Natural Product Drug Discovery Research Articles

Intramolecular Parallel [4+3] Cycloadditions of Cyclopropane 1,1-Diesters with [3]Dendralenes: Efficient Construction of [5.3.0]Decane and Corresponding Polycyclic Skeletons.

Aiming to develop efficient and general strategies for construction of complex and diverse polycyclic skeletons, we have successfully developed [4+3]IMPC (intramolecular parallel cycloaddition) of cyclopropane 1,1-diesters with [3]dendralenes. With a combination of the [4+3]IMPC and subsequent [4+n] cycloadditions, trans-[5.3.0]decane skeleton and its corresponding structurally complex and diverse polycyclic variants could be constructed efficiently. This novel [4+3] cycloaddition reaction mode of donor-acceptor cyclopropanes proceeds as a result of the ring-strain relief of a trans-[3.3.0]octane. We strongly believe that the developed methods will demonstrate potential applications in natural products synthesis and drug discovery.

Natural products in drug discovery: from classical methods to metabolomic approaches

Natural products in drug discovery: from classical methods to metabolomic approaches

A comparative metagenomics approach to marine natural product drug discovery in Hippospongia lachne

A comparative metagenomics approach to marine natural product drug discovery in Hippospongia lachne

English

The in silico simulations and predictions approach in evaluation of pharmacokinetic properties of new chemical entities (NCEs) is fast becoming an acceptable trend in natural products research and drug discovery. This paper focuses on the properties of trolline with respect to its anti-inflammatory and MCF-7 breast cancer cell line growth inhibition effects and an attempt to predict physico-chemical drug-like properties in silico. The compound was isolated for the first time from aerial parts of Mirabilis jalapa and the structure was elucidated by 1D and 2D NMR, FTIR and mass spectroscopic analyses. The compound was screened for anti-inflammatory and anti-MCF-7 cell lines proliferation using chemoluminiscence oxidative burst and MTT assays respectively. Predictions on physico-chemical properties central to oral route drug administration were done using commercial software Admet predictor. Results show anti-inflammatory effects at IC50 concentration of 53.8 µg/ml and 48% mortality of breast cancer cell lines at 50 µM concentration. Predictions suggest moderate solubility of 1.72 to 2.92 mg/ml across pH range of 1.6 to 6.8 in simulated solvent systems and effective jejunal permeability of 5.61 x 10-4 cm/s. The compound was also predicted to be 60% unbound to plasma proteins and an LD50 of 950 mg/kg in rats. The compound, trolline had clinically important bioactive effects, probably possess promising drug-like properties suitable for further high throughput screening. Key words: ADMET, anti-inflammatory, in silico prediction, Mirabilis jalapa, NMR, trolline.

Multicomponent Hetero-[4 + 2] Cycloaddition/Allylboration Reaction: From Natural Product Synthesis to Drug Discovery.

Multicomponent reactions (MCR), transformations employing three or more simple substrates in a single and highly atom-economical operation, are very attractive in both natural product synthesis and diversity-oriented synthesis of druglike molecules. Several popular multicomponent reactions were designed by combining two well-established individual reactions that utilize mutually compatible substrates. In this regard, it is not surprising that the merging of two reactions deemed as workhorses of stereoselective synthesis, the Diels-Alder cycloaddition and carbonyl allylboration, would produce a powerful and highly versatile tandem MCR process. The idea of using 1,3-dienylboronates in [4 + 2] cycloadditions as a means to produce cyclic allylic boronates was first reported by Vaultier and Hoffmann in 1987. In their seminal study, a 1-boronodiene was reacted with electron-poor alkenes, and the intermediate cycloadducts were isolated and added to aldehydes in a separate step leading to α-hydroxyalkylated carbocycles via a highly diastereoselective allylboration reaction. The one-pot three-component variant was realized in 1999 by Lallemand and co-workers, and soon after groups led by Hall and Carboni reported heterocyclic variants of the tandem [4 + 2] cycloaddition/allylboration to prepare α-hydroxyalkylated piperidine and pyran containing compounds, respectively. These classes of heterocycles are ubiquitous in Nature and are important components of pharmaceuticals. This Account summarizes the development and evolution of this powerful multicomponent reaction for accessing nonaromatic heterocycles and its many applications in natural products synthesis and drug discovery. The aza[4 + 2]cycloaddition/allylboration MCR was first optimized in our laboratory using 4-boronylhydrazonobutadienes and N-substituted maleimides, and it was exploited in the preparation of combinatorial libraries of polysubstituted imidopiperidines that feature as many as four elements of chemical diversity. Biological screening of these druglike imidopiperidine libraries unveiled promising bioactive agents such as A12B4C3, the first reported inhibitor of the human DNA repair enzyme, polynucleotide kinase-phosphatase (hPNKP). Related applications of this MCR in target-oriented synthesis also led to total syntheses of palustrine alkaloids. The inverse electron-demand oxa[4 + 2] cycloaddition/allyboration variant can take advantage of Jacobsen's chiral Cr(III)salen catalyst, affording a rare example of catalytic enantioselective MCR, one that provides a rapid access to α-hydroxyalkyl dihydropyrans in high enantio- and diastereoselectivity. This process exploits 3-boronoacrolein pinacolate as the heterodiene with ethyl vinyl ether or various 2-substituted enol ethers, along with a wide variety of aldehydes in the allylation stage. This versatile methodology was deployed in total syntheses of thiomarinol antibiotics, goniodiol and its derivatives, and the complex anticancer macrolide palmerolide A. More recent work from our laboratory centered on the regio- and stereoselective Suzuki-Miyaura cross-coupling of the dihydropyranyl boronates, thus providing a glimpse of the potential for new multicomponent variants that merge hetero[4 + 2] cycloadditions of 1-borylated heterodienes with transition metal-catalyzed transformations. This stereoselective MCR strategy holds great promise for provoking continuing applications in complex molecule synthesis and drug discovery, and is likely to inspire new and innovative MCR-based approaches to nonaromatic heterocycles.

Natural products for drug discovery

Natural products for drug discovery

Extractive determination of bioactive flavonoids from butterfly pea (Clitoria ternatea Linn.)

Recently, in the field of natural product drug discovery, there has been increasing interest in effective extraction and isolation of bioactive phytomolecules from plants for use as important starting materials or chemical intermediates for new drug development. In this investigation, various solvent extracts of butterfly pea (Clitoria ternatea Linn.) were evaluated in terms of phenolic content and antioxidant activity. Moreover, various parameters influencing optimal flavonoid extraction were studied based on determination of the quercetin and kaempferol yields by an improved high-performance liquid chromatography (HPLC) method. The results indicated that the total phenolics and 2,2′-azino-bis-3-ethylbenzothiazoline-6-sulfonic acid (ABTS) scavenging activity were maximum for the 80 % aqueous methanol extract, while the 1,1-diphenyl-2-picrylhydrazyl (DPPH) reducing power and flavonoid content were maximum in the methanol extract. Different solvent extracts showed significantly (p < 0.05) different phytochemical yield and antioxidant capacity. Furthermore, the total phenol and flavonoid contents revealed good (p < 0.001) correlations with scavenging potency. The maximum flavonoid content was found for methanol concentration, time, temperature, and solid-to-liquid ratio of 80 %, 60 min, 80 °C, and 1:20 g/mL, respectively. It is concluded that butterfly pea leaf can be considered a potential source of flavonoids with good antioxidant properties for use in dietary applications. The extraction protocols developed in this study can be readily scaled up for industrial applications.

Abstract 4847: Discovery, semisynthesis, and structure-activity relationship studies of hirsutinolide derivatives as new STAT3 inhibitors and anti-glioma agents

Abstract Clinically, natural product has played a pivotal role in anticancer drug discovery and development. Cancer chemotherapy and/or radiotherapy due to glioma treatment are not ideal, frequently cause unwanted adverse effects, and justify further research and development of alternative, novel, safe, and effective agents. In our continued efforts to identify new signal transducer and activator of transcription 3 (STAT3) and antiglioma agents with enhanced efficacy and specificity, we have initiated a collaborative and multidisciplinary natural product drug discovery project and the goal was to isolate, semisynthesize, and evaluate the potential of Vernonia cinerea-derived phytochemicals as STAT3 inhibitors with therapeutic remedy of human glioma and may be even more effective than the existing ones. To date, our preliminary studies have been conducted and resulted in the discovery of a class of sesquiterpene lactone hirsutinolide series with an á,â-unsaturated-ã-lactone ring as new STAT3 inhibitors. Specifically, on the basis of encouraging biological data and to expand the existing structure activity relationship (SAR) of isolated natural hirsutinolide analogues, chemical modifications were performed using conventional Steglich esterification protocol to produce a series of semisynthetic hirsutinolide derivatives in moderate to high yields. Thus far, biological evaluation revealed that several semisynthetic analogues showed low micromolar inhibitory activities against constitutively-active STAT3 and malignant glioma phenotype. SAR showed that a bulky and lipophilic ester functionality at position 13 is essential for STAT3 inhibition as well as whole cell based anticancer activity. A lipophilic side chain at position 8 also plays an important role in anticancer activity and may contribute a detrimental effect on specificity. In addition, the methoxy group at position 1 enhances the cell-type specificity and selectivity. Finally, selected promising lead candidates also demonstrated in vivo efficacy following oral gavage delivery, inhibiting human glioma tumor growth in subcutaneous mouse xenografts. Together, natural and chemically modified hirsutinolide-type sesquiterpene lactones represent a promising natural product class of new anticancer agents for the treatment of malignant human glioma. Citation Format: Mingming Zhang, Ui Joung Youn, Gabriella Miklossy, Supakit Wongwiwatthananukit, James Turkson, Leng Chee Chang, Dianqing Sun. Discovery, semisynthesis, and structure-activity relationship studies of hirsutinolide derivatives as new STAT3 inhibitors and anti-glioma agents. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 4847.

Underexplored Opportunities for Natural Products in Drug Discovery.

The importance of natural products in the treatment of human disease is well documented. While natural products continue to have a profound impact on human health, chemists have succeeded in generating semisynthetic analogues that sometimes overshadow the original natural product in terms of clinical significance. Synthetic efforts based on natural products have primarily focused on improving their drug-like features while targeting utility in the same biological space. A less documented phenomenon is that natural products can serve as powerful starting materials to generate drug substances with novel therapeutic utility that is unrelated to the biological space of the natural product starting material. In this Perspective, examples of natural product derived marketed drugs with therapeutic utility in clinical space that is different from the biological profile of the starting material are presented, demonstrating that this is not merely a theoretical concept but both a clinical reality and an underexplored opportunity.

Marine cyanobacteria-derived serotonin receptor 2C active fraction induces psychoactive behavioral effects in mice

Context: Marine cyanobacteria offer a robust resource for natural products drug discovery due to the secondary metabolites they produce.Objective: To identify novel cyanobacterial compounds that exhibit CNS psychoactive effects.Materials and methods: Cyanobacteria were collected from Las Perlas Archipelago, Panama and subjected to dichloromethane/methanol extraction and fractionation by column chromatography before being screened for affinity against a panel of CNS targets. A 50:50 ethyl acetate:methanol fraction of one cyanobacterial extract (2064H) was subjected to HPLC and the major peak was isolated (2064H3). At a dose of 20 μg per animal, 2064H and 2064H3 were tested in mice using behavioral assays that included the forced swim, open field and formalin tests.Results: 2064H was shown to bind to the serotonin 2C (5-HT2C) receptor, a known target for depression and pain treatment. 2064H showed 59.6% inhibition of binding of [3H]-mesulergine with an IC50 value of 179 ng/mL and did not show inhibition of binding greater than 45% with any other receptors tested. Both 2064H and 2064H3 decreased immobility time in the first minute of the tail suspension test. 2064H increased time, distance and number of entries in the center region in the first half of the open field test. 2064H increased overall nocifensive behaviors in the formalin test.Discussion and conclusion: Overall, manipulating the 5-HT2C receptor with these receptor-specific ligands derived from cyanobacteria altered pain, depression and anxiety-like behaviors, illustrating the importance of this receptor in affective behaviors. These results demonstrate the potential of cyanobacteria as a source for CNS active compounds.

Revival of Natural Products: Utilization of Modern Technologies

Over the years, natural products have the dominant status in the discovery of new effective therapeutic agents, but from 1990's, onward pharma-industry showed paradigm shift towards synthetic drugs. However, the strategic shift of the research and development (R&D) of major pharmaceutical organizations away from synthetic agents that interfere to interact with single targets for therapeutic effect reverse to the discovery of agents that provoke advantageous phenotypic effects, strongly augment the significance of natural products in drug discovery. This mini review encounters the various grounds for the revival of natural products as therapeutic agents. Keywords: Effective therapeutic modality, natural products, renew interest, stechnological advancement.

Withanolides: Biologically Active Constituents in the Treatment of Alzheimer's Disease.

The use of natural products in drug discovery and development have an important history. Several therapeutic agents have been investigated during the biological screenings of natural compounds. It is well documented that plants are possibly the core of novel substances that led to the discovery of new, novel, and effective therapeutic agents. Therefore, in the last few decades, scientists were thoroughly attempting for the search of benevolent drugs to protect mankind from various diseases and discomforts. The diverse chemical structures of natural products are the key element of their success in modern drug discovery. Cholinesterase enzyme inhibitors (ChEI) are chemicals which inhibit the splitting of cholinesterase enzymes (acetylcholinesterase and butyrylcholinesterase). Acetyl cholinesterase (AChE) and butyrylcholinesterase (BChE) are two types of cholinesterase enzymes that have been identified in vertebrates that are responsible for Alzheimer's disease and related dementia. Withanolides are affective plant secondary metabolites which inhibit acetylcholinesterase and butyrylcholinesterase enzyme and thus possibly will be the future drug for Alzheimer's disease. By viewing the importance of natural products in drug discovery and development, we present here, the importance of withanolides in the treatment of Alzheimer's disease. In this article, we also describe the classification and structural characterization of withanolides. This review comprises of 114 compounds.

Ultra-high resolution band-selective HSQC for nanomole-scale identification of chlorine-substituted 13 C in natural products drug discovery.

Ultra-high resolution band-selective HSQC (bsHSQC) has been employed for detection of 35 Cl-37 Cl isotope shifted 13 C NMR signals for assignment of regioisomerism in bromo-chloro natural products. Optimum pulse sequence and instrumental parameters for maximization of detection of the isotope shifts were explored. The chlorine isotope shifts (Δδ) were detected within crosspeaks and were shown to vary with hybridization of 13 C, substitution of 13 C, presence of β-chloro substituents, and their relative configuration. Deconvolution of Cl-substituted CH bsHSQC crosspeaks may provide other useful information, including a potentially MS-independent method for quantitating 37 Cl/35 C isotopic fractionation during the biosynthesis of halogenated natural products. Copyright © 2016 John Wiley & Sons, Ltd.

Chemoprevention in gastrointestinal physiology and disease. Targeting the progression of cancer with natural products: a focus on gastrointestinal cancer.

The last decade has witnessed remarkable progress in the utilization of natural products for the prevention and treatment of human cancer. Many agents now in the pipeline for clinical trial testing have evolved from our understanding of how human nutritional patterns account for widespread differences in cancer risk. In this review, we have focused on many of these promising agents arguing that they may provide a new strategy for cancer control: natural products once thought to be only preventive in their mode of action now are being explored for efficacy in tandem with cancer therapeutics. Natural products may reduce off-target toxicity of therapeutics while making cancers more amenable to therapy. On the horizon is the use of certain natural products, in their own right, as mitigants of late-stage cancer, a new frontier for small-molecule natural product drug discovery.

Cell-based bioreporter assay coupled to HPLC micro-fractionation in the evaluation of antimicrobial properties of the basidiomycete fungus Pycnoporus cinnabarinus

Context Identification of bioactive components from complex natural product extracts can be a tedious process that aggravates the use of natural products in drug discovery campaigns. Objective This study presents a new approach for screening antimicrobial potential of natural product extracts by employing a bioreporter assay amenable to HPLC-based activity profiling. Materials and methods A library of 116 crude extracts was prepared from fungal culture filtrates by liquid–liquid extraction with ethyl acetate, lyophilised, and screened against Escherichia coli using TLC bioautography. Active extracts were studied further with a broth microdilution assay, which was, however, too insensitive for identifying the active microfractions after HPLC separation. Therefore, an assay based on bioluminescent E. coli K-12 (pTetLux1) strain was coupled with HPLC micro-fractionation. Results Preliminary screening yielded six fungal extracts with potential antimicrobial activity. A crude extract from a culture filtrate of the wood-rotting fungus, Pycnoporus cinnabarinus (Jacq.) P. Karst. (Polyporaceae), was selected for evaluating the functionality of the bioreporter assay in HPLC-based activity profiling. In the bioreporter assay, the IC50 value for the crude extract was 0.10 mg/mL. By integrating the bioreporter assay with HPLC micro-fractionation, the antimicrobial activity was linked to LC-UV peak of a compound in the chromatogram of the extract. This compound was isolated and identified as a fungal pigment phlebiarubrone. Discussion and conclusion HPLC-based activity profiling using the bioreporter-based approach is a valuable tool for identifying antimicrobial compound(s) from complex crude extracts, and offers improved sensitivity and speed compared with traditional antimicrobial assays, such as the turbidimetric measurement.

Preparative isolation of a cytotoxic principle of a forest mushroom Suillus luteus by sodium dodecyl sulfate based "salting-in" countercurrent chromatography.

In the course of screening new anticancer natural products, an edible forest mushroom Suillus luteus (L. Ex Franch). Gray was found to have potent cytotoxicity against several human cancer cells. However, the lipophilic sample made some countercurrent chromatography solvent systems emulsify, which caused difficulties in the separation of its cytotoxic components. Here, we found that the addition of an organic salt sodium dodecyl sulfate could efficiently shorten the settling time of the mushroom sample solutions by eliminating the emulsification of two-phase solvent systems. Moreover, we found that sodium dodecyl sulfate could play a new "salting-in" role and made the partition coefficients of the solutes decrease with the increased concentrations. Thus, a sodium dodecyl sulfate based salting-in countercurrent chromatography method has been successfully established for the first time for preparative isolation of a cytotoxic principle of the mushroom. The active component was identified as isosuillin. Whole results indicated that sodium dodecyl sulfate could be used as an efficient salting-in reagent for two-phase solvent system selection and targeted countercurrent chromatography isolation. It is very useful for current natural products isolation and drug discovery.

Palladium catalysed meta-C-H functionalization reactions.

The directing group assisted site selective C-H functionalization approach is having a continuous impact in the field of natural product synthesis, drug discovery and material sciences. While ortho-selective C-H functionalization has been studied extensively, meta-selective C-H functionalization has been less explored. Recent studies have highlighted the efficacy of palladium as a catalyst in activating the meta-C-H bond of arenes. Notably, the introduction of a novel palladium catalysed directing template based approach to activate the remote meta-position has created a revolutionary impact towards seeking a solution to this long standing challenge. In this review we summarize recent advances in palladium catalysed meta-C-H functionalization that have helped in creating a new outlook towards modern organic synthesis.

A New Golden Age of Natural Products Drug Discovery

The 2015 Nobel Prize in Physiology or Medicine has been awarded to William C. Campbell, Satoshi Omura, and Youyou Tu for the discovery of avermectins and artemisinin, respectively, therapies that revolutionized the treatment of devastating parasite diseases. With the recent technological advances, a New Golden Age of natural products drug discovery is dawning.

Targeting the Hedgehog Signaling Pathway with Small Molecules from Natural Sources

Natural products drug discovery has allowed the identification of many biologically active compounds from plants, microbial species, and marine organisms. A significant number of these compounds are currently used as drugs in therapeutic protocols, while other naturally occurring chemical entities gave suggestions for designing nonnatural-product derived drugs or have been modified in their structure to have semi-synthetic analogues. In the last decade, experimental evidence that correlated the aberrant activation of the Hedgehog (Hh) signaling pathway with many types of cancer, prompted the researchers to check natural compounds for their ability to modulate this signaling cascade. As a result, many compounds from natural sources showed inhibitory activity toward one or more of the Hh signaling pathway components, such as Smoothened (Smo) and the downstream effectors Gli. On the other hand, only a few natural compounds were able to stimulate the same pathway. This review reports a survey of the compounds extracted from natural sources (especially plants) that showed activity in inhibiting the Hh signaling machinery by interfering with its components.

Biosynthetic engineering and fermentation media development leads to gram-scale production of spliceostatin natural products in Burkholderia sp.

A key challenge in natural products drug discovery is compound supply. Hundreds of grams of purified material are needed to advance a natural product lead through preclinical development. Spliceostatins are polyketide-nonribosomal peptide natural products that bind to the spliceosome, an emerging target in cancer therapy. The wild-type bacterium Burkholderia sp. FERM BP-3421 produces a suite of spliceostatin congeners with varying biological activities and physiological stabilities. Hemiketal compounds such as FR901464 were the first to be described. Due to its improved properties, we were particularly interested in a carboxylic acid precursor analog that was first reported from Burkholderia sp. MSMB 43 and termed thailanstatin A. Inactivation of the iron/α-ketoglutarate-dependent dioxygenase gene fr9P had been shown to block hemiketal biosynthesis. However, a 4-deoxy congener of thailanstatin A was the main product seen in the dioxygenase mutant. We show here that expression of the cytochrome P450 gene fr9R is a metabolic bottle neck, as use of an l-arabinose inducible system led to nearly complete conversion of the 4-deoxy analog to the target molecule. By integrating fermentation media development approaches with biosynthetic engineering, we were able to improve production titers of the target compound >40-fold, going from the starting ~60mg/L to 2.5g/L, and to achieve what is predominantly a single component production profile. These improvements were instrumental in enabling preclinical development of spliceostatin analogs as chemotherapy.