Chemically engineered extracts as an alternative source of bioactive natural product-like compounds

Chemically engineered essential oils prepared through thiocyanation under solvent-free conditions: chemical and bioactivity alteration

The generation of chemically engineered essential oils (CEEOs) prepared from bi-heteroatomic reactions using ammonium thiocyanate as a source of bioactive compounds is described. The impact of the reaction on the chemical composition of the mixtures was qualitatively demonstrated through GC-MS, utilizing univariate and multivariate analysis. The reaction transformed most of the components in the natural mixtures, thereby expanding the chemical diversity of the mixtures. Changes in inhibition properties between natural and CEEOs were demonstrated through acetylcholinesterase TLC autography, resulting in a threefold increase in the number of positive events due to the modification process. The chemically engineered Origanum vulgare L. essential oil was subjected to bioguided fractionation, leading to the discovery of four new active compounds with similar or higher potency than eserine against the enzyme. The results suggest that the directed chemical transformation of essential oils can be a valuable strategy for discovering new acetylcholinesterase (AChE) inhibitors.

A Fast and Efficient Molecular Networking Approach for Reactivity of Natural Products Exploration in Plant Extracts: Application to Diterpene Esters from Euphorbia dendroides

Natural products represent a rich source of bioactive compounds, covering a large chemical space. Even if challenging, this diversity can be extended by applying chemical modifications. However, these studies generally require multigram amounts of isolated natural products and face frequent testing failures. To overcome this limitation, we propose a rapid and efficient approach that uses molecular networking (MN) to visualize the new chemical diversity generated by simple chemical modifications of natural extracts. Moreover, the strategy deployed enables the most appropriate reagents to be defined quickly upstream of a reaction on a pure compound, in order to maximize chemical diversity. This methodology was applied to the latex extract of Euphorbia dendroides to follow the reactivity toward a series of Brønsted and Lewis acids of three class of diterpene esters identified in this species: jatrophane, terracinolide, and phorbol. Through the molecular networking interpretation, with the aim to illustrate our approach, BF3·OEt2 was selected for chemical modification on isolated jatrophane esters. Three rearranged compounds (3-5) were obtained, showing that the most appropriate reagents can be selected by MN interpretation.

Expanding Chemical Frontiers: Approaches for Generating Diverse and Bioactive Natural Product-Like Compounds Libraries from Extracts

The realms of natural products and synthetic compounds exhibit distinct chemical spaces that not only differ but also complement each other. While the convergence of these two domains has been explored through semisynthesis and conventional pharmacomodulation endeavours applied to natural frameworks, a recent and innovative approach has emerged that involves the combinatorial generation of libraries of 'natural product-like compounds' (NPLCs) through the direct synthetic derivatization of natural extracts. This has led to the production of numerous NPLCs that incorporate structural elements from both their natural (multiple saturated rings, oxygen content, chiral centres) and synthetic (aromatic rings, nitrogen and halogen content, drug-like properties) precursors. Through careful selection of extracts and reagents, specific bioactivities have been achieved, and this strategy has been deployed in various ways, showing great promise without reaching its full potential to date. This review seeks to provide an overview of reported examples involving the chemical engineering of extracts, showcasing a spectrum of natural product alterations spanning from simple substitutions to complete scaffold remodelling. It also includes an analysis of the accomplishments, perspectives and technical challenges within this field.

Divergent synthesis of fractionated Cannabis sativa extract led to multiple cannabinoids C-&O-glycosides with anti-proliferative/anti-metastatic properties

Here, we present an interesting, previously unreported method for fractionating a particular class of cannabinoids from the crude leaf extract of Cannabis sativa using HP-20 resins. In this study, we report a novel method of divergent synthesis of fractionated Cannabis sativa extract, which allows the generation of multiple cannabinoids C- and O-glycosides which react with the glycosyl donor 2,3,4,6-tetra-O-acetyl-d-mannosyl trichloroacetimidate (TAMTA) to create eight C- and O-β-d-cannabinoids glycosides (COCG), which are separated by HPLC and whose structures are characterized by 1D, 2D NMR, and mass spectrometry. These glycosides exhibit improved anti-proliferative and anti-metastatic effects against numerous cancer cell lines in vitro and are more water-soluble and stable than their parent cannabinoids. The in vitro testing of the pure cannabinoids (1-4) and their C- & O-glycosides (1a-4a) and 1b-4b exhibited anti-proliferative and anti-metastatic activities against a panel of eight human cancer cell lines in contrast to their respective parent molecules. Different cancer cell lines' IC50 values varied significantly when their cell viability was compared. In addition to the others, compounds 2a, 3a, 4a, and 2b, 3b were highly potent, with IC50values ranging from 0.74 µM (3a) to 51.40 µM (4a).Although2a(1.42 µM) and3a(0.74 µM) exhibited lower IC50values in the MiaPaca-2 cell line than4a(2.58 µM). But, in addition to the comparable anti-clonogenic activity of4ain MiaPaca-2 and Panc-1 cells, it manifested remarkable anti-invasive activity than either 2a or 3a.In contrast to 2a, 2b, 3a, and 3b and their respective parent compounds,4ahad substantial anti-invasive/anti-metastatic capabilities and possessed anti-proliferative activity.The effects of 4a treatment on MiaPaca-2 and Panc-1 cells include a dose-dependent increase in the expression of E-cadherin and a significant decrease in the expression of Zeb-1, Vimentin, and Snail1. Our results demonstrate that divergent synthesis of fractionated Cannabis sativa extract is a feasible and efficient strategy to produce a library of novel cannabinoid glycosides with improved pharmacological properties and potential anticancer benefits.

Bioactive cytochalasans from the desert soil-derived fungus Chaetomium madrasense 375 obtained via a chemical engineering strategy

The chemical engineering of natural extracts has emerged as an effective strategy for the production of diverse libraries of chemicals, making it integral to drug discovery. A chemical engineering strategy based on the epoxidation and ring-opening reactions was used to prepare diversity-enhanced extracts of Chaetomium madrasense 375. Eleven unnatural cytochalasan derivatives (1-11) with unique functional groups, such as amine and isoxazole, were isolated and characterized from these chemically engineered extracts of C. madrasense 375. The identification of these new structures was accomplished through comprehensive spectroscopic analysis, supplemented by synthetic considerations. Notably, compounds 5 and 13-16 displayed potent phytotoxic effects on Arabidopsis thaliana, while compounds 1, 2, 5, 10, and 12 demonstrated inhibitory activities on LPS-induced NO production in RAW264.7 cells. Among them, compound 1 was found to be able to inhibit the upregulated expression of the inducible nitric oxide synthase (iNOS) protein induced by LPS, while also decreasing the production of pro-inflammatory cytokines (IL-6) and influencing the phosphorylation of p38, ERK1/2, and JNK at 100 μM. Our findings demonstrate that the chemical engineering of natural product extracts can be an efficient technique for the generation of novel bioactive molecules.

<em>In silico</em> study of phytochemicals contained in brucea javanica in inhibiting the InhA enzyme as antituberculosis

Background: Currently Mycobacterium tuberculosis is found to be resistant to the treatment of tuberculosis with rifampin and isoniazid (INH) and often stated as multi-drug resistance (MDR). Knowledge and determination of biological properties of plant extracts is a source of drug candidates in various health fields. Therefore, natural products are important in the discovery of new drugs, especially in disease therapy, particularly for tropical dis- eases, tuberculosis. Brucea javanica, known as Buah Makasar, is found in many Asian countries including Indonesia. This plant fruit has a very bitter taste so it cannot be directly consumed and is often used as a traditional medicine to prevent some diseases, especially malaria. There has been no research on the effectiveness of Buah Makasar in tuberculosis. Objective: This study aims to identify compounds contained in Brucea javanica, namely bruceines, bruceosides and yadanzio-sides in inhibiting the InhA enzyme found in the wall of Mycobacterium tuberculosis. Methods: This in-silico study is using Molegro Virtual Docker (MVD) Ver. 5.5. We compared it to the native ligand, namely N-(4- Methylbenzoyl)-4-Benzylpiperidine (code: 4PI) and the reference drug standard, INH. Results: In-silico results show that yadanziosides found in Brucea javanica have the potential to inhibit the InhA enzyme. Bruceoside F (-190.76 Kcal/mol) has the lowest MolDock score among the 27 other compounds. It is also having lower MolDock score than the native ligand 4PI (-120.61 Kcal/mol) and INH (- 54.44 Kcal/mol). Conclusions: Brucea javanica can be considered as source of drug development for againts tuberculosis.

A New Tetracyclic Bromopyrrole-Imidazole Derivative through Direct Chemical Diversification of Substances Present in Natural Product Extract from Marine Sponge Petrosia (Strongylophora) sp

Chemical diversification of substances present in natural product extracts can lead to a number of natural product-like compounds with a better chance of desirable bioactivities. The aim of this work was to discover unprecedented chemical conversion and produce new compounds through a one-step reaction of substances present in the extracts of marine sponges. In this report, a new unnatural tetracyclic bromopyrrole-imidazole derivative, rac-6-OEt-cylindradine A (1), was created from a chemically diversified extract of the sponge Petrosia (Strongylophora) sp. We also confirmed that 1 originated from naturally occurring (-)-cylindradine A (2) via a new reaction pattern. Moreover, (-)-dibromophakellin (3) and 4,5-dibromopyrrole-2-carboxylic acid (4), as well as 2, were reported herein for the first time in this genus. Studies on the possible reaction mechanism and bioactivities were also conducted. The results indicate that the direct chemical diversification of substances present in natural product extracts can be a speedy and useful strategy for the discovery of new compounds.

Effect-directed analysis in food by thin-layer chromatography assays

Thin-layer chromatography (TLC) is widely used for food analysis and quality control. As an open chromatographic system, TLC is compatible with microbial-, biochemical-, and chemical-based derivatization methods. This compatibility makes it possible to run in situ bioassays directly on the plate to obtain activity-profile chromatograms, i.e., the effect-directed analysis of the sample. Many of the properties that can be currently measured using this assay format are related to either desired or undesired features for food related products. The TLC assays can detect compounds related to the stability of foods (antioxidant, antimicrobial, antibrowning, etc.), contaminants (antibiotics, pesticides, estrogenic compounds, etc.), and compounds that affect the absorption, metabolism or excretion of nutrients and metabolites or could improve the consumers health (enzyme inhibitors). In this article, different food related TLC-assays are reviewed. The different detection systems used, the way in which they are applied as well as selected examples are discussed.

Synthesis of natural product hybrids by the Ugi reaction in complex media containing plant extracts

Plant extracts are rich in a wide variety of molecules with diverse biological activities. Chemical engineering of plant extracts has provided a straightforward and simultaneous synthetic route for artificial molecules derived from plant products. This study achieved the synthesis of 13 natural product-like molecules by the Ugi multicomponent reaction using plant extracts as substrates. In particular, the engineering of a mixture of plant extracts demonstrated a unique synthetic route to a series of natural product hybrids, whereby otherwise unencountered naturally occurring molecules of different origins were chemically hybridized in complex media. Even though these reactions took place in complex media containing plant extracts, the well-designed process achieved a good conversion efficiency (~ 60%), chemoselectivity, and reproducibility. Additionally, some of the Ugi adducts exhibited promising inhibitory activity toward protease.

Psilostachyins as trypanocidal compounds: Bioguided fractionation of Ambrosia tenuifolia chemically modified extract

This work focusses on the chemical diversification of an Ambrosia tenuifolia extract and its bioguided fractionation, aiming to unveil the chemical entity responsible for the trypanocidal activity. Besides, a revision of the phytochemical study of this species, based on previous reports of the antiparasitic psilostachyins A and C as main compounds, was conducted. To improve the biological properties of a plant extract through a simple chemical reaction, the oxidative diversification of the dichloromethane extract of this plant species was carried out. A bioguided fractionation of a chemically modified extract was performed by evaluating the inhibitory activity against Trypanosoma cruzi trypomastigotes. This experiment led to the isolation of one of the most active compounds. In general terms, epoxidized metabolites were obtained as a result of the oxidation of the major metabolite of the species. The trypanocidal activity of some tested metabolites overperformed the reference drug, benznidazole, displaying no cytotoxicity at trypanocidal concentrations. Key structure-activity relationships were obtained for designing previously undescribed antiparasitic sesquiterpene lactones.

Antiviral Strategies Using Natural Source-Derived Sulfated Polysaccharides in the Light of the COVID-19 Pandemic and Major Human Pathogenic Viruses

Only a mere fraction of the huge variety of human pathogenic viruses can be targeted by the currently available spectrum of antiviral drugs. The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) outbreak has highlighted the urgent need for molecules that can be deployed quickly to treat novel, developing or re-emerging viral infections. Sulfated polysaccharides are found on the surfaces of both the susceptible host cells and the majority of human viruses, and thus can play an important role during viral infection. Such polysaccharides widely occurring in natural sources, specifically those converted into sulfated varieties, have already proved to possess a high level and sometimes also broad-spectrum antiviral activity. This antiviral potency can be determined through multifold molecular pathways, which in many cases have low profiles of cytotoxicity. Consequently, several new polysaccharide-derived drugs are currently being investigated in clinical settings. We reviewed the present status of research on sulfated polysaccharide-based antiviral agents, their structural characteristics, structure-activity relationships, and the potential of clinical application. Furthermore, the molecular mechanisms of sulfated polysaccharides involved in viral infection or in antiviral activity, respectively, are discussed, together with a focus on the emerging methodology contributing to polysaccharide-based drug development.

Development of Indole Alkaloid-Type Dual Immune Checkpoint Inhibitors Against CTLA-4 and PD-L1 Based on Diversity-Enhanced Extracts

Cancer immunotherapy involves the use of the immune system for cancer treatment. Recently, immune checkpoint-blocking antibodies have become integral for the treatment of some cancers. However, small molecules exhibit advantages over monoclonal antibody drugs, such as cell penetration, long half-life, and low manufacturing costs, and the possibility of oral administration. Thus, it is imperative to develop small-molecule immune checkpoint inhibitors. Previously, we have screened a library of synthetic indole-alkaloid-type compounds, which are produced by diversity-enhanced extracts of Japanese cornelian cherry, and reported that an unnatural pentacyclic compound inhibits CTLA-4 gene expression. In this study, immune checkpoint inhibitors with increased potency were developed by introducing substituents and conversion of functional groups based on the unnatural pentacyclic compound. The developed compounds suppressed not only CTLA-4 and PD-L1 gene expression but also protein expression on the cell surface. Their efficacy was not as potent as that of the existing small-molecule immune checkpoint inhibitors, but, to the best of our knowledge, the developed compounds are the first reported dual small-molecule inhibitors of CTLA-4 and PD-L1.

The heparin-mimicking arabinogalactan sulfates from Anogeissus latifolia gum: Production, structures, and anti-herpes simplex virus activity

Herpes simplex virus type 1(HSV-1) attaches to cell surface heparan sulfate aiming to enter into susceptible cells. In this work, we utilized a sulfur trioxide-pyridine in N,N-dimethylformamide (SO₃·Pyr/DMF) based amalgamated extraction-sulfation procedure for producing arabinogalactan sulfates from Anogeissus latifolia gum. Chemical, chromatographic, spectroscopic and chemical data revealed that the derived polymers contained varying molecular masses (31-69 kDa) and degrees of sulfation (0.1-0.5), but similar saccharide compositions. The highly active polymer (HSV-1: IC₅₀ and SI, respectively, of 127 μg/mL and 15.7) was a 69 kDa arabinogalactan holding sulfates at O-5 of arabinofuranosyl residues and showed no cytotoxicity as far as 2 mg/mL concentration. This chemically sulfated macromolecule acted by obstructing viral attachment and entry. Thus, SO₃·Pyr/DMF is suitable for producing new molecules with varied structures and altered pharmacological activities from plant sources.

Hydrazine-Containing Heterocycle Cytochalasan Derivatives From Hydrazinolysis of Extracts of a Desert Soil-Derived Fungus Chaetomium madrasense 375

"Diversity-enhanced extracts" is an effective method of producing chemical libraries for the purpose of drug discovery. Three rare new cytochalasan derivative chaetoglobosins B1-B3 (1-3) were obtained from chemically engineered crude broth extracts of Chaetomium madrasense 375 prepared by reacting with hydrazine monohydrate and four known metabolite chaetoglobosins (4-7) were also identified from the fungus. The structures were identified by NMR and MS analysis and electronic circular dichroism simulation. In addition, the antiproliferative activities of these compounds were also evaluated, and the drug-resistant activities of cytochalasans were evaluated for the first time. Compound 6 possessed potent activity against four human cancer cells (A549, HCC827, SW620, and MDA-MB-231), and two drug-resistant HCC827 cells (Gefitinib-resistant, Osimertinib-resistant) compared with the positive controls.

Six New Phenylpropanoid Derivatives from Chemically Converted Extract of Alpinia galanga (L.) and Their Antiparasitic Activities

Chemical conversion of the extract of natural resources is a very attractive way to expand the chemical space to discover bioactive compounds. In order to search for new medicines to treat parasitic diseases that cause high morbidity and mortality in affected countries in the world, the ethyl acetate extract from the rhizome of Alpinia galanga (L.) has been chemically converted by epoxidation using dioxirane generated in situ. The biological activity of chemically converted extract (CCE) of A. galanga (L.) significantly increased the activity against Leishmania major up to 82.6 ± 6.2 % at 25 μg/mL (whereas 2.7 ± 0.8% for the original extract). By bioassay-guided fractionation, new phenylpropanoids (1-6) and four known compounds, hydroquinone (7), 4-hydroxy(4-hydroxyphenyl)methoxy)benzaldehyde (8), isocoumarin cis 4-hydroxymelein (9), and (2S,3S,6R,7R,9S,10S)-humulene triepoxide (10) were isolated from CCE. The structures of isolated compounds were determined by spectroscopic analyses of 1D and 2D NMR, IR, and MS spectra. The most active compound was hydroquinone (7) with IC50 = 0.37 ± 1.37 μg/mL as a substantial active principle of CCE. In addition, the new phenylpropanoid 2 (IC50 = 27.8 ± 0.34 μg/mL) also showed significant activity against L. major compared to the positive control miltefosine (IC50 = 7.47 ± 0.3 μg/mL). The activities of the isolated compounds were also evaluated against Plasmodium falciparum, Trypanosoma brucei gambisense and Trypanosoma brucei rhodeisense. Interestingly, compound 2 was selectively active against trypanosomes with potent activity. To the best of our knowledge, this is the first report on the bioactive "unnatural" natural products from the crude extract of A. galanga (L.) by chemical conversion and on its activities against causal pathogens of leishmaniasis, trypanosomiasis, and malaria.

New alkaloids from the diversity-enhanced extracts of an endophytic fungus Aspergillus flavus GZWMJZ-288

Three new alkaloids (1-3) together with four previously reported compounds (4-7) were identified from the extracts and the diversity-enhanced extracts of the fermentation broth of the endophytic fungus, Aspergillus flavus GZWMJZ-288 associated with Garcinia multiflora. The structures of new compounds were respectively determined as 19-amino-19-dehydroxy 5-epi-α-cyclopiazonic acid (1), 2-hydroxymethyl-5-(3-oxobutan-2-yl)aminopyran-4(4H)-one (2) and 4-amino-2-hydroxymethylpyridin-5-ol (3) by spectroscopic analysis, ECD calculation and X-ray single crystal diffraction. Compounds 1 and 4 with 19-enamine were dynamic equilibrium of Z- and E- isomers in the solution but favored in Z- isomers in the solid state, while compound 7 with 19-enol was favored in Z- isomer in the solution but a mixture of Z- and E- isomers in solid state. This phenomenon could be explained by the quantum-mechanical energies calculations. Among the isolated compounds 1-7, compounds 1, 4 and 7 with a rare 1,3,4,5-tetrahydro-1-azaacenaphtho[3,4-c]pyrrolizidine skeleton showed α-glucosidase inhibitory activity with the IC₅₀ values of 41.97 ± 0.97, 232.57 ± 11.45 and 243.95 ± 3.36 μM, respectively, and the binding modes were performed by silico docking studies.

Exploiting the Amazing Diversity of Natural Source-Derived Polysaccharides: Modern Procedures of Isolation, Engineering, and Optimization of Antiviral Activities

Naturally occurring polysaccharide sulfates are highly diverse, owning variations in the backbone structure, linkage pattern and stereochemistry, branching diversity, sulfate content and positions of sulfate group(s). These structural characteristics bring about diverse sulfated polymers with dissimilar negative charge densities and structure-activity relationships. Herein, we start with a short discussion of techniques needed for extraction, purification, chemical sulfation, and structural characterization of polysaccharides. Processes of isolation and sulfation of plant-derived polysaccharides are challenging and usually involve two steps. In this context, we describe an integrated extraction-sulfation procedure that produces polysaccharide sulfates from natural products in one step, thereby generating additional pharmacological activities. Finally, we provide examples of the spectrum of natural source-derived polysaccharides possessing specific features of bioactivity, in particular focusing on current aspects of antiviral drug development and drug-target interaction. Thus, the review presents a detailed view on chemically engineered polysaccharides, especially sulfated derivatives, and underlines their promising biomedical perspectives.

Arylsulfonyl histamine derivatives as powerful and selective α-glucosidase inhibitors

A series of simple N-arylbenzenesulfonyl histamine derivatives were prepared and screened against α-glucosidase. Inhibition was in the micromolar range for several N α,N τ-di-arylsulfonyl compounds, with N α,N τ-di-4-trifluorobenzenesulfonyl histamine (IId) being the best inhibitor. Compound IId is a reversible and competitive α-glucosidase inhibitor, and presented good selectivity with respect to other target enzymes, including β-glucosidase and α-amylase, and interesting predicted physicochemical properties. Docking studies have been run to postulate ligand-enzyme interactions to account for the experimental results. In vivo, compound IId produced a similar hypoglycemic effect to acarbose with half of its dose.

A Tyrosinase Inhibitor from a Nitrogen-Enriched Chemically Engineered Extract

The enzyme tyrosinase is involved in the biosynthesis of melanin and the enzymatic browning of fruits and vegetables, and therefore, its inhibitors have potential to treat hyperpigmentary disorders or to function as food antibrowning agents. The use of hydrazine monohydrate as a reagent to prepare chemically engineered extracts can lead to semisynthetic compounds that contain the portion N-N, a fragment rarely found in natural products and present in some tyrosinase inhibitors. Here, we report the tyrosinase inhibition screening of a series of chemically engineered extracts that are diversified by reaction with hydrazine. LC-MS was used to evaluate the change in composition produced by the reaction. Bioguided fractionation of the most active chemically engineered extract, prepared from Matricaria recutita L., led to the discovery of a pyrazole that inhibits tyrosinase with an IC₅₀ value of 28.20 ± 1.13 μM. This compound was produced by a one-pot double chemical transformation of its natural precursor, which includes an unexpected selective removal of one -OH group.

An Isoform-Selective PTP1B Inhibitor Derived from Nitrogen-Atom Augmentation of Radicicol

A library of natural products and their derivatives was screened for inhibition of protein tyrosine phosphatase (PTP) 1B, which is a validated drug target for the treatment of obesity and type II diabetes. Of those active in the preliminary assay, the most promising was compound 2 containing a novel pyrrolopyrazoloisoquinolone scaffold derived by treating radicicol (1) with hydrazine. This nitrogen-atom augmented radicicol derivative was found to be PTP1B selective relative to other highly homologous nonreceptor PTPs. Biochemical evaluation, molecular docking, and mutagenesis revealed 2 to be an allosteric inhibitor of PTP1B with a submicromolar Ki. Cellular analyses using C2C12 myoblasts indicated that 2 restored insulin signaling and increased glucose uptake.

Quorum Sensing Inhibitors from Marine Microorganisms and Their Synthetic Derivatives

Quorum sensing inhibitors (QSIs) present a promising alternative or potent adjuvants of conventional antibiotics for the treatment of antibiotic-resistant bacterial strains, since they could disrupt bacterial pathogenicity without imposing selective pressure involved in antibacterial treatments. This review covers a series of molecules showing quorum sensing (QS) inhibitory activity that are isolated from marine microorganisms, including bacteria, actinomycetes and fungi, and chemically synthesized based on QSIs derived from marine microorganisms. This is the first comprehensive overview of QSIs derived from marine microorganisms and their synthetic analogues with QS inhibitory activity.

Effects of diosgenin and its derivatives on atherosclerosis

The effects of diosgenin are discussed with respect to endothelial dysfunction, lipid profile, macrophage foam cell formation, VSMC viability, thrombosis and inflammation during the formation of atherosclerosis.

Construction of a Meroterpenoid-Like Compounds Library Based on Diversity-Enhanced Extracts

The structural diversity of natural products and their derivatives have long contributed to the development of new drugs. However, the difficulty in obtaining compounds bearing skeletally novel structures has recently led to a decline of pharmaceutical research into natural products. This paper reports the construction of a meroterpenoid-like library containing 25 compounds with diverse molecular scaffolds obtained from diversity-enhanced extracts. This method constitutes an approach for increasing the chemical diversity of natural-product-like compounds by combining natural product chemistry and diversity-oriented synthesis. Extensive pharmacological screening of the library revealed promising compounds for anti-osteoporotic and anti-lymphoma/leukemia drugs. This result indicates that the use of diversity-enhanced extracts is an effective methodology for producing chemical libraries for the purpose of drug discovery.

Natural Products Extraction of the Future—Sustainable Manufacturing Solutions for Societal Needs

The production of plant-based extracts is significantly influenced by traditional techniques and the natural variability of feedstock. For that reason, the discussion of innovative approaches to improve the manufacturing of established products and the development of new products within the regulatory framework is essential to adapt to shifting quality standards. This perspective of members of the DECHEMA/ProcessNet working group on plant-based extracts outlines extraction business models and the regulatory framework regarding the extraction of traditional herbal medicines as complex extracts. Consequently, modern approaches to innovative process design methods like QbD (Quality by Design) and quality control in the form of PAT (Process Analytical Technology) are necessary. Further, the benefit of standardized laboratory equipment combined with physico-chemical predictive process modelling and innovative modular, flexible batch or continuous manufacturing technologies which are fully automated by advanced process control methods are described. A significant reduction of the cost of goods, i.e., by a factor of 4–10, and decreased investments of about 1–5 mil. € show the potential for new products which are in line with market requirements.

Natural products chemistry: The emerging trends and prospective goals

The role and contributions of natural products chemistry in advancements of the physical and biological sciences, its interdisciplinary domains, and emerging of new avenues by providing novel applications, constructive inputs, thrust, comprehensive understanding, broad perspective, and a new vision for future is outlined. The developmental prospects in bio-medical, health, nutrition, and other interrelated sciences along with some of the emerging trends in the subject area are also discussed as part of the current review of the basic and core developments, innovation in techniques, advances in methodology, and possible applications with their effects on the sciences in general and natural products chemistry in particular. The overview of the progress and ongoing developments in broader areas of the natural products chemistry discipline, its role and concurrent economic and scientific implications, contemporary objectives, future prospects as well as impending goals are also outlined. A look at the natural products chemistry in providing scientific progress in various disciplines is deliberated upon.

A Bioactive Trypanosoma cruzi Bromodomain Inhibitor from Chemically Engineered Extracts

A set of chemically engineered extracts enriched in compounds including N-N and N-O fragments in their structures was prepared. Bromodomain binding screening and bioguided fractionation led to the identification of one oxime hit that interacts with TcBDF3 with affinity in the submicromolar range and that shows interesting antiparasitic properties against the different life cycle stages of T. cruzi.

New α-Pyridones with Quorum-Sensing Inhibitory Activity from Diversity-Enhanced Extracts of a Streptomyces sp. Derived from Marine Algae

Four new α-pyrones (1-4) and eight known analogues (5-12) were identified from the secondary metabolites of Streptomyces sp. OUCMDZ-3436 derived from the marine green algae Enteromorpha prolifera. Seven new α-pyridones (14-20) were constructed by diversity-oriented synthesis, which has been an effective approach to expanding the chemical space of natural-product-like compounds. Compounds 16, 17, 19, and 20 were found to have inhibitory effect on the gene expression controlled by quorum sensing in Pseudomonas aeruginosa QSIS-lasI.

Nα-arylsulfonyl histamines as selective β-glucosidase inhibitors

N^α-benzenesulfonylhistamine, a new semi-synthetic β-glucosidase inhibitor, was obtained by bioactivity-guided isolation from a chemically engineered extract of Urtica urens L. prepared by reaction with benzenesulfonyl chloride. In order to identify better β-glucosidase inhibitors, a new series of N^α,N^τ-di-arylsulfonyl and N^α-arylsulfonyl histamine derivatives was prepared. Biological studies revealed that the β-glucosidase inhibition was in a micromolar range for several N^α-arylsulfonyl histamine compounds of the series, N^α-4-fluorobenzenesulfonyl histamine being the most powerful compound. Besides, this reversible and competitive inhibitor presented a good selectivity for β-glucosidase with respect to other target enzymes including α-glucosidase.

A selective β-glucosidase inhibitor was discovered using the chemically engineered extracts approach.

Antifungal photosensitive activity of Porophyllum obscurum (Spreng.) DC.: Correlation of the chemical composition of the hexane extract with the bioactivity

We report Porophyllum obscurum as a source of new photosensitizers with potential use in Photodynamic Therapy as an alternative for oropharyngeal candidiasis treatment. The antifungal photosensitive activity of different extracts from P. obscurum was evaluated by using microdilution and bioautographic assays. The Minimum Fungicidal Concentration for hexanic extract under UV-A irradiation was 0.98μg/mL, but it was inactive in experiments without irradiation. The bioassay-guided fractionation of this extract led to the isolation of four thiophenes responsible for the photosensitive activity: 2,2':5'2″terthiophene, 5-(3-buten-1-ynyl)-2,2'-bithiophene, 5-(4-acetoxy-1-butenyl)-2,2'- bithiophene and 5-(4-hydroxy-1-butenyl)-2,2'- bithiophene, with Minimum Fungicidal Concentrations ranging 0.24-7.81μg/mL under UV-A irradiation. The activity of the hexanic extract was evaluated against 25 clinical strains of Candida spp. isolates as etiological agents of oropharyngeal candidiasis. No differences in susceptibility were observed in strains resistant and susceptible to conventional antifungal drugs. Qualitative and quantitative chemical analyses of seven samples of P. obscurum collected in four different phenological stages were carried out showing that full flowering stage possesses the highest thiophenes content. These data also allowed us to establish a correlation between the thiophene composition of the different extracts and their antifungal photosensitive activity, according to a second order polynomial model with the equation: y=11.2603-0.6831*x+0.0108*x². The thiophenes isolated were the responsible of antifungal photosensitive activity and can be used for the future standardization of the extract. Results showed that P. obscurum hexanic extract could be potentially developed as an Herbal Medicinal Product to be applied as a photosensitizer in Photodynamic Therapy.

Strategies to diversify natural products for drug discovery

Natural product libraries contain specialized metabolites derived from plants, animals, and microorganisms that play a pivotal role in drug discovery due to their immense structural diversity and wide variety of biological activities. The strategies to greatly extend natural product scaffolds through available biological and chemical approaches offer unique opportunities to access a new series of natural product analogues, enabling the construction of diverse natural product-like libraries. The affordability of these structurally diverse molecules has been a crucial step in accelerating drug discovery. This review provides an overview of various approaches to exploit the diversity of compounds for natural product-based drug development, drawing upon a series of examples to illustrate each strategy.

Bioactivity-guided mixed synthesis accelerate the serendipity in lead optimization: Discovery of fungicidal homodrimanyl amides

The bioactivity-guided mixed synthesis was conceived, in which the designed mix-reactions were run in parallel for simultaneous construction of different kinds of analogs. The valuable ones were protruded by biological screening. This tactic will facilitate more rapid incorporation of bioactive candidates into pesticide chemists' repertoire, exemplified by the optimization of less explored homodrimanes as antifungal ingredients. The discovery of D9 as a potent fungicidal agent can be completed in <2 weeks by one student, with EC₅₀ of 3.33 mg/L and 2.45 mg/L against S. sclerotiorum and B. cinerea, respectively. To confirm the practicability, time-efficiency, and reliability, specific homodrimanes (82 derivatives) were synthesized and elucidated separately and determined for EC₅₀ values. The SAR correlated well with the intentionally mixed synthesis and the potential was further confirmed by the in vivo bioassay. This methodology will foster more efficient exploration of biologically relevant chemical space of natural products in pesticide discovery, and can also be tailored readily for the lead optimization in medicinal chemistry.

Reverse Phase Compatible TLC-Bioautography for Detection of Tyrosinase Inhibitors

INTRODUCTION

Reverse phase chromatography and bioautographic assays are key tools for natural product bioguided isolation; however, their direct coupling has not been fully achieved.

OBJECTIVES

To develop a bioautographic assay to detect tyrosinase inhibitors present in complex matrices sorbed on reverse phase (RP) TLC-plates that can be used for bioguided isolation of bioactive compounds.

METHODS

Enzyme gel entrapment with an amphiphilic copolymer was used for assay development. The gel turns into a brown "skin like" colour due to tyrosinase catalysed oxidation of l-tyrosine. The inhibitors are visualised as clear spots against a brown coloured background.

RESULTS

The assay was able to localise cinnamaldehyde in Cinnamomum cassia essential oil, as its main constituent with known tyrosinase inhibition properties. The assay allowed the detection of 0.03% (w/w) of kojic acid co-spotted with a methanolic extract of Sphaeralcea bonariensis and chromatographed on RP-TLC.

CONCLUSION

The developed assay is able to detect, with high sensitivity, tyrosinase inhibitors present in complex matrices that were chromatographed in RP-TLC. Results can be easily read by colour change, inhibitors appear as clear spots in a darker background. Copyright © 2016 John Wiley & Sons, Ltd.

Monoterpene Indole Alkaloid-Like Compounds Based on Diversity-Enhanced Extracts of Iridoid-Containing Plants and Their Immune Checkpoint Inhibitory Activity

A library of iridoid-conjugated indole alkaloid-like compounds was constructed from diversity-enhanced extracts, which constitutes an approach for increasing the chemical diversity of natural-product-like compounds by combining natural product chemistry and diversity-oriented synthesis. Pharmacological screening of the library revealed a seed compound that can be used for the development of small molecular immune checkpoint inhibitors.

A reversed-phase compatible thin-layer chromatography autography for the detection of acetylcholinesterase inhibitors

A dual readout autographic assay to detect acetylcholinesterase inhibitors present in complex matrices adsorbed on reversed-phase or normal-phase thin-layer chromatography plates is described. Enzyme gel entrapment with an amphiphilic copolymer was used for assay development. The effects of substrate and enzyme concentrations, pH, incubation time, and incubation temperature on the sensitivity and the detection limit of the assay were evaluated. Experimental design and response surface methodology were used to optimize conditions with a minimum number of experiments. The assay allowed the detection of 0.01% w/w of physostigmine in both a spiked Sonchus oleraceus L. extract chromatographed on normal phase and a spiked Pimenta racemosa (Mill.) J.W. Moore leaf essential oil chromatographed on reversed phase. Finally, the reversed-phase thin-layer chromatography assay was applied to reveal the presence of an inhibitor in the Cymbopogon citratus (DC.) Stapf essential oil. The developed assay is able to detect acetylcholinesterase inhibitors present in complex matrixes that were chromatographed in normal phase or reversed-phase thin-layer chromatography. The detection limit for physostigmine on both normal and reversed phase was of 1×10(-4) μg. The results can be read by a change in color and/or a change in fluorescence.

A New Fluorinated Tyrosinase Inhibitor from a Chemically Engineered Essential Oil

The generation of fluorinated essential oils as a source of bioactive compounds is described. Most of the components of the natural mixtures were altered, leading to the discovery of a new fluorinated tyrosinase inhibitor.

Ascochyta blight: isolation, characterization, and development of a rapid method to detect inhibitors of the chickpea fungal pathogen Ascochyta rabiei

Ascochyta blight is the major disease attacking chickpea (Cicer arietinum) around the world. Since its first time report of isolation in Argentina in 2012, the pathogen has caused severe economic losses and has acquired a great importance. We report here the isolation of Ascochyta rabiei from infected chickpea beans cultivated in Santa Fe, Argentina; its identification by morphological analysis and molecular biology techniques based on internal transcribed spacer (ITS) sequence alignment, its biochemical characterization regarding the capacity to produce proteinase and phospholipase enzymes, and its antifungal susceptibility to common used antifungal agents. In order to detect new inhibitors for A. rabiei from natural sources, a bioautographic method was developed. From the screening method developed, we found that extracts from cultures of Aspergillus parasiticus are active against A. rabiei.

Chemical diversification of essential oils, evaluation of complex mixtures and identification of a xanthine oxidase inhibitor

A set of chemically engineered essential oils has been generated through chemical diversification by reaction with bromine, leading to the discovery of a new brominated xanthine oxidase inhibitor.