Diterpenoid alkaloids from Aconitum anthoroideum that offer protection against MPP+-Induced apoptosis of SH-SY5Y cells and acetylcholinesterase inhibitory activity

Brunonianines D-F, three new C19-diterpenoid alkaloids from the Delphinium brunonianum, with therapeutic effect on ovarian cancer in vitro and in vivo

The current standard treatment for ovarian cancer consists of surgery to reduce the size of the tumor, followed by treatment with chemotherapeutic drugs, which have major side effects. Therefore, finding a new natural product drug with fewer side effects is a strategy. Delphinium brunonianum (D. brunonianum) is a traditional Tibetan medicine, mainly from southern Tibet, China, whereas the chemical constituents in this plant remain elusive. The major metabolites in the dichloromethane fraction of D. brunonianum were analyzed and purified by HPLC and various column chromatography techniques. Nine diterpenoid alkaloids (1-9) and one amide alkaloid (10) were isolated from D. brunonianum, including three novel C19-type diterpenoid alkaloids (Brunonianines D-F) (1-3). Their structures were elucidated by 1D/2D NMR, HR-ESI-MS and single-crystal X-ray diffraction analyses. All compounds were evaluated for toxicity in four tumor cell lines. Most of the compounds exhibited potent inhibitory effects on Skov-3 cell lines, with IC50 values ranging from 2.57 to 8.05 μM. The western blotting experiment was used to further analyze the expression levels of molecules in the Bax/Bcl-2/Caspase-3 signaling pathway for compound 1. Molecular docking was performed to predict the binding modes of Brunonianine D with target proteins. In vivo experiments were also performed and evaluated in real time by monitoring the size of the Skov-3 tumor. Additionally, tumor H&E staining and the TUNEL assay used to evaluate anti-tumor effects.

Exploring the Biomedical Potential of Terpenoid Alkaloids: Sources, Structures, and Activities

Terpenoid alkaloids are recognized as a class of compounds with limited numbers but potent biological activities, primarily derived from plants, with a minor proportion originating from animals and microorganisms. These alkaloids are synthesized from the same prenyl unit that forms the terpene skeleton, with the nitrogen atom introduced through β-aminoethanol, ethylamine, or methylamine, leading to a range of complex and diverse structures. Based on their skeleton type, they can be categorized into monoterpenes, sesquiterpenes, diterpenes, and triterpene alkaloids. To date, 289 natural terpenoid alkaloids, excluding triterpene alkaloids, have been identified in studies published between 2019 and 2024. These compounds demonstrate a spectrum of biological activities, including anti-inflammatory, antitumor, antibacterial, analgesic, and cardioprotective effects, making them promising candidates for further development. This review provides an overview of the sources, chemical structures, and biological activities of natural terpenoid alkaloids, serving as a reference for future research and applications in this area.

Brunonianines A-C, C20-diterpenoid alkaloids with cyano group from Delphinium brunonianum Royle

Cyano tends to have better biological activity, but it is rarely reported in natural products, especially in the C20-diterpene alkaloids. Herein, three unprecedented C20-diterpenoid alkaloids, brunonianines A-C (1-3), possessing rare cyano functional group as well as an atisine backbone constructed from a phenethyl substituent and a tetrahydropyran ring, along with four C19-alkaloids (4-7) and one amide alkaloids (8), were isolated from the whole plant of Delphinium brunonianum Royle. Compounds 1-3 are also the first atisine type diterpenoid alkaloids with cyano group obtained from nature. The structures of the previously undescribed compounds were elucidated by HR-ESI-MS, 1D/2D NMR spectroscopic data and electronic circular dichroism calculations and single-crystal X-ray diffraction. Reasonable speculations have also been made regarding the biogenic synthetic pathways of compounds 1-3. In addition, the inhibitory activity of all compounds was also tested against four tumor lines: A549, Caco-2, H460 and Skov-3, where compound 2 (IC50 2.20 ± 0.21 μM) showed better inhibitory activity against Skov-3 cells than the hydroxycamptothecin. Using flow cytometry, cell staining, migration and invasion analysis, and Western blot, compound 2 was found to arrest cells in the G2/M phase and was able to effectively inhibit cell motility to achieve potent anti-tumor effects. In addition, compound 2 can effectively induce apoptosis by activating the Bax/Bcl-2/Caspase-3 signaling pathway.

Kamaonensine A-G: Lycaconitine-type C19-diterpenoid alkaloids with anti-inflammatory activities from Delphinium kamaonense Huth

Delphinium kamaonense Huth is a sort of folkloric plant resource which is cultivated and planted with great ornamental and medicinal values. In this work, seven undescribed lycaconitine-type C19-diterpenoid alkaloids, especially a rare skeleton with -CH=N and N-oxide moieties, along with ten known compounds, were isolated from D. kamaonense, of which the structures were determined by various spectroscopic data, combined with calculated electronic circular dichroism (ECD) and single-crystal X-ray diffraction analysis. In vitro nitric oxide inhibitory activities assay of these compounds indicated that lycaconitine-type C19-diterpenoid alkaloids had significant anti-inflammatory inhibitory activities, with kamaonensine E being the most potent (0.9 ± 0.2 μM) stronger than positive (9.0 ± 1.3 μM). In the network pharmacology studies, binding three key targets mitogen-activated protein kinase 8 (MAPK8), mitogen-activated protein kinase 14 (MAPK14), and heat shock protein HSP 90-alpha (HSP90α), the anti-inflammatory mechanism might be related to MAPK signaling pathways. Furthermore, the molecular docking results revealed that the uncommon amides and methylenedioxy groups might be the most two promising pharmacophores for lycaconitine-type C19-diterpenoid alkaloids.

Four Pairs of Neuroprotective Aryldihydronaphthalene-Type Lignanamide Enantiomers from the Herbs of Solanum lyratum

Four pairs of aryldihydronaphthalene-type lignanamide enantiomers were isolated from Solanum lyratum (Solanaceae). The enantiomeric separation was accomplished by chiral-phase HPLC, and five undescribed compounds were elucidated. Analysis by various spectroscopy and ECD calculations, the structures of undescribed compounds were illuminated. The neuroprotective effects of all compounds were evaluated using H2 O2 -induced human neuroblastoma SH-SY5Y cells and AchE inhibition activity. Among them, compound 4 a exhibited remarkable neuroprotective effects at high concentrations of 25 and 50 μmol/L comparable to Trolox. Compound 1 a showed the highest AchE inhibition with the IC50 value of 3.06±2.40 μmol/L. Molecular docking of the three active compounds was performed and the linkage between the compounds and the active site of AchE was elucidated.

Neuropharmacological Potential of Diterpenoid Alkaloids

This study provides a narrative review of diterpenoid alkaloids (DAs), a family of extremely important natural products found predominantly in some species of Aconitum and Delphinium (Ranunculaceae). DAs have long been a focus of research attention due to their numerous intricate structures and diverse biological activities, especially in the central nervous system (CNS). These alkaloids originate through the amination reaction of tetra or pentacyclic diterpenoids, which are classified into three categories and 46 types based on the number of carbon atoms in the backbone structure and structural differences. The main chemical characteristics of DAs are their heterocyclic systems containing β-aminoethanol, methylamine, or ethylamine functionality. Although the role of tertiary nitrogen in ring A and the polycyclic complex structure are of great importance in drug-receptor affinity, in silico studies have emphasized the role of certain sidechains in C13, C14, and C8. DAs showed antiepileptic effects in preclinical studies mostly through Na⁺ channels. Aconitine (1) and 3-acetyl aconitine (2) can desensitize Na⁺ channels after persistent activation. Lappaconitine (3), N-deacetyllapaconitine (4), 6-benzoylheteratisine (5), and 1-benzoylnapelline (6) deactivate these channels. Methyllycaconitine (16), mainly found in Delphinium species, possesses an extreme affinity for the binding sites of α7 nicotinic acetylcholine receptors (nAChR) and contributes to a wide range of neurologic functions and the release of neurotransmitters. Several DAs such as bulleyaconitine A (17), (3), and mesaconitine (8) from Aconitum species have a drastic analgesic effect. Among them, compound 17 has been used in China for decades. Their effect is explained by increasing the release of dynorphin A, activating the inhibitory noradrenergic neurons in the β-adrenergic system, and preventing the transmission of pain messages by inactivating the Na⁺ channels that have been stressed. Acetylcholinesterase inhibitory, neuroprotective, antidepressant, and anxiolytic activities are other CNS effects that have been investigated for certain DAs. However, despite various CNS effects, recent advances in developing new drugs from DAs were insignificant due to their neurotoxicity.

Palladium-Catalyzed Synthesis, Acetylcholinesterase Inhibition, and Neuroprotective Activities of N-Aryl Galantamine Analogues

A series of new N-aryl galantamine analogues (5a-5x) were designed and synthesized by modification of galantamine, using Pd-catalyzed Buchwald-Hartwig cross-coupling reaction in good to excellent yields. The cholinesterase inhibitory and neuroprotective activities of N-aryl derivatives of galantamine were evaluated. Among the synthesized compounds, the 4-methoxylpyridine-galantamine derivative (5q) (IC₅₀ = 0.19 μM) exhibited excellent acetylcholinesterase inhibition activity, as well as significant neuroprotective effect against H₂O₂-induced injury in SH-SY5Y cells. Molecular docking, staining, and Western blotting analyses were performed to demonstrate the mechanism of action of 5q. Derivative 5q would be a promising multifunctional lead compound for the treatment of Alzheimer's disease.

Two new C18-diterpenoid alkaloids from Aconitum leucostomum Worosch

Two new lappaconitine-type C18-diterpenoid alkaloids, named as leucostosines C (1) and D (2), together with six known compounds (3-8), were isolated from the roots of Aconitum leucostomum Worosch. Their structures were elucidated by various spectroscopic analyses, including IR, HR-ESI-MS, NMR spectra and X-ray experiments. Leucostosine C is the first diterpenoid alkaloid bearing the 7-amino group. The isolated compounds were tested for the acetylcholinesterase (AChE) inhibitory effect and neuroprotective activity, none of them showed significant activities.

Biogenetic and biomimetic synthesis of natural bisditerpenoids: hypothesis and practices

Covering: up to March 2022Bisditerpenoids, or diterpenoid dimers, are a group of natural products with high structural variance, deriving from homo- or hetero-dimeric coupling of two diterpenoid units. They usually possess complex architectures resulting from the diversity of monomeric diterpenoids as building blocks and the dimerization processes. These compounds have attracted the attention of synthetic and biological scientists owing to the rarity of their natural origin and their significant biological activities. Herein, we provide a review highlighting some of the interesting bisditerpenoids reported since 1961 and showcase the chemical diversity in both their structures and biosynthesis, as well as their biological functions. This review focuses on the biosynthetic dimerization pathways of interesting molecules and their biomimetic synthesis, which may act as useful inspiration for the discovery and synthesis of more bisditerpenoids and further pharmacological investigations.

Isolation, crystal structure, DFT calculation and molecular docking of uncinatine-A isolated from Delphinium uncinatum

The main objective of our present research work was to explore molecular insight for potentially active new acetylcholinesterase inhibitor from the aerial parts of Delphinium uncinatum. New norditerpenoid alkaloids, uncinatine-A, was isolated from the basic alkaloidal fraction of D. uncinatum, based on bioactivity guided isolation. The structure of uncinatine-A was determined through latest spectroscopic techniques including single X-Ray diffraction technique. The structural data and electronic properties of uncinatine-A was also calculated by Density Functional Theory (DFT) using B3LYP/6-31þ G (p) basis set. The isolated natural product was evaluated for their acetyl cholinesterase inhibitory potential in dose dependent protocol (62.5-1000 μg/mL), followed by molecular docking studies. Significant competitive type inhibition activity (IC_{50 =} 207.73 ± 0.3) was shown by isolated natural norditerpenoid against cholinesterase targets in comparison with standard drugs available in the market such as galanthamine. The molecular docking results showed that isolated natural product was well accommodated by AChE in the active site with docking scores -11.0326. This is the first report indicating uncinatine-A as a potent acetylcholinesterase inhibitor and can be used as a target drug in cerebral dementia and Alzheimer diseases.

Determination of Anti-Alzheimer's Disease Activity of Selected Plant Ingredients

Neurodegenerative diseases, among which one of the more common is Alzheimer’s disease, are the one of the biggest global public health challenges facing our generation because of the increasing elderly population in most countries. With the growing burden of these diseases, it is essential to discover and develop new treatment options capable of preventing and treating them. Neurodegenerative diseases, among which one of the most common is Alzheimer’s disease, are a multifactorial disease and therefore demand multiple therapeutic approaches. One of the most important therapeutic strategies is controlling the level of acetylcholine—a neurotransmitter in cholinergic synapses—by blocking the degradation of acetylcholine using acetylcholinesterase inhibitors such as tacrine, galantamine, donepezil and rivastigmine. However, these drugs can cause some adverse side effects, such as hepatotoxicity and gastrointestinal disorder. Thus, the search for new, more effective drugs is very important. In the last few years, different active constituents from plants have been tested as potential drugs in neurodegenerative disease therapy. The availability, lower price and less toxic effects of herbal medicines compared with synthetic agents make them a simple and excellent choice in the treatment of neurodegenerative diseases. The empirical approach to discovering new drugs from the systematic screening of plant extracts or plant-derived compounds is still an important strategy when it comes to finding new biologically active substances. The aim of this review is to identify new, safe and effective compounds that are potential candidates for further in vivo and clinical tests from which more effective drugs for the treatment of Alzheimer’s disease could be selected. We reviewed the methods used to determine anti-Alzheimer’s disease activity. Here, we have discussed the relevance of plant-derived compounds with in vitro activity. Various plants and phytochemical compounds have shown different activity that could be beneficial in the treatment of Alzheimer’s disorders. Most often, medicinal plants and their active components have been investigated as acetylcholinesterase and/or butyrylcholinesterase activity inhibitors, modifiers of β-amyloid processing and antioxidant agents. This study also aims to highlight species with assessed efficacy, usable plant parts and the most active plant components in order to identify species and compounds of interest for further study. Future research directions are suggested and recommendations made to expand the use of medicinal plants, their formulations and plant-derived active compounds to prevent, mitigate and treat Alzheimer’s disease.

Antiplasmodial diterpenoid alkaloid from Aconitum heterophyllum Wall. ex Royle: Isolation, characterization, and UHPLC-DAD based quantification

ETHNOPHARMACOLOGICAL RELEVANCE

Aconitum heterophyllum Wall. ex Royle is a traditionally important medicinal plant having numerous therapeutic actions as documented in Ayurveda. This plant is traditionally known for combating worm infestation, fever, respiratory tract disease, vomiting, diarrhoea, diabetes, skin disorders, anaemia, and joint disorders. Further, it has been used alone and in combination with other plants to prepare various anti-malarial formulations. However, there is no report on the assessment of its anti-plasmodial activity, and the metabolite(s) responsible for this activity.

AIM OF THE STUDY

The main aim of this study was to conduct phytochemical investigation of A. heterophyllum roots for the preparation of extract, fractions, and isolation of pure molecules to identify active fractions/molecules responsible for the anti-plasmodial activity, and development of UHPLC-DAD based analytical method which can be used for the quantification of marker compounds in the extracts and fractions.

MATERIALS AND METHODS

Hydroalcoholic extract (1:1 v/v) and fractions (n-hexane, chloroform, ethyl acetate, n-butanol, and water) were prepared from the dried powdered roots of A. heterophyllum. Fractions were further subjected to silica gel column chromatography to isolate pure specialized secondary metabolites from this plant. All extracts, fractions, and pure molecules were evaluated against the chloroquine resistant Pf INDO and chloroquine sensitive Pf3D7 strains in culture for calculating their IC₅₀ values. UHPLC-DAD based analytical method was also developed for the first time for the quantification of marker compounds and quality assessment of this commercially important Himalayan medicinal plant.

RESULTS

Phytochemical investigation of A. heterophyllum root led to the isolation of six specialized metabolites viz. 2-O-cinnamoyl hetisine (1), atisinium (2), 4-oxabicyclo [3.2.2] nona-1(7),5,8-triene (3), atisinium cinnamate (4), aconitic acid (5), and atisinium formate (6). Compound 1 is a new hetisine type diterpenoid alkaloid, compounds 4 and 6 are new counter ionic forms observed with atisinium ion, and compound 3 is being reported for the first time from this genus. Chloroform fraction was found to be the most active with IC₅₀ (μg/mL) 1.01 (Pf INDO) and 1.32 (Pf3D7). The molecule 2-O-cinnamoyl hetisine (1), a new diterpenoid alkaloid isolated from chloroform fraction, showed promising antiplasmodial activities with IC₅₀ (μM) 1.92 (Pf INDO) and 10.8 (Pf 3D7). The activity of chloroform fraction was further validated by the developed UHPLC-DAD based method as the quantity of 2-O-cinnamoyl hetisine (1) was higher in the chloroform fraction (≅200 mg/g) than in all other fractions (<7 mg/g). Atisinium (2) and 2-O-cinnamoyl hetisine (1) were found to be the main marker compounds of this plant based on quantity and antiplasmodial activity, respectively.

CONCLUSION

This study provides the scientific rationale for the traditional use of this plant in treating malaria. Further, this study revealed that the anti-malarial potential of this plant might be due to the presence of diterpenoid alkaloids.

The diterpenoid alkaloids

The diterpenoid alkaloids are a family of extremely important natural products that have long been a research hotspot due to their myriad of intricate structures and diverse biological properties. This chapter systematically summarizes the past 11 years (2009-2019) of studies on the diterpenoid alkaloids, including the "so-called" atypical ones, covering the classification and biogenetic relationships, phytochemistry together with 444 new alkaloids covering 32 novel skeletons and the corrected structures, chemical reactions including conversion toward toxoids, synthetic studies, as well as biological activities. It should be noted that the synthetic studies, especially the total syntheses of various diterpenoid alkaloids, are for the first time reviewed in this treatise. This chapter, in combination with our four previous reviews in volumes 42, 59, 67, and 69, will present to the readers a more completed and updated profile of the diterpenoid alkaloids.

Chemistry and biological activities of hetisine-type diterpenoid alkaloids

Hetisine-type C₂₀-diterpenoid alkaloids (DAs) are one of the most important DA subtypes. During the past decades, a total of 157 hetisine-type DAs were obtained from plants from seven genera in three families, most of which were isolated from the genera Aconitum and Delphinium in the Ranunculaceae family. Structurally, hetisine-type DAs are characterized by a heptacyclic hetisane skeleton formed by the linkage of C(14)–C(20) and N–C(6) bonds in an atisine-type DA, and their structural diversity is created by the states of the N atom and various substituents. Pharmacological studies have revealed a wide range of pharmacological actions for hetisine-type DAs, including antiarrhythmic, antitumor, antimicrobial and insecticidal activities, as well as effects on peripheral vasculature, which are closely related to their chemical structures. In particular, the prominent antiarrhythmic effects and low toxicity of hetisine-type DAs highlight their potential in antiarrhythmic drug discovery. Hetisine-type DAs with diverse bioactivities are promising lead structures for further development as commercial agents in medicine.

Natural hetisine-type C₂₀-diterpenoid alkaloids with diverse structures showed multiple pharmacological activities, indicating great potential in drug discovery.

Diterpenoid alkaloids from the whole herb of Delphinium grandiflorum L

Seven previously undescribed diterpenoid alkaloids, eight reaction products and thirteen known compounds were isolated from the whole plant of Delphinium grandiflorum L. (Ranunculaceae). Grandiflonines A and B have an unprecedented C₂₀-diterpenoid alkaloid skeleton, which features inversion of the configuration of C-18. Their structures were determined by comprehensive analyses of spectroscopic data, X-ray diffraction and Mosher's method. The probable biosynthetic pathway of grandiflonine A was discussed. Additionally, the analgesic activity and anti-inflammatory activity by inhibition of NO production were evaluated. Among them, deoxylappaconitine (ED₅₀ = 0.35 mg/kg, TI = 46.22) showed significant analgesic activity that was superior to the reference drug lappaconitine (ED₅₀ = 3.5 mg/kg, TI = 3.34).

Three New C19-Diterpenoid Alkaloids from Aconitum novoluridum

Three new aconitine-type C₁₉-diterpenoid alkaloid namely novolunines A (1), B (2), and C (3), along with fifteen known diterpenoid alkaloids were isolated from the roots of Aconitum novoluridum, whose phytochemical investigations have never been reported before. The structures of three new alkaloids were established on the basis of spectra data (high-resolution electrospray ionization (HR-ESI)-MS, IR, one dimensional (1D)- and 2D-NMR). Noteworthily, novolunines A (1) and B (2) are two diterpenoid alkaloids bearing conformational isomerism. In addition, the diterpenoid alkaloids 1-3 did not show any anti-acetylcholinesterase (AChE) or anti-inflammatory activities.