Structurally diverse alkaloids with nine frameworks from Zephyranthes candida and their acetylcholinesterase inhibitory and anti-inflammatory activities

Targeted isolation of isopentenyl flavonoids from Daphne giraldii Nitsche based on feature-based molecular networking and their cytotoxic activities

Isopentenyl flavonoids were important chemical components in Daphne giraldii Nitsche with significant cytotoxic activities against hepatocellular carcinoma cells in previous study. In this study, Feature-Based Molecular Networking was utilized to perform the targeted isolation of the phytochemical investigation of D. giraldii. As a result, five undescribed isopentenyl flavonoids (1, 2a/2b, 3, and 4) were isolated from D. giraldii. Their structures and configurations were established by comprehensive spectral analysis and comparing experimental ECD and calculated data. In addition, all isolated compounds were evaluated for cytotoxic activities against hepatocellular carcinoma HepG2 and Hep3B cell lines. Specifically, compound 2 exhibited significant cytotoxic activities with IC50 values of 11.63 ± 0.22 μM and 0.10 ± 0.02 μM, respectively.

Recent progress in chemistry and bioactivity of novel enzyme inhibitors from natural products: A comprehensive review

The essence of enzymes is to maintain the normal activities of living organisms by catalyzing metabolic reactions and regulating cells. Inhibiting enzyme activity can slow the progression of certain diseases and cure them, making enzymes one of the major targets for disease treatment. The search and development of novel enzyme inhibitors are of great significance for the treatment of certain major diseases. One of the most prominent features of natural products is their complex and diverse structures, which often compliments the synthetic capabilities of medicinal chemistry. Considering the biosynthetic processes of natural molecules in organisms, they exhibit higher similarity and binding potential with biological structures, enabling them to serve as ligands for various enzymes and receptors. In this review, we summarized a total of 226 novel natural products with enzyme inhibitory activity published in 49 articles over the past three years (2022-2024). These natural products (including terpenes, alkaloids, flavonoids, phenylpropanoids, polyketides, peptides, anthraquinones, etc.) are derived from plants, microorganisms, and marine organisms. We also discuss some synthetic analogs, with a focus on their structures and biological activities. This review provides useful information for the research and development of novel enzyme inhibitors.

Discovering natural products as potential inhibitors of SARS-CoV-2 spike proteins

The ongoing global pandemic caused by the SARS-CoV-2 virus has demanded the urgent search for effective therapeutic interventions. In response, our research aimed at identifying natural products (NPs) with potential inhibitory effects on the entry of the SARS-CoV-2 spike (S) protein into host cells. Utilizing the Protein Data Bank Japan (PDBJ) and BindingDB databases, we isolated 204 S-glycoprotein sequences and conducted a clustering analysis to identify similarities and differences among them. We subsequently identified 33,722 binding molecules (BMs) by matching them with the sequences of 204 S-glycoproteins and compared them with 52,107 secondary metabolites (SMs) from the KNApSAcK database to identify potential inhibitors. We conducted docking and drug-likeness property analyses to identify several SMs with potential as drug candidates based on binding energy (BE), no Lipinski's rule violation (LV), psychochemical properties within the pink area of the bioavailability radar, and a bioavailability score (BAS) not less than 0.55. Fourteen SMs were predicted through computational analysis as potential candidates for inhibiting the three major types of S proteins. Our study provides a foundation for further experimental validation of these compounds as potential therapeutic agents against SARS-CoV-2.

Anti-inflammatory Principles of the Plant Family Amaryllidaceae

There is considerable interest in the utilisation of plants against inflammation. Over 50 species of the plant family Amaryllidaceae are known for such usage in traditional medicine. This review was undertaken to identify the chemical principles responsible for these anti-inflammatory effects. It describes the findings from in vitro, in vivo and in silico studies, as well as the probes made on the mechanisms of action. The literature search returned over 600 hits, of which around 130 were chosen for their relevance to the text. Over 140 compounds have thus far been screened for anti-inflammatory effects. These were mostly isoquinoline alkaloids but also included other classes of secondary metabolites such as chromones, flavonoids and triterpenoids. In vitro studies were carried out in mononuclear cells such as lymphocytes, monocytes, neutrophils and macrophages, against which no serious side effects were observed. The constituents were also effective against inflammation induced by physical and chemical stimuli in a variety of murine test subjects. Chief among the compounds were the isoquinoline alkaloids lycorine and narciclasine, which displayed potent effects against pain, swelling, asthma and arthritis, amongst others. From a mechanistic perspective, several of the compounds were shown to mediate in inflammatory pathways, notably via the modulation of both pro-inflammatory (such as NF-κB, TNF-α and IL-1) and anti-inflammatory (such as IL-10 and TGF-β) factors. Useful insights also emerged from active-site docking studies of some of the compounds. The Amaryllidaceae affords a rich and diverse platform for the discovery of potential anti-inflammatory drugs.

Undescribed Amaryllidaceae Alkaloids from Zephyranthes citrina and Their Cytotoxicity

This phytochemical study presents the isolation of eight alkaloids from Zephyranthes citrina Baker. The structures of the new alkaloids, zephycitrine (1) and 6-oxonarcissidine (2), were established by analysis of spectroscopic and spectrometric data. Processing the EtOH extract under acid-base conditions yielded the unreported isolation artifacts 3 and 4. This work also provides analytical data for alkaloids not properly described in the literature (5 and 6). The hippeastidine/zephyranine scaffolds in derivatives 3, 4, and 8-10 are also thoroughly discussed. Furthermore, a cytotoxicity screening of 25 Amaryllidaceae alkaloids isolated from Z. citrina was performed. Only the known alkaloids haemanthamine (12), haemanthidine (13), and lycorine (27) showed significant cell growth inhibition.

Visible light-induced Mallory reaction of tertiary benzanilides via iminium intermediates

The Mallory reaction, which involves the photocyclization of stilbenes/diarylethenes and their analogues into polycyclic aromatics, is of significant synthetic importance. However, its application to tertiary benzanilides has not been explored to date. Besides, most of the reported Mallory reactions require ultraviolet irradiation. In this study, we show the first Mallory reaction of tertiary benzanilides promoted by visible light via iminium intermediates formed in situ from tertiary benzanilide, Tf2O (triflic anhydride) and pyridine. UV/vis absorption spectroscopy combined with density functional theory (DFT) calculations revealed that the formation of the iminium intermediate decreased the HOMO-LUMO energy gap, thereby enhancing visible light absorption. This study provides a rapid and practical approach for the preparation of the phenanthridinone skeleton and provides a new idea for the design of new visible light photoswitches.

Flavonoidal alkaloids: Emerging targets for drug discovery from Nature's bounty

This paper explores the potential of flavonoid alkaloids, a unique class of compounds that contain both flavonoid and alkaloid structures, as emerging targets for drug discovery. These compounds exhibit diverse biological activities, such as anti-inflammatory, anti-cancer, and anti-diabetic effects, which are attributed to the combination of different flavonoid scaffolds and alkaloid groups. Flavonoid alkaloids have attracted researchers' attention due to their diverse structures and important bio-activities. Therefore, this review summarizes recent advances in the extraction, purification, structural characterization, synthesis pathways and biological activities of flavonoid alkaloids from natural sources. Finally, the potential prospects and challenges associated with this class of compounds in pharmacological research are discussed along with details of a mechanistic investigation and future clinical applications in this research field.

Chemical Composition of Achillea millefolium L. and Their Anti-Inflammatory Activity

A new monoterpene, (-)-10-hydroxydihydroactinidiolide (1), along with two known monoterpenes, loliolide (2) and (+)-isololiolide (3), three known megastigmanes, 3α-hydroxy-5β,6β-epoxy-β-ionone (4), 3α-hydroxy-5α,6α-epoxy-β-ionone (5), and (+)-dehydrovomifoliol (6), a eudesmane-type sesquiterpene, 4α-hydroxy-4β-methyldihydrocostol (7), a monoterpene, 8-hydroxycarvotanacetone (8), two flavonoids, chrysoeriol (9) and apigenin (10), and a phenylpropanoid, 3-(4-hydroxyphenyl)-1-propanol (11), were isolated from the whole plant of Achillea millefolium. The structure of compound 1 was identified according to spectroscopic data of HRMS and NMR, and its absolute configuration was assigned by 13C NMR calculations with DP4+ probability analyses and ECD calculations. The absolute configuration of compound 6 was determined by ECD calculations. Compounds 3, 6, 9 and 10 could dose-dependently inhibit the NO release in LPS-induced RAW264.7 cells.

Influence of Sucrose and Activated Charcoal on Phytochemistry and Vegetative Growth in Zephyranthes irwiniana (Ravenna) Nic. García (Amaryllidaceae)

Zephyranthes irwiniana (Ravenna) Nic. García is an endemic, red list threatened species from the Brazilian savanna (Cerrado) with pharmacological potential to treat the symptoms of Alzheimer's Disease (AD). This work analyzed the vegetative growth and phytochemistry of its potential compounds, in response to variations in sucrose concentration and activated carbon (AC). Seeds were germinated in vitro and in the greenhouse. The in vitro bulbs were separated in six treatments with different sucrose concentrations (30, 45 and 60 gL-1) and/or AC (1 gL-1). Biomass increases in individuals grown in the greenhouse were higher than those cultivated in vitro. Sucrose concentration significantly increased biomass and root number. AC had a positive influence on leaf and root size, and a negative influence on root number. GC-MS analyses indicated great variation in the abundance of α-terpenyl-acetate, ethyl linoleate, clionasterol and lycorine between treatments, with maximum concentrations of 53.06%, 38.68, 14.34% and 2.57%, respectively. Histolocalization tests indicated the presence of alkaloids in the leaf chlorenchyma and bulb cataphylls. Finally, the present study provided new evidence that the constitution of the culture medium directly influences the vegetative growth and phytochemistry of this species, providing a good medium condition for propagating the species under threat.

Discovery of highly functionalized grayanane diterpenoids from the flowers of Rhododendron molle as potent analgesics

A systematical investigation on the chemical constituents of the flowers of Rhododendron molle (Ericaceae) led to the isolation and characterization of thirty-eight highly functionalized grayanane diterpenoids (1-38), including twelve novel analogues molleblossomins A-L (1-12). Their structures were elucidated by comprehensive methods, including 1D and 2D NMR analysis, calculated ECD, 13C NMR calculations with DP4+ probability analysis, and single crystal X-ray diffraction. Molleblossomins A (1), B (2), and E (5) are the first representatives of 2β,3β:9β,10β-diepoxygrayanane, 2,3-epoxygrayan-9(11)-ene, and 5,9-epoxygrayan-1(10),2(3)-diene diterpenoids, respectively. Molleblossomins G (7) and H (8) represent the first examples of 1,3-dioxolane-grayanane conjugates furnished with the acetaldehyde and 4-hydroxylbenzylidene acetal moieties, respectively. All grayanane diterpenoids 1-38 were screened for their analgesic activities in the acetic acid-induced writhing model, and all of them exhibited significant analgesic activities. Diterpenoids 6, 13, 14, 17, 20, and 25 showed more potent analgesic effects than morphine at a lower dose of 0.2 mg/kg, with the inhibition rates of 51.4%, 68.2%, 94.1%, 66.9%, 97.7%, and 60.0%, respectively. More importantly, even at the lowest dose of 0.04 mg/kg, rhodomollein X (14), rhodojaponin VI (20), and rhodojaponin VII (22) still significantly reduced the number of writhes in the acetic acid-induced pain model with the percentages of 61.7%, 85.8%, and 64.6%, respectively. The structure-activity relationship was summarized and might provide some hints to design novel analgesics based on the functionalized grayanane diterpenoids.

Aromatic glycosides and lignans glycosides with their acetylcholinesterase inhibitory activities from the leaves of Picrasma quassioides

In this study, eight new natural products were isolated from the leaves of Picrasma quassioides. Spectroscopic techniques were used for the elucidation of their planar structures. Their absolute configurations were elucidated on the basis of electron circular dichroism (ECD) techniques combined with the P/M helicity rule for the 2,3-dihydrobenzofuran chromophore, and saccharide hydrolysis. Cholinesterase inhibitors are often used as Alzheimer's disease inhibitors.Thus, acetylcholinesterase and butyrylcholinesterase inhibitory activity of these eight compounds were tested, and results showed that only compound 6 showed weakly acetylcholinesterase inhibitory activity. In particular, molecular docking was used to illustrate the bindings between compound 6 and the active sites of AChE.

In vitro and in silico cholinesterase inhibitory potential of metabolites from Laurencia snackeyi (Weber-van Bosse) M. Masuda

Alzheimer's disease (AD) is a neurodegenerative disease that causes deterioration in intelligence and psychological activities. Yet, till today, no cure is available for AD. The marine environment is an important sink of bioactive compounds with neuroprotective potential with reduced adverse effects. Recently, we collected the red algae Laurencia snackeyi from Terumbu Island, Malaysia which is known to be rich in halogenated metabolites making it the most sought-after red algae for pharmaceutical studies. The red alga was identified based on basic morphological characteristics, microscopic observation and chemical data from literature. The purplish-brown algae was confirmed a new record. In Malaysia, this species is poorly documented in Peninsular Malaysia as compared to its eastern continent Borneo. Thus, this study intended to investigate the diversity of secondary metabolites present in the alga and its cholinesterase inhibiting potential for AD. The extract inhibited both acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) with IC50 values of  14.45 ± 0.34 μ g mL-1 and 39.59 ± 0.24 μ g mL-1, respectively. Subsequently, we isolated the synderanes, palisadin A (1), aplysistatin (2) and 5-acetoxypalisadin B (3) that was not exhibit potential. Mass spectrometry analysis detected at total of 33 additional metabolites. The computational aided molecular docking using the AChE and BChE receptors on all metabolites shortlisted 5,8,11,14-eicosatetraynoic acid (31) and 15-hydroxy-1-[2-(hydroxymethyl)-1-piperidinyl]prost-13-ene-1,9-dione (42) with best inhibitory properties, respectively with the lowest optimal combination of S-score and RMSD values. This study shows the unexplored potential of marine natural resources, however, obtaining sufficient biomass for detailed investigation is an uphill task. Regardless, there is a lot of potential for future prospects with a wide range of marine natural resources to study and the incorporation of synthetic chemistry, in vivo studies in experimental design.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-023-03725-6.

Structurally diverse monoterpene indole alkaloids with vasorelaxant activities from the branches of Alstonia scholaris

Seven undescribed monoterpene indole alkaloids alstoscholarinines A‒G, along with nineteen known alkaloids, were isolated from the branches of Alstonia scholaris (L.) R. Br. The isolated alkaloids were classified into ten framework types. The structures of the undescribed alkaloids were elucidated by extensive spectroscopic analysis, ECD calculation, and single-crystal X-ray diffraction analysis. Alstoscholarinine A is an unreported and unusual monoterpene indole alkaloid incorporating three nitrogen atoms, characterized by a compact 6/5/6/6/6/5 hexacyclic system bearing a piperidine ring and a unique oxazolidine ring. Alstoscholarinine B represents the first naturally C-17 nor-isositsirikine-type alkaloid. Plausible biosynthetic pathways of alstoscholarinines A and B were proposed. All isolates were evaluated for their vasorelaxant activities against phenylephrine-induced contraction of rat mesenteric arteries. Among them, seven alkaloids showed significant vasorelaxant activities with EC₅₀ values less than 10 μM. Importantly, the akuammicine-type alkaloids in this study showed much better vasorelaxant activities than other framework type alkaloids, indicating that this type of alkaloid may be a valuable source for the discovery of vasodilators. A preliminary structure-activity relationship for vasorelaxant activities of the isolated akuammicine-type alkaloids is also discussed.

Insight into tetrahydrofuran lignans from Isatis indigotica fortune with neuroprotective and acetylcholinesterase inhibitor activity

Nine tetrahydrofuran lignans, including three undescribed spiro-lignans, were isolated from Isatis indigotica Fortune (Brassicaceae). Extensive spectroscopic analyses achieved the structure elucidation of these tetrahydrofuran lignans, and quantum chemical calculation combined with the MAE_ΔΔδ parameter. Notably, isatispironeols A-B have a unique spiro[dienone-tetrahydrofuran] molecular core. These spiro[dienone-tetrahydrofuran] lignans showed comparable neuroprotective effects as the positive control in the H₂O₂-induced SH-SY5Y cells model. In addition, (-)-(7R,8S,1'R,7'R,8'R)-isatispironeol A possessed more significant AChE inhibitory activity, further interact sites were also predicted by the in silico assay.