Synthesis and biological evaluation of new piplartine analogues as potent aldose reductase inhibitors (ARIs)

Computational metabolomics reveals overlooked chemodiversity of alkaloid scaffolds in Piper fimbriulatum

Plant specialized metabolites play key roles in diverse physiological processes and ecological interactions. Identifying structurally novel metabolites, as well as discovering known compounds in new species, is often crucial for answering broader biological questions. The Piper genus (Piperaceae family) is known for its special phytochemistry and has been extensively studied over the past decades. Here, we investigated the alkaloid diversity of Piper fimbriulatum, a myrmecophytic plant native to Central America, using a metabolomics workflow that combines untargeted LC-MS/MS analysis with a range of recently developed computational tools. Specifically, we leverage open MS/MS spectral libraries and metabolomics data repositories for metabolite annotation, guiding isolation efforts toward structurally new compounds (i.e., dereplication). As a result, we identified several alkaloids belonging to five different classes and isolated one novel seco-benzylisoquinoline alkaloid featuring a linear quaternary amine moiety which we named fimbriulatumine. Notably, many of the identified compounds were never reported in Piperaceae plants. Our findings expand the known alkaloid diversity of this family and demonstrate the value of revisiting well-studied plant families using state-of-the-art computational metabolomics workflows to uncover previously overlooked chemodiversity. To contextualize our findings within a broader biological context, we employed a workflow for automated mining of literature reports of the identified alkaloid scaffolds and mapped the results onto the angiosperm tree of life. By doing so, we highlight the remarkable alkaloid diversity within the Piper genus and provide a framework for generating hypotheses on the biosynthetic evolution of these specialized metabolites. Many of the computational tools and data resources used in this study remain underutilized within the plant science community. This manuscript demonstrates their potential through a practical application and aims to promote broader accessibility to untargeted metabolomics approaches.

Non-covalent binding of chlorogenic acid to myofibrillar protein improved its bio-functionality properties and metabolic fate

As natural antioxidants added to meat products, polyphenols can interact with proteins, and the acid-base environment influenced the extent of non-covalent and covalent interactions between them. This study compared the bio-functional characteristics and metabolic outcomes of the myofibrillar protein-chlorogenic acid (MP-CGA) complexes binding in different environments (pH 6.0 and 8.5). The results showed that CGA bound with MP significantly enhanced its antioxidant activity and inhibitory effect on metabolism enzymes. CGA bound deeply into the MP structure hydrophobic cavity at pH 6.0, which reduced its degradation by digestive enzymes, thus increasing its bio-accessibility from 59.5% to 71.6%. The digestion products of the two complexes exhibited significant differences, with the non-covalent MP-CGA complexes formed at pH 6.0 showing significantly higher concentrations of rhetsinine and piplartine, two well-known compounds to modulate diabetes. This study demonstrated that non-covalent binding between protein and polyphenol in the acidic environment held greater promising prospects for improving health.

The protective effect of PL 1-3 on D-galactose-induced aging mice

The aging population has become an issue that cannot be ignored, and research on aging is receiving increasing attention. PL 1-3 possesses diverse pharmacological properties including anti-oxidative stress, inhibits inflammatory responses and anti-apoptosis. This study showed that PL 1-3 could protect mice, especially the brain, against the aging caused by D-galactose (D-gal). D-gal could cause oxidative stress, inflammation, apoptosis and tissue pathological injury and so on in aging mice. The treatment of PL 1-3 could increase the anti-oxidative stress ability in the serum, liver, kidney and brain of aging mice, via increasing the total antioxidant capacity and the levels of anti-oxidative defense enzymes (superoxide dismutase, glutathione peroxidase, and catalase), and reducing the end product of lipid peroxidation (malondialdehyde). In the brain, in addition to the enhanced anti-oxidative stress via upregulating the level of the nuclear factor erythroid 2-related factor 2 and heme oxygenase 1, PL 1-3 could improve the dysfunction of the cholinergic system via reducing the active of acetylcholinesterase so as to increase the level of acetylcholine, increase the anti-inflammatory and anti-apoptosis activities via downregulating the expressions of pro-inflammatory cytokines (interleukin-6 and tumor necrosis factor-α) and pro-apoptosis proteins (Bcl-2 associated X protein and Caspase-3) in the D-gal-induced aging mice, to enhance the anti-aging ability via upregulating the expression of sirtuin 1 and downregulating the expressions of p53, p21, and p16. Besides, PL 1-3 could reverse the liver, kidney and spleen damages induced by D-gal in aging mice. These results suggested that PL 1-3 may be developed as an anti-aging drug for the prevention and intervention of age-related diseases.

Anti-inflammatory potential of turmeric, amla, and black pepper mixture against sepsis-induced acute lung injury in rats

Acute lung injury (ALI), is a severe inflammatory lung disease. We tested the prophylactic effect of a functional food mix comprising three anti-inflammatory plant products: turmeric, amla, and black pepper (TAB) against lipopolysaccharide (LPS)-induced ALI in rats. Two-month-old male Wistar rats were randomly divided into three groups: control (C), LPS (5 mg/kg), and LPS with TAB (TAB). After 6 h of LPS injection, the rats were sacrificed by cervical decapitation to collect the lung tissue. Results showed that TAB partially ameliorated LPS-induced increase in circulating inflammatory cytokines (TNFα and IL6) and significantly prevented lung histopathological changes. TAB also suppressed LPS-activated ER stress markers (GRP78, pIRE1, and CHOP) and apoptotic markers (caspase-3 and - 12) in the lung. The anti-inflammatory effects of the TAB support its potential use as an adjuvant to mitigate ALI. Importantly, TAB's ingredients have been used for centuries as part of the diet with limited or no toxic effects.

Anti-Diabetic Effects and Molecular Mechanisms of Amide Alkaloids from Piper longum Based on Network Pharmacology Integrated with Cellular Assays

Piper longum is a well-known spice and traditional medicine. It was revealed to possess anti-diabetic activity, but few information about its active component and underlying mechanism could be available. In this study, retrofractamides A (1) and C (2) isolated from P. longum showed potent inhibitory activity against PTP1B. Therefore, the potential mechanism was predicted by network pharmacology and molecular docking. PI3K/AKT was obtained as the most remarkable pathway against type 2 diabetes mellitus (T2DM), and AKT1 and GSK3β were yielded as the top two core targets of retrofractamides A (1) and C (2). Molecular docking of compounds with AKT1 and GSK3β showed strong binding affinity between them. Additionally, cellular experiments with a L6 cell model was conducted to further verify the above predictions. Results indicated that retrofractamides A (1) and C (2) exerted anti-diabetic effect via activating PI3K/AKT pathway, and they promoted glucose consumption, glucose uptake, glycogen synthesis and glycolysis.

Palladium-Catalyzed Cascade Carbonylation to α,β-Unsaturated Piperidones via Selective Cleavage of Carbon-Carbon Triple Bonds

A direct and selective synthesis of α,β-unsaturated piperidones by a new palladium-catalyzed cascade carbonylation is described. In the presented protocol, easily available propargylic alcohols react with aliphatic amines to provide a broad variety of interesting heterocycles. Key to the success of this transformation is a remarkable catalytic cleavage of the present carbon-carbon triple bond by using a specific catalyst with 2-diphenylphosphinopyridine as ligand and appropriate reaction conditions. Mechanistic studies and control experiments revealed branched unsaturated acid 11 as crucial intermediate.

The promising potential of piperlongumine as an emerging therapeutics for cancer

In spite of the immense advancement in the diagnostic and treatment modalities, cancer continues to be one of the leading causes of mortality across the globe, responsible for the death of around 10 million patients every year. The foremost challenges faced in the treatment of this disease are chemoresistance, adverse effects of the drugs, and the high cost of treatment. Though scientific studies over the past few decades have foreseen and are focusing on the cancer-preventive and therapeutic potential of natural products and their underlying mechanism of action, many more of these agents are not still explored. Piperlongumine (PL), or piplartine, is one such alkaloid isolated from Piper longum Linn. which is shown to be safe and has significant potential in the prevention and therapy of cancer. Numerous shreds of evidence have established the ability of this alkaloid and its analogs and nanoformulations in modulating various complex molecular pathways such as phosphatidylinositol-3-kinase/protein kinase B /mammalian target of rapamycin, nuclear factor kappa-B, Janus kinases/signal transducer and activator of transcription 3, etc. and inhibit different hallmarks of cancer such as cell survival, proliferation, invasion, angiogenesis, epithelial-mesenchymal-transition, metastases, etc. In addition, PL was also shown to inhibit radioresistance and chemoresistance and sensitize the cancer cells to the standard chemotherapeutic agents. Therefore, this compound has high potential as a drug candidate for the prevention and treatment of different cancers. The current review briefly reiterates the anti-cancer properties of PL against different types of cancer, which permits further investigation by conducting clinical studies.

Overview of piperlongumine analogues and their therapeutic potential

Natural products have long been an important source for discovery of new drugs to treat human diseases. Piperlongumine (PL) is an amide alkaloid isolated from Piper longum L. (long piper) and other piper plants and has received widespread attention because of its diverse biological activities. A large number of PL derivatives have been designed, synthesized and assessed in many pharmacological functions, including antiplatelet aggregation, neuroprotective activities, anti-diabetic activities, anti-inflammatory activities, anti-senolytic activities, immune activities, and antitumor activities. Among them, the anti-tumor effects and application of PL and its derivatives are most extensively studied. We herein summarize the development of PL derivatives, the structure and activity relationships (SARs), and their therapeutic potential on the treatments of various diseases, especially against cancer. We also discussed the challenges and future directions associated with PL and its derivatives in these indications.

Chemical profile, traditional uses, and biological activities of Piper chaba Hunter: A review

ETHNOPHARMACOLOGICAL RELEVANCE

Piper chaba Hunter, called Chui Jhal or Choi Jhal, is commonly used as a culinary (spice) herb in India and Bangladesh. It exhibits numerous important biological activities and has been widely used in traditional medicine.

AIM OF THE STUDY

This review focuses on the chemical and pharmacological activities of a culinary ingredient P. chaba based on information extracted from the literature to highlight its use in traditional medicine.

METHODS

A literature search in known databases was conducted (till September 2019) for published articles using the relevant keywords.

RESULTS

Findings suggest that, to date, a number of important phytoconstituents such as dimeric alkaloids, and alkamides have been isolated from various parts of P. chaba. Extracts from P. chaba or derived compounds exhibit diverse biological activities, such as anti-microbial, anti-leishmanial, anti-malarial, anti-parasitic, cytotoxic/anticancer, adipogenic, hepato- and gastro-protective, anti-diabetic, analgesic, anti-diarrheal, depressive, anti-inflammatory, diuretic, anti-hypertensive, antipyretic, anti-ulcer, and immunomodulatory effect. Among the isolated compounds, chabamides, piperine, piplartine, retrofractamides A/B, methylenedioxyphenyl)-nona-2E,4E,8E-trienoic acid, n-butyl or n-pentyl amine, piperlonguminine, pipernonaline, dehydropipernonaline, N-isobutyl-(2E,4E)-octadecadienamide, and N-isobutyl-(2E,4E,14Z)-eicosatrienamide have documented important biological effects in various test systems.

CONCLUSIONS

Taken together, P. chaba may be a potential source of plant-based therapeutic lead compounds, which justify its uses in traditional medicine.

Piperlongumine analogue L50377 induces pyroptosis via ROS mediated NF-κB suppression in non-small-cell lung cancer

Natural products with potent activity and less toxicity provide major sources for development of novel anti-cancer drugs. Herein, we evaluated the effects and the underlying mechanisms of a novel piperlongumine (PL) analogue L50377 on non-small-cell lung cancer (NSCLC) cells. The results revealed that L50377 displayed greater potentials of suppressing cell growth than PL. In addition, L50377 promoted cell apoptosis and pyroptosis via stimulating reactive oxygen species (ROS) generation in NSCLC cells. More interestingly, ROS mediated NF-κB suppression might be implicated in the mechanisms of L50377-induced pyroptosis in NSCLC cells. Taken together, our results suggested that L50377 served as a novel chemical agent might have great potentials for NSCLC treatment.

Research progress in the biological activities of 3,4,5-trimethoxycinnamic acid (TMCA) derivatives

TMCA (3,4,5-trimethoxycinnamic acid) ester and amide are privileged structural scaffolds in drug discovery which are widely distributed in natural products and consequently produced diverse therapeutically relevant pharmacological functions. Owing to the potential of TMCA ester and amide analogues as therapeutic agents, researches on chemical syntheses and modifications have been carried out to drug-like candidates with broad range of medicinal properties such as antitumor, antiviral, CNS (central nervous system) agents, antimicrobial, anti-inflammatory and hematologic agents for a long time. At the same time, SAR (structure-activity relationship) studies have draw greater attention among medicinal chemists, and many of the lead compounds were derived for various disease targets. However, there is an urgent need for the medicinal chemists to further exploit the precursor in developing chemical entities with promising bioactivity and druggability. This review concisely summarizes the synthesis and biological activity for TMCA ester and amide analogues. It also comprehensively reveals the relationship of significant biological activities along with SAR studies.

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3,4,5-Trimethoxycinnamic acid (TMCA) derivatives show applications in different pathophysiological conditions due to its privileged structural scaffolds.

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Natural derived TMCA analogues and chemically modified TMCA ester and amide analogues and their bioactivities are focused in this review. Additionally, it also comprehensively summarized the relationship of significant biological activities along with SAR studies of synthetic TMCA derivatives.

Platinum-Catalyzed Desaturation of Lactams, Ketones, and Lactones

The development of a general platinum-catalyzed desaturation of N-protected lactams, ketones, and lactones to their conjugated α,β-unsaturated counterparts is reported. The reaction operates under mildly acidic conditions at room temperature or 50 °C. It is scalable and tolerates a wide range of functional groups. The complementary reactivity to the palladium-catalyzed desaturation is demonstrated in the efficient conversion of iodide, bromide, and sulfur-containing substrates.

Piperlongumine decreases cognitive impairment and improves hippocampal function in aged mice

Piperlongumine (PL), a biologically active compound from the Piper species, has been shown to exert various pharmacological effects in a number of conditions, including tumours, diabetes, pain, psychiatric disorders and neurodegenerative disease. In this study, we evaluated the therapeutic effects of PL on hippocampal function and cognition decline in aged mice. PL (50 mg/kg/day) was intragastrically administrated to 23‑month‑old female C57BL/6J mice for 8 weeks. Novel object recognition and nest building behaviour tests were used to assess cognitive and social functions. Additionally, immunohistochemistry and western blot analysis were performed to examine the effects of PL on the hippocampus. We found that the oral administration of PL significantly improved novel object recognition and nest building behaviour in aged mice. Although neither the percentage area occupied by astrocytes and microglia nor the level of 4‑hydroxynonenal protein, a specific marker of lipid peroxidation, were altered by PL treatment, the phosphorylation levels of N‑methyl‑D‑aspartate receptor subtype 2B (NR2B), calmodulin‑dependent protein kinase II alpha (CaMKIIα) and extracellular signal‑regulated kinase 1/2 (ERK1/2) were markedly increased in the hippocampus of aged mice following the administration of PL. We also found that PL treatment resulted in a CA3‑specific increase in the phosphorylation level of cyclic AMP response element binding protein, which is recognized as a potent marker of neuronal plasticity, learning and memory. Moreover, the number of doublecortin‑positive cells, a specific marker of neurogenesis, was significantly increased following PL treatment in the dentate gyrus of the hippocampus. On the whole, these data demonstrate that PL treatment may be a potential novel approach in the treatment of age‑related cognitive impairment and hippocampal changes.

Hypoglycemic Efficacy of Docking Selected Natural Compounds against α-Glucosidase and α-Amylase

The inhibition of α-glucosidase and α-amylase is a clinical strategy for the treatment of type II diabetes, and herbal medicines have been reported to credibly alleviate hyperglycemia. Our previous study has reported some constituents from plant or herbal sources targeted to α-glucosidase and α-amylase via molecular docking and enzymatic measurement, but the hypoglycemic potencies in cell system and mice have not been validated yet. This study was aimed to elucidate the hypoglycemic efficacy of docking selected compounds in cell assay and oral glucose and starch tolerance tests of mice. All test compounds showed the inhibition of α-glucosidase activity in Caco-2 cells. The decrease of blood sugar levels of test compounds in 30 min and 60 min of mice after OGTT and OSTT, respectively and the decreased glucose levels of test compounds were significantly varied in acarbose. Taken altogether, in vitro and in vivo experiments suggest that selected natural compounds (curcumin, antroquinonol, HCD, docosanol, tetracosanol, rutin, and actinodaphnine) via molecular docking were confirmed as potential candidates of α-glucosidase and α-amylase inhibitors for treating diabetes.

Senolytic activity of piperlongumine analogues: Synthesis and biological evaluation

Selective clearance of senescent cells (SCs) has emerged as a potential therapeutic approach for age-related diseases, as well as chemotherapy- and radiotherapy-induced adverse effects. Through a cell-based phenotypic screening approach, we recently identified piperlongumine (PL), a dietary natural product, as a novel senolytic agent, referring to small molecules that can selectively kill SCs over normal or non-senescent cells. In an effort to establish the structure-senolytic activity relationships of PL analogues, we performed a series of structural modifications on the trimethoxyphenyl and the α,β-unsaturated δ-valerolactam rings of PL. We show that modifications on the trimethoxyphenyl ring are well tolerated, while the Michael acceptor on the lactam ring is critical for the senolytic activity. Replacing the endocyclic C2-C3 olefin with an exocyclic methylene at C2 render PL analogues 47-49 with increased senolytic activity. These α-methylene containing analogues are also more potent than PL in inducing ROS production in WI-38 SCs. Similar to PL, 47-49 reduce the protein levels of oxidation resistance 1 (OXR1), an important oxidative stress response protein that regulates the expression of a variety of antioxidant enzymes, in cells. This study represents a useful starting point toward the discovery of senolytic agents for therapeutic uses.

Piperlongumine (piplartine) as a lead compound for anticancer agents - Synthesis and properties of analogues: A mini-review

Piperlongumine, also known as piplartine, is an amide alkaloid of Piper longum L. (long piper), a medical plant known from Ayurvedic medicine. Although was discovered well over fifty years ago, its pharmacological properties have been uncovered in the past decade. In particular, piperlongumine has been most extensively studied as a potential anticancer agent. Piperlongumine has exhibited cytotoxicity against a broad spectrum of human cancer cell lines, as well as demonstrated antitumor activity in rodents. Piperlongumine has also been found to be a proapoptotic, anti-invasive, antiangiogenic agent and synergize with modern chemotherapeutic agents. Because of its clinical potential, several studies were undertaken to obtain piperlongumine analogues, which have exhibited more potent activity or more appropriate drug-like parameters. In this review, the synthesis of piperlongumine analogues and piperlongumine-based hybrid compounds, as well as their anticancer properties and the molecular basis for their activity are explored. General structure-activity relationship conclusions are drawn and directions for the future research are indicated.

Novel Ligustrazine-Based Analogs of Piperlongumine Potently Suppress Proliferation and Metastasis of Colorectal Cancer Cells in Vitro and in Vivo

Piperlongumine 1 increases reactive oxygen species (ROS) levels and preferably induces cancer cell apoptosis by triggering different pathways. However, the poor solubility of 1 limits its intensive investigation and clinical application. Ligustrazine possesses a water-soluble pyrazine skeleton and can inhibit proliferation and metastasis of cancer cells. We synthesized compound 3 by replacement of the trimethoxyphenyl of 1 with ligustrazine moiety and further introduced 2-Cl, -Br, and -I to 3 for synthesis of 4-6, respectively. Compound 4 possessed 14-fold greater aqueous solubility than 1 and increased ROS levels in colorectal cancer HCT-116 cells. Additionally, 4 preferably inhibited proliferation, migration, invasion, and heteroadhesion of HCT-116 cells. Treatment with 4 suppressed tumor growth and lung metastasis in vivo and prolonged the survival of tumor-bearing mice. Furthermore, 4 mitigated TGF-β1-induced epithelial-mesenchymal transition and Wnt/β-catenin activation by inhibiting the Akt and GSK-3β phosphorylation in HCT-116 cells. Collectively, 4 displayed significant antiproliferation and antimetastasis activities, superior to 1.

Effect of piplartine and cinnamides on Leishmania amazonensis, Plasmodium falciparum and on peritoneal cells of Swiss mice

CONTEXT

Plants of the Piperaceae family produce piplartine that was used to synthesize the cinnamides.

OBJECTIVE

To assess the effects of piplartine (1) and cinnamides (2-5) against the protozoa responsible for malaria and leishmaniasis, and peritoneal cells of Swiss mice.

MATERIALS AND METHODS

Cultures of Leishmania amazonensis, Plasmodium falciparum-infected erythrocytes, and peritoneal cells were incubated, in triplicate, with different concentrations of the compounds (0 to 256 μg/mL). The inhibitory concentration (IC50) in L. amazonensis and cytotoxic concentration (CC50) in peritoneal cell were assessed by the MTT method after 6 h of incubation, while the IC50 for P. falciparum-infected erythrocytes was determined by optical microscopy after 48 or 72 h of incubation; the Selectivity Index (SI) was calculated by CC50/IC50.

RESULTS

All compounds inhibited the growth of microorganisms, being more effective against P. falciparum after 72 h of incubation, especially for the compounds 1 (IC50 = 3.2 μg/mL) and 5 (IC50 = 6.6 μg/mL), than to L. amazonensis (compound 1 = 179.0 μg/mL; compound 5 = 106.0 μg/mL). Despite all compounds reducing the viability of peritoneal cells, the SI were <10 to L. amazonensis, whereas in the cultures of P. falciparum the SI >10 for the piplartine (>37.4) and cinnamides 4 (>10.7) and 5 (= 38.4).

DISCUSSION AND CONCLUSION

The potential of piplartine and cinnamides 4 and 5 in the treatment of malaria suggest further pre-clinical studies to evaluate their effects in murine malaria and to determine their mechanisms in cells of the immune system.

Spectroscopic (far or terahertz, mid-infrared and Raman) investigation, thermal analysis and biological activity of piplartine

Research in the field of medicinal plants including Piper species like long pepper (Piper longum L.- Piperaceae) is increasing all over the world due to its use in traditional and Ayurvedic medicine. Piplartine (piperlongumine, 5,6-dihydro-1-[(2E)-1-oxo-3-(3,4,5-trimethoxyphenyl)-2-propenyl]-2(1H)-pyridinone), a biologically active alkaloid/amide was isolated from the phytochemical investigations of Piper species, as long pepper. This alkaloid has cytotoxic, anti-fungal, anti-diabetic, anti-platelet aggregation, anti-tumoral, anxiolytic, anti-depressant, anti-leishmanial, and genotoxic activities, but, its anticancer property is the most promising and has been widely explored. The main purpose of the work is to present a solid state characterization of PPTN using thermal analysis and vibrational spectroscopy. Quantum mechanical calculations based on the density functional theory was also applied to investigate the molecular conformation and vibrational spectrum, which was compared with experimental results obtained by Raman scattering, far (terahertz) and mid-infrared adsorption spectroscopy. NBO analysis has been performed which predict that most intensive interactions in PPTN are the hyperconjugative interactions between n(1) N6 and π*(O1C7) having delocalization energy of 50.53kcal/mol, Topological parameters have been analyzed using 'AIM' analysis which governs the three bond critical points (BCPs), one di-hydrogen, and four ring critical points (RCPs). MEP surface has been plotted which forecast that the most negative region is associated with the electronegative oxygen atoms (sites for nucleophilic activity). Theoretically, to confirm that the title compound has anti-cancer, anti-diabetic and anti-platelet aggregation activities, it was analyzed by molecular docking interactions with the corresponding target receptors. The obtained values of H-bonding parameters and binding affinity prove that its anti-cancer activity is the more prominent than the other properties.

Gas-phase fragmentation of protonated piplartine and its fungal metabolites using tandem mass spectrometry and computational chemistry

Piplartine, an alkaloid produced by plants in the genus Piper, displays promising anticancer activity. Understanding the gas-phase fragmentation of piplartine by electrospray ionization tandem mass spectrometry can be a useful tool to characterize biotransformed compounds produced by in vitro and in vivo metabolism studies. As part of our efforts to understand natural product fragmentation in electrospray ionization tandem mass spectrometry, the gas-phase fragmentation of piplartine and its two metabolites 3,4-dihydropiplartine and 8,9-dihydropiplartine, produced by the endophytic fungus Penicillium crustosum VR4 biotransformation, were systematically investigated. Proposed fragmentation reactions were supported by ESI-MS/MS data and computational thermochemistry. Cleavage of the C-7 and N-amide bond, followed by the formation of an acylium ion, were characteristic fragmentation reactions of piplartine and its analogs. The production of the acylium ion was followed by three consecutive and competitive reactions that involved methyl and methoxyl radical eliminations and neutral CO elimination, followed by the formation of a four-member ring with a stabilized tertiary carbocation. The absence of a double bond between carbons C-8 and C-9 in 8,9-dihydropiplartine destabilized the acylium ion and resulted in a fragmentation pathway not observed for piplartine and 3,4-dihydropiplartine. These results contribute to the further understanding of alkaloid gas-phase fragmentation and the future identification of piplartine metabolites and analogs using tandem mass spectrometry techniques. Copyright © 2017 John Wiley & Sons, Ltd.

Novel non-trimethoxylphenyl piperlongumine derivatives selectively kill cancer cells

Piperlongumine (PL) is a natural alkaloid with broad biological activities. Twelve analogues have been designed and synthesized with non-substituted benzyl rings or heterocycles in this work. Most of the compounds showed better anticancer activities than the parent PL without apparent toxicity in normal cells. Elevation of cellular ROS levels was one of the main anticancer mechanisms of these compounds. Cell apoptosis and cell cycle arrest for the best compound ZM90 were evaluated and similar mechanism of action with PL was demonstrated. The SAR was also characterized, providing worthy directions for further optimization of PL compounds.

Piperlongumine derived cyclic sulfonamides (sultams): Synthesis and in vitro exploration for therapeutic potential against HeLa cancer cell lines

A novel modification of piperlongumine is designed, bearing a cyclic sulphonamide (sultam) and its synthesis is described. For the first time herein we report the synthesis and biological evaluation of the natural product derived cyclic sulfonamides using Grubbs second generation catalyst (Grubbs II) via ring closing metathesis approach. Synthesis of a series of piperlongumine derived sultams is done in a moderate to good yield using Wittig reaction, Ring-Closing Metathesis (RCM) and, amide synthesis by using mixed anhydride, approach. All synthesized compounds were evaluated for anticancer activity and some demonstrated dose dependent reduction in HeLa cell growth. Of these 7, 10 and 14 significantly reduced the cell growth. Consequently their calculated GI50 values were found to be 0.1 or <0.1 μM.

Piperlongumine (piplartine) and analogues: Antiproliferative microtubule-destabilising agents

Piperlongumine (piplartine, 1) is a small molecule alkaloid that is receiving intense interest due to its antiproliferative and anticancer activities. We investigated the effects of 1 on tubulin and microtubules. Using both an isolated tubulin assay, and a combination of sedimentation and western blotting, we demonstrated that 1 is a tubulin-destabilising agent. This result was confirmed by immunofluorescence and confocal microscopy, which showed that microtubules in MCF-7 breast cancer cells were depolymerized when treated with 1. We synthesised a number of analogues of 1 to explore structure-activity relationships. Compound 13 had the best cytotoxic profile of this series, showing potent effects in human breast carcinoma MCF-7 cells whilst being relatively non-toxic to non-tumorigenic MCF-10a cells. These compounds will be further developed as potential clinical candidates for the treatment of breast cancer.

Horner-Wadsworth-Emmons approach to piperlongumine analogues with potent anti-cancer activity

Natural products with anti-cancer activity play a vital role in lead and target discovery. We report here the synthesis and biological evaluation of the plant-derived alkaloid, piperlongumine and analogues. Using a Horner-Wadsworth-Emmons coupling approach, a selection of piperlongumine-like compounds were prepared in good overall yield from a novel phosphonoacetamide reagent. A number of the compounds displayed potent anti-cancer activity against colorectal (HCT 116) and ovarian (IGROV-1) carcinoma cell lines, via a mechanism of action which may involve ROS generation. Contrary to previous reports, no selective action in cancer cell (MRC-5) was observed for piperlongumine analogues.

Design, Synthesis and Pharmacological Evaluation of Novel Piperlongumine derivatives as Potential Antiplatelet Aggregation Candidate

A series of novel piperlongumine derivatives (4a-i, 6a-i) were designed and synthesized. The inhibitory activities of platelet aggregation induced by ADP and AA in vitro have been evaluated by bron turbidimetry and liver microsomal incubated assay. The assay results show that compounds 4e and 6e exhibited remarkable potency to that of the positive control piplartine and aspirin.

A mild and efficient approach to enantioenriched α-hydroxyethyl α,β-unsaturated δ-lactams

A straightforward approach toward enantioenriched α-substituted α,β-unsaturated δ-lactams is described. Although a considerable number of approches toward α,β-unsaturated δ-lactams have been reported, there are relatively few examples of enantioenriched α,δ-disubstituted α,β-unsaturated δ-lactams formation. The δ-stereocenter was formed by addition of allylmagnesium bromide to an N-tert-butylsulfinyl imine. The α,β-unsaturated δ-lactam was furnished by ring-closing metathesis. Although Baylis-Hillman chemistry failed on this cyclic compound, introduction of the hydroxyethyl group prior to ring-closing metathesis was successful. A Baylis-Hillman reaction was used to introduce the substituent at the α-position of the α,β-unsaturated lactam.

Bioactivity Focus of α-Cyano-4-hydroxycinnamic acid (CHCA) Leads to Effective Multifunctional Aldose Reductase Inhibitors

Bioactivity focus on α-cyano-4-hydroxycinnamic acid (CHCA) scaffold results in a small library of novel multifunctional aldose reductase (ALR2) inhibitors. All the entities displayed good to excellent inhibition with IC50 72-405 nM. (R,E)-N-(3-(2-acetamido-3-(benzyloxy)propanamido)propyl)-2-cyano-3-(4-hydroxy phenyl)acrylamide (5f) was confirmed as the most active inhibitor (IC50 72.7 ± 1.6 nM), and the best antioxidant. 5f bound to ALR2 with new mode without affecting the aldehyde reductase (ALR1) activity, implicating high selectivity to ALR2. 5f was demonstrated as both an effective ALR2 inhibitor (ARI) and antioxidant in a chick embryo model of hyperglycemia. It attenuated hyperglycemia-induced incidence of neural tube defects (NTD) and death rate, and significantly improved the body weight and morphology of the embryos. 5f restored the expression of paired box type 3 transcription factor (Pax3), and reduced the hyperglycemia-induced increase of ALR2 activity, sorbitol accumulation, and the generation of ROS and MDA to normal levels. All the evidences support that 5f may be a potential agent to treat diabetic complications.

Piperlongumine Suppresses Growth and Sensitizes Pancreatic Tumors to Gemcitabine in a Xenograft Mouse Model by Modulating the NF-kappa B Pathway

Pancreatic cancer is an aggressive malignancy, which generally respond poorly to chemotherapy. Hence, novel agents that are safe and effective are highly needed. The aim of this study was to investigate whether piperlongumine, a natural product isolated from the fruit of the pepper Piper longum, has any efficacy against human pancreatic cancer when used either alone or in combination with gemcitabine in vitro and in a xenograft mouse model. In vitro, piperlongumine inhibited the proliferation of pancreatic cancer cell lines, potentiated the apoptotic effects of gemcitabine, inhibited the constitutive and inducible activation of NF-κB, and suppressed the NF-κB-regulated expression of c-Myc, cyclin D1, Bcl-2, Bcl-xL, Survivin, XIAP, VEGF, and matrix metalloproteinase-9 (MMP-9). Furthermore, in an in vivo xenograft model, we found piperlongumine alone significantly suppressed tumor growth and enhanced the antitumor properties of gemcitabine. These results were consistent with the downregulation of NF-κB activity and its target genes, decreased proliferation (PCNA and Ki-67), decreased microvessel density (CD31), and increased apoptosis (TUNEL) in tumor remnants. Collectively, our results suggest that piperlongumine alone exhibits significant antitumor effects against human pancreatic cancer and it further enhances the therapeutic effects of gemcitabine, possibly through the modulation of NF-κB- and NF-κB-regulated gene products.

Design and synthesis of a C7-aryl piperlongumine derivative with potent antimicrotubule and mutant p53-reactivating properties

Small molecules that can restore biological function to the p53 mutants found in human cancers have been highly sought to increase the anticancer efficacy. In efforts to generate hybrid anticancer drugs that can impact two or more targets simultaneously, we designed and developed piperlongumine (PL) derivatives with an aryl group inserted at the C-7 position. This insertion bestowed a combretastatin A4 (CA4, an established microtubule disruptor) like structure while retaining the piperlongumine configuration. The new compounds exhibited potent antiproliferative activities against eight cancer cell lines, in particular, were more cytotoxic against the SKBR-3 breast cancer cells which harbor a R175H mutation in p53 suppressor. KSS-9, a representative aryl PL chosen for further studies induced abundant ROS generation and protein glutathionylation. KSS-9 strongly disrupted the tubulin polymerization in vitro, destabilized the microtubules in cells and induced a potent G2/M cell cycle block. More interestingly, KSS-9 showed the ability to reactivate the p53 mutation and restore biological activity to the R175H mutant protein present in SKBR3 cells. Several procedures, including immunocytochemistry using conformation-specific antibodies for p53, immunoprecipitation combined with western blotting, electrophoretic shift mobility shift assays showed a reciprocal loss of mutant protein and generation of wild-type like protein. p53 reactivation was accompanied by the induction of the target genes, MDM2, p21cip1 and PUMA. Mechanistically, the redox-perturbation in cancer cells by the hybrid drug appears to underlie the p53 reactivation process. This anticancer drug approach merits further development.

Design, synthesis and anti-proliferative activities of novel 7′-O-substituted schisantherin A derivatives

A series of schisantherin A (1) derivatives were efficiently synthesized utilizing Yamaguchi esterification (2,4,6-trichlorobenzoyl chloride, Et₃N, THF, DMAP, toluene) at the C-7′ position of the schisantherin A core.

Synthesis and Biological Evaluation of Novel Gigantol Derivatives as Potential Agents in Prevention of Diabetic Cataract

As a continuation of our efforts directed towards the development of natural anti-diabetic cataract agents, gigantol was isolated from Herba dendrobii and was found to inhibit both aldose reductase (AR) and inducible nitric oxide synthase (iNOS) activity, which play a significant role in the development and progression of diabetic cataracts. To improve its bioefficacy and facilitate use as a therapeutic agent, gigantol (compound 14f) and a series of novel analogs were designed and synthesized. Analogs were formulated to have different substituents on the phenyl ring (compounds 4, 5, 8, 14a-e), substitute the phenyl ring with a larger steric hindrance ring (compounds 10, 17c) or modify the carbon chain (compounds 17a, 17b, 21, 23, 25). All of the analogs were tested for their effect on AR and iNOS activities and on D-galactose-induced apoptosis in cultured human lens epithelial cells. Compounds 5, 10, 14a, 14b, 14d, 14e, 14f, 17b, 17c, 23, and 25 inhibited AR activity, with IC50 values ranging from 5.02 to 288.8 μM. Compounds 5, 10, 14b, and 14f inhibited iNOS activity with IC50 ranging from 432.6 to 1188.7 μM. Compounds 5, 8, 10, 14b, 14f, and 17c protected the cells from D-galactose induced apoptosis with viability ranging from 55.2 to 76.26%. Of gigantol and its analogs, compound 10 showed the greatest bioefficacy and is warranted to be developed as a therapeutic agent for diabetic cataracts.

Synthesis of piperlongumine analogues and discovery of nuclear factor erythroid 2-related factor 2 (Nrf2) activators as potential neuroprotective agents

The cellular antioxidant system plays key roles in blocking or retarding the pathogenesis of adult neurodegenerative disorders as elevated oxidative stress has been implicated in the pathophysiology of such diseases. Molecules with the ability in enhancing the antioxidant defense thus are promising candidates as neuroprotective agents. We reported herein the synthesis of piperlongumine analogues and evaluation of their cytoprotection against hydrogen peroxide- and 6-hydroxydopamine-induced neuronal cell oxidative damage in the neuron-like PC12 cells. The structure-activity relationship was delineated after the cytotoxicity and protection screening. Two compounds (4 and 5) displayed low cytotoxicity and confer potent protection of PC12 cells from the oxidative injury via upregulation of a panel of cellular antioxidant molecules. Genetically silencing the transcription factor Nrf2, a master regulator of the cellular stress responses, suppresses the cytoprotection, indicating the critical involvement of Nrf2 for the cellular action of compounds 4 and 5 in PC12 cells.

Heme oxygenase-1 determines the differential response of breast cancer and normal cells to piperlongumine

Piperlongumine, a natural alkaloid isolated from the long pepper, selectively increases reactive oxygen species production and apoptotic cell death in cancer cells but not in normal cells. However, the molecular mechanism underlying piperlongumine-induced selective killing of cancer cells remains unclear. In the present study, we observed that human breast cancer MCF-7 cells are sensitive to piperlongumine-induced apoptosis relative to human MCF-10A breast epithelial cells. Interestingly, this opposing effect of piperlongumine appears to be mediated by heme oxygenase-1 (HO-1). Piperlongumine upregulated HO-1 expression through the activation of nuclear factor-erythroid-2-related factor-2 (Nrf2) signaling in both MCF-7 and MCF-10A cells. However, knockdown of HO-1 expression and pharmacological inhibition of its activity abolished the ability of piperlongumine to induce apoptosis in MCF-7 cells, whereas those promoted apoptosis in MCF-10A cells, indicating that HO-1 has anti-tumor functions in cancer cells but cytoprotective functions in normal cells. Moreover, it was found that piperlongumine-induced Nrf2 activation, HO-1 expression and cancer cell apoptosis are not dependent on the generation of reactive oxygen species. Instead, piperlongumine, which bears electrophilic α,β-unsaturated carbonyl groups, appears to inactivate Kelch-like ECH-associated protein-1 (Keap1) through thiol modification, thereby activating the Nrf2/HO-1 pathway and subsequently upregulating HO-1 expression, which accounts for piperlongumine-induced apoptosis in cancer cells. Taken together, these findings suggest that direct interaction of piperlongumine with Keap1 leads to the upregulation of Nrf2-mediated HO-1 expression, and HO-1 determines the differential response of breast normal cells and cancer cells to piperlongumine.

Activity of alkaloids on peptic ulcer: what's new?

Peptic ulcer is a common disease characterized by lesions that affect the mucosa of the esophagus, stomach and/or duodenum, and may extend into the muscular layer of the mucosa. Natural products have played an important role in the process of development and discovery of new drugs, due to their wide structural diversity and present, mostly specific and selective biological activities. Among natural products the alkaloids, biologically active secondary metabolites, that can be found in plants, animals or microorganisms stand out. The alkaloids are compounds consisting of a basic nitrogen atom that may or may not be part of a heterocyclic ring. This review will describe 15 alkaloids with antiulcer activity in animal models and in vitro studies.

Synthesis and biological evaluation of piperlongumine derivatives as potent anti-inflammatory agents

Piperlongumine (PL) and its derivatives were synthesized by the direct reaction between acid chloride of 3,4,5-trimethoxycinnamic acid and various amides/lactams. Later their anti-inflammatory effects were evaluated in lipopolysaccharide (LPS)-induced RAW-264.7 macrophages. Of the piperlogs prepared in this study, the maximum (91%) inhibitory activity was observed with PL (IC50=3 μM) but showed cytotoxicity whereas compound 3 (IC50=6 μM) which possess α,β-unsaturated γ-butyrolactam moiety offered good level (65%) of activity with no cytotoxicity. This study revealed that amide/lactam moiety connected to cinnamoyl group with minimum 3 carbon chain length and α,β-unsaturation is fruitful to show potent anti-inflammatory activity.

Piperlongumine chemosensitizes tumor cells through interaction with cysteine 179 of IκBα kinase, leading to suppression of NF-κB-regulated gene products

Recently, two different reports appeared in prominent journals suggesting a mechanism by which piperlongumine, a pyridine alkaloid, mediates anticancer effects. In the current report, we describe another novel mechanism by which this alkaloid mediates its anticancer effects. We found that piperlongumine blocked NF-κB activated by TNFα and various other cancer promoters. This downregulation was accompanied by inhibition of phosphorylation and degradation of IκBα. Further investigation revealed that this pyridine alkaloid directly interacts with IκBα kinase (IKK) and inhibits its activity. Inhibition of IKK occurred through interaction with its cysteine 179 as the mutation of this residue to alanine abolished the activity of piperlongumine. Inhibition in NF-κB activity downregulated the expression of proteins involved in cell survival (Bcl-2, Bcl-xL, c-IAP-1, c-IAP-2, survivin), proliferation (c-Myc, cyclin D1), inflammation (COX-2, IL6), and invasion (ICAM-1, -9, CXCR-4, VEGF). Overall, our results reveal a novel mechanism by which piperlongumine can exhibit antitumor activity through downmodulation of proinflammatory pathway.