Tigliane-Type Diterpene Esters from the Fruits of Shirakiopsis indica and Their Anti-HIV Activity.

Four new diterpene esters, shirakindicans A-D (1-4), along with eight related known diterpene esters (5-12), were isolated from the fruits of the Bangladeshi medicinal plant Shirakiopsis indica. The structures of 1-4 were elucidated by spectroscopic data analysis and electronic circular dichroism (ECD) calculations. Shirakindican A (1) was assigned as a tigliane-type diterpene ester possessing an unusual 6ß-hydroxy-1,7-dien-3-one structure, while shirakindican B (2) exhibits a tiglia-1,5-dien-3,7-dione structure. The anti-HIV activities of the isolated diterpene esters were evaluated and showed significant activities for sapintoxins A (5) and D (11), with EC50 values of 0.0074 and 0.044 µM, respectively, and TI values of 1 100 and 5 290. Sapatoxin A (12) also exhibited anti-HIV activity with an EC50 value of 0.13 µM and a TI value of 161.

Bioactivity inspired C19-diterpenoid alkaloids for overcoming multidrug-resistant cancer.

The pharmacological activities of C19-diterpenoid alkaloids are related to their basic skeletons (e.g., aconitine-type or lycoctonine-type). Also, few studies have been reported on the chemosensitizing effects of diterpenoid alkaloids. Consequently, this study was aimed at determining the chemosensitizing effects of synthetic derivatives of lycoctonine-type C19-diterpenoid alkaloids on a P-glycoprotein (P-gp)-overexpressing multidrug-resistant (MDR) cancer cell line KB-VIN. The acyl-derivatives of delpheline and delcosine showed moderate cytotoxicity against chemosensitive cancer cell lines. Among non-cytotoxic synthetic analogs (1-14), several derivatives effectively and significantly sensitized MDR cells by interfering with the drug transport function of P-gp to three anticancer drugs, vincristine, paclitaxel, and doxorubicin. The chemosensitizing effect of derivatives 2, 4, and 6 on KB-VIN cells against vincristine were more potent than 5 µM verapamil, and derivatives 4 and 13 were more effective than 5 µM verapamil for paclitaxel. Among them, 2 in particular increased the sensitivity of KB-VIN cells to vincristine by 253-fold.

Eleven new C19-diterpenoid alkaloids from Delphinium elatum cv. Pacific Giant.

Diterpenoid alkaloids, the main components of plants of the genera Aconitum, Delphinium, and Garrya, are a group of natural products with notable chemical properties and biological activities. Several C19-diterpenoid alkaloid components from Delphinium elatum cv. Pacific Giant, as well as their derivatives, exhibited cytotoxic activity against lung, prostate, cervical, and vincristine-resistant cervical cancer cell lines. In the current phytochemical investigation on the seeds of D. elatum cv. Pacific Giant, eleven new C19-diterpenoid alkaloids, elapaciline (1), meladine (2), melapacitine (3), iminoeladine (4), 19-oxopaciline (5), 19-oxopacinine (6), N-deethyldelpheline (7), N-deethylpacinine (8), N-deethyl-19-oxoeladine (9), N-deethyl-N-formyleladine (10), and N-deethyl-N-formyldelpheline (11), together with 15 known C19-diterpenoid alkaloids were isolated. Their structures were elucidated by extensive spectroscopic methods including NMR (1D and 2D), IR, and MS (HRMS). Three known diterpenoid alkaloids, 6-dehydrodelcorine (12), delelatine (23), and 6-dehydroeldelidine (24), were isolated for the first time from this plant. Six of the new C19-diterpenoid alkaloids (2, 4-7, and 11) and three of the known diterpenoid alkaloids (18, 23, and 24) were evaluated for cytotoxic activity against five human tumor cell lines.

Identification of anti-HIV macrocyclic daphnane orthoesters from Wikstroemia ligustrina by LC-MS analysis and phytochemical investigation.

Macrocyclic daphnane orthoesters (MDOs) have attracted significant research interest for the drug discovery to cure HIV infection based on the "Shock and Kill" strategy. In the present study, the first chemical study on Wikstroemia ligustrina (Thymelaeaceae) was carried out by LC-MS analysis and phytochemical investigation. Nine daphnane diterpenoids (1-9) including seven MDOs were detected by LC-MS analysis. Further phytochemical investigation resulted in the isolation and structural elucidation of five daphnanes (1, 2, 5, 8, and 9) with potent anti-HIV activity. Taking the isolated MDO (1) as a model compound, the MS/MS fragmentation pathway was also elucidated.

Hyperdioxanes, dibenzo-1,4-dioxane derivatives from the roots of Hypericum ascyron.

Six dibenzo-1,4-dioxane derivatives (1-6) were isolated from the roots of a Hypericaceous plant Hypericum ascyron. Spectroscopic analyses revealed 2 and 4-6 to be new compounds. The partial racemic natures of 1-3 were concluded by chiral HPLC analyses, while 5 was confirmed to be a racemate. The absolute configurations 1-4 were deduced on the basis of ECD calculations. Biological activity evaluation of the dibenzo-1,4-dioxane derivatives along with two related compounds: hyperdioxanes A (7) and B (8), previously isolated from the same plant material by our group demonstrated that 7 exhibit an anti-HIV activity (IC50 5.3 µM, TI 7.2) while 8 showed an inhibitory effect on IL-1ß production (inhibition rate: 72.3% at 6.3 µM) from LPS-stimulated microglial cells.

Sesquiterpene Lactone Deoxyelephantopin Isolated from Elephantopus scaber and Its Derivative DETD-35 Suppress BRAFV600E Mutant Melanoma Lung Metastasis in Mice.

Melanoma is a highly metastatic disease with an increasing rate of incidence worldwide. It is treatment refractory and has poor clinical prognosis; therefore, the development of new therapeutic agents for metastatic melanoma are urgently required. In this study, we created a lung-seeking A375LM5IF4g/Luc BRAFV600E mutant melanoma cell clone and investigated the bioefficacy of a plant sesquiterpene lactone deoxyelephantopin (DET) and its novel semi-synthetic derivative, DETD-35, in suppressing metastatic A375LM5IF4g/Luc melanoma growth in vitro and in a xenograft mouse model. DET and DETD-35 treatment inhibited A375LM5IF4g/Luc cell proliferation, and induced G2/M cell-cycle arrest and apoptosis. Furthermore, A375LM5IF4g/Luc exhibited clonogenic, metastatic and invasive abilities, and several A375LM5IF4g/Luc metastasis markers, N-cadherin, MMP2, vimentin and integrin α4 were significantly suppressed by treatment with either compound. Interestingly, DET- and DETD-35-induced Reactive Oxygen Species (ROS) generation and glutathione (GSH) depletion were found to be upstream events important for the in vitro activities, because exogenous GSH supplementation blunted DET and DETD-35 effects on A375LM5IF4g/Luc cells. DET and DETD-35 also induced mitochondrial DNA mutation, superoxide production, mitochondrial bioenergetics dysfunction, and mitochondrial protein deregulation. Most importantly, DET and DETD-35 inhibited lung metastasis of A375LM5IF4g/Luc in NOD/SCID mice through inhibiting pulmonary vascular permeability and melanoma cell (Mel-A+) proliferation, angiogenesis (VEGF+, CD31+) and EMT (N-cadherin) in the tumor microenvironment in the lungs. These findings indicate that DET and DETD-35 may be useful in the intervention of lung metastatic BRAFV600E mutant melanoma.

Paliasanines A-E, 3,4-Methylenedioxyquinoline Alkaloids Fused with a Phenyl-14-oxabicyclo[3.2.1]octane Unit from Melochia umbellata var. deglabrata.

Five new quinoline alkaloids, paliasanines A-E (1-5), and 17 known compounds (6-22) were isolated from a methanol extract of Melochia umbellata var. deglabrata leaves. Their chemical structures were elucidated by analysis of HRMS and 1D and 2D NMR spectroscopic data. Compounds 1-5 are the first naturally occurring 3,4-methylenedioxyquinolines incorporating an oxabicyclo[3.2.1]octane unit. Compounds 6 and 7 displayed selective cytotoxicity (IC50 5.9-8.4 µM) against A549 and MCF-7 cell lines, while compounds 1-5 were not active. Compounds 1-3 did not exhibit an anti-HIV effect in MT4 cells, although the related quinolone derivative waltherione A exhibited significant activity. These preliminary results indicate that the 3-methoxy-4-quinolone skeleton might be preferred for both antiproliferative and anti-HIV activities.

Recent advances in natural anti-HIV triterpenoids and analogs.

The human immunodeficiency virus/acquired immunodeficiency syndrome (HIV/AIDS) epidemic is one of the world's most serious health challenges. Although combination antiretroviral therapy provides effective viral suppression, current medicines used against HIV cannot completely eradicate the infectious disease and often have associated toxicities and severe side effects in addition to causing drug resistance. Therefore, the continued development of new antiviral agents with diverse structures and novel mechanisms of action remains a vital need for the management of HIV/AIDS. Natural products are an important source of drug discovery, and certain triterpenes and their analogs have demonstrated potential as pharmaceutical precursors for the treatment of HIV. Over the past decade, natural triterpenoids and analogs have been extensively studied to find new anti-HIV drugs. This review discusses the anti-HIV triterpenoids and analogs reported during the period of 2009-2019. The article includes not only a comprehensive review of the recent anti-HIV agent development from the perspective of medicinal chemistry, but also discusses structure-activity relationship analyses of the described triterpenoids.

Development of anti-influenza agents from natural products.

The influenza pandemic continues to threaten public health due to its high morbidity and mortality rates, despite some successes in antiviral research. Natural drugs are important alternative therapies in the treatment of and recovery from influenza and have been the subjects of intense investigation during the last few decades. Many reports have shown that the development of novel bioactive chemicals extracted from natural drugs has significant advantages. Oseltamivir is a successful case of an anti-influenza drug synthesized using two natural products, quinic acid, and shikimic acid, as starting materials. In China, traditional Chinese medicine (TCM) plays an important role in the treatment of influenza. TCM herbal extracts and prescriptions or their isolated bioactive constituents have shown significant therapeutic and preventive effects against influenza. For example, the roots of Isatis indigotica (Banlangen) fight viral infection by targeting both the virus and the host and have significantly different effects than those of synthetic chemicals. Lianhuaqingwen capsule exerts its anti-influenza activity by regulating the immune response to interfere with both viral and host reactions and might well be an alternative therapeutic option to treat influenza virus infection. This paper reviews the chemical ingredients, crude extracts, and TCM prescriptions with anti-influenza activity reported during the period of 2010-September 2019. We hope that this comprehensive review will not only fuel research on anti-influenza active natural products and TCM research but also provide a promising alternative candidate for further anti-influenza drug development.

Cucurbitane-Type Triterpenoids from the Vines of Momordica charantia and Their Anti-inflammatory Activities.

Seven new cucurbitane-type triterpenoids, kuguaovins A-G (1-7), and five known ones were isolated from the rattans of wild Momordica charantia. Their structures were established by spectroscopic data analyses, including 1D and 2D NMR, IR, and MS techniques. The absolute configurations of the cucurbitanes were determined from NOESY data and partially by X-ray crystallographic analysis. In pharmacological studies, compounds 1-7 and 9-12 exhibited weak anti-inflammatory effects (IC50 = 15-35 µM), based on an anti-NO production assay.

Wilforine resensitizes multidrug resistant cancer cells via competitive inhibition of P-glycoprotein.

BACKGROUND AND PURPOSE: Multidrug resistance (MDR) remains the main obstacle in cancer treatment and overexpression of P-glycoprotein (P-gp) is one of the most common causes of chemoresistance. The development of novel P-gp inhibitors from natural products is a prospective strategy to combat MDR cancers. Among the natural sesquiterpene compounds, sesquiterpene pyridine alkaloids exhibit various biological properties. Therefore, in the present study, we evaluated the modulatory effects of wilforine on P-gp expression and function. The molecular mechanisms and kinetic models of wilforine-mediated P-gp inhibition were further investigated. METHODS: The human P-gp stable expression cells (ABCB1/Flp-InTM-293) and human cervical cancer cells (sensitive: HeLaS3; MDR: KBvin) were used. The cell viability was assessed by SRB assay. The inhibitory effect of wilforine on P-gp efflux and the underlying mechanism were evaluated by assays for calcein-AM uptake, rhodamine123 and doxorubicin efflux, ATPase activity, real-time quantitative RT-PCR, apoptosis, and cell cycle analysis. Molecular docking was performed by the docking software CDOCKER with BIOVIA Discovery Studio 4.5 (D.S. 4.5). RESULTS: We found that wilforine significantly inhibited the efflux activity of P-gp in a concentration-dependent manner. Further kinetic analysis demonstrated that wilforine significantly inhibited P-gp efflux function by competitive inhibition and stimulated the basal P-gp ATPase activity. In addition, wilforine re-sensitized MDR cancer cells to chemotherapeutic drugs. The docking model indicated that wilforine was bound to residues of P-gp such as LEU884, LYS887, THR176 and ASN172. CONCLUSION: These results suggest a novel future therapeutic strategy for MDR cancer using wilforine as an adjuvant treatment with chemotherapy.

Anti-HIV tigliane diterpenoids from Reutealis trisperma.

Bioassay-guided fractionation of the n-butanol extract from the branches and leaves of Reutealis trisperma resulted in the isolation of six undescribed (crotignoids L ~ Q) together with two known (12-deoxyphorbol-13-hexadecanoate and 12-deoxyphorbol-13-myristate) tigliane diterpenoids. Their structures, especially the absolute configurations, were determined from extensive spectroscopic studies, including 2D NMR spectra, CD data analysis and electronic circular dichroism (ECD) calculations. All isolates were tested for anti-HIV activity against HL4-3 virus in MT4 cells. Except for crotignoid Q, the remaining seven tigliane diterpenoids exhibited potent anti-HIV activity with IC50 values ranging from 0.0023 to 4.03 µM.

Kalshiolin A, new lignan from Kalimeris shimadai.

The Asian plant Kalimeris shimadai has been used as food and ethnologic medicine for over a thousand years. In this study, we isolated and identified one new lignan, kalshiolin A (1), and 12 known lignans (2-13). The structures were characterized by the comprehensive analyses of spectroscopic data (HR-ESI-MS, IR, 1D, and 2D-NMR) and the absolute configuration of 1 was determined from ECD calculations. The new compound 1 was also screened for cytotoxic activity but did not show significant potency (IC50 35.9-43.3 µM) against A549, MDA-MB-231, MCF7, KB, and KB-VIN cell lines.

Cytotoxic diterpenoid alkaloid from Aconitum japonicum subsp. subcuneatum.

We explored new cytotoxic C19-diterpenoid alkaloid, lipojesaconitine (1), from rhizoma of Aconitum japonicum THUNB. subsp. subcuneatum (NAKAI) KADOTA. Two additional non-cytotoxic new C19-diterpenoid alkaloids, 10-hydroxychasmanine (2) and 3-hydroxykaracoline (3), together with eight known C19- and C20-diterpenoid alkaloids (4-11) were also isolated. Their structures were elucidated by extensive spectroscopic methods including NMR (1D and 2D), IR, and MS (HRMS). Six known diterpenoid alkaloids, foresticine (5), neolinine (6), aconicarchamine A (7), 9-hydroxynominine (8), kobusine (9), and torokonine (10), were isolated for the first time from A. japonicum subsp. subcuneatum. Alkaloid 1 showed cytotoxicity with IC50 values ranging from 6.0 to 7.3 µM against four human tumor cell lines, except a multidrug-resistant subline, suggesting that 1 was likely exported by P-glycoprotein.

Prenylated Acetophloroglucinol Dimers from Acronychia trifoliolata: Structure Elucidation and Total Synthesis.

The isolation of 12 secondary metabolites, including seven new acetophenone monomers, from the 50% CH3OH/CH2Cl2 extract (N089419-L/6) of Acronychia trifoliolata was reported previously. In the present work, three new prenylated acetophenone dimers (1-3) and five known dimers (4-8) were isolated, and their structures were elucidated by using various NMR spectroscopic techniques and HRMS. Among the new dimers, an unprecedented 4-isobutyl-3-isopropyltetrahydro-2H-pyran ring was observed in the structure of 1. This study is the first to report the formation of a 2H-pyran ring between two prenylated acetophloroglucinols. Only four related dimers have been reported before, and they were formylated phloroglucinol dimers from the family Eucalypteae. Compounds 2 and 3 are acrovestone-like dimers, and the structure of 3 was confirmed by total synthesis. The evaluation of the antiproliferative activity of isolated and synthesized acrovestone-like dimers indicated that a double bond in the prenyl-like moiety as found in the more active compounds might be important for mediating activity, while the pendant isobutyl group seems to be less important.

Synthesis and Structure-Activity Relationship Correlations of Gnidimacrin Derivatives as Potent HIV-1 Inhibitors and HIV Latency Reversing Agents.

Currently, due to the HIV latency mechanism, the search continues for effective drugs to combat this issue and provide a cure for AIDS. Gnidimacrin activates latent HIV-1 replication and inhibits HIV-1 infection at picomolar concentrations. This natural diterpene was able to markedly reduce the latent HIV-1 DNA level and the frequency of latently infected cells. Therefore, gnidimacrin is an excellent lead compound, and its anti-HIV potential merits further investigation. Twenty-nine modified gnidimacrin derivatives were synthesized and evaluated in assays for HIV replication and latency activation to establish which molecular structures must be maintained and which can tolerate changes that may be needed for better pharmacological properties. The results indicated that hydroxyl substituents at C-5 and C-20 are essential, while derivatives modified at 3-OH with aromatic esters retain anti-HIV replication and latent activation activities. The half-lives of the potent GM derivatives are over 20 h, which implies that they are stable in the plasm even though they contain ester linkages. The established structure-activity relationship should be useful in the development of gnidimacrin or structurally related compounds as clinical trial candidates.

Structure-activity relationships and evaluation of esterified diterpenoid alkaloid derivatives as antiproliferative agents.

Diterpenoid alkaloids with remarkable chemical properties and biological activities are frequently found in plants of the genera Aconitum, Delphinium, and Garrya. However, little information has been reported on the antiproliferative effects of the diterpenoid alkaloid constituents of Aconitum and Delphinium plants. C-1 and 14 esterifications of delcosine (1) were carried out to provide 39 new diterpenoid alkaloid derivatives (3-14, 16-29, 3a-7a, 9a, 13a, 13b, 14a, 14b, 16a, 17a, 24a, 35a). Selected compounds (3-14, 16-29, 3a-7a, 9a, 13a, 13b, 14a, 14b, 16a, 17a, 24a, 35a) were evaluated for antiproliferative activity against three to five human tumor cell lines including triple-negative breast cancer (TNBC) and P-glycoprotein (P-gp) overexpressing multidrug-resistant (MDR) subline. Several newly synthesized delcosine derivatives (6, 7, 13, 13a, 13b) showed substantial suppressive effects against all human tumor cell lines tested. In contrast, the natural alkaloids (1, 31, 33) showed no effect. Most of the active compounds were delcosine derivatives with two specific substitution patterns-C-1 and C-1,14. In particular, 1-acyldelcosine derivative (5-7) displayed more potency than 1,14-diacyldelcosine derivatives (5a-7a). These acylated alkaloid derivatives caused accumulation of TNBC cells at sub-G1 within 24 h. 1-Acylation of 1 appears to be critical for producing antiproliferative activity in this alkaloid class and a means to provide promising new leads for further development into antitumor agents.

New Dammarane-type Saponins from Gynostemma pentaphyllum.

Six new dammarane-type saponins, gypenosides CP1-6 (16), along with 19 known compounds 7⁻25, were isolated and characterized from the aerial parts of Gynostemma pentaphyllum. Among these compounds, eight dammarane-type saponins, 2, 5, 6, 7, 11, 12, 13, and 15, exhibited the greatest antiproliferative effects against two human tumor cell lines (A549 and HepG2).

Tenulin and isotenulin inhibit P-glycoprotein function and overcome multidrug resistance in cancer cells.

BACKGROUND: Multidrug resistance (MDR) in cancer is one of the main obstacles in treatment with chemotherapy. Drug efflux through P-glycoprotein is the major mechanism involved in MDR. A potential strategy to provide the best possible clinical outcomes is to develop P-glycoprotein (P-gp) inhibitors from natural products. PURPOSE: The present study investigated the effects of the natural sesquiterpene lactone tenulin and its derivative isotenulin on human P-gp; the mechanisms of kinetic interactions were also explored. METHODS: The human P-gp (ABCB1/Flp-In™-293) stable expression cells were established by using the Flp-In™ system. The effects of tenulin and isotenulin on cell viability were evaluated by SRB assays in established cell lines, sensitive cancer cell line (HeLaS3), and resistant cancer cell line (KB-vin). The transporter inhibition ability was evaluated by calcein-AM uptake assays. The P-gp inhibition kinetics of tenulin and isotenulin were evaluated by rhodamine123 and doxorubicin efflux assays. The ATPase activity was evaluated with the Pgp-Glo™ Assay System. RESULTS: Tenulin and isotenulin significantly inhibited the P-gp efflux function by stimulating P-gp ATPase activity. Tenulin and isotenulin interacted with the effluxes of rhodamine 123 and doxorubicin through a competitive and noncompetitive mechanism, respectively. The combinations of tenulin and isotenulin with chemotherapeutic drugs significantly resensitized MDR cancer cells. CONCLUSION: These results suggested that tenulin and isotenulin are potential candidates to be developed for synergistic treatment of MDR cancers.

Carbazole Alkaloids from Clausena anisum-olens: Isolation, Characterization, and Anti-HIV Evaluation.

Two new carbazole alkaloids (1,2) and six known carbazole alkaloids (3-8) were isolated from Clausena anisum-olens. Their structures were elucidated based on extensive spectroscopic analysis. All isolated compounds (1-8) were evaluated for their anti-HIV effects on virus replication in MT-4 lymphocytes infected by HIV-1NL4-3 Nanoluc-sec virus, and new carbazole alkaloid 1 exhibited anti-HIV activity with an EC50 value of 2.4 µg/mL and SI of 7.1.