Taraxasterane- and ursane-type triterpenes from Nerium oleander and their biological activities

Structure-Activity Relationship of Oleanane-Type Pentacyclic Triterpenoids on Nuclear Factor κB Activation and Intracellular Trafficking and N-Linked Glycosylation of Intercellular Adhesion Molecule-1

In our previous study, two oleanane-type pentacyclic triterpenoids (oleanolic acid and maslinic acid) were reported to affect the N-glycosylation and intracellular trafficking of intercellular adhesion molecule-1 (ICAM-1). The present study was aimed at investigating the structure-activity relationship of 13 oleanane-type natural triterpenoids with respect to the nuclear factor κB (NF-κB) signaling pathway and the expression, intracellular trafficking, and N-glycosylation of the ICAM-1 protein in human lung adenocarcinoma A549 cells. Hederagenin, echinocystic acid, erythrodiol, and maslinic acid, which all possess two hydroxyl groups, decreased the viability of A549 cells. Celastrol and pristimerin, both of which possess an α,β-unsaturated carbonyl group, decreased cell viability but more strongly inhibited the interleukin-1α-induced NF-κB signaling pathway. Oleanolic acid, moronic acid, and glycyrrhetinic acid interfered with N-glycosylation without affecting the cell surface expression of the ICAM-1 protein. In contrast, α-boswellic acid and maslinic acid interfered with the N-glycosylation of the ICAM-1 protein, which resulted in the accumulation of high-mannose-type N-glycans. Among the oleanane-type triterpenoids tested, α-boswellic acid and maslinic acid uniquely interfered with the intracellular trafficking and N-glycosylation of glycoproteins.

New triterpenoids from the aerial parts of the Uygur medicine Salvia deserta

Phytochemical investigation on the aerial parts of Salvia deserta led to the isolation of eight new pentacyclic triterpenoids including three oleanane- (1 - 3) and five ursane-type (4 - 8) triterpenoids, whose structures were elucidated based on extensive spectroscopic analysis and quantum chemical calculation. Weak immunosuppressive potency was observed for compounds 1, 2, and 4 - 8 via inhibiting the secretion of cytokines TNF-α and IL-6 in LPS-induced macrophages RAW264.7 at 20 μM. In addition, compounds 1, 2, and 4 - 6 exhibited moderate protective activity on t-BHP-induced oxidative injury in HepG2 cells.

Synergistic Combination of NAPROC-13 and NMR 13C DFT Calculations: A Powerful Approach for Revising the Structure of Natural Products

This article describes the structure revision of nine triterpenoids that have been reported corresponding to the same 13C NMR data set. In addition, 13C NMR calculation shows that some chemical shift assignments must be swapped. Our analysis improves the fit between the experimental and calculated data. Correcting misassigned structures and correctly assigning each signal is essential for elucidating new structurally related compounds. Furthermore, the ambiguity of several compounds, the structure of which differs in the literature and the Sci-Finder database, has been eliminated. Misassigned structures were found by chemical shift searches in NAPROC-13, and the results provide two or more different compounds with the same 13C NMR data. The process to determine the correct, most likely structural proposal in agreement with the experimental 13C NMR data was carried out by DFT calculations.

Interaction of Odoroside A, A Known Natural Cardiac Glycoside, with Na+/K+-ATPase

The nature of odoroside A, a cardiac glycoside (CG) extracted from Nerium oleander, as well as its chemical structure is quite similar to a well-known CG, ouabain possessing a steroid skeleton, a five-membered unsaturated lactone ring, and a sugar moiety as a common structure. Like ouabain, odoroside A inhibits the activity of Na⁺/K⁺-ATPase (NKA) and shows significant anticancer activity, however its inhibitory mechanism remains unknown. CGs show various physiological activities, including cardiotonic and anticancer activities, through the inhibition of NKA by direct interaction. Additionally, X-ray crystallographic analysis revealed the inhibitory mechanism of ouabain and digoxin in relation to NKA. By using different molecular modeling techniques, docking simulation of odoroside A and NKA was conducted based on the results of these X-ray crystallographic analyses. Furthermore, a comparison of the results with the binding characteristics of three known CGs (ouabain, digoxin, and digitoxin) was also conducted. Odoroside A fitted into the CG binding pocket on the α-subunit of NKA revealed by X-ray crystallography. It had key interactions with Thr797 and Phe783. Also, three known CGs showed similar interactions with Thr797 and Phe783. Interaction modes of odoroside A were quite similar to those of ouabain, digoxin, and digitoxin. Docking simulations indicated that the sugar moiety enhanced the interaction between NKA and CGs, but did not show enhanced NKA inhibitory activity because the sugar moiety was placed outside the entrance of active site. Thus, these results suggest that the inhibitory mechanism of odoroside A to NKA is the same as the known CGs.

Anti-hyperuricemic bioactivity of Alstonia scholaris and its bioactive triterpenoids in vivo and in vitro

ETHNOPHARMACOLOGY RELEVANCE

One folk use of Alstonia scholaris (L.) R. Br. in "Dai" ethno-medicine system is to treat gouty arthritis, which might be caused by hyperuricemia, but anti-hyperuricemic investigation of A. scholaris were rarely reported.

AIM OF THE STUDY

To verify anti-hyperuricemic property of A. scholaris, and explore its bioactive compounds in vivo and in vitro.

MATERIALS AND METHODS

The anti-hyperuricemic bioactivity of the non-alkaloids fraction and compounds were evaluated with potassium oxonate (PO) induced hyperuricemia mice model in vivo, and monosodium urate (MSU) induced human renal tubular epithelial cells (HK-2) was selected to test in vitro, respectively, with benzobromarone as the positive control. 11 triterpenoids were isolated by phytochemical methods and their structures were elucidated by spectroscopic analysis and ECD calculation.

RESULTS

The non-alkaloids fraction of A. scholaris decreased the serum uric acid (UA) level in mice model significantly at the doses of 100 mg/kg and 200 mg/kg, and then nine ursane- and two oleanane-triterpenoids including four new compounds (1-3 and 10) were isolated from the bioactive fraction, in which compounds 1, 4, 5, 6 and 10 exhibited better anti-hyperuricemic tendency in vitro by promoting the excretion of UA in MSU-induced HK-2 cell model at a concentration of 5 μM. Furthermore, compounds 1 and 4 were proved to reduce the serum UA level in mice significantly at 5 mg/kg in vivo.

CONCLUSIONS

The results supported the traditional use of A. scholaris in treating gouty arthritis, and also provided new bioactive triterpenoids for further chemical and pharmacological investigation.

Minor terpenoids from the stems and twigs of Rhododendron ovatum

Four minor undescribed terpenoids, including a monoterpenoid (1) and three triterpenoids (3, 6 and 7), together with 26 known terpenoids were isolated from the stems and twigs of Rhododendron Ovatum. Their structures were identified by extensive spectroscopic analyses and electronic circular dichroism (ECD) techniques. Compound 10 showed excellent cytotoxicity against human colon cancer cell (HCT-116) with IC₅₀ value of 2.56 μM. Compounds 9 and 19 exhibited partly inhibitory effects on nitric oxide production stimulated by lipopolysaccharide-induced neuroinflammation in microglia cells at 10 μM with inhibition ratios of 39.70% and 28.08%, respectively.

Structural Analysis of Diastereomeric Cardiac Glycosides and Their Genins Using Ultraperformance Liquid Chromatography-Tandem Mass Spectrometry

Ultraperformance liquid chromatography coupled with electrospray ionization tandem mass spectrometry (UPLC-ESI-MS/MS) is an economical and indispensable tool in natural product research to investigate novel metabolites, biomarker discovery, chemical diversity exploration, and structure elucidation. In this study, the structural analysis of 38 naturally occurring cardiac glycosides (CGs) in various tissues of Nerium oleander was achieved by the extensive use of mass spectrometry. The chemical diversity of CGs was described on the basis of characteristic MS/MS fragmentation patterns, accurate mass measurement, and published scientific information on CGs from Nerium oleander. It was observed that only six genins, viz., Δ¹⁶anhydrogitoxigenin, Δ¹⁶adynerigenin, gitoxigenin, oleandrigenin, digitoxigenin, and adynerigenine, produce 38 diverse chemical structures of CGs. Among them, 20 were identified as diastereomers having a difference in a sugar (l-oleandrose, β-d-diginose, and β-d-sarmentose) unit. However, the differentiation of diastereomeric CGs was not possible by only MS/MS fragments. Thus, the diastereomer's chromatographic elution order was assigned on the basis of the relative retention time (RRt) of two reference standards (odoroside A and oleandrin) among their diastereomers. Besides this, the in-source fragmentation of CGs and the MS/MS of m/z 325 and 323 disaccharide daughter ions also exposed the intrinsic structure information on the sugar units. The daughter ions m/z 162, 145, 113, 95, and 85 in MS/MS spectra indicated the abundance of l-oleandrose, β-d-diginose, and β-d-sarmentose sugars. At the same time, m/z 161, 143, 129, and 87 product ions confirmed the presence of a β-d-digitalose unit. As a result, the UPLC-ESI/TQD system was successfully utilized for the structure characterization of CGs in Nerium oleander tissues.

Leaf Extract of Nerium oleander L. Inhibits Cell Proliferation, Migration and Arrest of Cell Cycle at G2/M Phase in HeLa Cervical Cancer Cell

BACKGROUND

Cervical cancer is one of the most common gynaecological malignant tumors reported in women. Although a number of early screening and treatment options are available, mortality due to cervical cancer remains high. Nerium oleander L. is a potential medicinal plant that possesses a wide spectrum of pharmacological and physiological activities including anticancer activities.

OBJECTIVE

This study aims to evaluate the antiproliferative activity, inhibition of cell migration and cell cycle arrest by the chloroform extract of leaves of Nerium Oleander L. in HeLa cervical cancer cells. The chloroform extract of Catharanthus roseus which contains anti-cancer compounds, Vinblastin and Vincristin, was used as a positive control for this study.

METHODS

The chloroform extracts of Nerium oleander L. and Catharanthus roseus were prepared using the standard protocol. The cytotoxic effects were studied by MTT assay. Cell migration was studied by in vitro scratch assay. Analysis of the cell cycle was carried out by Propidium iodide staining and Flow Cytometry. The expression level of various proteins was evaluated by immunocytochemistry.

RESULTS

In this study, we showed that the leaf extract of Nerium oleander inhibited the growth of HeLa cervical cancer cells in culture and inhibited cell migration. Besides, it arrested the cell cycle at the G2/M phase. The Epidermal Growth Factor Receptor (EGFR) expression and phosphorylated p-Rb (Ser 780) level were significantly downregulated by leaf extract of Nerium oleander.

CONCLUSION

The extract of Nerium oleander L. contains potential bioactive compounds that inhibit HeLa cell proliferation, cell migration and arrest cell cycle at the G₂/M phase.

Recent Advances in the Semisynthesis, Modifications and Biological Activities of Ocotillol-Type Triterpenoids

Ginseng is one of the most widely consumed herbs in the world and plays an important role in counteracting fatigue and alleviating stress. The main active substances of ginseng are its ginsenosides. Ocotillol-type triterpenoid is a remarkably effective ginsenoside from Vietnamese ginseng that has received attention because of its potential antibacterial, anticancer and anti-inflammatory properties, among others. The semisynthesis, modification and biological activities of ocotillol-type compounds have been extensively studied in recent years. The aim of this review is to summarize semisynthesis, modification and pharmacological activities of ocotillol-type compounds. The structure-activity relationship studies of these compounds were reported. This summary should prove useful information for drug exploration of ocotillol-type derivatives.

Plant triterpenoid saponins: biosynthesis, in vitro production, and pharmacological relevance

The saponins are a diverse class of natural products, with a broad scale distribution across different plant species. Chemically characterized as triterpenoid glycosides, they posses a 30C oxidosqualene precursor-based aglycone moiety (sapogenin), to which glycosyl residues are subsequently attached to yield the corresponding saponin. Based on the chemically distinct aglycone moieties, broadly, they are divided into triterpenoid saponins (dammaranes, ursanes, oleananes, lupanes, hopanes, etc.) and the sterol glycosides. This review aims to present in detail the biosynthesis patterns of the different aglycones from a common precursor and their glycosylation patterns to yield the functionally active glycoside. The review also presents recent advances in the pharmacological activities of these saponins, particularly as potent anti-neoplastic pharmacophores, antioxidants, or anti-viral/antibacterial agents. Since alternate production pedestals for these pharmacologically important triterpenes via cell and tissue cultures are an attractive option for their sustainable production, recent trends in the variety and scale of in vitro production of plant triterpenoids have also been discussed.

Chemical, molecular and structural studies of Boswellia species: β-Boswellic Aldehyde and 3-epi-11β-Dihydroxy BA as precursors in biosynthesis of boswellic acids

The distribution and biosynthesis of boswellic acids (BAs) is scarce in current literature. Present study aims to elucidate the BAs biosynthetic and its diversity in the resins of Boswellia sacra and Boswellia papyrifera. Results revealed the isolation of new (3β, 11β-dihydroxy BA) and recently known (as new source, β-boswellic aldehyde) precursors from B. sacra resin along with α-amyrin. Following this, a detailed nomenclature of BAs was elucidated. The quantification and distribution of amyrins (3-epi-α-amyrin, β-amyrin and α-amyrin) and BAs in different Boswellia resins showed highest amyrin and BAs in B. sacra as compared with B. serrata and B. papyrifera. Distribution of BAs significantly varied in the resin of B. sacra collected from dry mountains than coastal trees. In B. sacra, high content of α-amyrin was found in the roots but it lacked β-amyrin and BAs. The leaf part showed traces of β-ABA and AKBA but was deficient in amyrins. This was further confirmed by lack of transcript accumulation of amyrin-related biosynthesis gene in leaf part. In contrast, the stem showed presence of all six BAs which are attributed to existence of resin-secretory canals. In conclusion, the boswellic acids are genus-specific chemical constituents for Boswellia species albeit the variation of the amounts among different Boswellia species and grades.

Enhancing anticancer activity through the combination of bioreducing agents and triterpenes

AIM

Triterpenes are natural compounds, whose wide biological activity predestines them for application as promising new chemotherapeutics. In this paper, we report the results of our investigations into the substitution of oleanolic acid with aromatic and nitroaromatic moieties acting as bioreducing agents.

RESULTS

The process of reduction of nitro groups was investigated through cyclic voltammetry, UV-Vis and electron paramagnetic resonance spectroelectrochemistry. The cytotoxic activity against selected cancer cell lines was determined, showing a significant increase in cytotoxicity when the triterpene is equipped with a nitroaromatic moiety.

CONCLUSION

We believe this approach to the functionalization is promising in terms of enhancing anticancer activity. We also indicate electrochemical techniques as advantageous preclinical screening methods for the identification of cytotoxic agents.

Betulinic acid and oleanolic acid, natural pentacyclic triterpenoids, interfere with N-linked glycan modifications to intercellular adhesion molecule-1, but not its intracellular transport to the cell surface

Betulinic acid (3β-hydroxy-20(29)-lupen-28-oic acid), oleanolic acid (3β-hydroxy-olean-12-en-28-oic acid), and ursolic acid (3β-hydroxy-urs-12-en-28-oic acid) are close structural isomers of natural pentacyclic triterpenoid carboxylic acids. We recently identified a unique biological effect of ursolic acid, its inhibition of the intracellular trafficking of glycoproteins. In the present study, we demonstrated that betulinic acid and oleanolic acid did not inhibit the interleukin-1α-induced expression of cell-surface intercellular adhesion molecule-1 (ICAM-1) in human lung carcinoma A549 cells. Nevertheless, betulinic acid and, to a lesser extent, oleanolic acid interfered with N-linked glycan modifications to ICAM-1 in a similar manner to castanospermine (an inhibitor of endoplasmic reticulum α-glucosidases I and II), but not swainsonine (an inhibitor of Golgi α-mannosidase II). Consistent with these results, betulinic acid and oleanolic acid inhibited yeast α-glucosidase activity, but not Jack bean α-mannosidase activity. Thus, to the best of our knowledge, this is the first study to show that betulinic acid and oleanolic acid interfere with N-linked glycan modifications to ICAM-1, but not its intracellular transport to the cell surface.

Ursolic acid, a natural pentacyclic triterpenoid, inhibits intracellular trafficking of proteins and induces accumulation of intercellular adhesion molecule-1 linked to high-mannose-type glycans in the endoplasmic reticulum

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Ursolic acid inhibits cell-surface expression of ICAM-1.

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Ursolic acid induces accumulation of high-mannose-type ICAM-1 in ER.

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Ursolic acid induces morphological changes of Golgi apparatus.

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Ursolic acid inhibits intracellular trafficking of proteins.

Ursolic acid (3β-hydroxy-urs-12-en-28-oic acid) is a natural pentacyclic triterpenoid that is present in many plants, including medicinal herbs, and foods. Ursolic acid was initially identified as an inhibitor of the expression of intercellular adhesion molecule-1 (ICAM-1) in response to interleukin-1α (IL-1α). We report here a novel biological activity: ursolic acid inhibits intracellular trafficking of proteins. Ursolic acid markedly inhibited the IL-1α-induced cell-surface ICAM-1 expression in human cancer cell lines and human umbilical vein endothelial cells. By contrast, ursolic acid exerted weak inhibitory effects on the IL-1α-induced ICAM-1 expression at the protein level. Surprisingly, we found that ursolic acid decreased the apparent molecular weight of ICAM-1 and altered the structures of N-linked oligosaccharides bound to ICAM-1. Ursolic acid induced the accumulation of ICAM-1 in the endoplasmic reticulum, which was linked mainly to high-mannose-type glycans. Moreover, in ursolic-acid-treated cells, the Golgi apparatus was fragmented into pieces and distributed over the cells. Thus, our results reveal that ursolic acid inhibits intracellular trafficking of proteins and induces the accumulation of ICAM-1 linked to high-mannose-type glycans in the endoplasmic reticulum.

Triterpenoids from the roots of Rhaphiolepis indica var. tashiroi and their anti-inflammatory activity

Two new triterpenoids, 2α,3β-dihydroxyolean-11,13(18)-dien-19β,28-olide (1) and 3β,5β-dihydroxyglutinol (2), together with eight known compounds (3-10) were isolated from the roots of Rhaphiolepis indica var. tashiroi (Rosaceae). The structures of 1-10 were determined by spectroscopic techniques. Among these isolates, 2α,3β-dihydroxyolean-13(18)-en-28-oic acid (9) exhibited inhibitory effect on N-formyl-methionyl-leucyl-phenylalanine (fMLP)-induced superoxide production, with an IC50 value of 16.50 μM.

Ursolic Acid Inhibits Na+/K+-ATPase Activity and Prevents TNF-α-Induced Gene Expression by Blocking Amino Acid Transport and Cellular Protein Synthesis

Pro-inflammatory cytokines, such as tumor necrosis factor (TNF)-α, induce the expression of a wide variety of genes, including intercellular adhesion molecule-1 (ICAM-1). Ursolic acid (3β-hydroxy-urs-12-en-28-oic acid) was identified to inhibit the cell-surface ICAM-1 expression induced by pro-inflammatory cytokines in human lung carcinoma A549 cells. Ursolic acid was found to inhibit the TNF-α-induced ICAM-1 protein expression almost completely, whereas the TNF-α-induced ICAM-1 mRNA expression and NF-κB signaling pathway were decreased only partially by ursolic acid. In line with these findings, ursolic acid prevented cellular protein synthesis as well as amino acid uptake, but did not obviously affect nucleoside uptake and the subsequent DNA/RNA syntheses. This inhibitory profile of ursolic acid was similar to that of the Na+/K+-ATPase inhibitor, ouabain, but not the translation inhibitor, cycloheximide. Consistent with this notion, ursolic acid was found to inhibit the catalytic activity of Na+/K+-ATPase. Thus, our present study reveals a novel molecular mechanism in which ursolic acid inhibits Na+/K+-ATPase activity and prevents the TNF-α-induced gene expression by blocking amino acid transport and cellular protein synthesis.

Characterization of the anticancer properties of monoglycosidic cardenolides isolated from Nerium oleander and Streptocaulon tomentosum

AIM OF THE STUDY

For identification of the active constituents we investigated the anticancer activity of cardenolides from Streptocaulon tomentosum Wight & Arn. (Asclepiadaceae) and from Nerium oleander L. (Apocynaceae) which are both used against cancer in the traditional medicine in their region of origin.

MATERIAL, METHODS AND RESULTS

The antiproliferative activity of cardenolides isolated from roots of Streptocaulon tomentosum (IC(50)<1-15.3 μM after 2 days in MCF7) and of cardenolide containing fractions from the cold aqueous extract of Nerium oleander leaves ("Breastin", mean IC(50) 0.85 μg/ml in a panel of 36 human tumor cell lines), their influence on the cellular viability and on the cell cycle (block at the G2/M-phase or at the S-phase in tumor cells, respectively) were determined using different cell lines. The murine cell line L929 and normal non-tumor cells were not affected. Bioactivity guided fractionation of Breastin resulted in the isolation of the monoglycosidic cardenolides oleandrine, oleandrigeninsarmentoside, neritaloside, odoroside H, and odoroside A (IC(50)-values between 0.010 and 0.071 μg/ml).

CONCLUSIONS

The observed anticancer activities of extracts and isolated cardenolides are in agreement with the ethnomedicinal use of Streptocaulon tomentosum and Nerium oleander. The most active anticancer compounds from both species are monoglycosidic cardenolides possessing the 3β,14β-dihydroxy-5β-card-20(22)-enolide structure with or without an acetoxy group at C-16. The results indicate that the cytotoxic effects are induced by the inhibition of the plasma membrane bound Na(+)/K(+)-ATPase.

Structural characterization of a pectic polysaccharide from Nerium indicum flowers

A polysaccharide fraction, J6, was isolated from the hot-water extract of flowers of oleander Nerium indicum Mill., using ethanol precipitation, cetyltrimethylammonium bromide (CTAB) complexing, anion-exchange chromatography and gel permeation chromatography. J6 was found to contain L-rhamnose, L-arabinose, D-galactose, and D-galacturonic acid, in the ratio of 10.1:49.8:30.1:10.0. Its structure was investigated by methylation analysis, periodate oxidation, Smith degradation, partial acid hydrolysis, electrospray ionization mass spectrometry and NMR spectroscopic methods. It was found that J6 is an RG-I type polysaccharide, which contains a rhamnogalacturonan backbone, with various branches attached to O-4 of L-rhamnose. The branches probably involve (1-->4)-beta-D-galactan, branched L-arabino-(1-->3)(1-->6)-beta-D-galactan, and (1-->5)-alpha-L-arabinan. J6 stimulated NO production of macrophage RAW264.7 cells in a preliminary test.

Odoroside A and ouabain inhibit Na+/K+-ATPase and prevent NF-kappaB-inducible protein expression by blocking Na+-dependent amino acid transport

Inflammatory cytokines, such as tumor necrosis factor (TNF)-alpha and interleukin-1 (IL-1), trigger the activation of transcription factor NF-kappaB that induces the expression of a variety of genes, including intercellular adhesion molecule (ICAM)-1. Odoroside A [3beta-O-(beta-D-diginosyl)-14-hydroxy-5beta,14beta-card-20(22)-enolide] was found to inhibit the cell-surface expression of ICAM-1 induced by TNF-alpha and IL-1 at comparable concentrations in human lung carcinoma A549 cells. In this study, the molecular mechanism underlying the inhibition of TNF-alpha-induced cell-surface ICAM-1 expression by odoroside A together with the specific Na(+)/K(+)-ATPase inhibitor ouabain was further investigated. Odoroside A and ouabain neither prevented IkappaBalpha degradation nor NF-kappaB translocation to the nucleus upon TNF-alpha stimulation. While odoroside A and ouabain had no inhibitory effect on the induction of ICAM-1 mRNA, they inhibited the TNF-alpha-induced ICAM-1 expression at the protein level. Consistent with these results, odoroside A and ouabain potently reduced de novo protein synthesis, largely due to its ability to block Na(+)-dependent transport of amino acids across the plasma membrane, but not to interfering with the translation machinery. As a direct molecular target, odoroside A was found to inhibit the ATP-hydrolyzing activity of Na(+)/K(+)-ATPase as potently as ouabain. These results clearly demonstrate that odoroside A and ouabain prevent NF-kappaB-inducible protein expression by blocking the Na(+)-dependent amino acid transport.

Triterpenoids

This review covers the isolation and structure determination of triterpenoids including squalene derivatives, protostanes, lanostanes, holostanes, cycloartanes, dammaranes, euphanes, tirucallanes, tetranortriterpenoids, quassinoids, lupanes, oleananes, friedelanes, ursanes, hopanes, isomalabaricanes and saponins. The literature from January 2005 to December 2006 is reviewed and 478 references are cited.