Stephapierrines A-H, new tetrahydroprotoberberine and aporphine alkaloids from the tubers of Stephania pierrei Diels and their anti-cholinesterase activities

Furostanol glycosides, stilbenoids and nucleosides from the roots of Smilax perfoliata, and evaluation of their cytotoxic and anticholinesterase activities

Three undescribed compounds including two furosteroid glycosides (perfoloside and 22-O-methylperfoloside) and one stilbenedimer (perfolostilbene) together with 21 known compounds were isolated from the roots of Smilax perfoliata. The structural elucidation was established by extensive uses of HRMS, 1D and 2D spectroscopic techniques. The assignment of the stereocenters in perfolostilbene was based on NOESY data and ECD calculation. Among the isolates, two compounds showed marginal cytotoxic activity against KB and Hela cell lines while seven stilbenoids showed strong to weak antiacetylcholinesterase and antibutyrylcholinesterase activities with IC50 ranging between 2-197 µM.

Aporphine alkaloids and a naphthoquinone derivative from the leaves of Phaeanthus lucidus Oliv. and their α-glucosidase inhibitory activity

Three previously undescribed aporphine alkaloids, phaeanthuslucidines E-G, one previously undescribed naphthoquinone derivative, phaeanthusnaphthoquinone, and three known compounds were isolated from an EtOAc extract of the leaves of Phaeanthus lucidus Oliv. The structures of all previously undescribed compounds were established through extensive spectroscopic investigations and high-resolution mass spectroscopy. The 6aR configuration of phaeanthuslucidines E-G was assigned by comparing their ECD spectra and specific rotation values with the reported known compounds. Some isolated compounds were evaluated for their α-glucosidase inhibitory activity. Among these compounds, phaeanthuslucidine E showed the highest α-glucosidase inhibitory activity with an IC50 value of 17.9 ± 0.4 μM. The molecular docking of phaeanthuslucidine E was further studied.

Bioactive cholinesterase inhibitions of clerodanes from the flowers of Croton krabas and molecular docking studies

The first investigation of the phytochemical profile of the flowers of Croton krabas led to the isolation of two new clerodane diterpenes, 6S-crotocaudin (1) and crotocaudin B (2), together with two known clerodanes, 6S-crotoeurin C (3) and isoteucvin (4). The structures and absolute configurations of isolated clerodanes were elucidated by extensive analysis of NMR spectroscopic data, mass spectrometry and ECD calculations. Compounds 1-4 demonstrated significant inhibitory activity towards acetylcholinesterase (AChE). Notably, compound 2 exhibited the strongest AChE inhibition (IC50 1.01 µM). Compounds 3 and 4 showed potent butyrylcholinesterase (BChE) inhibitory activity with IC50 values of 1.09 and 1.12 µM, respectively. The molecular docking results revealed that 2 bound to the catalytic anionic site (CAS) and peripheral anionic site (PAS) of AChE, while 3 occupied in the CAS of BChE.

Synthesis, Antiacetylcholinesterase Activity, and Molecular Dynamics Simulation of Aporphine-benzylpyridinium Conjugates

A series of aporphines conjugated with an N-benzylpyridinium moiety through an amide-bond linkage were synthesized and evaluated for their acetylcholinesterase (AChE) inhibitory activity. The conjugation of the N-benzylpyridinium group significantly enhanced the AChE inhibitory activity of the core aporphine. The halogen substituents on the benzyl group affected the activity of the conjugates. Both (S)- and (R)-enantiomers of three conjugates with low IC50 values were synthesized and evaluated for their activities. All (S)-enantiomers exhibited higher activity than the corresponding (R)-enantiomers. The (S)-enantiomer of 2-chlorobenzylpyridinium-containing aporphine was the most potent inhibitor in this study with an IC50 value of 0.06 ± 0.003 μM. Molecular dynamics simulation analysis revealed that both enantiomers can interact with the AChE binding site, whereas the (S)-enantiomer possessed slightly stronger interaction than the (R)-enantiomer, presumably because of their different orientations, as evidenced by molecular docking. The N-benzylpyridinium dehydroaporphine conjugates were also synthesized but were less active than the corresponding aporphine conjugates.

Amaryllidaceae alkaloids from the bulbs of Crinum latifolium L. and their cholinesterase inhibitory activities

Eleven previously undescribed Amaryllidaceae alkaloids, crinalatifolines A-K (1-11), and two first naturally occurring alkaloids, dihydroambelline (12) and N-demethyldihydrogalanthamine (13), were isolated from the bulbs of Crinum latifolium L. Additionally, thirty-seven known alkaloids and one alkaloid artifact were also isolated from this plant species. Their structures and absolute configurations were elucidated using extensive spectroscopic techniques, including IR, NMR, MS, and ECD. Evaluations of the cholinesterase inhibitory activities of most of these compounds were conducted. Among the tested compounds, ungeremine exhibited the highest potency against acetylcholinesterase and butyrylcholinesterase, with the IC50 values of 0.10 and 1.21 μM, respectively. These values were 9.4- and 2.4-fold more potent than the reference drug galanthamine.

Naturally Occurring Cholinesterase Inhibitors from Plants, Fungi, Algae, and Animals: A Review of the Most Effective Inhibitors Reported in 2012-2022

Since the development of the "cholinergic hypothesis" as an important therapeutic approach in the treatment of Alzheimer's disease (AD), the scientific community has made a remarkable effort to discover new and effective molecules with the ability to inhibit the enzyme acetylcholinesterase (AChE). The natural function of this enzyme is to catalyze the hydrolysis of the neurotransmitter acetylcholine in the brain. Thus, its inhibition increases the levels of this neurochemical and improves the cholinergic functions in patients with AD alleviating the symptoms of this neurological disorder. In recent years, attention has also been focused on the role of another enzyme, butyrylcholinesterase (BChE), mainly in the advanced stages of AD, transforming this enzyme into another target of interest in the search for new anticholinesterase agents. Over the past decades, Nature has proven to be a rich source of bioactive compounds relevant to the discovery of new molecules with potential applications in AD therapy. Bioprospecting of new cholinesterase inhibitors among natural products has led to the discovery of an important number of new AChE and BChE inhibitors that became potential lead compounds for the development of anti-AD drugs. This review summarizes a total of 260 active compounds from 142 studies which correspond to the most relevant (IC50 ≤ 15 μM) research work published during 2012-2022 on plant-derived anticholinesterase compounds, as well as several potent inhibitors obtained from other sources like fungi, algae, and animals.

An Enzymatic Strategy for the Selective Methylation of High-Value-Added Tetrahydroprotoberberine Alkaloids

Tetrahydroprotoberberines (THPBs) are plant-specific alkaloids with significant medicinal value. They are present in trace amounts in plants and are difficult to chemically synthesize due to stereoselectivity and an unfavorable environment. In this study, a selective methylation strategy was developed for the biocatalysis of seven high-value-added THPB compounds using 4'-O-methyltransferase (Cj4'OMT), norcoclaurine 6-O-methyltransferase (Cj6OMT), and (S)-scoulerine 9-O-methyltransferase (SiSOMT and PsSOMT) in engineered E. coli. The methyltransferases Cj4'OMT, Cj6OMT, PsSOMT, and SiSOMT were expressed heterologously in E. coli. Compound 1 (10-methoxy-2,3,9-tetrahydroxyberbine) was synthesized using the recombinant E. coli strain Cj4'OMT and the substrate 2,3,9,10-tetrahydroxyberbine. Compound 2 (9-methoxy-2,3,10-tetrahydroxyberbine) was produced in the recombinant Escherichia coli (E. coli) strain PsSOMT, and compounds 2 and 3 (discretamine) were produced in the recombinant E. coli strain SiSOMT. Compounds 4 (9,10-methoxy-2,3-tetrahydroxyberbine) and 5 (corypalmine) were obtained by co-culturing the recombinant strains Cj4'OMT and SiSOMT with substrate. Compounds 6 (scoulerine) and 7 (isoscoulerine) were produced by co-culturing the substrate with the recombinant strains Cj4'OMT and Cj6OMT. To increase the yield of novel compound 2, the flask culture conditions of the engineered SiSOMT strain were optimized, resulting in the production of 165.74 mg/L of this compound. This study thus presents an enzymatic approach to the synthesis of high-value-added THPBs with minimum environmental wastage.

Bioactive Isoquinoline Alkaloids with Diverse Skeletons from Fissistigma polyanthum

Six new isoquinoline alkaloids, including aporphine alkaloids (2, 3, 9, and 10), a benzylisoquinoline alkaloid (13), and a protoberberine alkaloid (17), were isolated from the roots of Fissistigma polyanthum, along with a new furanone (20) and 13 known isoquinoline alkaloids (1, 4-8, 11, 12, 14-16, 18, and 19). The structures of the new compounds were elucidated by the analysis of spectroscopic data. Compounds 1 and 2 are rare oxalyl-fused dehydroaporphine alkaloids. Compound 12 presented the most potent dual-target activities on AChE inhibition and Aβ aggregation inhibition, while compounds 13 and 19 simultaneously exhibited discernible AChE and BChE inhibitions with antioxidant activities. The activity results indicate that F. polyanthum alkaloids have a potential of inhibition and prevention of Alzheimer's disease mainly through both ChEs and β-amyloid pathways in addition to antioxidant activity.

Aporphines: A privileged scaffold in CNS drug discovery

Aporphine alkaloids embedded in 4H-dibenzo[de,g]quinoline four-ring structures belong to one of the largest subclasses of isoquinoline alkaloids. Aporphine is a privileged scaffold in the field of organic synthesis and medicinal chemistry for the discovery of new therapeutic agents for central nervous system (CNS) diseases, cancer, metabolic syndrome, and other diseases. In the past few decades, aporphine has attracted continuing interest to be widely used to develop selective or multitarget directed ligands (MTDLs) targeting the CNS (e.g., dopamine D_1/2/5, serotonin 5-HT_1A/2A/2C and 5-HT₇, adrenergic α/β receptors, and cholinesterase enzymes), thereby serving as valuable pharmacological probes for mechanism studies or as potential leads for CNS drug discovery. The aims of the present review are to highlight the diverse CNS activities of aporphines, discuss their SAR, and briefly summarize general synthetic routes, which will pave the way for the design and development of new aporphine derivatives as promising CNS active drugs in the future.

Protective effects of Stephania pierrei tuber-derived oxocrebanine against LPS-induced acute lung injury in mice

Acute lung injury and acute respiratory distress syndrome (ALI/ARDS) have high mortality rates. Though corticosteroids are commonly used for the treatment of these conditions, their efficacy has not been conclusively demonstrated and their use can induce various adverse reactions. Hence, the application of corticosteroids as therapeutic modalities for ALI/ARDS is limited. Meanwhile, the aporphine alkaloid oxocrebanine isolated from Stephania pierrei tubers has demonstrated anti-inflammatory efficacy in murine/human macrophage cell lines stimulated by lipopolysaccharide (LPS). Accordingly, the primary objectives of the present study are to investigate the anti-inflammatory effects of oxocrebanine on LPS-induced murine alveolar epithelial (MLE-12) cells and its efficacy against LPS-induced murine ALI. Results show that oxocrebanine downregulates the abundance of interleukin (IL)-1beta, IL-6, and inducible nitric oxide synthase, as well as the phosphorylation of nuclear factor-kappaB (NF-κB), stress-activated protein kinase (SAPK)/c-Jun N-terminal kinase (JNK), p38, protein kinase B (Akt), and glycogen synthase kinase-3beta signalling proteins in LPS-induced MLE-12 cells. Moreover, in a murine ALI model, oxocrebanine lowers lung injury scores and lung wet/dry weight ratios while reducing inflammatory cell infiltration. It also suppresses LPS-induced tumour necrosis factor-alpha and IL-6 in the bronchoalveolar lavage fluid and plasma. Moreover, oxocrebanine downregulates NF-κB, SAPK/JNK, p38, and Akt phosphorylation in the lung tissues of LPS-treated mice. Taken together, the foregoing results show that oxocrebanine provides significant protection against LPS-induced ALI in mice primarily by suppressing various inflammatory signalling pathways in alveolar epithelial cells and lung tissues. Hence, oxocrebanine might prove effective as an anti-inflammatory agent for the treatment of lung inflammation.

Diverse alkaloids from the aerial parts of Aconitum carmichaelii and antiproliferative activity of costemline via inhibiting SIRT1/ROCK1/P-STAT3 pathways

Six undescribed alkaloids together with 15 known alkaloids were isolated from the aerial parts of Aconitum carmichaelii. Their structures were elucidated extensively by NMR and HRESIMS spectroscopy. The absolute configurations of N-formyllaurotetanine, and the known compounds glaucine-β-N-oxide and glaucine-α-N-oxide were established by electronic circular dichroism (ECD) spectra. Notably, it was the discovery of rare indole alkaloids from the genus Aconitum, and biosynthetic pathway of compounds 1 and 6 was deduced. Evaluation of the antiproliferative activity of these alkaloids demonstrated that costemline exhibited significant anti-proliferation effects against HCT116, SKOV3, and A549 cells with IC₅₀ values of 5.6, 14.2, and 6.8 μM, respectively. Costemline could also inhibit the cell invasion activity of HCT116 cells. Mechanistic studies in HCT116 cells suggested that the antiproliferative activity of costemline was attributable to SIRT1/ROCK1/P-STAT3 pathways regulation. This study revealed the potential for developing and utilizing the aerial parts of Aconitum carmichaelii.

Alkaloids with cholinesterase inhibitory activities from the bulbs of Crinum × amabile Donn ex Ker Gawl

Seven previously undescribed alkaloids, crinamabilines A-G, two non-alkaloidal compounds, crinamabidiene and 6-phenylpiperonyl alcohol, two first naturally occurring alkaloids, 3-epibuphanisine and (+)-1β,2β-epoxy-epicrinine, together with nineteen known alkaloids, were isolated from the bulbs of Crinum × amabile Donn ex Ker Gawl. Their structures and absolute configurations were elucidated by NMR, MS and ECD spectroscopic techniques. Ungeremine displayed the most potent inhibitory activity against acetylcholinesterase (IC₅₀ 0.21 μM), which was about 6-fold more active than the reference drug, galanthamine (IC₅₀ 1.23 μM). Ungeremine also exhibited the strongest inhibitory activity against butyrylcholinesterase (IC₅₀ 3.57 μM), which was comparable to galanthamine (IC₅₀ 3.11 μM). The molecular docking studies were performed and were well in agreement with the experimental results.

Oxocrebanine from Stephania pierrei exerts macrophage anti-inflammatory effects by downregulating the NF-κB, MAPK, and PI3K/Akt signalling pathways

Plant-derived medicinal compounds are increasingly being used to treat acute and chronic inflammatory diseases, which are generally caused by aberrant inflammatory responses. Stephania pierrei Diels, also known as Sabu-lueat in Thai, is a traditional medicinal plant that is used as a remedy for several inflammatory disorders. Since aporphine alkaloids isolated from S. pierrei tubers exhibit diverse pharmacological characteristics, we aimed to determine the anti-inflammatory effects of crude extracts and alkaloids isolated from S. pierrei tubers against lipopolysaccharide (LPS)-activated RAW264.7 macrophages. Notably, the n-hexane extract strongly suppressed nitric oxide (NO) while exhibiting reduced cytotoxicity. Among the five alkaloids isolated from the n-hexane extract, the aporphine alkaloid oxocrebanine exerted considerable anti-inflammatory effects by inhibiting NO secretion. Oxocrebanine also significantly suppressed prostaglandin E₂, tumour necrosis factor-α, interleukin (IL)-1β, IL-6, inducible nitric oxide synthase, and cyclooxygenase (COX)-2 protein expression by inactivating the nuclear factor κB, c-Jun NH₂-terminal kinase, extracellular signal-regulated kinase 1/2, and phosphatidylinositol 3-kinase/Akt inflammatory signalling pathways. Molecular docking analysis further revealed that oxocrebanine has a higher affinity for toll-like receptor 4/myeloid differentiation primary response 88 signalling targets and the COX-2 protein than native ligands. Thus, our findings highlight the potential anti-inflammatory effects of oxocrebanine and suggest that certain alkaloids of S. pierrei could be used to treat inflammatory diseases.

Liriogerphines A-D, a Class of Sesquiterpene-Alkaloid Hybrids from the Rare Chinese Tulip Tree Plant

Liriogerphines A-D (1-4, respectively), an unprecedented class of hybrids of germacranolide-type sesquiterpenoids and aporphine-type alkaloids, were isolated from the rare medicinal plant Liriodendron chinense. Their structures were elucidated by comprehensive spectroscopic analyses combined with electronic circular dichroism calculations and X-ray crystallographic data. Biosynthetically, an aza-Michael addition reaction is proposed to be involved in the assemblies of this class of hybrids. Compound 4 exhibited cytotoxicity against leukemia cells via inducing apoptosis and inhibiting Bcl-2 expression.

Spatial Distribution and Stability of Cholinesterase Inhibitory Protoberberine Alkaloids from Papaver setiferum

During a research program to identify new cholinesterase inhibitors of natural origin, two new 7,8-didehydroprotoberberine alkaloids (1 and 2) and nine known compounds (3-11) were isolated from the capsules of the common ornamental poppy, Papaver setiferum (previously P. pseudo-orientale). Despite their reported instability, the 7,8-didehydroprotoberberines isolated herein appeared relatively stable, particularly as their trifluoroacetic acid salts. The spatial distributions of the isolated alkaloids were also analyzed using desorption electrospray ionization imaging mass spectrometry. The alkaloids were localized predominantly within the walls and vascular bundles of the capsules, with the highest relative abundances occurring in the lower half of the capsules toward the peduncle. The relative abundances of the alkaloids were also compared across plant development stages. Although most alkaloids did not show clear patterns in their concentration across development stages, the concentration of suspected oxidation products clearly spiked upon plant death. Finally, all isolated natural products were screened for inhibitory activities against a panel of cholinesterases, from both human and animal sources. These studies identified several competitive inhibitors of cholinesterases with potency in the low micromolar range (1-4, 6, 7), offering new lead compounds for the development of cholinesterase inhibitory drugs.