The antimalarial activity of indole alkaloids and hybrids

Applications of magnetic solid-phase extraction in the sample preparation of natural product analysis (2020-2023)

Sample preparation, including extraction, separation, and purification, is a vital process for natural product analysis. As an attractive sample pretreatment method, magnetic solid-phase extraction (MSPE) has gained plenty of attention, mainly due to its simpler operation, less consumption of organic solvents, and shorter processing time than traditional SPE. This updated review is devoted to summarizing the applications of MSPE based on different magnetic nanomaterials in the analysis of various natural products in complex matrixes, such as biological samples, plants, and Chinese herbal preparations in the past four years (2020-2023). The preparation and fabrication of different materials are briefly introduced. Furthermore, the extraction mechanism and interaction forces between adsorbent and analytes are elaborated, and the advantages and disadvantages of different adsorbents coupled with various analytical methods for MSPE of different natural products are summarized. Moreover, the future trends and opportunities for MSPE in the natural product analysis are discussed. It is expected that this work can provide updated information for future research on the applications of MSPE in such fields.

Polyamine-containing natural products: structure, bioactivity, and biosynthesis

Covering: 2005 to August, 2023Polyamine-containing natural products (NPs) have been isolated from a wide range of terrestrial and marine organisms and most of them exhibit remarkable and diverse activities, including antimicrobial, antiprotozoal, antiangiogenic, antitumor, antiviral, iron-chelating, anti-depressive, anti-inflammatory, insecticidal, antiobesity, and antioxidant properties. Their extraordinary activities and potential applications in human health and agriculture attract increasing numbers of studies on polyamine-containing NPs. In this review, we summarized the source, structure, classification, bioactivities and biosynthesis of polyamine-containing NPs, focusing on the biosynthetic mechanism of polyamine itself and representative polyamine alkaloids, polyamine-containing siderophores with catechol/hydroxamate/hydroxycarboxylate groups, nonribosomal peptide-(polyketide)-polyamine (NRP-(PK)-PA), and NRP-PK-long chain poly-fatty amine (lcPFAN) hybrid molecules.

Alkaloidal Extracts from Avicennia africana P. Beauv. (Avicenniaceae) Leaf: An Antiplasmodial, Antioxidant, and Erythrocyte Viable

Background

The emergence of drug-resistant parasites impedes disease management and eradication efforts. Hence, a reinvigorated attempt to search for potent lead compounds in the mangroves is imperative.

Aim

This study evaluates in vitro antiplasmodial activity, antioxidant properties, and cytotoxicity of A. africana leaf alkaloidal extracts.

Methods

The A. africana leaves were macerated with 70% ethanol to obtain a total crude extract. Dichloromethane and chloroform-isopropanol (3 : 1, v/v) were used to extract the crude alkaloids and quaternary alkaloids from the total crude. The antiplasmodial activities of the alkaloidal extracts were performed against 3D7 P. falciparum chloroquine-sensitive clone via the SYBR Green I fluorescence assay with artesunate serving as the reference drug. The alkaloidal extracts were further evaluated for antioxidant properties via the total antioxidant capacity (TAC), the total glutathione concentration (GSH), the DPPH (2,2-diphenyl-1-picrylhydrazyl) assay, and the ferric-reducing antioxidant power (FRAP) methods. The cytotoxic activity of the alkaloidal extracts was tested on erythrocytes using a 3-(4,5-dimethylthiazol-2-yl)-5-diphenyltetrazolium bromide-MTT assay with little modification. The phytocompounds in the alkaloidal extracts were identified via gas chromatography-mass spectrometry (GC-MS) techniques.

Results

The total crude extract showed good antiplasmodial activity (IC50 = 11.890 µg/mL). The crude and quaternary alkaloidal extracts demonstrated promising antiplasmodial effects with IC50 values of 6.217 and 6.285 µg/mL, respectively. The total crude and alkaloidal extracts showed good antioxidant properties with negligible cytotoxicity on erythrocytes with good selectivity indices. The GC-MS spectral analysis of crude alkaloidal extracts gave indole and isoquinoline alkaloids and several other compounds. Dexrazoxane was found to be the main compound predicted, with an 86% peak area in the quaternary alkaloidal extract.

Conclusion

The crude and quaternary alkaloidal extracts exhibited antiplasmodial activities and ability to inhibit oxidative stress with negligible toxicity on erythrocytes. This may be good characteristics to avoid oxidative stress related to Plasmodium infection in the treatment of malaria.

Recent developments in the synthesis of hybrid antimalarial drug discovery

In this 21st century, Malaria remains a global burden and causes massive economic trouble to disease-endemic nations. The control and eradication of malaria is a major challenge that requires an urgent need to develop novel antimalarial drugs. To overcome the aforementioned situation, several researchers have given significant effort to develop hybrid antimalarial agents in the search for new antimalarial drugs. Hence, we have summarized those developments of hybrid antimalarial agents from 2017 to till date. This review illustrates the current progress in the recent synthesis of hybrid antimalarial agents along with focusing on their antimalarial evaluation to find the most potent hybrids. This present mini-review will also be useful for the scientific community for the development of new antimalarial drugs to eradicate malaria.

Indole-Based Compounds as Potential Drug Candidates for SARS-CoV-2

The COVID-19 pandemic has posed a significant threat to society in recent times, endangering human health, life, and economic well-being. The disease quickly spreads due to the highly infectious SARS-CoV-2 virus, which has undergone numerous mutations. Despite intense research efforts by the scientific community since its emergence in 2019, no effective therapeutics have been discovered yet. While some repurposed drugs have been used to control the global outbreak and save lives, none have proven universally effective, particularly for severely infected patients. Although the spread of the disease is generally under control, anti-SARS-CoV-2 agents are still needed to combat current and future infections. This study reviews some of the most promising repurposed drugs containing indolyl heterocycle, which is an essential scaffold of many alkaloids with diverse bio-properties in various biological fields. The study also discusses natural and synthetic indole-containing compounds with anti-SARS-CoV-2 properties and computer-aided drug design (in silico studies) for optimizing anti-SARS-CoV-2 hits/leads.

Palladium-Catalyzed Tandem Nucleophilic Addition/C-H Functionalization of Anilines and Bromoalkynes for the Synthesis of 2-Phenylindoles

A novel and efficient palladium-catalyzed annulation of anilines with bromoalkynes for the synthesis of 2-phenylindoles has been described. This approach features excellent regio- and stereoselectivities and good functional group tolerance. Preliminary mechanistic studies indicate that anilines undergo anti-nucleophilic addition to bromoalkynes to generate (Z)-N-(2-bromo-1-phenylvinyl) anilines, followed by sequential C-H functionalization to deliver different substituted 2-phenylindoles. This method provides potential applications for the construction of various biologically active compounds.

Nauclea officinalis: A Chinese medicinal herb with phytochemical, biological, and pharmacological effects

Nauclea officinalis (N. officinalis), a medicinal plant of the genus Nauclea in the family Rubiaceae, is used in the treatment of fever, pneumonia, pharyngolaryngitis, and enteritis in China. Extracts of N. officinalis include alkaloids, phenolic acids, pentacyclic triterpenoids, and flavonoids, which exert all kinds of pharmacological effects, for instance anti-inflammatory, anti-tumor, antibacterial, and antiviral and therefore show good effectiveness. To gain a comprehensive and deep understanding, the medicinal chemistry and chemical biology of N. officinalis are summarized in this review to provide a theoretical basis. The pharmacological effects were reviewed to provide evidence or insights into potential opportunities for further studies and medicinal exploitation of N. officinalis.

An innovative extraction strategy for herbal medicine by adopting p-sulphonatocalix[6]/[8]arenes

INTRODUCTION

Alkaloids exist in various herbal medicine widely and exhibit diverse biological and pharmacological activities. p-Sulphonatocalix[6]arenes (SC6A) and p-sulphonatocalix[8]arenes (SC8A) are water-soluble supramolecular macrocycles and are applied to the extraction of alkaloids from herbal products.

OBJECTIVE

In this study, an innovative method of SC6A/SC8A assisted extraction of the alkaloids from herbs was established.

METHODS

SC6A and SC8A were designed to extract 27 alkaloids from seven herbal medicines. Based on the significant solubilisation and extraction effect, Stephaniae Tetrandrae Radix (Fangji, FJ) was selected to obtain the optimal extraction process by adopting single factor test and orthogonal experiment. Then, the alkaloids and SC6A/SC8A were separated by one-step alkalisation and SCnA were reused. The host-guest complexes between alkaloids and SCnA were determined by competitive fluorescence titration, differential scanning calorimetry (DSC), Fourier-transform infrared (FTIR) and proton nuclear magnetic resonance (¹ H-NMR) analysis.

RESULTS

The optimum condition for SC6A assisted extraction was 5:1:80 (g/g/mL) for herbs/SC6A/solution ratio, 355-250 μm particle size and ultrasonicate 0.5 h, whilst 10:1:40 (g/g/mL) for herbs/SC8A/solution ratio, 355-250 μm particle size and ultrasonicate 0.5 h for SC8A assisted extraction. The total yield of alkaloids (fangchinoline and tetrandrine) from FJ was increased by 4.87 times and 5.97 times with SC6A and SC8A. Moreover, a good reusability of SC6A/SC8A was achieved by alkalisation dissociation. Host-guest complexes were determined by competitive fluorescence titration at a molar ratio of 1:1 between most alkaloids (25/27, except evodiamine and rutaecarpine) and SC6A/SC8A. The complex structure was proved by DSC, FTIR and ¹ H-NMR analysis.

CONCLUSION

The study provided an effective eco-friendly and energy-saving extraction method of alkaloids from herbal medicine.

β-Methyltryptamine Provoking the Crucial Role of Strictosidine Synthase Tyr151-OH for Its Stereoselective Pictet-Spengler Reactions to Tryptoline-type Alkaloids

Strictosidine synthase (STR), the gate enzyme for monoterpenoid indole alkaloid biosynthesis, catalyzes the Pictet-Spengler reaction (PSR) of various tryptamine derivatives with secologanin assisted by "indole sandwich" stabilization. Continuous exploration with β-methyltryptamine (IPA) stereoselectively delivered the C6-methylstrictosidines and C6-methylvincosides by enzymatic and nonenzymatic PSR, respectively. Unexpectedly, the first "nonindole sandwich" binding mode was witnessed by the X-ray structures of STR1-ligand complexes. Site-directed mutagenesis revealed the critical cryptic role of the hydroxyl group of Tyr151 in IPA biotransformation. Further computational calculations demonstrated the adjustable IPA position in STR1 upon the binding of secologanin, and Tyr151-OH facilitates the productive PSR binding mode via an advantageous hydrogen-bond network. Further chemo-enzymatic manipulation of C6-methylvincosides successfully resulted in the discovered antimalarial framework (IC50 = 0.92 μM).

Synthesis and Antiplasmodial Activity of Bisindolylcyclobutenediones

Malaria is one of the most dangerous infectious diseases. Because the causative Plasmodium parasites have developed resistances against virtually all established antimalarial drugs, novel antiplasmodial agents are required. In order to target plasmodial kinases, novel N-unsubstituted bisindolylcyclobutenediones were designed as analogs to the kinase inhibitory bisindolylmaleimides. Molecular docking experiments produced favorable poses of the unsubstituted bisindolylcyclobutenedione in the ATP binding pocket of various plasmodial protein kinases. The synthesis of the title compounds was accomplished by sequential Friedel-Crafts acylation procedures. In vitro screening of the new compounds against transgenic NF54-luc P. falciparum parasites revealed a set of derivatives with submicromolar activity, of which some displayed a reasonable selectivity profile against a human cell line. Although the molecular docking studies suggested the plasmodial protein kinase PfGSK-3 as the putative biological target, the title compounds failed to inhibit the isolated enzyme in vitro. As selective submicromolar antiplasmodial agents, the N-unsubstituted bisindolylcyclobutenediones are promising starting structures in the search for antimalarial drugs, albeit for a rational development, the biological target addressed by these compounds has yet to be identified.

An insight in anti-malarial potential of indole scaffold: A review

Malaria is a major parasitic disease in tropical and sub-tropical regions. Pertaining to the sustaining resistance in malarial parasite against the available drugs, novel treatment options are the need of the hour. In this resolve recently, focus has shifted to finding the natural alternatives that possess anti-plasmodial activity for combatting malaria. Drawing on the text written in ancient scriptures and Ayurveda, natural compounds are now being screened for their therapeutic properties. Indole is one such natural compound, present in all living organisms, it displays a range of therapeutic activities including anticancer, anti-inflammatory, antimalarial etc. In this review, we have discussed various indole scaffold as well as the semi-synthetic drugs containing indole moiety that have been synthesized for malaria treatment.