409.2 and this ion underwent successive loss of C13H27● and C3H7● units to give ions appearing at m/z 227.1 and 185.0 successively (Figure 2). The isolated aliphatic acid was therefore identified as Hexatriacontanoic acid.

3.2 Total polyphenol content and antiradical activity

The total polyphenol content was performed only on the acetone extract since phytochemical screening indicated that no phenolic compound was present in hexane extract. These results indicated the presence of polyphenolic compounds in the ethyl acetate extract and the total phenolic content of the said acetone extract was found to be 0.166±0.008 gGAE/100gRM. This value is less that that obtained by Talla and co-workers for propolis of Ngaoundal 2.32 ± 0.37-8.64 ± 0.47 gGAE/100gRM [18] and also those of Njintang and co-workers 10.99 ± 2.56-12.12 ± 2.24 g/100g [19] for some Cameroonian samples. This difference could be explained the difference in environmental conditions and local flora of site of collection of the propolis samples.

According to Melo and co-workers [20], anti-oxidant activity can be classified based on the performance of crude extracts as follows: good activity (IC50 < 69 µg/mL); moderate activity (69 µg/mL < IC50 < 161 µg/mL); low activity (IC50 > 161 µg/mL) [20]. The percentage inhibition was dose-dependent or concentration-dependent. The IC50 were deduced by graphical means and presented in table 1 and higher values imply low activity and vice versa. The acetone extract had a higher activity with IC50 of 141 μg/mL compared to hexane extract with IC50 267 μg/mL. This could be explained by the absence of polyphenols in the hexane extract because the higher activity of acetone extract corroborates with its polyphenol content 0.166 ± 0.008 gGAE/100gRM. Ascorbic acid (vitamin C) possesses higher anti-radical activity (IC50 = 9 μg/mL) than the tested samples.

Table 1

IC50 values of tested samples.

SampleIC50 (μg/mL)Percentage inhibition (%)
AE14150.37
HE26738.75
Vitamin C985.63

  1. AE: Acetone extract. HE: Hexane extract.

4 Conclusion

Evaluation of antiradical activity carried out on the acetone extract showed a moderate one with percentage inhibition of 50.37% with an IC50 of 140 μg/mL while that of the hexane hexane extract showed low antiradical activity with percentage inhibition of 38.75% and IC50 of 267 μg/mL. The acetone extract has low polyphenols content of 0.166 ± 0.008 gGAE/100gRM. Column chromatographic separation on silica gel of the hexane extract yielded compounds 1 to 3. The structures of these compounds were elucidated based on NMR and mass spectroscopic data lup-20(29)-en-3-one (1), a mixture of α and ß-amyrin (2) and lastly hexatriacontanoic acid (3) which is described for the first time from propolis.

  1. Conflict of interest: Authors declare no conflict of interest.

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Received: 2019-07-03
Accepted: 2019-08-05
Published Online: 2020-04-02

© 2020 Abakar Ali Mahamat et al., published by De Gruyter

This work is licensed under the Creative Commons Attribution 4.0 International License.

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  69. Stability-indicating HPLC-DAD assay for simultaneous quantification of hydrocortisone 21 acetate, dexamethasone, and fluocinolone acetonide in cosmetics
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  87. Synthesis and efficacy of herbicidal ionic liquids with chlorsulfuron as the anion
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  93. A turbidity sensor development based on NL-PI observers: Experimental application to the control of a Sinaloa’s River Spirulina maxima cultivation
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  104. A new phenyl alkyl ester and a new combretin triterpene derivative from Combretum fragrans F. Hoffm (Combretaceae) and antiproliferative activity
  105. Erratum
  106. Erratum to: A one-step incubation ELISA kit for rapid determination of dibutyl phthalate in water, beverage and liquor
  107. Review Articles
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  118. Characterization of soil water by the means of hydrogen and oxygen isotope ratio at dry-wet season under different soil layers in the dry-hot valley of Jinsha River
  119. Composition and diurnal variation of floral scent emission in Rosa rugosa Thunb. and Tulipa gesneriana L.
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  121. The degradation, biodegradability and toxicity evaluation of sulfamethazine antibiotics by gamma radiation
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  131. Physicochemical properties of selected herbicidal products containing nicosulfuron as an active ingredient
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  136. Special Issue on the 4th Green Chemistry 2018
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  149. Corrosion study of copper in aqueous sulfuric acid solution in the presence of (2E,5E)-2,5-dibenzylidenecyclopentanone and (2E,5E)-bis[(4-dimethylamino)benzylidene]cyclopentanone: Experimental and theoretical study
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  153. Special Issue on Advances in Chemistry and Polymers
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  159. Advancing biodiesel production from microalgae Spirulina sp. by a simultaneous extraction–transesterification process using palm oil as a co-solvent of methanol
  160. Topical Issue on Applications of Mathematics in Chemistry
  161. Omega and the related counting polynomials of some chemical structures
  162. M-polynomial and topological indices of zigzag edge coronoid fused by starphene
https://doi.org/10.1515/chem-2020-0016
Keywords for this article
Propolis; antiradical activity on DPPH; polyphenol content; hexatriacontanoic acid
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