Pseudo-Natural Products: Expanding chemical and biological space by surpassing natural constraints

This review explores the recent advancements in the design and synthesis of pseudo-natural products (pseudo-NPs) by employing innovative principles and strategies, heralding a transformative era in chemistry and biology. Pseudo-NPs, produced through in silico fragmentation and the de novo recombination of natural product fragments, reveal compounds endowed with distinct biological activities. Their advantage lies in transcending natural product structures, fostering diverse possibilities. Research in this area over the past decade has yielded unconventional combinations of natural product fragments, leading to the identification of novel compounds possessing unique scaffolds and biological significance, thereby contributing to the discovery of new therapeutics. The pseudo-NPs exert potent biological effects through various signaling pathways. In chemical biology and medicinal chemistry, designing pseudo-NPs is an important strategy, harnessing molecular hybridization and bioinspired synthesis to generate diverse compounds with remarkable biological activities, underscoring their immense potential in drug discovery and development.

Exploring the osteogenic potential of semisynthetic triterpenes from Combretum leprosum: An in vitro and in silico study

Combretum leprosum Mart. is a plant of the Combretaceae family, widely distributed in the Northeast region of Brazil, popularly used as an anti-inflammatory agent, and rich in triterpenes. This study evaluated in vitro and in silico potential osteogenic of two semisynthetic triterpenes (CL-P2 and CL-P2A) obtained from the pentacyclic triterpene 3β,6β,16β-trihydroxylup-20(29)-ene (CL-1) isolated from C. leprosum. Assays were carried out in cultured murine osteoblasts (OFCOL II), first investigating the possible toxicity of the compounds on these cells through viability assays (MTT). Cell proliferation and activation were investigated by immunohistochemical evaluation of Ki-67, bone alkaline phosphatase (ALP) activity, and mineralization test by Von Kossa. Molecular docking analysis was performed to predict the binding affinity of CL-P2 and CL-P2A to target proteins involved in the regulation of osteogenesis, including: bone morphogenetic protein 2 (BMP-2), proteins related to Wingless-related integration (WNT) pathway (Low-density lipoprotein receptor-related protein 6-LRP6 and sclerostin-SOST), and receptor activator of nuclear factor (NF)-kB-ligand (RANK-L). Next, Western Blot and immunofluorescence investigated BMP-2, WNT, RANK-L, and OPG protein expressions in cultured murine osteoblasts (OFCOL II). None of the CL-P2 and CL-P2A concentrations were toxic to osteoblasts. Increased cell proliferation, ALP activity, and bone mineralization were observed. Molecular docking assays demonstrated interactions with BMP-2, LRP6, SOST, and RANK-L/OPG. There was observed increased expression of BMP-2, WNT, and RANK-L/OPG proteins. These results suggest, for the first time, the osteogenic potential of CL-P2 and CL-P2A.

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.

Rapid Access to Tigliane, Ingenane, and Rhamnofolane Diterpenes from a Lathyrane Precursor via Biomimetic Skeleton Transformation Strategy

Bioinspired skeleton transformation of a tricyclic lathyrane-type Euphorbia diterpene was conducted to efficiently construct a tetracyclic tigliane diterpene on a gram scale via a key aldol condensation. The tigliane diterpene was then respectively converted into naturally rare ingenane and rhamnofolane diterpenes through a semipinacol rearrangement and a visible-light-promoted regioselective cyclopropane ring-opening reaction. This work provides a concise strategy for high-efficiency access to diverse polycyclic Euphorbia diterpene skeletons from abundant lathyrane-type natural products and paves the way for biological activity investigation of naturally rare molecules.

Anticancer Effects of Abietane Diterpene 7α-Acetoxy-6β-hydroxyroyleanone from Plectranthus grandidentatus and Its Semi-Synthetic Analogs: An In Silico Computational Approach

The abietane diterpenoid 7α-acetoxy-6β-hydroxyroyleanone (Roy) isolated from Plectranthus grandidentatus demonstrates cytotoxicity across numerous cancer cell lines. To potentiate anticancer attributes, a series of semi-synthetic Roy derivatives were generated and examined computationally. ADMET predictions were used to evaluate drug-likeness and toxicity risks. The antineoplastic potential was quantified by PASS. The DFT models were used to assess their reactivity and stability. Molecular docking determined cancer-related protein binding. MS simulations examined ligand-protein stability. Additionally, network pharmacology was used to identify potential targets and signaling pathways. Favorable ADME attributes and acceptable toxicity profiles were determined for all compounds. Strong anticancer potential was shown across derivatives (Pa 0.819-0.879). Strategic modifications altered HOMO-LUMO gaps (3.39-3.79 eV) and global reactivity indices. Favorable binding was revealed against cyclin-dependent kinases, BCL-2, caspases, receptor tyrosine kinases, and p53. The ligand exhibited a stable binding pose in MD simulations. Network analysis revealed involvement in cancer-related pathways. In silico evaluations predicted Roy and derivatives as effective molecules with anticancer properties. Experimental progress is warranted to realize their chemotherapeutic potential.

Natural products for combating multidrug resistance in cancer

Cancer cells frequently develop resistance to chemotherapeutic therapies and targeted drugs, which has been a significant challenge in cancer management. With the growing advances in technologies in isolation and identification of natural products, the potential of natural products in combating cancer multidrug resistance has received substantial attention. Importantly, natural products can impact multiple targets, which can be valuable in overcoming drug resistance from different perspectives. In the current review, we will describe the well-established mechanisms underlying multidrug resistance, and introduce natural products that could target these multidrug resistant mechanisms. Specifically, we will discuss natural compounds such as curcumin, resveratrol, baicalein, chrysin and more, and their potential roles in combating multidrug resistance. This review article aims to provide a systematic summary of recent advances of natural products in combating cancer drug resistance, and will provide rationales for novel drug discovery.

Identification of terpenoids as dihydropteroate synthase and dihydrofolate reductase inhibitors through structure-based virtual screening and molecular dynamic simulations

Bacterial infections are rising, and antimicrobial resistance (AMR) in bacteria has worsened the scenario, requiring extensive research to find alternative therapeutic agents. Terpenoids play an essential role in protecting plants from herbivores and pathogens. The present study was designed to focus on in silico evaluation of terpenoids for their affinity towards two necessary enzymes, i.e. DHFR and DHPS, which are involved in forming 5, 6, 7, 8-tetrahydrofolate, a key component in bacterial DNA synthesis proteins. Additionally, to account for activity against resistant bacteria, their affinity towards the L28R mutant of DHFR was also assessed in the study. The structure-based drug design approach was used to screen the compound library of terpenes for their interaction with active sites of DHFR and DHPS. Further, compounds were screened based on their dock score, pharmacokinetic properties, and binding affinities. A total of five compounds for each target protein were screened, having dock scores better than their respective standard drug molecules. CNP0169378 (-8.4 kcal/mol) and CNP0309455 (-6.5 kcal/mol) have been identified as molecules with a higher affinity toward the targets of DHFR and DHPS, respectively. At the same time, one molecule CNP0298407 (-5.8 kcal/mol for DHPS, -7.6 kcal/mol for DHFR, -6.1 kcal/mol for the L28R variant), has affinity for both proteins (6XG5 and 6XG4). All the molecules have good pharmacokinetic properties. We further validated the docking study by binding free energy calculations using the MM/GBSA approach and molecular dynamics simulations.Communicated by Ramaswamy H. Sarma.

Biological activity and structural modification of isosteviol over the past 15 years

Isosteviol is a tetracyclic diterpenoid obtained by hydrolysis of stevioside. Due to its unique molecular skeleton and extensive pharmacological activities, isosteviol has attracted more and more attention from researchers. This review summarized the structural modification, pharmacological activity and microbial transformation of isosteviol from 04/2008 to 10/2023. In addition, the research history, structural characterization, and pharmacokinetics of isosteviol were also briefly reviewed. This review aims to provide useful literature resources and inspirations for the exploration of diterpenoid drugs.

Molecular Hybridization of Alkaloids Using 1,2,3-Triazole-Based Click Chemistry

Alkaloids found in multiple species, known as 'driver species', are more likely to be included in early-stage drug development due to their high biodiversity compared to rare alkaloids. Many synthetic approaches have been employed to hybridize the natural alkaloids in drug development. Click chemistry is a highly efficient and versatile reaction targeting specific areas, making it a valuable tool for creating complex natural products and diverse molecular structures. It has been used to create hybrid alkaloids that address their limitations and serve as potential drugs that mimic natural products. In this review, we highlight the recent advancements made in modifying alkaloids using click chemistry and their potential medicinal applications. We discuss the significance, current trends, and prospects of click chemistry in natural product-based medicine. Furthermore, we have employed computational methods to evaluate the ADMET properties and drug-like qualities of hybrid molecules.

Challenges in natural product-based drug discovery assisted with in silico-based methods

The application of traditional medicine by humans for the treatment of ailments as well as improving the quality of life far outdates recorded history. To date, a significant percentage of humans, especially those living in developing/underprivileged communities still rely on traditional medicine for primary healthcare needs. In silico-based methods have been shown to play a pivotal role in modern pharmaceutical drug discovery processes. The application of these methods in identifying natural product (NP)-based hits has been successful. This is very much observed in many research set-ups that use rationally in silico-based methods in combination with experimental validation techniques. The combination has rendered the use of in silico-based approaches even more popular and successful in the investigation of NPs. However, identifying and proposing novel NP-based hits for experimental validation comes with several challenges such as the availability of compounds by suppliers, the huge task of separating pure compounds from complex mixtures, the quantity of samples available from the natural source to be tested, not to mention the potential ecological impact if the natural source is exhausted. Because most peer-reviewed publications are biased towards "positive results", these challenges are generally not discussed in publications. In this review, we highlight and discuss these challenges. The idea is to give interested scientists in this field of research an idea of what they can come across or should be expecting as well as prompting them on how to avoid or fix these issues.

Biological Evaluation of 8-Methoxy-2,5-dimethyl-5H-indolo[2,3-b] Quinoline as a Potential Antitumor Agent via PI3K/AKT/mTOR Signaling

Chemotherapy is commonly used clinically to treat colorectal cancer, but it is usually prone to drug resistance, so novel drugs need to be developed continuously to treat colorectal cancer. Neocryptolepine derivatives have attracted a lot of attention because of their good cytotoxic activity; however, cytotoxicity studies on colorectal cancer cells are scarce. In this study, the cytotoxicity of 8-methoxy-2,5-dimethyl-5H-indolo[2,3-b] quinoline (MMNC) in colorectal cells was evaluated. The results showed that MMNC inhibits the proliferation of HCT116 and Caco-2 cells, blocks the cell cycle in the G2/M phase, decreases the cell mitochondrial membrane potential and induces apoptosis. In addition, the results of western blot experiments suggest that MMNC exerts cytotoxicity by inhibiting the expression of PI3K/AKT/mTOR signaling pathway-related proteins. Based on these results, MMNC is a promising lead compound for anticancer activity in the treatment of human colorectal cancer.

Failure, Success, and Future Direction of Alzheimer Drugs Targeting Amyloid-β Cascade: Pros and Cons of Chemical and Biological Modalities

Alzheimer's disease (AD) is the most prevalent cause of dementia and has become a health concern worldwide urging for an effective therapeutic. The amyloid hypothesis, currently the most pursued basis of AD drug discovery, points the cause of AD to abnormal production and ineffective removal of pathogenic aggregated amyloid-β (Aβ). AD therapeutic research has been focused on targeting different species of Aβ in the amyloidogenic process to control Aβ content and recover cognitive decline. Among the different processes targeted, the clearance mechanism has been found to be the most effective, supported by the recent clinical approval of an Aβ-targeting immunotherapeutic drug which significantly slowed cognitive decline. Although the current AD drug discovery field is extensively researching immunotherapeutic drugs, there are numerous properties of immunotherapy in need of improvements that could be overcome by an equally performing chemical drug. Here, we review chemical and immunotherapy drug candidates, based on their mechanism of modulating the amyloid cascade, selected from the AlzForum database. Through this review, we aim to summarize and evaluate the prospect of Aβ-targeting chemical drugs.

Iron mediated reductive cyclization/oxidation for the generation of chemically diverse scaffolds: An approach in drug discovery

Chemically diverse scaffolds represent a main source of biologically important starting points in drug discovery. Herein, we report the development of such diverse scaffolds from nitroarene/ nitro(hetero)arenes using a key synthetic strategy. In a pilot-scale study, the synthesis of 10 diverse scaffolds was achieved. The 1,7-phenanthroline, thiazolo[5,4-f]quinoline, 2,3-dihydro-1H-pyrrolo[2,3-g]quinoline, pyrrolo[3,2-f]quinoline, 1H-[1,4]oxazino[3,2-g]quinolin-2(3H)-one, [1,2,5]oxadiazolo[3,4-h]quinoline, 7H-pyrido[2,3-c]carbazole, 3H-pyrazolo[4,3-f]quinoline, pyrido[3,2-f]quinoxaline were obtained from nitro hetero arenes in ethanol using iron-acetic acid treatment followed by reaction under oxygen atmosphere. This diverse library is compliant with the rule of five for drug-likeness. The mapping of chemical space represented by these scaffolds revealed a significant contribution to the underrepresented chemical diversity. Crucial to the development of this approach was the mapping of biological space covered by these scaffolds which revealed neurotropic and prophylactic anti-inflammatory activities. In vitro, neuro-biological assays revealed that compounds 14a and 15a showed excellent neurotropic potential and neurite growth compared to controls. Further, anti-inflammatory assays (in vitro and in vivo models) exhibited that Compound 16 showed significant anti-inflammatory activity by attenuating the LPS-induced TNF-α and CD68 levels by modulating the NFkB pathway. In addition, treatment with compound 16 significantly ameliorated the LPS-induced sepsis conditions, and pathological abnormalities (in lung and liver tissues) and improved the survival of the rats compared to LPS control. Owing to their chemical diversity along with bioactivities, it is envisaged that new quality pre-clinical candidates will be generated in the above therapeutic areas using identified leads.

Stimuli-responsive (nano)architectures for phytochemical delivery in cancer therapy

The use of phytochemicals for purpose of cancer therapy has been accelerated due to resistance of tumor cells to conventional chemotherapy drugs and therefore, monotherapy does not cause significant improvement in the prognosis and survival of patients. Therefore, administration of natural products alone or in combination with chemotherapy drugs due to various mechanisms of action has been suggested. However, cancer therapy using phytochemicals requires more attention because of poor bioavailability of compounds and lack of specific accumulation at tumor site. Hence, nanocarriers for specific delivery of phytochemicals in tumor therapy has been suggested. The pharmacokinetic profile of natural products and their therapeutic indices can be improved. The nanocarriers can improve potential of natural products in crossing over BBB and also, promote internalization in cancer cells through endocytosis. Moreover, (nano)platforms can deliver both natural and synthetic anti-cancer drugs in combination cancer therapy. The surface functionalization of nanostructures with ligands improves ability in internalization in tumor cells and improving cytotoxicity of natural compounds. Interestingly, stimuli-responsive nanostructures that respond to endogenous and exogenous stimuli have been employed for delivery of natural compounds in cancer therapy. The decrease in pH in tumor microenvironment causes degradation of bonds in nanostructures to release cargo and when changes in GSH levels occur, it also mediates drug release from nanocarriers. Moreover, enzymes in the tumor microenvironment such as MMP-2 can mediate drug release from nanocarriers and more progresses in targeted drug delivery obtained by application of nanoparticles that are responsive to exogenous stimulus including light.

Discovery of Natural Sesquiterpene Lactone 1-O-Acetylbritannilactone Analogues Bearing Oxadiazole, Triazole, or Imidazole Scaffolds for the Development of New Fungicidal Candidates

In recent decades, natural products have been considered important resources for developing of new agrochemicals because of their novel architectures and multibioactivities. Consequently, herein, 1-O-acetylbritannilactone (ABL), a natural sesquiterpene lactone from Inula britannica L., was used as a lead for further modification to discover fungicidal candidates. Six series of ABL-based derivatives containing an oxadiazole, triazole, or imidazole moiety were designed and synthesized, and their antifungal activities were also evaluated in vitro and in vivo. Bioassay results revealed that compounds 8d, 8h, and 8j (EC₅₀ = 61.4, 30.9, and 12.4 μg/mL, respectively) exhibited more pronounced inhibitory activity against Fusarium oxysporum than their precursor ABL (EC₅₀ > 500 μg/mL) and positive control hymexazol (EC₅₀ = 77.2 μg/mL). Derivatives 8d and 11j (EC₅₀ = 19.6 and 41.5 μg/mL, respectively) exhibited more potent antifungal activity toward Cytospora mandshurica than ABL (EC₅₀ = 68.3 μg/mL). Compound 10 exhibited excellent and broad-spectrum antifungal activity against seven phytopathogenic fungal mycelia. Particularly, the inhibitory activity of compound 10 against the mycelium of Botrytis cinerea was more than 10.8- and 2.3-fold those of ABL and hymexazol, respectively. Meanwhile, derivative 10 (IC₅₀ = 47.7 μg/mL) displayed more pronounced inhibitory activity against the spore of B. cinerea than ABL (IC₅₀ > 500 μg/mL) and difenoconazole (IC₅₀ = 80.8 μg/mL). Additionally, the in vivo control efficacy of compound 10 against B. cinerea was further studied using infected tomatoes (protective effect = 58.4%; therapeutic effect = 48.7%). The preliminary structure-activity relationship analysis suggested that the introduction of the 1,3,4-oxadiazole moiety (especially the 1,3,4-oxadiazole heterocycle containing the 4-chlorophenyl, 2-furyl, or 2-pyridinyl group) on the skeleton of ABL was more likely to produce potential antifungal compounds. These findings pave the way for further design and development of ABL-based derivatives as potential antifungal agents.

Bromotyrosine-Derived Metabolites from a Marine Sponge Inhibit Pseudomonas aeruginosa Biofilms

Pseudomonas aeruginosa forms stable biofilms, providing a major barrier for multiple classes of antibiotics and severely impairing treatment of infected patients. The biofilm matrix of this Gram-negative bacterium is primarily composed of three major exopolysaccharides: alginate, Psl, and Pel. Here, we studied the antibiofilm properties of sponge-derived natural products ianthelliformisamines A-C and their combinations with clinically used antibiotics. Wild-type P. aeruginosa strain and its isogenic exopolysaccharide-deficient mutants were employed to determine the interference of the compounds with biofilm matrix components. We identified that ianthelliformisamines A and B worked synergistically with ciprofloxacin to kill planktonic and biofilm cells. Ianthelliformisamines A and B reduced the minimum inhibitory concentration (MIC) of ciprofloxacin to 1/3 and 1/4 MICs, respectively. In contrast, ianthelliformisamine C (MIC = 53.1 µg/mL) alone exhibited bactericidal effects dose-dependently on both free-living and biofilm populations of wild-type PAO1, PAO1ΔpslA (Psl deficient), PDO300 (alginate overproducing and mimicking clinical isolates), and PDO300Δalg8 (alginate deficient). Interestingly, the biofilm of the clinically relevant mucoid variant PDO300 was more susceptible to ianthelliformisamine C than strains with impaired polysaccharide synthesis. Ianthelliformisamines exhibited low cytotoxicity towards HEK293 cells in the resazurin viability assay. Mechanism of action studies showed that ianthelliformisamine C inhibited the efflux pump of P. aeruginosa. Metabolic stability analyses indicated that ianthelliformisamine C is stable and ianthelliformisamines A and B are rapidly degraded. Overall, these findings suggest that the ianthelliformisamine chemotype could be a promising candidate for the treatment of P. aeruginosa biofilms.

Co-Expression of Transcriptional Regulators and Housekeeping Genes in Streptomyces spp.: A Strategy to Optimize Metabolite Production

The search for novel bioactive compounds to overcome resistance to current therapeutics has become of utmost importance. Streptomyces spp. are one of the main sources of bioactive compounds currently used in medicine. In this work, five different global transcriptional regulators and five housekeeping genes, known to induce the activation or overproduction of secondary metabolites in Streptomyces coelicolor, were cloned in two separated constructs and expressed in 12 different strains of Streptomyces spp. from the in-house CS collection. These recombinant plasmids were also inserted into streptomycin and rifampicin resistant Streptomyces strains (mutations known to enhance secondary metabolism in Streptomyces). Different media with diverse carbon and nitrogen sources were selected to assess the strains' metabolite production. Cultures were then extracted with different organic solvents and analysed to search for changes in their production profiles. An overproduction of metabolites already known to be produced by the biosynthesis wild-type strains was observed such as germicidin by CS113, collismycins by CS149 and CS014, or colibrimycins by CS147. Additionally, the activation of some compounds such as alteramides in CS090a pSETxkBMRRH and CS065a pSETxkDCABA or inhibition of the biosynthesis of chromomycins in CS065a in pSETxkDCABA when grown in SM10 was demonstrated. Therefore, these genetic constructs are a relatively simple tool to manipulate Streptomyces metabolism and explore their wide secondary metabolites production potential.

Phytochemical and Biological Investigation of an Indigenous Plant of Bangladesh, Gynura procumbens (Lour.) Merr.: Drug Discovery from Nature

Gynura procumbens (Lour.) Merr. (Family: Asteraceae) is a tropical Asian medicinal plant found in Thailand, China, Malaysia, Indonesia, and Vietnam. It has long been utilized to treat a variety of health concerns in numerous countries around the world, such as renal discomfort, constipation, diabetes mellitus, rheumatism, and hypertension. The chemical investigation resulted in the isolation and characterization of six compounds from the methanol (MeOH) extract of the leaves of Gynura procumbens, which were identified as phytol (1), lupeol (2), stigmasterol (3), friedelanol acetate (4), β-amyrin (5), and a mixture of stigmasterol and β-sitosterol (6). In-depth investigations of the high-resolution ¹H NMR and ¹³C NMR spectroscopic data from the isolated compounds, along with comparisons to previously published data, were used to clarify their structures. Among these, the occurrence of Compounds 1 and 4 in this plant are reported for the first time. The crude methanolic extract (CME) and its different partitionates, i.e., petroleum ether (PESF), chloroform (CSF), ethyl acetate (EASF), and aqueous (AQSF) soluble fractions, were subjected to antioxidant, cytotoxic, thrombolytic, and anti-diabetic activities. In a DPPH free radical scavenging assay, EASF showed the maximum activity, with an IC₅₀ value of 10.78 µg/mL. On the other hand, CSF displayed the highest cytotoxic effect with an LC₅₀ value of 1.94 µg/mL compared to 0.464 µg/mL for vincristine sulphate. In a thrombolytic assay, the crude methanolic extract exhibited the highest activity (63.77%) compared to standard streptokinase (70.78%). During the assay for anti-diabetic activity, the PESF showed 70.37% of glucose-lowering activity, where standard glibenclamide showed 63.24% of glucose-reducing activity.

Using a Bioactive Eremophila-Derived Serrulatane Scaffold to Generate a Unique Carbamate Library for Anti-infective Evaluations

The known Eremophila microtheca-derived diterpenoid 3,7,8-trihydroxyserrulat-14-en-19-oic acid (1) was targeted for large-scale purification, as this bioactive plant compound has proven to be an attractive scaffold for semisynthetic studies and subsequent library generation. Compound 1 was converted to a selectively protected trimethyl derivative, 3-hydroxy-7,8-dimethoxyserrulat-14-en-19-oic acid methyl ester (2), using simple and rapid methylation conditions. The resulting scaffold 2 was reacted with a diverse series of commercially available isocyanates to generate an 11-membered carbamate-based library. The chemical structures of the 11 new semisynthetic analogues were fully characterized by spectroscopic and spectrometric analysis. All natural products and semisynthetic compounds were evaluated for their anthelmintic, antimalarial, and anti-HIV activities. Compound 3 was shown to elicit the greatest antiplasmodial activity of all compounds tested, with IC₅₀ values of 4.6 and 11.6 μM against Plasmodium falciparum 3D7 and Dd2, respectively. Compound 11 showed the greatest inhibition of development to fourth-stage Haemonchus contortus larvae (L4) and induction of a skinny (Ski) phenotype (67.5% of nematodes) at 50 μM. Compound 7, which inhibited 59.0% of HIV production at 100 μg/mL, was the carbamate analogue that displayed the best antiviral activity.

Synthesis of Aza-Bridged Perhydroazulene Chimeras of Tropanes and Hederacine A

We report the synthesis of two novel azaperhydroazulene tropane-hederacine chimeras A and B, which contain an 8-azabicyclo[3.2.1]octane ring and a 7-azabicyclo[4.1.1]octane ring, respectively. The synthesis of both chimeras was achieved by epoxide ring opening and was governed by the stereochemistry of the hydroxy-epoxide unit. Finally, a density functional theory study was conducted to explain the regioselectivity of the cyclization and the importance of the stereochemistry of the hydroxyl group.

Recent advances of LSD1/KDM1A inhibitors for disease therapy

Lysine-specific demethylase 1 (LSD1/KDM1A) dysregulation is closely associated with the pathological processes of various diseases, especially hematologic malignancies. Significant progresses have been made in the field of LSD1-targeted drug discovery. Nine LSD1 inhibitors including tranylcypromine, ORY-1001, ORY-2001, GSK-2879552, IMG-7289, INCB059872, TAK-418, CC-90011 and SP-2577 have entered clinical stage for disease treatment as either mono- or combinational therapy. This review updates LSD1 inhibitors reported during 2022. Design strategies, structure-activity relationship studies, binding model analysis and modes of action are highlighted. In particular, the unique multiple-copies binding mode of quinazoline derivatives paves new ways for the development of reversible LSD1 inhibitors by blocking the substrate entrance. The design strategy of clinical candidate TAK-418 also provides directions for further optimization of novel irreversible LSD1 inhibitors with low hematological side effects. The influence of the stereochemistry on the potency against LSD1 and its homolog LSD2 is briefly discussed. Finally, the challenges and prospects of LSD1-targeted drug discovery are also given.

Synthesis, Optical Properties, and Antiproliferative Evaluation of NBD-Triterpene Fluorescent Probes

A fluorescent labeling protocol for hydroxylated natural compounds with promising antitumor properties has been used to synthesize, in yields of 72-86%, 12 derivatives having fluorescent properties and biological activity. The reagent used for the synthesis of these fluorescent derivatives was 7-nitrobenzo-2-oxa-1,3-diazole chloride (NBD-Cl). The linkers employed to bind the NBD-Cl reagent to the natural compounds were ω-amino acids (Aa) of different chain lengths. The natural triterpene compounds chosen were oleanolic and maslinic acid, as their corresponding 28-benzylated derivatives. Thus, 12 NBD-Aa-triterpene conjugates have been studied for their optical fluorescence properties and their biological activities against cell proliferation in three cancer cell lines (B16-F10, HT-29, and HepG2), compared with three nontumor cell lines (HPF, IEC-18, and WRL68) from different tissues. The results of the fluorescence study have shown that the best fluorescent labels are those in which the ω-amino acid chain is shorter, and the carboxylic group is not benzylated. Analysis by confocal microscopy showed that these compounds were rapidly incorporated into cells in all three cancer cell lines, with these same derivatives showing the highest toxicity against the cancer cell lines tested. Then, the fluorescent labeling of these NBD-Aa-triterpene conjugates enabled their uptake and subcellular distribution to be followed in order to probe in detail their biological properties at the cellular and molecular level.

Structure-Based Identification of Natural-Product-Derived Compounds with Potential to Inhibit HIV-1 Entry

Broadly neutralizing antibodies (bNAbs) are potent in neutralizing a wide range of HIV strains. VRC01 is a CD4-binding-site (CD4-bs) class of bNAbs that binds to the conserved CD4-binding region of HIV-1 envelope (env) protein. Natural products that mimic VRC01 bNAbs by interacting with the conserved CD4-binding regions may serve as a new generation of HIV-1 entry inhibitors by being broadly reactive and potently neutralizing. This study aimed to identify compounds that mimic VRC01 by interacting with the CD4-bs of HIV-1 gp120 and thereby inhibiting viral entry into target cells. Libraries of purchasable natural products were virtually screened against clade A/E recombinant 93TH057 (PDB: 3NGB) and clade B (PDB ID: 3J70) HIV-1 env protein. Protein-ligand interaction profiling from molecular docking and dynamics simulations showed that the compounds had intermolecular hydrogen and hydrophobic interactions with conserved amino acid residues on the CD4-binding site of recombinant clade A/E and clade B HIV-1 gp120. Four potential lead compounds, NP-005114, NP-008297, NP-007422, and NP-007382, were used for cell-based antiviral infectivity inhibition assay using clade B (HXB2) env pseudotype virus (PV). The four compounds inhibited the entry of HIV HXB2 pseudotype viruses into target cells at 50% inhibitory concentrations (IC₅₀) of 15.2 µM (9.7 µg/mL), 10.1 µM (7.5 µg/mL), 16.2 µM (12.7 µg/mL), and 21.6 µM (12.9 µg/mL), respectively. The interaction of these compounds with critical residues of the CD4-binding site of more than one clade of HIV gp120 and inhibition of HIV-1 entry into the target cell demonstrate the possibility of a new class of HIV entry inhibitors.

Computer Science Technology in Natural Products Research: A Review of Its Applications and Implications

Computational approaches to drug development are rapidly growing in popularity and have been used to produce significant results. Recent developments in information science have expanded databases and chemical informatics knowledge relating to natural products. Natural products have long been well-studied, and a large number of unique structures and remarkable active substances have been reported. Analyzing accumulated natural product knowledge using emerging computational science techniques is expected to yield more new discoveries. In this article, we discuss the current state of natural product research using machine learning. The basic concepts and frameworks of machine learning are summarized. Natural product research that utilizes machine learning is described in terms of the exploration of active compounds, automatic compound design, and application to spectral data. In addition, efforts to develop drugs for intractable diseases will be addressed. Lastly, we discuss key considerations for applying machine learning in this field. This paper aims to promote progress in natural product research by presenting the current state of computational science and chemoinformatics approaches in terms of its applications, strengths, limitations, and implications for the field.

Neuroprotective Strategies for Stroke by Natural Products: Advances and Perspectives

Cerebral ischemic stroke is a disease with high prevalence and incidence. Its management focuses on rapid reperfusion with intravenous thrombolysis and endovascular thrombectomy. Both therapeutic strategies reduce disability, but the therapy time window is short, and the risk of bleeding is high. Natural products (NPs) have played a key role in drug discovery, especially for cancer and infectious diseases. However, they have made little progress in clinical translation and pose challenges to the treatment of stroke. Recently, with the investigation of precise mechanisms in cerebral ischemic stroke and the technological development of NP-based drug discovery, NPs are addressing these challenges and opening up new opportunities in cerebral stroke. Thus, in this review, we first summarize the structure and function of diverse NPs, including flavonoids, phenols, terpenes, lactones, quinones, alkaloids, and glycosides. Then we propose the comprehensive neuroprotective mechanism of NPs in cerebral ischemic stroke, which involves complex cascade processes of oxidative stress, mitochondrial damage, apoptosis or ferroptosis-related cell death, inflammatory response, and disruption of the blood-brain barrier (BBB). Overall, we stress the neuroprotective effect of NPs and their mechanism on cerebral ischemic stroke for a better understanding of the advances and perspective in NPs application that may provide a rationale for the development of innovative therapeutic regimens in ischemic stroke.

Cyclooxygenase-2 (COX-2) as a Target of Anticancer Agents: A Review of Novel Synthesized Scaffolds Having Anticancer and COX-2 Inhibitory Potentialities

Cancer is a serious threat to human beings and is the second-largest cause of death all over the globe. Chemotherapy is one of the most common treatments for cancer; however, drug resistance and severe adverse effects are major problems associated with anticancer therapy. New compounds with multi-target inhibitory properties are targeted to surmount these challenges. Cyclooxygenase-2 (COX-2) is overexpressed in cancers of the pancreas, breast, colorectal, stomach, and lung carcinoma. Therefore, COX-2 is considered a significant target for the synthesis of new anticancer agents. This review discusses the biological activity of recently prepared dual anticancer and COX-2 inhibitory agents. The most important intermolecular interactions with the COX-2 enzyme have also been presented. Analysis of these agents in the active area of the COX-2 enzyme could guide the introduction of new lead compounds with extreme selectivity and minor side effects.

(-)-Epigallocatechin Gallate is a Noncompetitive Inhibitor of NAD Kinase

Nicotinamide adenine dinucleotide kinase (NADK) controls the intracellular NADPH content and provides reducing power for the synthesis of macromolecules and anti-ROS. Moreover, NADK is considered to be a synthetic lethal gene for KRAS mutations. To discover NADK-targeted probes, a high-throughput screening assay was established and optimized with a Z factor of 0.71. The natural product (-)-epigallocatechin gallate (EGCG) was found to be a noncompetitive inhibitor of NADK with K i = 3.28 ± 0.32 μΜ. The direct binding of EGCG to NADK was determined by several biophysical methods, including NMR spectroscopy, surface plasmon resonance (SPR) assay, and hydrogen-deuterium exchange mass spectrometry (HDX-MS). The SPR assay showed a K d of 1.78 ± 1.15 μΜ. The HDX-MS experiment showed that EGCG was bound at the non-substrate-binding sites of NADK. Besides, binding mode prediction and derivative activity analysis revealed a potential structure-activity relationship between EGCG and NADK. Furthermore, EGCG can specifically inhibit the proliferation of KRAS-mutated lung cancer cell lines without affecting KRAS wild-type lung cancer cell lines.

Morita–Baylis–Hillman reaction of 3-formyl-9H-pyrido[3,4-b]indoles and fluorescence studies of the products

β-Carboline is a privileged class of the alkaloid family and is associated with a broad spectrum of biological properties. 3-Formyl-9H-pyrido[3,4-b]indole is a such potent precursor belonging to this family which can be tailored for installing diversity at various positions of β-carboline to generate unique molecular hybrids of biological importance. The present work is a step towards this and assimilates the results related to the exploration of 3-formyl-9H-β-carbolines for the synthesis of β-carboline C-3 substituted MBH adducts followed by evaluation of their fluorescent characteristic. The effect of contact time, solvent system, concentration and substituents was also studied during investigation of fluorescence properties of these derivatives.

Identification of Anthelmintic Bishomoscalarane Sesterterpenes from the Australian Marine Sponge Phyllospongia bergquistae and Structure Revision of Phyllolactones A-D

High-throughput screening of the NatureBank marine extract library (7616 samples) identified an extract derived from the Australian marine sponge Phyllospongia bergquistae with activity against Hemonchus contortus (barber's pole worm), an economically important parasitic nematode. Bioassay-guided fractionation of the CH₂Cl₂/MeOH extract from P. bergquistae led to the purification of four known bishomoscalarane sesterterpenes, phyllolactones A-D (1-4). The absolute configurations of phyllolactones B (2) and C (3) were determined by single-crystal X-ray diffraction analysis; literature and data analyses revealed the need for these chemical structures to be revised. Compounds 2-4 induced a lethal, skinny (Ski) phenotype in larvae of H. contortus at concentrations between 5.3 and 10.1 μM. These data indicate that the bishomoscalarane sesterterpene structure class warrants further investigation for nematocidal or nematostatic activity.

Protective Effect of Fustin Against Ethanol-Activated Gastric Ulcer via Downregulation of Biochemical Parameters in Rats

The fustin plant-derived bioflavonoid obtained from a common plant known as lacquer tree from family Anacardiaceae, formally known as Rhus verniciflua Stokes, is known to exert a variety of therapeutic properties. The current investigation proved the anti-ulcerative property of fustin on ethanol-induced gastric ulcers in an experimental animal model. The fustin 50 and 100 mg/kg was studied in an experimental rat model by performing an 8 day protocol. The ulcer index, pH, total acidic content, and biochemical parameters such as glutathione (GSH), superoxide dismutase (SOD), catalase activity (CAT), malondialdehyde (MDA), interleukin-1β, prostaglandin E-2, tumor necrosis factor-α (TNF-α), myeloperoxidase, and nitric oxide (NO) in serum were measured. The gastric parameter such as ulcer index, pH, and acidic content was maintained in the fustin groups compared to the ethanol control group. Clinical presentation of gastric ulcers includes a significant increase in serum levels, GSH, SOD, and CAT and decreased MDA, TNF-α, interleukin-1β, and prostaglandin E-2 parameters in contrast to normal groups. The treatment regimen with fustin has significantly restored all serum parameters in test groups. The current study helps to develop reasonable phytochemical options for the innervations of chemical-induced gastric ulcers.

Filamentous Thermosensitive Mutant Z: An Appealing Target for Emerging Pathogens and a Trek on Its Natural Inhibitors

Simple Summary

Antimicrobial resistance (AMR) is a pressing issue worldwide that must be addressed swiftly. It is driven by spontaneous evolution, bacterial mutation, and the dissemination of resistant genes via horizontal gene transfer. Researchers are working on many novel targets, which can become a pathway to inhibit harmful bacteria. Filamentous Thermosensitive mutant-Z (Fts-Z) is one such bacterial target that has gained popularity amongst scientists due to its conserved nature in bacteria and absence in eukaryotes. The aim of this work was to review the Fts-Z mechanism of action along with current studies on natural inhibitors for Fts-Z.

Abstract

Antibiotic resistance is a major emerging issue in the health care sector, as highlighted by the WHO. Filamentous Thermosensitive mutant Z (Fts-Z) is gaining significant attention in the scientific community as a potential anti-bacterial target for fighting antibiotic resistance among several pathogenic bacteria. The Fts-Z plays a key role in bacterial cell division by allowing Z ring formation. Several in vitro and in silico experiments have demonstrated that inhibition of Fts-Z can lead to filamentous growth of the cells, and finally, cell death occurs. Many natural compounds that have successfully inhibited Fts-Z are also studied. This review article intended to highlight the structural–functional aspect of Fts-Z that leads to Z-ring formation and its contribution to the biochemistry and physiology of cells. The current trend of natural inhibitors of Fts-Z protein is also covered.

Natural product drug discovery in the artificial intelligence era

Natural products (NPs) are primarily recognized as privileged structures to interact with protein drug targets. Their unique characteristics and structural diversity continue to marvel scientists for developing NP-inspired medicines, even though the pharmaceutical industry has largely given up. High-performance computer hardware, extensive storage, accessible software and affordable online education have democratized the use of artificial intelligence (AI) in many sectors and research areas. The last decades have introduced natural language processing and machine learning algorithms, two subfields of AI, to tackle NP drug discovery challenges and open up opportunities. In this article, we review and discuss the rational applications of AI approaches developed to assist in discovering bioactive NPs and capturing the molecular "patterns" of these privileged structures for combinatorial design or target selectivity.

Natural product 1,2,3,4,6-penta-O-galloyl-β-D-glucopyranose is a reversible inhibitor of glyceraldehyde 3-phosphate dehydrogenase

Aerobic glycolysis, also known as the Warburg effect, is a hallmark of cancer cell glucose metabolism and plays a crucial role in the activation of various types of immune cells. Glyceraldehyde 3-phosphate dehydrogenase (GAPDH) catalyzes the conversion of D-glyceraldehyde 3-phosphate to D-glycerate 1,3-bisphosphate in the 6th critical step in glycolysis. GAPDH exerts metabolic flux control during aerobic glycolysis and therefore is an attractive therapeutic target for cancer and autoimmune diseases. Recently, GAPDH inhibitors were reported to function through common suicide inactivation by covalent binding to the cysteine catalytic residue of GAPDH. Herein, by developing a high-throughput enzymatic screening assay, we discovered that the natural product 1,2,3,4,6-penta-O-galloyl-β-D-glucopyranose (PGG) is an inhibitor of GAPDH with K_i = 0.5 μM. PGG blocks GAPDH activity by a reversible and NAD⁺ and Pi competitive mechanism, suggesting that it represents a novel class of GAPDH inhibitors. In-depth hydrogen deuterium exchange mass spectrometry (HDX-MS) analysis revealed that PGG binds to a region that disrupts NAD⁺ and inorganic phosphate binding, resulting in a distal conformational change at the GAPDH tetramer interface. In addition, structural modeling analysis indicated that PGG probably reversibly binds to the center pocket of GAPDH. Moreover, PGG inhibits LPS-stimulated macrophage activation by specific downregulation of GAPDH-dependent glucose consumption and lactate production. In summary, PGG represents a novel class of GAPDH inhibitors that probably reversibly binds to the center pocket of GAPDH. Our study sheds new light on factors for designing a more potent and specific inhibitor of GAPDH for future therapeutic applications.

Biocatalytic and chemical derivatization of fungal meroditerpenoid chevalone E

Fungal meroditerpenoids include diverse molecules with structural complexity and a broad range of biological activities. We have previously obtained meroditerpenoid chevalone E (1) and its oxidized analogues by heterologously expressing...

Fustin Inhibits Oxidative Free Radicals and Inflammatory Cytokines in Cerebral Cortex and Hippocampus and Protects Cognitive Impairment in Streptozotocin-Induced Diabetic Rats

The phytogenic flavanol component of the plant Rhus verniciflua Stokes is fustin which is implicated in various disease aliments and has promising therapeutic efficacy and a long history of its uses in the Indian medicinal system. The present study investigated the ameliorative effect of fustin in streptozotocin (STZ) induced cognitive impairments in the diabetic animal paradigm. A total of five different animal groups were used for the present study.The preclinical efficacy of fustin at 50 mg/kg and 100 mg/kg was studied in diabetic male rats by employing a 35-day study design. In the present investigation the Morris water maze test (MWM) and elevated plus maze (EPM) test were employed as behavioral paradigms for the assessment of memory impairments. The study design also carried out certain biochemical parameters which include glutathione (GSH), superoxide dismutase (SOD), catalase activity (CAT), malondialdehyde (MDA), nitric oxide (NO), relative interleukin-6 (IL-6), and IL-1B in samples obtained from cerebral cortex and hippocampus. The behavioral parameters with MWM and EPM were significant restored in fustin treatment groups as compared to elevated levels in the diabetic control group. Furthermore, fustin significantly improved the altered levels of several biochemical parameters for cognitive dysfunction such as GSH, SOD, CAT, MDA, NO, and relative IL-6 and IL-1B compared to a diabetic control group. The present investigation highlights certain preclinical pieces of evidence that strongly indicate that fustin might restore the normal cognitive function in the experimental animal paradigm.

Identification of NLRP3 as a covalent target of 1,6-O,O-diacetylbritannilactone against neuroinflammation by quantitative thiol reactivity profiling (QTRP)

Neuroinflammation plays a key etiological role in the progressive neuronal damage of neurodegenerative diseases. Our phenotypic-based screening discovered 1,6-O,O-diacetylbritannilactone (OABL, 1) from Inula britannica exhibited the potential anti-neuroinflammatory activity as well as a favorable blood-brain barrier penetration. 1 and its active derivative Br-OABL (2) with insert of Br at the C-14 position both modulated TLR4/NF-kB/MAPK pathways. However, proteome-wide identification of 1 binding proteins remains unclear. Here, we employed an adapted isoTOP-ABPP, quantitative thiol reactivity profiling (QTRP) approach, to identify and quantify thiol reactivity binding proteins in murine microglia BV-2 cells. We screened out 15 proteins co-targeted by 1 and 2, which are involved in cellular response to oxidative stress and negative regulation NF-κB transcription factor in biological processes. In site-specific profiling, NLRP3 was identified as a covalent target of 1 and 2 for the first time, and the Cys⁴⁸³ of NLRP3 NACHT domain was identified as one active-site of NLRP3 cysteine residues that can be covalently modified by the α-methylene-γ-lactone moiety. Furthermore, NLRP3 was validated to be directly binded by 1 and 2 by cellular thermo shift assay (CETSA) and activity-based protein profiling (ABPP), and NLRP3 functions were also verified by small interfering RNA approach. Notably, OABL treatment (i.p., 20 mg/kg/day) for 21 days reduced inflammation in 5XFAD mice brain. Together, we applied the QTRP to uncover the binding proteins of OABL in BV-2 cells, among which NLRP3 was revealed as a new covalent target of 1 and 2 against neuroinflammation.

Towards the De Novo Design of HIV-1 Protease Inhibitors Based on Natural Products

Acquired immunodeficiency syndrome (AIDS) caused by the human immunodeficiency virus (HIV) continues to be a public health problem. In 2020, 680,000 people died from HIV-related causes, and 1.5 million people were infected. Antiretrovirals are a way to control HIV infection but not to cure AIDS. As such, effective treatment must be developed to control AIDS. Developing a drug is not an easy task, and there is an enormous amount of work and economic resources invested. For this reason, it is highly convenient to employ computer-aided drug design methods, which can help generate and identify novel molecules. Using the de novo design, novel molecules can be developed using fragments as building blocks. In this work, we develop a virtual focused compound library of HIV-1 viral protease inhibitors from natural product fragments. Natural products are characterized by a large diversity of functional groups, many sp³ atoms, and chiral centers. Pseudo-natural products are a combination of natural products fragments that keep the desired structural characteristics from different natural products. An interactive version of chemical space visualization of virtual compounds focused on HIV-1 viral protease inhibitors from natural product fragments is freely available in the supplementary material.

An Update on Pharmacological Relevance and Chemical Synthesis of Natural Products and Derivatives with Anti SARS-CoV-2 Activity

Natural products recognized traditionally as a vital source of active constituents in pharmacotherapy. The COVID-19 infection caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is highly transmissible, pathogenic, and considered an ongoing global health emergency. The emergence of COVID-19 globally and the lack of adequate treatment brought attention towards herbal medicines, and scientists across the globe instigated the search for novel drugs from medicinal plants and natural products to tackle this deadly virus. The natural products rich in scaffold diversity and structural complexity are an excellent source for antiviral drug discovery. Recently the investigation of several natural products and their synthetic derivatives resulted in the identification of promising anti SARS-CoV-2 agents. This review article will highlight the pharmacological relevance and chemical synthesis of the recently discovered natural product and their synthetic analogs as SARS-CoV-2 inhibitors. The summarized information will pave the path for the natural product-based drug discovery of safe and potent antiviral agents, particularly against SARS-CoV-2.

Design, synthesis and screening of a drug discovery library based on an Eremophila-derived serrulatane scaffold

Chemical studies of the aerial parts of the Australian desert plant Eremophila microtheca afforded the targeted and known diterpenoid scaffolds, 3,7,8-trihydroxyserrulat-14-en-19-oic acid and 3-acetoxy-7,8-dihydroxyserrulat-14-en-19-oic acid. The most abundant serrulatane scaffold was converted to the poly-methyl derivatives, 3-hydroxy-7,8-dimethoxyserrulat-14-en-19-oic acid methyl ester and 3,7,8-trimethoxyserrulat-14-en-19-oic acid methyl ester using simple and rapid methylation conditions consisting of DMSO, NaOH and MeI at room temperature. Subsequently a 12-membered amide library was synthesised by reacting the methylated scaffolds with a diverse series of commercial primary amines. The chemical structures of the 12 undescribed semi-synthetic analogues were fully characterised following 1D/2D NMR, MS, UV, ECD and [α]_D data analyses. All compounds were evaluated for their anthelmintic, anti-microbial and anti-viral activities. While none of the compounds significantly inhibited motility or development of the exsheathed third-stage larvae (xL3s) of a pathogenic ruminant parasite, Haemonchus contortus, the tri-methylated analogue induced a skinny phenotype in fourth-stage larvae (L4s) after seven days of treatment (IC₅₀ = 14 μM). Anti-bacterial and anti-fungal activities were not observed at concentrations up to 20 μM. Activity against HIV latency reversal was tested in inducible, chronically-infected cells, with the tri-methylated analogue being the most active (EC₅₀ = 38 μM).

Antitubercular and antibacterial activities of isoxazolines derived from natural products: Isoxazolines as inhibitors of Mycobacterium tuberculosis InhA

Isoxazoline derivatives of the natural products eugenol, 1’- S-acetoxychavicol acetate and sclareol are prepared through 1,3-dipolar cycloaddition reactions in an aqueous buffered system. The compounds are evaluated for their antitubercular and antibacterial activities. Compounds 2, 2a and 3f display strong antitubercular activity with minimum inhibitory concentration values of 26.68, 17.89 and 14.58 µM, respectively. Furthermore, derivative 3f exhibits antibacterial activity against Bacillus cereus (minimum inhibitory concentration value of 29.16 µM). Isoxazoline derivatives of 1’- S-acetoxychavicol acetate demonstrate improvements in cytotoxicity, and derivative 3f of sclareol demonstrates improved antitubercular and antibacterial activities. Isoxazolines derived from natural products exhibit Mycobacterium tuberculosis enoyl-acyl carrier protein reductase (InhA) inhibitory activity, and molecular modelling predicts that they form hydrogen bonding and hydrophobic interactions with NADH and with the key residues of the InhA binding site.

Applications of Norrish type I and II reactions in the total synthesis of natural products: a review

Natural products and their analogue have played a key role in the drug discovery and development process. In the laboratory, the total synthesis of secondary metabolites is very useful in ascertaining the hypothetical complex structure of molecules of natural origin. Total synthesis of natural products using Norrish type I and II reactions as a crucial step has been explored in this overview. Norrish reactions are important photo-induced transformations of carbonyl compounds in organic synthetic chemistry and are connected in numerous industrially and biologically relevant procedures and the processing of carbonyl compounds in the atmosphere. The present review tries to focus on the brilliant applications of Norrish type I and II photochemical reactions as a key step in the total synthesis of natural products and highlights on natural sources, structures, and biological activities of the promising natural products for the first time elegantly.

1,10-Seco-Eudesmane sesquiterpenoids as a new type of anti-neuroinflammatory agents by suppressing TLR4/NF-κB/MAPK pathways

Dysregulation of neuroinflammation is a key pathological factor in the progressive neuronal damage of neurodegenerative diseases. An in-house natural products library of 1407 compounds were screened against neuroinflammation in lipopolysaccharide (LPS)-activated microglia cells to identify a novel hit 1,6-O,O-diacetylbritannilactone (OABL) with anti-neuroinflammatory activity. Furthermore, a 1,10-seco-eudesmane sesquiterpenoid library containing 33 compounds was constructed by semisynthesis of a major component 1-O-acetylbritannilactone (ABL) from the traditional Chinese medicinal herb Inula Britannica L. Compound 15 was identified as a promising anti-neuroinflammatory agent by nitrite oxide (NO) production screening. 15 could attenuate tumor necrosis factor-α (TNF-α) and prostaglandin E2 (PGE2) productions, and inhibit the expression of inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) at a submicromolar level. Mechanistic study revealed that 15 significantly modulated TLR4/NF-kB and p38 MAPK pathways, and upregulated the anti-oxidant response HO-1. Besides, 15 promoted the conversion of the microglia from M1 to M2 phenotype by increasing levels of arginase-1 and IL-10. The structure-activity relationships (SARs) analysis indicated that the α-methylene-γ-lactone motifs, epoxidation of C5=C10 bond and bromination of C14 were important to the activity. Parallel artificial membrane permeation assay (PAMPA) also demonstrated that 15 and OABL can overcome the blood-brain barrier (BBB). In all, compound 15 is a promising anti-neuroinflammatory lead with potent anti-inflammatory effects via the blockage of TLR4/NF-κB/MAPK pathways, favorable BBB penetration property, and low cytotoxicity.

Contemporary advancements in the semi-synthesis of bioactive terpenoids and steroids

Many natural products have intriguing biological properties that arise from their fascinating chemical structures. However, the intrinsic complexity of the structural skeleton and the reactive functional groups on natural products pose tremendous challenges to chemical syntheses. Semi-synthesis uses chemical compounds isolated from natural sources as the starting materials to produce other novel compounds with distinct chemical and medicinal properties. In particular, advancements in various types of sp3 C-H bond functionalization reactions and skeletal rearrangement methods have contributed to the re-emergence of semi-synthesis as an efficient approach for the synthesis of structurally complex bioactive natural products. Here, we begin with a brief discussion of several bioactive natural products that were obtained via a semi-synthetic approach between 2008 and 2015 and we then discuss in-depth contemporary advancements in the semi-synthesis of bioactive terpenoids and steroids reported during 2016-2020.

In vitro identification and characterisation of iron chelating catechol-containing natural products and derivatives

Iron is an essential component for multiple biological processes. Its regulation within the body is thus tightly controlled. Dysregulation of iron levels within the body can result in several disorders associated with either excess iron accumulation, including haemochromatosis and thalassaemia, or iron deficiency. In cases of excess body iron, therapy involves depleting body iron levels either by venesection, typically for haemochromatosis, or using iron chelators for thalassemia. However, the current chelation options for people with iron overload are limited, with only three iron chelators approved for clinical use. This presents an opportunity for improved therapeutics to be identified and developed. The aim of this study was to examine multiple compounds from within the Davis open access natural product-based library (512 compounds) for their ability to chelate iron. In silico analysis of this library initially identified nine catechol-containing compounds and two closely related compounds. These compounds were subsequently screened using an in vitro DNA breakage assay and their ability to chelate biological iron was also examined in an iron-loaded hepatocyte cellular assay. Toxicity was assessed in hepatocyte and breast cancer cell lines. One compound, RAD362 [N-(3-aminopropyl)-3,4-dihydroxybenzamide] was able to protect against DNA damage, likely through the prevention of free radicals generated via the Fenton reaction; RAD362 treatment resulted in decreased ferritin protein levels in iron-loaded hepatocytes. Lastly, RAD362 resulted in significantly less cell death than the commonly used iron chelator deferoxamine. This is the first study to identify compound RAD362 as an iron chelator and potential therapeutic.

Total Synthesis of 6-Hydroxymetatacarboline-d Discovered from Mycena metata via the Pictet-Spengler Reaction Followed by the Horner-Wadsworth-Emmons Reaction

Total synthesis of a new β-carboline alkaloid, 6-hydroxymetatacarboline-d, which was isolated from fruiting bodies of Mycena metata was accomplished in 14 steps. The synthetic strategy features the Pictet-Spengler reaction to construct the tricyclic core followed by amide coupling and the Horner-Wadsworth-Emmons reaction.