Novel Bisamide Alkaloids Enantiomers from Pepper Roots (Piper nigrum L.) with Acetylcholinesterase Inhibitory and Anti-Neuroinflammatory Effects

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.

Dimeric Amide Alkaloid Enantiomers from Piper longum L. with Anti-Inflammatory and Antidiabetic Effects

The fruit of Piper longum L. (Piperaceae), commonly used as a spice in various culinary applications, is renowned for its rich nutritional profile and potential medicinal properties. In this study, a molecular network-based dereplication strategy was employed to isolate 12 dimeric amide alkaloid enantiomers (1-12) from P. longum fruits, including eight pairs of cyclobutane-type dimers (1-8) and four pairs of cyclohexene-type dimers (9-12). Notably, five pairs of cyclobutane-type dimers, namely, piperlongramides E-I (1-5), and one pair of cyclohexene-type dimers, piperlongramide J (9), were identified as undescribed compounds. The structures of these compounds were elucidated by comprehensive spectroscopic data, electronic circular dichroism (ECD) calculations, and X-ray diffraction analysis. Additionally, these compounds, for the first time, were subjected to chiral resolution. In vitro bioactivity screening revealed that compounds (+)-10, (-)-10, and (+)-3 exhibited notable anti-inflammatory effects in an LPS-induced RAW 264.7 macrophage model, with IC50 values of 23.42 ± 1.04, 32.72 ± 0.54, and 33.52 ± 1.75 μM, respectively. Furthermore, compound (+)-3 also demonstrated significant inhibitory activity againstα-glucosidase, with an IC50 of 11.69 ± 0.91 μM. Compounds (+)-9, (+)-7, and (-)-9, exhibited promising inhibitory activity against PTP1B with IC50 values of 3.30 ± 0.09, 4.30 ± 0.18, and 4.37 ± 0.37 μM, respectively, indicating their potential antidiabetic effects. This study highlights the promising application of these amide alkaloid dimers in the development of functional foods and pharmaceutical products, thereby expanding the health-promoting potential of P. longum fruits.

Structural diversity, biological activities and biosynthetic pathways of [2 + 2] and [4 + 2] amide alkaloid dimers from Piperaceae: An updated review

The Piperaceae family is distributed widely in tropical and subtropical areas. It encompasses around 5 genera and over 3000 species. They are distinguished by the substantial chemical diversity and potential medicinal applications. Amide alkaloids, as the main secondary metabolites in the Piperaceae family, exhibit various biological activities, and the discovery of [2 + 2] and [4 + 2] amide alkaloid dimers has led to a surge in phytochemical research on Piperaceae plants. Although the identification of these dimers has been gradually increasing in recent years, there remains a lack of comprehensive and systematic evaluations of these compounds. This review aims to summarize the latest advancements in the research on natural amide alkaloid dimers, focusing on their structural diversity, biological activities and biosynthetic pathways, and the enzymatic advances of [2 + 2] and [4 + 2] cyclase enzymes. Until October 2024, research has documented 99 amide alkaloid dimers, including 37 dimers possessing [2 + 2] cyclobutanes skeletons and 62 [4 + 2] cyclohexene skeletons derived from the Piperaceae family. These compounds demonstrate a range of in vitro biological activities including anti-inflammatory, anticancer, acetylcholinesterase inhibitory, anti-platelet aggregation, hepatoprotective, antimalarial, antitubercular, anti-diabetic and notable interactions with CYP3A4 and CYP2D6 enzymes. A systematic review of these [2 + 2] and [4 + 2] amide alkaloid dimers in Piperaceae family can provide a critical scientific foundation and theoretical support for the discovery and development of novel pharmaceutical agents.

Hydroxyl-Amide Alkaloids from Pepper Roots: Potential Sources of Natural Antioxidants and Tyrosinase Inhibitors

Pepper (Piper nigrum L.) is a widely used spice plant known for its fruits and roots, which serve as flavor enhancers in culinary applications and hold significant economic value. Despite the popularity of pepper fruits, their roots remain relatively understudied, with limited research conducted on their bioactive components. This study focused on discovering and separating the primary bioactive amide alkaloids found in pepper roots. The process involved using the antioxidant activity of crude fractions and the Global Natural Products Social Molecular Networking analysis platform. The process led to the discovery of 23 previously unknown hydroxyl-amide alkaloids. Notably, compounds 11, 12, and 14 showed excellent antioxidant activity, while compound 11 exhibited significant inhibitory effects on mushroom tyrosinase. Theoretical exploration of enzyme-ligand interactions was conducted through molecular docking and molecular dynamics simulation. The findings of this study highlight the potential of hydroxyl-amide alkaloids as antioxidant products and natural food preservatives in the pharmaceutical and food cosmetic industries.

Pipersarmenoids, new amide alkaloids from Piper sarmentosum

A chemical investigation of the aerial parts of Piper sarmentosum resulted in the isolation and identification of 14 amide alkaloids, including three new amide alkaloids, pipersarmenoids A - C (1-3), three new natural amide alkaloids, pipersarmenoids D - F (4-6), and 8 known analogues, N-p-coumaroyltyramine (7), piperlotine C (8), piperlotine D (9), pellitorine (10), sarmentine (11), aurantiamide acetate (12), 1-cinnamoyl pyrrolidine (13) and sarmentamide B (14). Their structures were determined by spectroscopic analysis including HRESIMS and 1D and 2D NMR. The cytotoxicity, neuroinflammation-inhibiting and acetylcholinesterase (AChE) inhibitory activities of those compounds were tested. Compounds 1, 2 and 12 inhibited NO production induced by LPS in BV2 cells with IC50 values of 9.36, 12.53 and 10.77 μM, respectively. Moreover, 1, 2, 7 and 11 showed moderate inhibitory activity on AChE with IC50 values ranging from 37.56 to 48.84 μM.

Discovery of 23,24-diols containing ergosterols with anti-neuroinflammatory activity from Penicillium citrinum TJ507

Citristerones A-E (1-5), five new 23,24-diols containing ergosterols, along with three known analogues, were isolated from the endophytic fungus Penicillium citrinum TJ507 obtained from Hypericum wilsonii N. Robson. Their structures and absolute configurations were determined by NMR, HRESIMS, Snatzke's method, X-ray diffraction analyses and ECD calculation. Subsequently, the anti-neuroinflammatory effects of these isolates were screened using lipopolysaccharide (LPS)-induced BV-2 microglial cells, and citristerone B (2) showed outstanding anti-neuroinflammatory activity, with IC50 value of 0.60 ± 0.04 μM. Moreover, immunofluorescence and western blot analysis suggested that citristerone B not only reduced the release of nitric oxide (NO) and proinflammatory cytokines in LPS-induced BV-2 microglial cells, but also significantly inhibited the expression of TNF-α, iNOS and NF-κB, along with the production of cellular ROS.

Two pairs of bioactive cyclohexene alkaloid enantiomers from the roots of Piper nigrum

Two pairs of cyclohexene amide alkaloid enantiomers were obtained from the root of Piper nigrum. Their plane structures were established by NMR and HRESIMS spectra. The absolute configurations of 1a/1b and 2a/2b were determined by the comparison between the experimental and calculated electronic circular dichroism (ECD) spectra. All identified compounds were tested for inhibitory effects on acetylcholinesterase (AChE) in vitro. Notably, compounds 1b and 2b showed strong inhibitory effects on AChE and the interaction between proteins and compounds was discussed by molecular docking studies.

Target isolation of diverse sesquiterpenoid from the stems of Daphne genkwa based on molecular networking

Guiding by LC-MS/MS analysis and the Global Natural Products Social (GNPS) Molecular Networking, three undescribed sesquiterpenoids, stedapgens A-C, and two known analogues were discovered in the barks of Daphne genkwa Sieb. et Zucc. The structures were determined by analysis of their spectroscopic data and quantum-chemical calculations. All the isolated novel compounds were tested for their acetylcholinesterase inhibitory activities with IC50 = 0.754 ± 0.059, 0.696 ± 0.026, and 0.337 ± 0.023 μg/ml. Among them, stedapgen A displayed promising inhibitory activities against AChE, and the binding sites were predicted by molecular docking.

Four pairs of neolignan enantiomers with distinctive isochroman moiety from the fruits of Crataegus pinnatifida and their protective activities against H2O2-induced SH-SY5Y cells

Four pairs of neolignan enantiomers (±)-1- (±)-4 with a distinctive isochroman moiety, including seven undescribed compounds, were isolated and identified from the fruits of Crataegus pinnatifida. Structural characterization of these compounds was established through comprehensive spectroscopic analyses, as well as quantum chemical calculations of ECD and NMR data. The preliminary bioassay displayed that compounds (+)-2 and (±)-3 exerted protective activities against H2O2-induced human neuroblastoma SH-SY5Y cells compared with the positive control. These bioactive compounds could be potential candidates for further pharmaceutical applications.

Expanded Application of Piper nigrum: Guided Isolation of Alkaloids with Inhibitory Activities of AChE/BuChE and Aβ Aggregation

Piper nigrum is a popular crop that can be used as seasoning or as an additive but its active ingredients also have an effect on the nervous system. Nineteen new amide alkaloids (1a/1b, 2-5, 6a/6b, 7, 8a/8b, 9, 10a/10b, 11a-11b, 12-14) were isolated from P. nigrum, guided by inhibitory activity of AChE and LC-MS/MS based on GNPS. The configurations were determined by extensive spectral analysis, Bulkiness rule, and NMR calculations. The inhibitory activities of AChE/BuChE and Aβ aggregation were tested, and the results showed compounds 2, 7, and 12 had significant inhibitory activities. These components were identified in the crude fraction and their relative quantities were tested, which suggested that compound 2 was the index component in the active site from P. nigrum.

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.

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.