Pharmacognosy Reviews

REVIEW ARTICLE
Year
: 2018  |  Volume : 12  |  Issue : 24  |  Page : 166--176

Terpenoids as cytotoxic compounds: A perspective


Ved Prakash 
 Department of Biotechnology, Motilal Nehru National Institute of Technology Allahabad, Uttar Pradesh, India

Correspondence Address:
Ved Prakash
Department of Biotechnology, Motilal Nehru National Institute of Technology Allahabad, Uttar Pradesh
India

Abstract

Natural products serve as safe and effective therapeutic agents for the drug discovery. Plants produce bioactive secondary metabolites such as terpenoids, alkaloids, tannins, saponins, and others, which have profusely been studied for anti-infective, anticancer, anti-inflammatory potential, and metabolic disorders to name a few. Terpenoids constitute the largest class of natural compound. The study investigates the novel cytotoxic compound of the terpenoid family isolated from different natural sources. The anticancerous activities of the compounds discussed in this review are taken from the published articles showing activity against specific cancer cell lines. The compounds exclusively belong to terpenoid family. Considering the huge potential of plant-based natural products in drug discovery program and the contribution of terpenoid in the production of anticancer compounds, it can be exploited for more reliable economical and environmentally safe bioactive molecules.



How to cite this article:
Prakash V. Terpenoids as cytotoxic compounds: A perspective.Phcog Rev 2018;12:166-176


How to cite this URL:
Prakash V. Terpenoids as cytotoxic compounds: A perspective. Phcog Rev [serial online] 2018 [cited 2018 Dec 16 ];12:166-176
Available from: http://www.phcogrev.com/text.asp?2018/12/24/166/243198


Full Text



 Introduction



Cancer is the uncontrolled unregulated growth of cells that generally invade and destroy normal cells. Cancer alone accounts for 2%–3% of the total death occurring across the globe. About 3500 million people lose their life every year suffering from cancer worldwide. Although major treatments include usage of chemopreventive agents, it is of limited use by toxic effect that damages body tissues.[1] Products obtained from natural sources have always plays a vital role in treating and checking human diseases since ancient times.[2] The structural diversity of natural products and their wide application in therapeutic has always been recognized by pharma industries.[3] Terpenoids account for the major class of secondary metabolites produced by plants [4] and have been widely considered as therapeutic agent. As per the World Health Organization report, extracts derived from folklore medicinal plants are widely used in indigenous therapies of 80% of the global population. Even today more than 50% of the modern approved clinical drugs have originated from natural sources.[5]

Terpenoids are organic compounds derived from five-carbon units (isoprene) assembled and modified in different ways. The classification of terpenoids is based on the isoprene units which are commonly classified as monoterpenoids (C10), for example, limonene, geraniol, and sesquiterpenoids; (C15), for example, artemisinin, humulene, and diterpenoids; (C20), for example, abietic acid, podocarpic acid, and sesterterpenoids; (C25), for example, manoalide and triterpenoids; and (C30), for example, squalene and cortisone.

 Monoterpenoid



Monoterpenes comprise two isoprene units that may be linear or cyclic. These are abundantly available in essential oils and used for flavors, but a large number of bioactive compounds have been isolated that significantly was found active against specific cancer cell lines. These compounds have potential to act as a lead molecule for further drug development. Structure of all the compounds has been drawn and shown in [Figure 1]; [Table 1] shows the details of compounds.{Figure 1}{Table 1}

From the leaves of Tabernaemontana corymbosa, two compounds bistabercarpamines A (1) (1) and B (2) (2) were isolated. Bistabercarpamine A (1) (1) showed moderate activity against cell growth of HepG2 cells showing IC50 of 38.14 ± 1.1 μM.[6]

In other study, β-pinene (3) was identified as major composition of oils achieved by hydrodistillation of Xylopia parviflora fruits. Against cancer cell line (MCF-7) and normal cell lines (adult retinal pigment epithelial-19), it showed cytotoxic activity with IC50 of 0.155 μL/mL and 0.166 μL/mL.[7]

From the fruit and bark of Rothmannia wittii, compound 10-O-acetylmacrophyllide (2) (4) was isolated which showed cytotoxic action showing IC50 value of 6.82 μg/mL in contradiction of the NCI-H187 cancer cell line.[8]

Ferula ovina roots led to the identification of stylosin (5). The compound on administration to 5637 cells showed IC50 values of 37, 35, and 31 μg/ml after 24, 48, and 72 h, respectively.[9]

Compound tabernaelegantine B (6) and D (7) were isolated from the stem bark of Muntafara sessilifolia that showed activity against MRC-5 cells with IC50 values of 0.47 and 1.89 μM and against L-6 cells IC50 values of 0.42 and 2.7 μM, respectively.[10]

Shoots of Plectranthus hadiensis-derived fraction were extracted which have major composition of geraniol (41.1%), geranyl acetate (29.5%), and nerol (10.4%) which showed activity against HCT-5 cell line with IC50 value of 17.27 ± 0.620 μg/mL.[11]

 Diterpenoid



Basic skeleton of diterpenoid is made up of 20 carbons that consist of four isoprene units and are derivatived from geranylgeranyl pyrophosphate. They are found in almost all plant families. Anticancer compounds belonging to diterpenoid class have been discussed below. Structure of all the compounds has been drawn and shown in [Figure 2]; [Table 2] shows the details of compounds.{Figure 2}{Table 2}

Cultured Perovskia atriplicifolia yielded a new compound named perovskiaol (1) (8). Bioassay to determine its anticancer properties depicted inhibitory action on cell lines of NB4, HepG2, and A549 with IC50 values of 2.35, 0.81 μm, and 1.47, respectively.[12]

Asperolide A (9), marine-derived compound, inhibited cell division in cell of NCI-H460 by inducing G2/M arrest along with activating Ras/Raf/MEK/ERK signaling and p53-dependent p21 pathway. The study depicted cytotoxicity against NCI-H460 with IC50 value of 35 μM (2 × IC50).[13]

Clerodane diterpenoid (10) was isolated from seeds of Polyalthia cerasoides. Compounds exhibited antiproliferative action against CACO-2 cell line showing IC50 value of 28.6 ± 4.34 nM/ml for clerodane diterpenoid.[14]

Caesalppans A–F (1–6) (11–16) was identified from seeds of Caesalpinia sappan. The compound was evaluated for its antiproliferative potential against cell lines HeLa, AtT20, and KB using the MTT method and showed IC50 value of 19.3–42.7 μM.[15]

Salyunnanins A–F, 1-6 (17–22) was extracted from roots of Salvia yunnanensis. The inhibitory potential of these metabolites in contradiction of HeLa, PC3, NCI-H460, MCF-7, KB-3–1, and K562 was evaluated in vitro. A range of IC50 values of 0.86–10.1 μM was observed.[16]

7-(2-oxohexyl)-11-hydroxy-6,12-dioxo-7,9 (11),13-abietatriene(=7-[2-oxohexyl]-taxodione) (23) was isolated from root culture of Agrobacterium rhizogenes-mediated root culture of Salvia austriaca. Compound exhibited high anticancer activity in contradiction to HL-60, NALM-6, and WM-115 with IC50 values between 0.63 and 0.72 μM.[17]

From the fruits of Rubus chingii, compound 15-O-β-d-apiofuranosyl-(1→2)-β-d-glucopyranosyl-18-O-β-d-glucopyranosyl-13(E)-ent-labda-8 (9),13 (14)-diene-3β,15,18-triol (3) (24) was obtained. Compound was found active against A549 cell line with an IC50 value of 2.32 μM.[18]

Methanolic extract from leaves of Blumea lacera resulted in the isolation of new compound 6E, 10E,14Z-(3S)-17-hydroxyge-ranyllinalool-17-O-β-d-glucopyranosyl-(1→2)-(α-l-rhamnopyranosyl-

[1→6])-β-d-glucopyranoside (1) (25) which was found potent against MCF-7 breast cancer cells with IC50 value of 8.3 μM.[19]

From fermentation of extract of Stevia rebaudiana new terpenes and sterebins O (1) (26), P1 (2) (27), and P2 (3) (28) were identified. Against B16 cell lines, all metabolites were found cytotoxic with IC50 values of 9.8 μM, 17 μM, and 75 μM.[20]

 Sesquiterpene



Three isoprene units form a sesquiterpene. In higher plants, these are found in abundance. The precursor molecule for sesquiterpene is farnesyl pyrophosphate which by skeletal rearrangement gives rise to different structures. Structure of all the compounds has been drawn and shown in [Figure 3]; [Table 3] shows the details of compounds.{Figure 3}{Table 3}

α-Santalol, (29) a sesquiterpene present in oil of sandalwood, showed to induce apoptosis in in vitro cell cultures. Breast cancer treated at the time interval of 6 h and 9 h with α-santalol showed downregulation of surviving in concentration-dependent manner. Downregulation by α-santalol is not directed through the PI3K-AKT pathway.[21]

Hoaensieremone (3) (30) was extracted from stems of Drypetes congestiflora. The compound was found active in contradiction to A549 and B16F10 cell lines showing IC50 values of 27.5 and 41.3 mm, respectively.[22] Two compounds, namely syreiteate A (1) (31) and syreiteate B (2) (32), were extracted from Ferula dissecta (Ledeb). Ledeb roots, both compounds, were found active against cervical cancer HeLa cell line showing 13.2 and 19.3 μM of IC50.[23]

From the leaves of Artemisia argyi, two new compounds, artemisinin A (1) (33) and isoartemisolide (2) (34), were isolated. Isoartemisolide (34) exhibited IC50 value of 4 μM in BV-2 microglial cells.[24]

α-Cadinol (35) was isolated from dried plant materials of Abies nephrolepis which showed inhibitory effect on Colo-205, A549, and QGY-7703 with IC50 values of 8.1, 8.6, and 4.6 μg/mL, respectively.[25]

From aerial section of Pteris multifida Poir., compound (2R)-pterosinP(1) (36), a C14-pterosin sesquiterpenoid and dehydropterosin B (3) (37) and a novel natural product, were isolated. Compound 3 showed anticancer activity against PANC-1 and NCI-H446 cell lines, exhibiting IC50 values of 14.63 and 5.19 μM, respectively.[26]

The new eremoligularin bieremoligularolide (5) (38) was isolated from the roots of Ligularia muliensis, and the compound showed inhibitory effect on HL-60, SMMC-7721, and HeLa with IC50 values of 3.81 ± 0.59, 11.16 ± 1.18, and 6.15 ± 1.12 μg/mL, respectively.[27]

The roots of Saussurea costus extracted in ethyl acetate resulted in recognition of sesquiterpene lactones arbusculin B (1) (39), α-cyclocostunolide (2) (40), costunolide (3) (41), dehydrocostuslactone (4) (42), parthenolide (5) (43), zaluzanin D (6) (44), and eupatoriopicrin (7) (45) were tested for cytotoxicity and had IC50s between 0.8 and 22 μM.[28]

New metabolite 1-oxoeudesm-11 (13)-ene-12,8α-lactone (7) (46) was found from the whole plant of Carpesium divaricatum. The compound showed inhibitory effect against KB and MCF-7 with IC50 values of 24.1 and 18.8 μM, respectively. The compound showed to activate mitochondria and generate reactive oxygen species to cause cell death in MCF-7 cells.[29]

Caesalpinone A (1) (47) was isolated from the pods of Caesalpinia spinosa Kuntze (Tara). 1D and 2D nuclear magnetic resonance (NMR) spectra were exploited to decipher structure of the compound. The compound showed inhibitory action against HL-60, SW-480, SMMC-7721, A549, and MCF-7 with IC50 of <40.[30]

Sesquiterpene abiesesquine A (48) lanosta-7,9(11) and 24-trien-26-oic acid (49) were identified from aerial parts of Abies holophylla which showed cytotoxic effect against RAW264.7, Colo-205, LOVO, and QGY-7703 with IC50 values of 113.1 μM, 0.9, 4.2, and 2.0 μM, respectively.[31]

In a study, new β-dihydroagarofuranoid sesquiterpenes (1a, 2a, 8b, 9b)-1, 8-bis (acetyloxy)-2, 9-bis (benzoyloxy)-14-hydroxy-b-dihydroagarofuran (50) was isolated from the whole plant of Aesculus californica, it inhibited the growth of MCF-7 cells with an IC50 of 17 ± 1 μM.[32]

Two sesquiterpene lactones linderolide G (1) (51) and lindestrene (16) (52) was isolated from the roots of Lindera strychnifolia. Spectroscopic observations followed by Cd analysis led to deciphering of the structure. Compound exhibited cytotoxic action against HSC-T6 with IC50 values of 2.9% and 73.1% inhibition at 100 μg/ml.[33]

Dihydro-b-agarofuran (53) sesquiterpenes were extracted from the aerial parts of Schaefferia argentinensis Speg. The in vitro antiproliferative activity was studied in T47D, MCF-7, and MDA-MB231 human cancer cell lines which showed IC50 value of > 68.1 uM.[34]

A new sesquiterpene lactones dehydrooopodin (5) was obtained from Ferula oopoda roots. The configuration of this compound was deciphered by 1D and 2D NMR. Antiproliferative activity of compounds was tested against MCF-7 and K562 by alamarBlue assay. The compound isolated showed significant cytotoxicity with IC50 values of 15 and 5 mM, respectively.[35]

 Triterpene



Structure of all the compounds has been drawn and shown in [Figure 4]; [Table 4] shows the details of compounds. Lupeol (54) was isolated from Dillenia indica L. Using sulforhodamine B method, ethanolic extract of fruits, stems, and leaves was evaluated for cytotoxicity against following sulforhodamine B method the cytotoxicity of ethanolic extracts of leaves, stems and fruits, was evaluated against two cell lines: colon carcinoma cell line (HCT-116) and liver carcinoma cell line (HEPG2) which showed an IC50 value of 9.8 μg and 20.1 μg respectively.[36]{Figure 4}{Table 4}

Alisma orientalis rhizome led to identification of protostane-type triterpenoids, alisol B (3) (55), and alisol B 23-acetate (4) (56), and the compound showed cytotoxic activity against HepG2, MDA-MB231, and MCF-7 with IC50 values of 16.28, 14.47, and 6.66 μM for compound 3 and 18.01, 15.97, and 13.56 μM for compound 4, respectively.[37]

A novel triterpene kaunial (57) was flowers of Kaunia lasiophthalma G. which was identified whose structure was deciphered by spectroscopic data. The cytotoxic activity was tested in contradiction to HCC1937, JIMT-1, L56Br-C1, MCF-7, and SK-BR-3 breast cancer cell line. It was compared against MCF-10A which is normal-like breast epithelial cell line. Compound 1 was found most potent against all evaluated cell line bearing IC50 value between 0.67 and 7.0 mM.[38]

Two compounds 30-hydroxy-11α-methoxy-18 β-olean-12-en-3-one' (58) and Asiatic acid (59) were identified from acetonic/ethanolic extract of the leaves of Maytenus procumbens (LMP). In cytotoxic activity against HeLa, CACO-2, NIH3T3, T47D, and HT29 cell lines, LMP exhibited IC50 of 51.22, 68.79, 76.59, 76.64, and 78.49 μg/ml, respectively.[39]

The ethanolic extract of branching shoot of Euscaphis japonica led to identification of euscaphic acids G, (60) Hederagenin, (61) Arjunic acid (62), the isolated compounds were evaluated for its cytotoxic activity against NCIH460 cells, HT-29 cells, and CEM cells resulting in IC50 of 1.64 ± 0.87, 2.11 ± 1.54, 1.73 ± 0.64 μM, respectively.[40]

Four new triterpenoid schisanlactone C (8) (63), schisanlactone D (14) (64), schisanlactone H (11) (65), and kadsulactone (15) (66) were identified from the fruit of Schisandra glaucescens Diels. In contradiction to B16 cell lines, compound displayed cytotoxic effect with IC50 values ranging from 3.64 to 27.00 μM.[41]

New triterpenoids triregeloic acid (3) (67) was identified from the stems of Tripterygium regelii. Compound structure was identified by analyzing their NMR spectroscopic and HRESIMS data. The cytotoxicity was tested against MCF-7 which showed inhibitory effects of 24.1%.[42]

From the leaves and branches of Abies faxoniana, a novel triterpenoid 3-oxo-9-lanosta-722Z, 24-trien-26,23-olide (68) was isolated. Compound showed cytotoxicities in contradiction to MCF-7 and A549 cells showing IC50 values of 6.5 and 5.7 μM, respectively.[43]

New triterpenoid 20-hydroxy-24-dammare-n 3-one (11) (69), bourjotinolone B (17) (70), (20S, 24R) epoxydammarane-12, 25-diol-3-one (4) (71), and methyl shoreate (6) (72) were isolated from the stem bark of Toona sinensis. Compound structure was determined by extensive spectroscopic techniques, comprising 1D-, 2D-NMR, and HR-ESI-MS experimental data. The compound showed cytotoxic effect against SGC-7901 which showed IC50 value of 9.8, 6.1, 24.6, and 23.2 μM.[44]

Brachyantheraoside A2 (73) (compound 9) was isolated from air-dried plants of Stauntonia brachyanthera. The compound showed cytotoxic activity against UGT1A having IC50 value of 16.3 μM.[45]

Ethanolic extract of Chrysosplenium carnosum led to the isolation of 6 β-hydroxy-3-oxoolean-12-en-27-oic acid (1) (74), 3 β,6 β-dihydroxy-olean-12-en-27-oic acid (3) (75) and 3β, 24β dihydroxyolean-12-en-27-oic acid (4) (76). Spectroscopic method was used to determine their structure. The compound showed inhibitory activity in contradiction to B16F10 and SP2/0 cells with IC50 value of 15.7–18.3 μM and from 13.1 to 31.5 μM.[46]

Compound urmiensolide B (1) (77) and urmiensic acid (2) (78) with unique carbon backbones were identified from the shoots of Salvia urmiensis Bunge. Identified compounds showed inhibitory activity in contradiction to MCF-7 cells showing IC50 values of 2.8 and 1.6 μM, respectively.[47]

Neoabiestrine F (6) (79) was isolated from Abies recurvata. Its configuration was determined by NMR and MS spectroscopic data. Compound exhibited cytotoxicity against THP-1 tumor cells with an IC50 value of 17.8 μg/mL.[48]

From seeds of Cipadessa baccifera, two limonoids cipaferen H (80) and granatumin E (81) were identified. The compound showed antiproliferative effect in contradiction to B16, ACHN cell lines showing an IC50 value of 8.51 and 7.0 μg/mL.[49]

The Abies faxoniana leaves and branches led to identification of compound neoabieslactone I whose structure was predicted by CD and spectroscopic technique. Compound was found active in contradiction to HCT-116, MCF-7, and A549 cell lines with IC50 values of 8.9, 7.6, and 4.2 μM, respectively.[50]

 Conclusion



The inclination toward natural product has led the onset for the discovery of new bioactive metabolites that could be targeted for specific therapeutic use. As terpenoid is the largest class of secondary metabolites being produced by plants with its bioactivity against cancer cell lines, it serves a potential drug candidate. A number of compounds of terpenoid family have been highlighted in the review. Plant-based terpenoid constituents can subside nuclear factor-κB (NF-κB) signaling, the major regulator in the pathway of cancer. Various ranges of metabolites have been isolated, and their structures have been deciphered using the advance analytical techniques which serve a base in the development of drugs. The novel scaffolds identified could be treated as potential candidates for the treatment of various types of cancer. The future prospect offers the work to be carried out in areas of process optimization, epigenetic modification, better germplasm selection, and use of plant tissue culture technique to enhance the yield of bioactive metabolites to significant level. There is immense potential to use these metabolites in the development of cheaper more sustainable anticancer drug.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

References

1Kathiresan K, Boopathy NS, Kavitha S. Coastal vegetation – An underexplored source of anticancer drugs. Indian Journal of Natural products and Resources 2006;5:115-9.
2Chin YW, Balunas MJ, Chai HB, Kinghorn AD. Drug discovery from natural sources. AAPS J 2006;8:E239-53.
3Strohl WR. The role of natural products in a modern drug discovery program. Drug Discov Today 2000;5:39-41.
4Prakash V. Terpenoids as source of anti-inflammatory compounds. Asian J Pharm Clin Res 2017;10:68-76.
5Baker JT, Borris RP, Carté B, Cordell GA, Soejarto DD, Cragg GM, et al. Natural product drug discovery and development: New perspectives on international collaboration. J Nat Prod 1995;58:1325-57.
6Ma K, Wang JS, Luo J, Yang MH, Yao HQ, Sun HB, et al. Bistabercarpamines A and B, first vobsasinyl-chippiine-type bisindole alkaloid from Tabernaemontana corymbosa. Tetrahedron Lett 2014;55:101-4.
7Bakarnga-Via I, Hzounda JB, Fokou PV, Tchokouaha LR, Gary-Bobo M, Gallud A, et al. Composition and cytotoxic activity of essential oils from xylopia aethiopica (Dunal) A. Rich, Xylopia parviflora (A. Rich) benth.) and Monodora myristica (Gaertn) growing in chad and Cameroon. BMC Complement Altern Med 2014;14:125.
8Chaipukdee N, Kanokmedhakul K, Kanokmedhakul S, Lekphrom R, Pyne SG. Two new bioactive iridoids from Rothmannia wittii. Fitoterapia 2016;113:97-101.
9Rassouli FB, Matin MM, Iranshahi M, Bahrami AR. Investigating the cytotoxic and apoptosis inducing effects of monoterpenoid stylosin in vitro. Fitoterapia 2011;82:742-9.
10Girardot M, Deregnaucourt C, Deville A, Dubost L, Joyeau R, Allorge L, et al. Indole alkaloids from Muntafara sessilifolia with antiplasmodial and cytotoxic activities. Phytochemistry 2012;73:65-73.
11Menon DB, Gopalakrishnan VK. Terpenoids isolated from the shoot of Plectranthus hadiensis induces apoptosis in human colon cancer cells via the mitochondria-dependent pathway. Nutr Cancer 2015;67:697-705.
12Jiang ZY, Zhu LY, Zhou J, Hu QF, Yang GY, Huang XZ, et al. A novel C22 terpenoid from the cultured Perovskia atriplicifolia. Helv Chim Acta 2016;99:452-6.
13Lv C, Sun W, Sun H, Wei S, Chen R, Wang B, et al. Asperolide A, a marine-derived tetranorditerpenoid, induces G2/M arrest in human NCI-H460 lung carcinoma cells, is mediated by p53-p21 stabilization and modulated by ras/Raf/MEK/ERK signaling pathway. Mar Drugs 2013;11:316-31.
14Ravikumar YS, Mahadevan KM, Manjunatha H, Satyanarayana ND. Antiproliferative, apoptotic and antimutagenic activity of isolated compounds from Polyalthia cerasoides seeds. Phytomedicine 2010;17:513-8.
15Xu X, Yuan J, Zhou X, Li W, Zhu N, Wu H, et al. Cassane diterpenes with oxygen bridge from the seeds of Caesalpinia sappan. Fitoterapia 2016;112:205-10.
16Wu CY, Liao Y, Yang ZG, Yang XW, Shen XL, Li RT, et al. Cytotoxic diterpenoids from Salvia yunnanensis. Phytochemistry 2014;106:171-7.
17Kuźma L, Wysokińska H, Różalski M, Krajewska U, Kisiel W. An unusual taxodione derivative from hairy roots of Salvia austriaca. Fitoterapia 2012;83:770-3.
18Zhong R, Guo Q, Zhou G, Fu H, Wan K. Three new labdane-type diterpene glycosides from fruits of Rubus chingii and their cytotoxic activities against five humor cell lines. Fitoterapia 2015;102:23-6.
19Akter R, Uddin S J, Tiralongo J, Grice I D, & Tiralongo E. A new cytotoxic diterpenoid glycoside from the leaves of Blumea lacera and its effects on apoptosis and cell cycle. Nat Prod Res 2016;30:2688-93.
20Kamauchi H, Kon T, Kinoshita K, Takahashi K, Koyama K. Three new terpenoids, sterebins O, P1, and P2, isolated from stevia Rebaudiana fermented by saccharomyces cerevisiae. Tetrahedron Lett 2014;55:7203-5.
21Bommareddy A, Crisamore K, Fillman S, Brozena S, Steigerwalt J, Landis T, et al. Survivin down-regulation by α-santalol is not mediated through PI3K-AKT pathway in human breast cancer cells. Anticancer Res 2015;35:5353-7.
22Chen WH, Han CR, Hui Y, Zhang DS, Song XM, Chen GY, Song XP. Terpenoids from the Stems of Drypetes congestiflora. Helvetica Chimica Acta 2015;98:724-30.
23Huang J, Han HY, Li GY, Wang HY, Zhang C, Zhang K, et al. Two new terpenoid benzoates with antitumor activity from the roots of ferula Dissecta. J Asian Nat Prod Res 2013;15:1100-6.
24Wang S, Li J, Sun J, Zeng KW, Cui JR, Jiang Y, et al. NO inhibitory guaianolide-derived terpenoids from Artemisia argyi. Fitoterapia 2013;85:169-75.
25Ou-Yang DW, Wu L, Li YL, Yang PM, Kong DY, Yang XW, et al. Miscellaneous terpenoid constituents of Abies nephrolepis and their moderate cytotoxic activities. Phytochemistry 2011;72:2197-204.
26Ouyang DW, Ni X, Xu HY, Chen J, Yang PM, Kong DY, et al. Pterosins from pteris multifida. Planta Med 2010;76:1896-900.
27Wu QH, Liu CM, Chen YJ, Gao K. Terpenoids from the roots of Ligularia muliensis. Helv Chim Acta 2006;89:915-22.
28Julianti T, Hata Y, Zimmermann S, Kaiser M, Hamburger M, Adams M, et al. Antitrypanosomal sesquiterpene lactones from Saussurea costus. Fitoterapia 2011;82:955-9.
29Xie WD, Wang XR, Ma LS, Li X, Row KH. Sesquiterpenoids from carpesium divaricatum and their cytotoxic activity. Fitoterapia 2012;83:1351-5.
30Mu W, Tang H, Li Y, He D, Ma R, Wang L, et al. Caesalpinone A, a new type of gorgonane sesquiterpenoid containing an unprecedented 1,15-bridge, from the pods of Caesalpinia spinosa kuntze. Fitoterapia 2016;112:233-6.
31Xia JH, Zhang SD, Li YL, Wu L, Zhu ZJ, Yang XW, et al. Sesquiterpenoids and triterpenoids from Abies holophylla and their bioactivities. Phytochemistry 2012;74:178-84.
32Weng JR, Yen MH, Lin WY. Cytotoxic constituents from Celastrus paniculatus induce apoptosis and autophagy in breast cancer cells. Phytochemistry 2013;94:211-9.
33Liu Q, Ahn JH, Kim SB, Lee C, Hwang BY, Lee MK. Sesquiterpene lactones from the roots of Lindera strychnifolia. Phytochemistry 2013;87:112-8.
34García ME, Motrich RD, Caputto BL, Sánchez M, Palermo JA, Estévez-Braun A, et al. Agarofuran sesquiterpenes from Schaefferia argentinensis. Phytochemistry 2013;94:260-7.
35Kasaian J, Iranshahy M, Masullo M, Piacente S, Ebrahimi F, Iranshahi M, et al. Sesquiterpene lactones from ferula oopoda and their cytotoxic properties. J Asian Nat Prod Res 2014;16:248-53.
36Abdel-Kader EM, Shakour ZT. Phytochemical and cytotoxicity investigations of Dillenia indica L. Grown in Egypt. World J Pharm Res 2015;4:334-47.
37Xu W, Li T, Qiu JF, Wu SS, Huang MQ, Lin LG, et al. Anti-proliferative activities of terpenoids isolated from Alisma orientalis and their structure-activity relationships. Anticancer Agents Med Chem 2015;15:228-35.
38Maldonado EM, Svensson D, Oredsson SM, Sterner O. A novel cytotoxic terpenoid from the flowers of Kaunia Lasiophthalma Griseb. Phytochem Lett 2014;8:105-8.
39Momtaz S, Hussein AA, Ostad SN, Abdollahi M, Lall N. Growth inhibition and induction of apoptosis in human cancerous HeLa cells by Maytenus procumbens. Food Chem Toxicol 2013;51:38-45.
40Zhang LJ, Cheng JJ, Liao CC, Cheng HL, Huang HT, Kuo LM, et al. Triterpene acids from Euscaphis japonica and assessment of their cytotoxic and anti-NO activities. Planta Med 2012;78:1584-90.
41Yu HY, Li J, Liu Y, Wu WM, Ruan HL. Triterpenoids from the fruit of Schisandra glaucescens. Fitoterapia 2016;113:64-8.
42Fan D, Parhira S, Zhu GY, Jiang ZH, Bai LP. Triterpenoids from the stems of Tripterygium regelii. Fitoterapia 2016;113:69-73.
43Wang GW, Lv C, Jin HZ, Shen YH, Zhang WD. Epimeric spirolactone-type triterpenoids from Abies faxoniana rehd. Fitoterapia 2016;113:91-6.
44Tang J, Xu J, Zhang J, Liu WY, Xie N, Chen L, et al. Novel tirucallane triterpenoids from the stem bark of Toona sinensis. Fitoterapia 2016;112:97-103.
45Liu D, Li S, Qi JQ, Meng DL, Cao YF. The inhibitory effects of nor-oleanane triterpenoid saponins from Stauntonia brachyanthera towards UDP-glucuronosyltransferases. Fitoterapia 2016;112:56-64.
46Lu MY, Liao ZX, Ji LJ, Sun HF. Triterpenoids of Chrysosplenium carnosum. Fitoterapia 2013;85:119-24.
47Farimani MM, Bahadori MB, Koulaei SA, Salehi P, Ebrahimi SN, Khavasi HR, et al. New ursane triterpenoids from Salvia urmiensis bunge: Absolute configuration and anti-proliferative activity. Fitoterapia 2015;106:1-6.
48Li YL, Gao YX, Yang XW, Jin HZ, Ye J, Simmons L, et al. Cytotoxic triterpenoids from Abies recurvata. Phytochemistry 2012;81:159-64.
49Siva B, Poornima B, Venkanna A, Prasad KR, Sridhar B, Nayak VL, et al. Methyl angolensate and mexicanolide-type limonoids from the seeds of Cipadessa baccifera. Phytochemistry 2014;98:174-82.
50Wang GW, Lv C, Yuan X, Ye J, Jin HZ, Shan L, et al. Lanostane-type triterpenoids from Abies faxoniana and their DNA topoisomerase inhibitory activities. Phytochemistry 2015;116:221-9.