Efficient access to isomeric 2,3-dihydroxy lupanes: first synthesis of alphitolic acid

Pentacyclic triterpenoids as potential ACL inhibitors from the rare medicinal plant Semiliquidambar cathayensis

An extensive phytochemical investigation on the rare medicinal plant Semiliquidambar cathayensis (family: Hamamelidaceae) led to the isolation of four new (1-4, named semiliquidacids A-D, respectively) and 25 related known pentacyclic triterpenoids. The new structures with absolute configurations were elucidated by spectroscopic methods, electronic circular dichroism (ECD) calculations, and single-crystal X-ray diffraction analysis. Compound 1 represents the first naturally occurring ursane-type triterpenoid featuring an uncommon C-25 formyl group. Compound 4 and oleanolic acid (13) exhibited remarkable inhibitory effects against the ATP-citrate lyase (ACL, an emerging drug target for hyperlipidemia and related metabolic disorders) with IC50 values of 6.5 and 11.9 μM, respectively. The molecular interaction and binding mode between the bioactive triterpenoids and ACL were elaborated by conducting a molecular docking study. Meanwhile, the chemotaxonomic significance of the isolated triterpenoids has been briefly discussed.

New Lupanes from Alstonia scholaris Reducing Uric Acid Level

Twelve lupanes including three new compounds named alstoscholarilups A-C (1: -3: ) were isolated from the leaves of Alstonia scholaris. Their structures were elucidated by spectroscopic analysis and ECD calculation. Structurally, compound 1: with a rare A ring-seco skeleton formed lactone and degraded C-3, while 2: with a 28-nor and 3: with a 29-nor-lupane skeleton supported the phytochemical diversity and novelty of the plant. Pharmacologically, compounds 4, 7: , and 10: reduced the serum uric acid (UA) levels of mice significantly.

Triterpene constituents from the fruits of Cyclocarya paliurus and their anti-HIV-1IIIB activity

Four new norceanothane-type triterpenes, cyclopalin A-D (1-4), and sixteen known compounds (5-20) were obtained from the fruits of Cyclocarya paliurus. Their structures were determined by spectroscopic data, experimental electronic circular dichroism (ECD) and X-ray single crystal analyses. All isolated compounds were assayed for their anti-HIV-1_IIIB activity. Compound 18 exhibited potent anti-HIV-1_IIIB activity with an EC₅₀ value of 1.32 μM (SI = 151.52).

Betulinic acid derived amides are highly cytotoxic, apoptotic and selective

Betulinic and platanic acid derived amides were prepared and screened for their cytotoxic activity. All of the compounds were shown to be cytotoxic for a panel of human tumor cell lines, and especially apoptotic betulinic acid derived compounds 6, 8 and 19 showed low EC₅₀ values. Of special interest was a 4-isoquinolinyl amide of 3-O-acetyl-betulinic acid (compound 19), being the most cytotoxic compound of this series and holding EC₅₀ values as low as EC₅₀ = 1.48 μM (A375 melanoma cells) while being significantly less cytotoxic for non-malignant fibroblasts NIH 3T3 with a selectivity index of >91.2. This finding parallels previous results obtained for SAA21, a augustic acid derived compound thus making the 4-isoquinolinyl moiety to a privileged scaffold.

Expedient Synthesis of Alphitolic Acid and Its Naturally Occurring 2- O-Ester Derivatives

The expedient synthesis of alphitolic acid (1) as well as its natural C-3-epimer and 2- O-ester derivatives was accomplished in a few steps from the readily commercially available betulin (9). A Rubottom oxidation delivered an α-hydroxy group in a stereo- and chemoselective manner. The diastereoselective reduction of the α-hydroxy ketone was key to accessing the 1,2-diol moiety of this class of natural products. Our concise and stereoselective synthetic protocol allowed the gram-scale synthesis of these natural products, which will facilitate future biological evaluations.

Anti-Proliferative Activity of Triterpenoids and Sterols Isolated from Alstonia scholaris against Non-Small-Cell Lung Carcinoma Cells

(1) Background: In China and South Asia, Alstonia scholaris (Apocynaceae) is an important medicinal plant that has been historically used in traditional ethnopharmacy to treat infectious diseases. Although various pharmacological activities have been reported, the anti-lung cancer components of A. scholaris have not yet been identified. The objective of this study is to evaluate the active components of the leaf extract of A. scholaris, and assess the anti-proliferation effects of isolated compounds against non-small-cell lung carcinoma cells; (2) Methods: NMR was used to identify the chemical constitutes isolated from the leaf extract of A. scholaris. The anti-proliferative activity of compounds against non-small-cell lung carcinoma cells was assessed by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay; (3) Results: Eight triterpenoids and five sterols were isolated from the hexane portion of A. scholaris, and structurally identified as: (1) ursolic acid, (2) oleanolic acid, (3) betulinic acid, (4) betulin, (5) 2β,3β,28-lup-20(29)-ene-triol, (6) lupeol, (7) β-amyrin, (8) α-amyrin, (9) poriferasterol, (10) epicampesterol, (11) β-sitosterol, (12) 6β-hydroxy-4-stigmasten-3-one, and (13) ergosta-7,22-diene-3β,5α,6β-triol. Compound 5 was isolated from a plant source for the first time. In addition, compounds 9, 10, 12, and 13 were also isolated from A. scholaris for the first time. Ursolic acid, betulinic acid, betulin, and 2β,3β,28-lup-20(29)-ene-triol showed anti-proliferative activity against NSCLC, with IC50 of 39.8, 40.1, 240.5 and 172.6 μM, respectively.; (4) Conclusion: These findings reflect that pentacyclic triterpenoids are the anti-lung cancer chemicals in A. scholaris. The ability of ursolic acid, betulinic acid, betulin, and 2β,3β,28-lup-20(29)-ene-triol to inhibit the proliferative activity of NSCLC can constitute a valuable group of therapeutic agents in the future.

Anti-Inflammatory Chemical Profiling of the Australian Rainforest Tree Alphitonia petriei (Rhamnaceae)

Chronic inflammation is an important pathological condition in many human diseases, and due to the side effects of the currently used non-steroidal anti-inflammatory drugs, discovery of novel anti-inflammatory drugs is of general interest. Anti-inflammatory activity guided compound isolation from the plant Alphitonia petriei led to the isolation of the known plant sterols emmolic acid (1), alphitolic acid (2), trans- and cis-coumaroyl esters of alphitolic acid (3 and 4) and betulinic acid (5). A detailed spectroscopic analysis led to the structure elucidation of the alphitolic acid derivatives (1–5), and the semi-synthetic emmolic acid acetate (6). When tested in LPS (Lipopolysaccharides) + IFN-γ (Interferon gamma) activated RAW 264.7 macrophages, all compounds except (1) exhibited potent anti-inflammatory activity (IC₅₀ values as low as 1.7 μM) in terms of downregulation of NO and TNF-α production, but also demonstrated some considerable cytotoxicity.

Cytotoxic Ceanothane- and Lupane-Type Triterpenoids from the Roots of Ziziphus jujuba

Ziziphus jujuba, a plant in the family Rhamnaceae, is used in several Asian countries as a food and traditional medicine. Fifteen new ceanothane-type (1-15) and three new lupane-type triterpenoids (16-18) were isolated from the roots of Z. jujuba, as well as 12 previously known triterpenoids (19-30). Their structures were elucidated by 1D and 2D NMR spectroscopic and HR mass spectrometric data analysis. Compounds 12 and 13 were found to possess a rare E-ring γ-lactone structure, and 14 was assigned as the first 2,28-dinorlupane derivative isolated as a natural product. Twenty-five of the isolates were examined for cytotoxicity against human hepatocellular carcinoma HepG2 cells, and compounds 6-8, 14, 17, 23, 25, 29, and 30 showed cytotoxicity with IC50 values ranging from 1.9 to 5.9 μM.

Protective effect and mechanism of action of lupane triterpenes from Cornus walteri in cisplatin-induced nephrotoxicity

The present study reports a renoprotective effect and the mechanism of action of lupane triterpenes isolated from Cornus walteri in cisplatin-induced renal toxicity. A phytochemical investigation of the MeOH extract of the stems and stem bark of C. walteri resulted in the isolation and identification of twelve lupane triterpenes. Among these, betulinic acid, 29-oxobetulinic acid, betulin 3-acetate, and lupeol ameliorated cisplatin-induced nephrotoxicity to 80% of the control value at 125 μM. Upregulated phosphorylation of JNK, ERK, and p38 following cisplatin treatment were markedly decreased after co-treatment with betulinic acid, 29-oxobetulinic acid, betulin 3-acetate, and lupeol. In addition, the protein expression level of cleaved caspase-3 and the percentage of apoptotic cells were also significantly reduced after co-treatment with betulinic acid, 29-oxobetulinic acid, betulin 3-acetate, and lupeol. These results show that blocking the MAPK signaling cascade plays a critical role in mediating the renoprotective effect of betulinic acid, 29-oxobetulinic acid, betulin 3-acetate, and lupeol isolated from C. walteri extract.

Discovery of triterpenoids as reversible inhibitors of α/β-hydrolase domain containing 12 (ABHD12)

Background

α/β-hydrolase domain containing (ABHD)12 is a recently discovered serine hydrolase that acts in vivo as a lysophospholipase for lysophosphatidylserine. Dysfunctional ABHD12 has been linked to the rare neurodegenerative disorder called PHARC (polyneuropathy, hearing loss, ataxia, retinosis pigmentosa, cataract). In vitro, ABHD12 has been implicated in the metabolism of the endocannabinoid 2-arachidonoylglycerol (2-AG). Further studies on ABHD12 function are hampered as no selective inhibitor have been identified to date. In contrast to the situation with the other endocannabinoid hydrolases, ABHD12 has remained a challenging target for inhibitor development as no crystal structures are available to facilitate drug design.

Methodology/Principal Findings

Here we report the unexpected discovery that certain triterpene-based structures inhibit human ABHD12 hydrolase activity in a reversible manner, the best compounds showing submicromolar potency. Based on structure activity relationship (SAR) data collected for 68 natural and synthetic triterpenoid structures, a pharmacophore model has been constructed. A pentacyclic triterpene backbone with carboxyl group at position 17, small hydrophobic substituent at the position 4, hydrogen bond donor or acceptor at position 3 accompanied with four axial methyl substituents was found crucial for ABHD12 inhibitor activity. Although the triterpenoids typically may have multiple protein targets, we witnessed unprecedented selectivity for ABHD12 among the metabolic serine hydrolases, as activity-based protein profiling of mouse brain membrane proteome indicated that the representative ABHD12 inhibitors did not inhibit other serine hydrolases, nor did they target cannabinoid receptors.

Conclusions/Significance

We have identified reversibly-acting triterpene-based inhibitors that show remarkable selectivity for ABHD12 over other metabolic serine hydrolases. Based on SAR data, we have constructed the first pharmacophore model of ABHD12 inhibitors. This model should pave the way for further discovery of novel lead structures for ABHD12 selective inhibitors.

Identification of pentacyclic triterpenes derivatives as potent inhibitors against glycogen phosphorylase based on 3D-QSAR studies

Naturally occurring pentacyclic triterpenes (PT), a novel class of inhibitors against glycogen phosphorylase (GP), hold promise for the treatment of type-2 diabetes and other diseases with disorders in glycogen metabolism. To identify novel and more potent GP inhibitors, the receptor-based comparative molecular field analysis (CoMFA) and comparative molecular similarity analysis (CoMSIA) approaches were performed to investigate the quantitative structure-activity relationships (QSAR) among 106 PT analogues. The validated models demonstrated that the elongated or bulky substitutions in C17 position and/or C2, C3 positions are favorable. Then based on the structural information extracted from these models, 56 derivatives were synthesized and biochemically tested in this study. The IC50 value of the most potent compound P50 was found to be 1.1 μM.