New amide and diterpene alkaloids with anticholinesterase activity from Delphinium cyphoplectrum roots.

BACKGROUND: The cholinergic hypothesis posits a robust correlation between the onset of Alzheimer's disease and a pronounced deficit in acetylcholine, a pivotal neurotransmitter crucial for the central cholinergic nervous system's function, pivotal for memory and learning. Diterpene alkaloids exhibit intricate and distinctive chemical structures that facilitate their passage through the blood-brain barrier. Moreover, their potent pharmacological attributes render them promising candidates for addressing central nervous system disorders. OBJECTIVES: This investigation aims to scrutinize the alkaloidal composition of Delphinium cyphoplectrum (Ranunculaceae) roots, further exploring their anticholinesterase inhibitory activity and mode of inhibition. METHOD: Innovative chromatography techniques were repetitively employed to purify the alkaloids. Acetylcholinesterase (AChE) inhibition assays were conducted using Ellman's tests. The mode of inhibition was meticulously characterized through Michaelis-Menten, and Lineweaver-Burk plots. Conducting molecular docking studies, we employed the AUTO DOCK 4.2 software package. RESULTS: Eight alkaloids were identified including five C19-diterpene alkaloids (6,14,16,18-tetramethoxy-1,7,8-trihydroxy-4-methylaconitane (1), 6,16,18-trimethoxy-1,7,8,14-tetrahydroxy-4-methylaconitane (2), 6,8,16,18-tetramethoxy-1,7,14-trihydroxy-4-methylaconitane (3), 6,14,16-trimethoxy-1,7,8,18-tetrahydroxy-4-methylaconitane (4), and 14-O-acetyl-8,16-dimethoxy-1,6,7,18-tetrahydroxy-4-methylaconitane (5)), an epoxy C18-diterpene alkaloid (6,8,16-trimethoxy-1,7,14-trihydroxy-3,4-epoxyaconitane (6)), a known (pyrrolidin-2-one (7) and an undescribed amide alkaloid (1-(2'-hydroxylethylamine)-3,5,5,-trimethyl-1,5-dihydro-2H-pyrrol-2-one (8). All diterpene alkaloids underwent assessment for acetylcholinesterase (AChE) inhibition assay and displayed noteworthy AChE activity, surpassing that of the reference drug (with IC50 values of 13.7, 21.8, 23.4, 28.2, 40.4, and 23.9 for compounds 1-6, respectively, in comparison to 98.4 for Rivastigmine). Analysis of Michaelis-Menten and Lineweaver-Burk plots represents an uncompetitive mode of inhibition for compound 1 on AChE. Notably, computational docking simulations indicated that all diterpene alkaloids were accommodated within the same enzymatic cleft as the reference ligand, and displaying superior free binding energy values (from - 10.32 to -8.59 Kcal.mol-1) in contrast to Rivastigmine (-6.31 Kcal.mol-1). CONCLUSION: The phytochemical analysis conducted on the roots of Delphinium cyphoplectrum yielded the identification of eight alkaloidal compounds including one C18-diterpene, five C19-diterpene, one pyrrolidine and one amide alkaloids. AChE inhibition assay and molecular simulations unveiled remarkable significant potency attributed to the C19-diterpene alkaloids by the order of 1 > 2 > 3,6 > 4 > 5. Presence of hydroxyl group on C-1, C-7, C-8, C-14, and C-18 increased the effect. The best in vitro activity was recorded for compound 1 able to bind to Asp72 in the narrow region of PAS, while interacting by pi-sigma with Phe330 at the hydrophobic region of the gorge involving the acyl and choline binding site. This observation underscores the substantial promise of this category of natural products in the realm of drug discovery for Alzheimer's Disease, offering a compelling avenue for further research and therapeutic development.

Synthesis and structure-activity relationship of lipo-diterpenoid alkaloids with potential target of topoisomerase IIα for breast cancer treatment.

Aconitine linoleate (11) isolated from the Aconitum sinchiangense W. T. Wang exhibited significant anti-tumor activity. Based on this, a series of novel lipo-diterpenoid alkaloids were synthesized and evaluated for their anticancer activities against MCF-7 and MCF-7/ADR cell lines. Seventeen compounds, including 18-20, 22, 24-32, 36, 39, 41-42 possessed higher anti-proliferative activities (IC50 < 20 µM) against MCF-7 cell lines, which were better than the reference drug etoposide (IC50 = 18.01 ± 1.64 µM), among which compound 24 (IC50 = 4.00 ± 0.30 µM) was found to be the most potent derivative, being 4.5-fold more active than etoposide. Meanwhile, eighteen compounds, including 18-22, 24, 26-32, 36, 38-39, 41-42 presented excellent activities (IC50 < 20 µM) against MCF-7/ADR cell lines, better than etoposide (IC50 = 35.48 ± 0.29 µM) and doxorubicin (IC50 = 67.61 ± 6.5 µM). The most potent compound (19) was 13.5- and 25.7-fold more active than etoposide and doxorubicin against MCF-7/ADR cell lines, respectively. The structure-activity relationship (SAR) studies indicated that the 3-OH, 8-lipo, 14-benzene ring, and nitrogen atom with proper alkaline are crucial elements for anti-proliferative activity of target lipo-diterpenoid compounds. The proper length, the double bonds or di-fluoro-substituted at C-8 fatty acid chain, the para-donating electron group on 14-benzene group, and 13-OH are all favorable for the enhancement of anti-proliferative activities. In conclusion, the introduction of the 8-lipo group into aconitine leads to significant increase of anti-proliferative activity against MCF-7 and MCF-7/ADR cells, which suggests these kinds of lipo-alkaloids are powerful and promising antitumor compounds for breast cancer, especially for drug-resistant breast cancer.

An unexpected Lewis acid-mediated structural conversion of a Euphorbia Diterpene: From a Lathyrane skeleton to diterpene pseudo-alkaloids.

Three types of new Euphorbia diterpene pseudo-alkaloids possessing 5/6/7/3 (1), 5/6/6/4 (2-5), and 5/7/7/4 (6-7) fused ring skeletons were obtained through an unexpected BF3·Et2O/CH3CN-mediated structural conversion and amination of lathyrane diterpene (Euphorbia factor L1), in which the solution acetonitrile had been introduced into the Euphorbia diterpene as a nitrogen source and tandem amination/oxirane-opening (cyclopropane-opening)/oxa-Michael addition reaction was involved in the conversion. The structures of new Euphorbia diterpene pseudo-alkaloids were elucidated by a combination of spectroscopic data and single crystal X-ray diffraction analysis. The basic skeletons of Euphorbia diterpene pseudo-alkaloids 1 and 2-5 could fall into the structural types of euphoractine B and euphoractine A diterpenes, respectively, suggesting the possible biogenetic pathway relationship between lathyrane diterpene with euphoractines A and B types diterpenes. Pseudo-alkaloids 1-7 did not show any potential cytotoxicity against several tumor cell lines.

Isolation and identification of two pairs of cytotoxic diterpene tautomers and their tautomerization mechanisms.

Discovering anticancer drugs that do not have adverse side effects has been a developing research field worldwide in recent decades. In this work, four previously undescribed cytotoxic diterpenoids were isolated from the aerial parts of Isodon excisoides. Interestingly, these four diterpenoids were two pairs of tautomers that were first reported in plants. Their structures were further elucidated using various spectroscopic methods. The tautomerization phenomenon and mechanism for these two pairs of tautomers were emphatically described. The theoretical simulation results indicated that the diterpene tautomerization is greatly related to certain factors, including the existence of a transition state, the change of bond length and the level of conversion energy; the tautomerization for the two pairs of tautomers is mainly caused by proton transfer. For bioassays, the cytotoxicities of the tautomers against five human cancer cell lines were also investigated. The results indicated that each of the four diterpenoids showed significant cytotoxicity in at least three cell lines and could serve as potential anticancer agents for further investigation.

A new diterpenoid alkaloid from Aconitum hemsleyanum.

A new C19-diterpenoid alkaloid named hemsleyaline (1), along with fourteen known alkaloids (2-15), were isolated from the roots of Aconitum hemsleyanum Pritz. (Ranunculaceae), a herbal medicine in southwest China. Their structures were established on the basis of extensive spectroscopic analyses. Compound 1 showed mild cholinesterase inhibitory effect with IC50 value of 471 ± 9 µM.

Asymmetric Total Synthesis of Arcutinidine, Arcutinine, and Arcutine.

We have accomplished the asymmetric total synthesis of arcutinidine, arcutinine, and arcutine, three arcutine-type C20-diterpenoid alkaloids. A pentacyclic intermediate was rapidly assembled by using two Diels-Alder reactions. We developed a cascade sequence of Prins cyclization and Wagner-Meerwein rearrangement to construct the core of arcutinidine, which was then elaborated into an oxygenated pentacycle through a scalable route. Chemoselective reductive amination followed by spontaneous imine formation furnished the pyrroline motif in the final stage. We clarified the S configuration of the α-carbon of the acyl group within arcutine through chemical synthesis and crystallographic analysis.

Cytotoxic Effects of Diterpenoid Alkaloids Against Human Cancer Cells.

Diterpenoid alkaloids are isolated from plants of the genera Aconitum, Delphinium, and Garrya (Ranunculaceae) and classified according to their chemical structures as C18-, C19- or C20-diterpenoid alkaloids. The extreme toxicity of certain compounds, e.g., aconitine, has prompted a thorough investigation of how structural features affect their bioactivities. Therefore, natural diterpenoid alkaloids and semi-synthetic alkaloid derivatives were evaluated for cytotoxic effects against human tumor cells [A549 (lung carcinoma), DU145 (prostate carcinoma), MDA-MB-231 (triple-negative breast cancer), MCF-7 (estrogen receptor-positive, HER2-negative breast cancer), KB (identical to cervical carcinoma HeLa derived AV-3 cell line), and multidrug-resistant (MDR) subline KB-VIN]. Among the tested alkaloids, C19-diterpenoid (e.g., lipojesaconitine, delcosine and delpheline derivatives) and C20-diterpenoid (e.g., kobusine and pseudokobusine derivatives) alkaloids exhibited significant cytotoxic activity and, thus, provide promising new leads for further development as antitumor agents. Notably, several diterpenoid alkaloids were more potent against MDR subline KB-VIN cells than the parental drug-sensitive KB cells.

The Methylene-Cycloalkylacetate (MCA) Scaffold in Terpenyl Compounds with Potential Pharmacological Activities.

Recently, the methylene-cycloakylacetate (MCA) scaffold has been reported as a potential pharmacophore for neurite outgrowth activity. In this work, natural diterpenes that embed MCA fragments are reviewed, as they are major components of Halimium viscosum: ent-halimic acid, the prototype for these bioactive compounds. Herein, structures, sources, and activities for the natural diterpenes, as well as their synthetic derivatives of interest, are reviewed.

Prenylated Indole Diterpene Alkaloids from a Mine-Soil-Derived Tolypocladium sp.

Ten new prenylated indole diterpene alkaloids, tolypocladin A-J (1-10), including four chlorinated metabolites, have been isolated from a culture of a mine-soil-derived fungus, Tolypocladium sp. XL115. The structures and absolute configurations of 1-10 were determined by spectroscopic analysis, ECD calculations, and comparison with known compounds. Compounds 1 and 8 displayed significant antimicrobial activities. In addition, compound 1 also showed weak cytotoxic activity against all tested human cancer cell lines and suppressed the growth and viability of the patient-derived HCC cells T1224.

An indole diterpenoid isolated from the fungus Drechmeria sp. and its antimicrobial activity.

One new indole diterpenoid, drechmerin I (1), was isolated from the fermentation broth of Drechmeria sp. isolated from the root of Panax notoginseng. Its structure was elucidated based on 1 D and 2 D nuclear magnetic resonance (NMR), high resolution electrospray ionization mass spectrum (HRESIMS), and electronic circular dichroism (ECD) spectroscopic analyses as well as TD DFT calculations of ECD spectra. Drechmerin I (1) was assayed for its antimicrobial activity against Candida albicans, Staphylococcus aureus, Bacillus cereus, B. subtillis, Pseudomonas aeruginosa, and Klebsiella pneumonia, respectively. Drechmerin I (1) showed antimicrobial activities against B. subtillis with an MIC value of 200 µg/mL. The interaction of S. aureus peptide deformylase with drechmerin I (1) was investigated by molecular docking.

Four new C19-diterpenoid alkaloids from Aconitum hemsleyanum var. circinatum.

Four new C19-diterpenoid alkaloids, hemaconitines A-D (1-4), were isolated from the roots of Aconitum hemsleyanum var. circinatum. Their structures were elucidated as 19R-hydroxyl-secoyunnaconitine (1), (3R)-hydroxyl-liwaconitine (2), 14-anisoyl-leucanthumsine E (3), and 19R -acetonyl-8-O-methyltalatisamine (4) by extensive spectroscopic analysis (IR, UV, HR-ESI-MS, 1D, and 2D NMR).

Neuroprotective Effects of Ferruginol, Jatrophone, and Junicedric Acid Against Amyloid-ß Injury in Hippocampal Neurons.

Soluble amyloid-ß (Aß) oligomers have been recognized as early neurotoxic intermediates with a key role in the synaptic dysfunction observed in Alzheimer's disease (AD). Aß oligomers block hippocampal long-term potentiation (LTP) and impair rodent spatial memory. Additionally, the presence of Aß oligomers is associated with imbalanced intracellular calcium levels and apoptosis in neurons. In this context, we evaluated the effects of three diterpenes (ferruginol, jatrophone, and junicedric acid) that are found in medicinal plants and have several forms of biological activity. The intracellular calcium levels in hippocampal neurons increased in the presence of ferruginol, jatrophone, and junicedric acid, a result that was consistent with the observed increase in CA1 synaptic transmission in mouse hippocampal slices. Additionally, assays using Aß peptide demonstrated that diterpenes, particularly ferruginol, restore LTP and reduce apoptosis. Recovery of the Aß oligomer-induced loss of the synaptic proteins PSD-95, synapsin, VGlut, and NMDA receptor subunit 2A was observed in mouse hippocampal slices treated with junicedric acid. This cascade of events may be associated with the regulation of kinases, e.g., protein kinase C (PKC) and calcium/calmodulin-dependent protein kinase II (CaMKII), in addition to the activation of the canonical Wnt signaling pathway and could thus provide protection against Aß oligomers, which trigger synaptic dysfunction. Our results suggest a potential neuroprotective role for diterpenes against the Aß oligomers-induced neurodegenerative alterations, which make them interesting molecules to be further studied in the context of AD.

Mechanism of Action of the Cytotoxic Asmarine Alkaloids.

The asmarines are a family of cytotoxic natural products whose mechanism of action is unknown. Here, we used chemical synthesis to reverse engineer the asmarines and understand the functions of their individual components. We found that the potent asmarine analog "delmarine" arrested the mammalian cell cycle in the G1 phase and that both cell cycle arrest and cytotoxicity were rescued by cotreatment with ferric and ferrous salts. Cellular iron deprivation was clearly indicated by changes in iron-responsive protein markers, and cytotoxicity occurred independently of radical oxygen species (ROS) production. Chemical synthesis allowed for annotation of the distinct structural motifs required for these effects, especially the unusual diazepine, which we found enforced an iron-binding tautomer without distortion of the NCNO dihedral angle out of plane. With this information and a correlation of cytotoxicity with logP, we could replace the diazepine by lipophilic group appendage to N9, which avoided steric clash with the N6-alkyl required to access the aminopyridine. This study transformed the asmarines, scarce marine metabolites, into easily synthesized, modular chemotypes that may complement or succeed iron-selective binders in clinical trials and use.

A three-component coupling approach to the ACE-ring substructure of C19-diterpene alkaloids.

C19-diterpene alkaloids are a class of alkaloids with pharmacologically important activities having an intricately fused hexacyclic ABCDEF-ring system. Here we report expeditious assembly of the ACE-ring substructure 4a by applying a three-component coupling strategy. A radical-polar crossover reaction between an AE-ring radical precursor, a C-ring radical acceptor and an aldehyde was realized by the actions of Et3B and O2, resulting in the installation of three new stereocenters and extension of the carbon chain corresponding to the B-ring. As the ACE-ring 4a possesses the correct C4,11-quaternary and C10-tertiary carbons, 4a would serve as an advanced intermediate for constructing the entire C19-diterpene alkaloid structures.

Two New C19-Diterpenoid Alkaloids from Aconitum nagarum var. lasiandrum.

Continuous investigations of the roots of Aconitum nagarum var. lasiandrum led to the isolation of two new C19-diterpenoid alkaloids, lasiandrine (1) and lasiandroline (2). Their structures were elucidated on the basis of extensive interpretation of spectroscopic and mass spectrometric data.