Undulaterpene A: A new triterpene fatty acid ester from pulicaria undulata
Hossam Mohamed Abdallah1, Gamal A Mohamed2, Sabrin R M. Ibrahim3, Hani Z Asfour4, Maan T Khayat5
1 Department of Natural Products and Alternative Medicine, Faculty of Pharmacy, King Abdulaziz University, Jeddah, Saudi Arabia; Department of Pharmacognosy, Faculty of Pharmacy, Cairo University, Cairo, Egypt
2 Department of Natural Products and Alternative Medicine, Faculty of Pharmacy, King Abdulaziz University, Jeddah, Saudi Arabia; Department of Pharmacognosy, Faculty of Pharmacy, Al-Azhar University, Assiut Branch, Assiut, Egypt
3 Department of Pharmacognosy and Pharmaceutical Chemistry, College of Pharmacy, Taibah University, Al Madinah Al Munawwarah, Saudi Arabia; Department of Pharmacognosy, Faculty of Pharmacy, Assiut University, Assiut, Egypt
4 Department of Medical Microbiology and Parasitology, Faculty of Medicine, Princess Al-Jawhara Center of Excellence in Research of Hereditary Disorders, King Abdulaziz University, Jeddah, Saudi Arabia
5 Department of Pharmaceutical Chemistry, Faculty of Pharmacy, King Abdulaziz University, Jeddah, Saudi Arabia
|Date of Submission||28-Dec-2018|
|Date of Decision||12-Feb-2019|
|Date of Web Publication||19-Sep-2019|
Hossam Mohamed Abdallah
Department of Natural Products and Alternative Medicine, Faculty of Pharmacy, King Abdulaziz University, Jeddah 21589, Saudi Arabia. Department of Pharmacognosy, Faculty of Pharmacy, Cairo University, Cairo 11562
Source of Support: None, Conflict of Interest: None
| Abstract|| |
Background: Natural products display a remarkable role not only in the synthesis, design, and discovery of new drugs but also as the most prominent source of innovative drugs and bioactive substances. Genus Pulicaria (Asteraceae) includes about 100 species that are widely distributed in Europe, Asia, and Africa. Objective: In this work, the chemical investigation of Pulicaria undulata aerial parts was performed. In addition, the cytotoxic activity of the isolated metabolites was estimated toward various cell lines. Materials and Methods: Plant extract was subjected to fractionation and different column chromatography to isolate the biometabolites. Their structures were verified using nuclear magnetic resonance, infrared, ultraviolet, and high-resolution mass spectrometry, as well as compared with the literature. The cytotoxic effect was evaluated in vitro toward various cell lines: HCT-116 (colorectal adenocarcinoma), MCF-7 (human breast adenocarcinoma), and A549 (lung carcinoma). Results: A new triterpene fatty acid ester, undulaterpene A (1) (3β,16β-dihydroxylup-20 (29)-ene 3-decanoate) and four known metabolites: 3-O-acetyl-pseudotaraxasterol (2), pseudotaraxasterol (3), stigmasterol (4), and tomentosin (5) were separated. Compound 1 displayed cytotoxic potential toward hormone-dependent breast carcinoma cell line (MCF7), colon carcinoma cell line (HCT116), and lung carcinoma cell line (A549) cell lines with half maximal inhibitory concentrations (IC50s) 8.2, 6.9, and 12.4 μM, respectively in comparison to doxorubicin (IC50s 0.14, 0.39, and 1.15 μM, respectively). However, 2, 3, and 4 displayed activity toward HCT-116 with IC50s 13.2, 23.1, and 16.4 μM, respectively. Conclusion: This work led to the identification of a new triterpene fatty acid ester (1) and four known metabolites (2–5) from P. undulata growing in Saudi Arabia. The new compound showed moderate cytotoxic potential against hormone-dependent breast carcinoma cell line (MCF7), colon carcinoma cell line (HCT116), and lung carcinoma cell line (A549) cancer cell lines.
Keywords: Asteraceae, cytotoxic activity, Pulicaria undulata, triterpenes, undulaterpene A
|How to cite this article:|
Abdallah HM, Mohamed GA, M. Ibrahim SR, Asfour HZ, Khayat MT. Undulaterpene A: A new triterpene fatty acid ester from pulicaria undulata. Phcog Mag 2019;15:671-4
|How to cite this URL:|
Abdallah HM, Mohamed GA, M. Ibrahim SR, Asfour HZ, Khayat MT. Undulaterpene A: A new triterpene fatty acid ester from pulicaria undulata. Phcog Mag [serial online] 2019 [cited 2021 Jun 13];15:671-4. Available from: http://www.phcog.com/text.asp?2019/15/65/671/267185
- A new triterpene fatty acid ester, undulaterpene A (1), and four known metabolites (2–5) were separated from the aerial parts of Pulicaria undulata. Their structural was determined by various spectral analyses. The cytotoxic potential of the isolated metabolites was assessed toward MCF-7, HCT-116and A549 cell lines using 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay.
Abbreviations used: CC: Column chromatography; CHCl3: Chloroform; CDCl3: Deuterated chloroform; COSY: Correlation spectroscopy; DMSO: Dimethyl sulfoxide; EIMS: Electron impact mass spectrometry; EtOAc: Ethyl acetate; GCMS: Gas chromatography coupled with mass spectrometry; HCl: Hydrochloric acid; H2O: Water; HMBC: Heteronuclear multiple bond correlation experiment; HRESI: High-resolution electrospray ionization; HRMS: High-resolution mass spectrometry; HRESIMS: High-resolution electrospray ionization–mass spectrometry; HSQC: Heteronuclear single quantum correlation; IC50: Half maximal inhibitory concentration; IR: Infrared; KBr: Potassium bromide; KOH: Potassium hydroxide; MeOH: Methanol; NMR: Nuclear magnetic resonance; NOESY: Nuclear Overhauser effect spectroscopy; RP: Reversed phase; SiO2: Silica gel; TLC: Thin-layer chromatography; VIS: Visible; VLC: Vacuum liquid chromatography; UV: Ultraviolet.
| Introduction|| |
Natural products display a remarkable role not only in the synthesis, design, and discovery of new drugs but also as the most prominent source of innovative drugs and bioactive substances. Genus Pulicaria (tribe Inuleae and family Asteraceae) includes about 100 species that are widely distributed in Europe, Asia, and Africa. The plants of this genus have been used in traditional medicines for treating various aliments as back pain, inflammation, menstrual cramps, intestinal disorders, dysentery, and diarrhea., They possessed various bioactivities such as cytotoxic, antipyretic, antioxidant, antispasmodic, antimicrobial, antihistaminic, analgesic, hepatoprotective, anti-inflammatory, cardioprotective, and nephroprotective.,,, This genus is known to be rich in sesqui-, di-, and tri-terpenoids, phenolics, and sterols., Moreover, many sesquiterpenes isolated from this genus have been shown to exhibit a wide range of biological activities.,, In course of our ongoing search for bioactive metabolites from Saudi plants, the chemical investigation of Pulicaria undulata aerial parts afforded a new lupeol fatty acid ester: undulaterpene A (1) and four known metabolites (2–5) [Figure 1]. The structural elucidation of these compounds was carried out by extensive spectral data analysis. In addition, the cytotoxic activity of the isolated metabolites was evaluated toward various cell lines.
| Materials And Methods|| |
General experimental procedures
Shimadzu 400 infrared (IR) and Shimadzu 1601 ultraviolet (UV)/visible spectrophotometers were utilized for measuring IR and UV spectra, respectively. Measuring the optical rotation was performed using JASCO DIP-370 polarimeter. Gas chromatography coupled with mass spectrometry (GCMS) analysis was done using Clarus 500 GC-MS under the same conditions as previously stated. Mass spectrometers, LTQ Orbitrap, and JEOL JMS-SX/SX 102A were used for high-resolution electrospray ionization (HRESI) and electron impact mass spectrometry (EIMS) measurements, respectively. Nuclear magnetic resonance (NMR) spectra were performed using INOVA 850 BRUKER. Chromatographic operations were done using reversed phase (RP)-18 and silica gel (SiO2) 60 (0.04–0.063 mm). Thin-layer chromatography (TLC) plates (SiO260 F254) were utilized for TLC. The compounds were purified using RP-18 LiChrolut extraction tube (6 mL). The ethyl acetate (EtOAc):N-hexane systems: S1(5:95), S2(10:90), and S3(15:85) were used for TLC.
P.undulata aerial parts were obtained from Gabal Al-Ateeq, Al Madinah Al Munawwarah, Saudi Arabia, in April 2016. The plant identification was carried out based on the library database and morphological features. This was proved by Emad Al-Sharif (Associate Professor of Plant Ecology, King Abdulaziz University). A specimen (PU 2016-1) was stored at the herbarium (Department of Natural Products and Alternative Medicine).
Extraction and isolation
Dried powdered aerial parts (270 g) were extracted with MeOH (4 × 2.5 L). The total concentrated extract (16.4 g) was mixed with distilled water (H2O) (200 mL). Successively, it was fractionated using chloroform (CHCl3) (4 × 500 mL) and EtOAc (4 × 500 mL). Each fraction was evaporated to obtain CHCl3(7.3 g), EtOAc (2.3 g), and aqueous (5.5 g) fractions. SiO2 column of the CHCl3 fraction (7.3 g) using n-hexane: EtOAc gradient gave eight subfractions: Pulicaria undulata chloroform PUC-1 to PUC-8. Subfraction PUC-3 (590 mg) was submitted to SiO2 column chromatography (CC) using n-hexane:EtOAc gradient to give 1, which was purified on RP-18 LiChrolut extraction tube using gradient H2O:acetonitrile to get 1 (11.4 mg). SiO2 CC of PUC-4 (1.2 g) using gradient n-hexane:EtOAc afforded impure 2 and 3. They were separately purified on RP-18 LiChrolut extraction tube with gradient H2O:acetonitrile to yield 2 (21.9 mg) and 3 (13.2 mg). PUC-5 (910 mg) was subjected to SiO2 CC using gradient n-hexane:EtOAc to afford 4, which was purified by repeated SiO2 CC to obtain 4 (41 mg). PUC-6 (1.1 g) was chromatographed using EtOAc:N-hexane: (2:98–30:70) over SiO2 CC to give 5, which was purified on RP-18 CC using gradient H2O: MeOH to get 5 (24.7 mg).
Undulaterpene A (1)
White amorphous powder Rf = 0.54 (S1); (α)D* 35.7 (c 0.2, MeOH); UV λmax(log ε): 221 (4.21), 239 (3.98) nm; IR (potassium bromide) γmax: 3436, 2954, 1697, 1665, 887, 728 cm−1; NMR data are presented in [Table 1]; HRESI–mass spectrometry (HRESIMS): M/z 597.5251 [M*H]* (calcd for 597.5247, C40H69O3).
|Table 1: Nuclear magnetic resonance spectral data of compound 1 (CDCl3, 850 and 214 MHz)|
Click here to view
Alkaline hydrolysis of compound 1
Six milliliters of 3% potassium hydroxide in MeOH was added to 5 mg of 1 and left to stand for 25 min at room temperature. Then, the mixture was neutralized with 1 N hydrochloric acid in MeOH, extracted with CHCl3, and finally concentrated. SiO2 CC of the residue using gradient n-hexane: EtOAc gave a methyl ester of decanoic acid, which was identified by GC-MS and EIMS m/z: 186 [M]* and GC-MS: tR36.6 min.
The cytotoxic potential of 1 toward MCF-7, A549, and HCT-116 cell lines was assessed as previously. Dimethyl sulfoxide and doxorubicin were the negative and positive controls, respectively.,,,
| results and Discussion|| |
Purification of metabolites
The known metabolites such as 3-O-acetyl-pseudotaraxasterol (2), pseudotaraxasterol (3), stigmasterol (4) and tomentosin (5) were assigned by comparing of their spectral data with literature [Figure 1].
Structural characterization of 1
Compound 1 was separated as white amorphous powder and had a positive Liebermann–Burchard reaction, indicating its triterpenoidal nature. It had a pseudo-molecular ion peak at m/z 597.5251 [M*H]* (calcd for 597.5247, C40H69O3) in the HRESIMS compatible with C40H68O3 molecular formula, indicating seven double bond equivalent. It displayed UV maxima at 221 and 239 nm. Its IR revealed bands at 1697 (C=O), 3436 (OH), 1665 and 887 (exocyclic double bond) and 728/cm (long aliphatic chain)., The NMR and MS spectra indicated that 1 was a dihydroxy lupene derivative with a fatty acid moiety [Figures S1-S6].,, The13 C and heteronuclear single-quantum correlation (HSQC) spectra suggested the existence of 40 carbon resonances, including eight methyls, 18 methylenes, and seven methines: two of them for oxymethines at δC80.5 (C-3) and 76.9 (C-16) and seven quaternary carbons including carbonyl (δC173.8, C-1'). The1 H and13 C NMR showed characteristic signals for six tertiary methyls at δH0.84/δC28.0 (H-23/C-23), 0.83/16.2 (H-24/C-24), 0.85/16.0 (H-25/C-25), 1.03/16.6 (H-26/C-26), 0.98/16.1 (H-27/C-27), and 0.79/11.7 (H-28)/C-28) and an allylic methyl at δH1.68/δC19.3 (H-30/C-30) reminiscent of a lupeol-type triterpene. Their assignment was deduced from the heteronuclear multiple bond correlation (HMBC) cross-peaks of H-26 to C-9, C-7, C-8, and C-14, H-24 and H-23 to C-5 and C-4, H-25 to C-9, C-5, and C-1, H-27 to C-15, C-14, and C-8, H-28 to C-22, C-17 and C-16, and H-30 to C-20, C-19, and C-29. Moreover, two doublet signals at δH4.70 and 4.60 (each d, J = 1.7 Hz, H-29) having HSQC cross-peaks to carbon at δC109.9, together with carbon at δC150.0 (C-20), characterized the existence of an exocyclic methylene. It had cross peaks to C-30, C-19, and C-21 in the HMBC. Furthermore, two oxymethines groups at δH4.46/δC80.5 (H-3/C-3) and 3.61/δC76.9 (H-16/C-16) were observed. Their position was secured by the HMBC cross-peaks of H-1, H-5, H-23 and H-24/C-3 and H-18 and H-28/C-16 [Figure 2], suggesting 1 was a 3β,16β-dihydroxy lup-20 (29)-ene derivative.,, In addition, the triplet methylene at (δH2.28, H-2'), terminal methyl (δH0.88, H-10') and methylene signals (δH1.23–1.26) characterized a fatty acyl moiety in 1. Further, this was also aided by the13 C signals at δC14.1, 173.8, and 29.1–29.7 for terminal methyl, ester carbonyl group, and long chain of methylene groups, respectively. The fatty acid moiety comprised a C10 chain by alkaline hydrolysis of 1 to afford a methyl ester of decanoic acid that was specified by a molecular ion peak at m/z 186 [M]* in GC-MS and EIMS and assured by a characteristic peak at m/z 442.3896 [M * H-C10H19O]* in HRESIMS. The cross peak of H-3/C-1' in the HMBC and the H-3/C-3 downfield shift confirmed the linkage of the long chain fatty acid moiety at C-3. The relative configuration at C-16 and C-3 was assigned by comparison of the13 C and1 H NMR shifts with those of related metabolites,, and further confirmed by the nuclear Overhauser effect spectroscopy peaks of H-3/H-24, H-5 and H-27 and H-16/H-18 and H-27. Thus, 1 was 3β,16β-dihydroxy lup-20 (29)-ene derivative, having a decanoic acid unit at C-3. From the above evidence and by comparison with literature, 1 was identified as 3β,16β-dihydroxylup-20(29)-ene 3-decanoate and named undulaterpene A.
|Figure 2: Key heteronuclear multiple bond correlation correlations of compound 1|
Click here to view
Cancer is one of the major causes of death worldwide. The major treatments of cancer are radiotherapy and chemotherapy, which unfortunately proved to be toxic to other living cells of the body. Thus, several studies have focused on natural products as an ideal target for the discovery of potential bioactive metabolites or lead structures for new cytotoxic agents. Triterpenes group is among the bioactive metabolites, which exhibit cytotoxic capacities toward different tumor cells with low effect toward normal cells. Therefore, the isolated metabolites were assessed for their cytotoxic potential toward A549, HCT-116, and MCF-7 cell lines using MTT assay [Figure S7]. Interestingly, 1 displayed cytotoxic potential toward MCF-7, HCT-116, and A549 with half maximal inhibitory concentrations (IC50) 8.2, 6.9, and 12.4 μM, respectively, in comparing with doxorubicin (IC500.14, 0.39, and 1.15 μM, respectively). However, 2, 3, and 4 displayed cytotoxic activity toward HCT-116 (IC50s 13.2, 23.1, and 16.4 μM, respectively). Compound 5 exhibited only activity against MCF-7 (IC5013.1 μM). Moreover, 3 and 4 had moderate activity toward A549 and MCF-7 with IC50 values of 22.3 and 17.2 μM and 15.3 and 12.6 μM, respectively, compared to doxorubicin (IC501.15 and 0.14 μM, respectively).
| Conclusion|| |
This study led to the identification of a new triterpene fatty acid ester (1) and four known metabolites (2–5) from the aerial parts of P. undulata growing in Saudi Arabia. The new compound showed moderate cytotoxic activity against A549, HCT-116, and MCF-7 cancer cell lines.
Authors acknowledge with thanks Deanship of Scientific Research (DSR) for technical and financial support.
Financial support and sponsorship
This project was funded by the DSR at King Abdulaziz University, Jeddah, under grant no. (G-43-166-1439). The authors, therefore, acknowledge with thanks DSR for technical and financial support.
Conflicts of interest
There are no conflicts of interest
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[Figure 1], [Figure 2]