1 H and 13 C NMR data, occurrence, biosynthesis, and biological activity of Piper amides

Amide and phenylpropanoid glycosides from the fruits of Piper longum L. and their anti-inflammatory activity

Ten glycosidic compounds (1-10), including two novel amide glycosides and one new phenylpropanoid glycoside, were isolated from the fruits of Piper longum L. These novel compounds were identified as (E)-N-feruloylpiperidine 4'-O-β-d-glucopyranosyl-(1 → 4)-β-d-glucopyranoside (1), (E)-N-p-coumaroylpiperidine 4'-O-β-d-glucopyranosyl-(1 → 4)-β-d-glucopyranoside (2), and (E)-cinnamyl alcohol 9-O-β-d-glucopyranosyl-(1 → 4)-α-l-rhamnose-(1 → 6)-β-d-glucopyranoside (3) by detailed spectroscopic and spectrometric techniques. Acid hydrolysis was employed to determine the glycosidic linkages, facilitating the structural elucidation of these compounds. The anti-inflammatory activities of all isolated compounds were assessed, and the results demonstrated that compounds 8 and 9 exhibited moderate inhibitory effects on nitric oxide (NO) production in lipopolysaccharide (LPS)-stimulated RAW264.7 cells.

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.

Isolation, Structure Elucidation, and Bioactivity Evaluation of Two Alkaloids From Piper chaba H. Stem: A Traditional Medicinal Spice and Its Chemico-Pharmacological Aspects

Bangladesh is endowed with an abundance of excellent medicinal plant resources. A well-known traditional medicinal plant Piper chaba H. from the Piperaceae family is rich in bioactive phytochemicals that have antidiarrheal, antimicrobial, analgesic, antioxidant, anticancer, and cytotoxic effects. This plant is locally known as "Chuijhal," and the stem is used as spices. In the current research program, the stems of the P. chaba plant were selected and its chemical and biological investigations such as antidiarrheal, antimicrobial, and analgesic effects were performed. Moreover, docking models were accomplished by exploiting PyRx-Virtual Screening software and implied that isolated compounds of P. chaba exert different pharmacological activity by inhibiting their targeted receptors. Phytochemical investigations revealed the isolation of Chingchengenamide A, a relatively rare alkaloid from the stems of P. chaba. Another alkaloid Chabamide I which is a piperine dimer was also isolated. Their structures were confirmed by comparing these compounds' spectral data (1H and 13C NMR) with their previously published spectral data. Antidiarrheal activity shows a percent reduction of diarrhea by 46.67% and 40%, respectively, for Chabamide I and Chingchengenamide A (at 20 mg/kg b.w.) compared with an 80% reduction by standard loperamide. Similarly, the percent reduction of writhing was 53.06% and 42.86%, respectively, for Chabamide I and Chingchengenamide A at similar doses compared with an 80% reduction by diclofenac sodium considered as standard. Both the alkaloids showed auspicious outcomes against test microorganisms during disk diffusion antimicrobial assay. Molecular docking and ADME/T analysis of the alkaloids also validate a potent pharmacological basis for the traditional utilization of P. chaba in treating diarrhea, pain, and microbial infection. These results emphasize the need to investigate P. chaba as a potential source of natural therapies for common health issues, laying the foundation for future research.

N-Cinnamoylpyrrole-derived alkaloids from the genus Piper as promising agents for ischemic stroke by targeting eEF1A1

BACKGROUND

Ischemic stroke (IS) is a serious cerebrovascular disease characterized by significantly elevated mortality and disability rates, and the treatments available for this disease are limited. Neuroinflammation and oxidative stress are deemed the major causes of cerebral ischemic injury. N-Cinnamoylpyrrole alkaloids form a small group of natural products from the genus Piper and have not been extensively analyzed pharmacologically. Thus, identifying the effect and mechanism of N-cinnamoylpyrrole-derived alkaloids on IS is worthwhile.

PURPOSE

The present research aimed to explore the antineuroinflammatory and antioxidative stress effects of N-cinnamoylpyrrole-derived alkaloids isolated from the genus Piper and to explain the effects and mechanism on IS.

METHODS

N-cinnamoylpyrrole-derived alkaloids were isolated from Piper boehmeriaefolium var. tonkinense and Piper sarmentosum and identified by various chromatographic methods. Lipopolysaccharide (LPS)-induced BV-2 microglia and a mouse model intracerebroventricularly injected with LPS were used to evaluate the antineuroinflammatory and antioxidative stress effects. Oxygen‒glucose deprivation/reperfusion (OGD/R) and transient middle cerebral artery occlusion (tMCAO) models were used to evaluate the effect of PB-1 on IS. To elucidate the fundamental mechanism, the functional target of PB-1 was identified by affinity-based protein profiling (ABPP) strategy and verified by cellular thermal shift assay (CETSA), drug affinity responsive target stability (DARTS), and circular dichroism (CD) analyses. The effect of PB-1 on the NF-κB and NRF2 signaling pathways was subsequently evaluated via western blotting and immunofluorescence staining.

RESULTS

The results showed that N-cinnamoylpyrrole-derived alkaloids significantly affected neuroinflammation and oxidative stress. The representative compound, PB-1 not only inhibited neuroinflammation and oxidative stress induced by LPS or OGD/R insult, but also alleviated cerebral ischemic injury induced by tMCAO. Further molecular mechanism research found that PB-1 promoted antineuroinflammatory and antioxidative stress activities via the NF-κB and NRF2 signaling pathways by targeting eEF1A1.

CONCLUSION

Our research initially unveiled that the therapeutic impact of PB-1 on cerebral ischemic injury might rely on its ability to target eEF1A1, leading to antineuroinflammatory and antioxidative stress effects. The novel discovery highlights eEF1A1 as a potential target for IS treatment and shows that PB-1, as a lead compound that targets eEF1A1, may be a promising therapeutic agent for IS.

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.

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

The roots of Piper nigrum L., a seasoning for cooking various types of broths, are renowned for their high nutritional content and potential medicinal benefits. In this study, nine pairs of novel cyclohexene-type bisamide alkaloids (1a/1b-9a/9b) were isolated from the pepper roots using molecular network analysis strategies. Their structures were determined by extensive spectroscopic data, electronic circular dichroism (ECD) calculations, and X-ray diffraction analyses. Using an intermolecular Diels-Alder reaction, a strategy for the synthesis of bisamide alkaloids from different monomeric amide alkaloids was developed. Furthermore, these compounds were chirally separated for the first time, and compounds 3a and 5a/5b showed significant anti-neuroinflammation effects in the models of lipopolysaccharide(LPS)-induced BV2 microglial cells. Meanwhile, compounds 6b and 7a displayed concentration-dependent inhibitory activities against acetylcholinesterase with IC₅₀ values of 6.05 ± 1.10 and 3.81 ± 0.10 μM, respectively. These findings confirmed that these bisamide alkaloids could be applied in functional food formulations and pharmaceutical products as well as facilitate the further development and usage of pepper roots.

Exploring the Chemical Space of Kawakawa Leaf (Piper excelsum)

The chemical profiles of kawakawa (Piper excelsum) leaves were analysed through targeted and non-targeted LC-MS/MS. The phytochemical profile was obtained for both aqueous extracts representative of kawakawa tea and methanolic extracts. Sixty-four compounds were identified from eight leaf sources including phenylpropanoids, lignans, flavonoids, alkaloids and amides. Eight of these compounds were absolutely quantified. The chemical content varied significantly by leaf source, with two commercially available sources of dried kawakawa leaves being relatively high in phenylpropanoids and flavonoids compared with field-collected fresh samples that were richer in amides, alkaloids and lignans. The concentrations of pharmacologically active metabolites ingested from the traditional consumption of kawakawa leaf as an aqueous infusion, or from novel use as a seasoning, are well below documented toxicity thresholds.

Anti-Neuroinflammatory Components from Clausena lenis Drake

Clausena lenis Drake (C. lenis) is a folk medicinal herb to treat influenza, colds, bronchitis, and malaria. The 95% and 50% ethanol extract of C. lenis showed significant nitric oxide (NO) inhibition activity in BV-2 microglial cells stimulated by lipopolysaccharide (LPS). Bio-guided isolation of the active extract afforded five new compounds, including a chlorine-containing furoquinoline racemate, (±)-claulenine A (1), an amide alkaloid, claulenine B (2), a prenylated coumarin, claulenin A (3), a furocoumarin glucoside, clauleside A (4), and a multi-prenylated p-hydroxybenzaldehyde, claulenin B (5), along with 33 known ones. Their structures were determined via spectroscopic methods, and the absolute configurations of new compounds were assigned via the electronic circular dichroism (ECD) calculations and single-crystal X-ray diffraction analysis. Compounds 2, 23, 27, 28, 33, and 34 showed potent anti-neuroinflammatory effects on LPS-induced NO production in BV-2 microglial cells, with IC₅₀ values in the range of 17.6–40.9 μM. The possible mechanism was deduced to interact with iNOS through molecular docking.

Pipercyclobutanamide D, a new member of the cyclobutanamide-type alkaloid, from the roots of Piper nigrum

From the EtOH-soluble extract of the roots of Piper nigrum, one new dimeric alkamide, pipercyclobutanamide D (1) was isolated. Its structure was elucidated on the basis of NMR spectroscopic interpretation. The relative configuration of 1 was determined based on the NOESY analysis. Compound 1 showed α-glucosidase inhibitory activity with an IC₅₀ value of 158.5 µM. In addition, compound 1 exhibited cytotoxicity against the MCF-7 and HepG2 cell lines with the IC₅₀ values of 45.6 and 63.9 µM, respectively. Plausible biosynthetic pathway for the formation of 1 was proposed based on regioselective [2 + 2] cycloaddition reaction.

New Tyramine- and Aporphine-Type Alkamides with NO Release Inhibitory Activities from Piper puberulum

Three new tyramine-type alkamides (1-3), three new natural products (4-6), five new N-acylated/formylated aporphine alkamides with different ratios of rotational isomers (7-11), and 20 known alkamides (12-31) were isolated from an EtOH extract of the stems and leaves of Piper puberulum. The absolute configurations of compounds 7, 8, and 10 were determined by single-crystal X-ray diffraction analysis. In the biological activity assay, compounds 3, 5, and 10-23 displayed inhibitory effects against lipopolysaccharide-induced NO release in BV-2 microglial cells, exhibiting IC₅₀ values of 0.93-45 μM.

A pyridinium anionic ring-opening reaction applied to the stereodivergent syntheses of Piperaceae natural products

A stereodivergent strategy has been devised to access the diene motif found in biologically active compounds from the Piperaceae family. Herein the first total syntheses of 2E,4E configured piperchabamide E (2) and its enantiomer (ent-2), as well as 2E,4Z configured scutifoliamide B (3), are narrated. The mainstay in the adopted approach is the gram-scale conversion of quaternized pyridine in a practical three-step sequence to access isomerically pure conjugated bromodiene esters 2E,4E8 and 2E,4Z9 by differential crystallization. Even though the developed oxidation protocol forms the basis of the entailed divergent strategy, the geometrical integrity of the involved bromodiene motive can be controlled by the choice of solvent. Thus, while oxidation of pure bromodienal 2E,4Z7 in methanol yields equal amounts of bromodiene esters 2E,4E8 and 2E,4Z9, only bromodiene ester 2E,4Z10 is formed in isopropanol. Subseqently, capitalizing on a stereoretentive Suzuki cross-coupling and direct amidation of the corresponding esters, the featured natural products can be accessed in five and six steps, respectively. The somewhat surprising (R)-configured amine portion, which has been assigned to piperchabamide E (2), is facilitated by a Curtius rearrangement. Following this, the actual amine portion is shown to be (S)-configured.

Isolation and Characterization of Acetylcholinesterase Inhibitors from Piper longum and Binding Mode Predictions

Restoration of cholinergic function is considered a rational approach to enhance cognitive performance. Acetylcholinesterase inhibitors are still the best therapeutic option for Alzheimer's disease. The fruits of Piper longum have been used in traditional medicines for the treatment of memory loss. It was demonstrated that the dichloromethane extract of these fruits is able to inhibit acetylcholinesterase. Thus, the aim of this study was to identify the contained acetylcholinesterase inhibitors. The active zones were presented via TLC-bioautography, and five compounds were isolated in the process of a bioassay-guided phytochemical investigation. Their structures were characterized as piperine, methyl piperate, guineenisine, pipercide, and pellitorine using spectroscopy and spectrometry methods (UV, IR, MS, ¹H-, and ¹³C-NMR). In vitro acetylcholinesterase inhibitory activities of the isolates and their IC₅₀ values were determined via a colorimetric assay. Three of them exhibited enzyme inhibitory activities, with piperine being the most potent compound (IC₅₀ of 0.3 mM). In order to investigate the binding mode of the tested compounds, docking studies were performed using the X-ray crystal structure of acetylcholinesterase from Tetronarce californica with the Protein Data Bank code 1EVE. The content of the active compounds in the extract was determined by a developed HPLC method. Piperine was present in the maximum quantity in the fruits (0.57%), whereas methyl piperate contained the minimum content (0.10%).

A piperic acid CoA ligase produces a putative precursor of piperine, the pungent principle from black pepper fruits

Black pepper (Piper nigrum L.) is known for its high content of piperine, a cinnamoyl amide derivative regarded as largely responsible for the pungent taste of this widely used spice. Despite its long history and worldwide use, the biosynthesis of piperine and related amides has been enigmatic up to now. In this report we describe a specific piperic acid CoA ligase from immature green fruits of P. nigrum. The corresponding enzyme was cloned and functionally expressed in E. coli. The recombinant enzyme displays a high specificity for piperic acid and does not accept the structurally related feruperic acid characterized by a similar C-2 extension of the general C6-C3 phenylpropanoid structure. The enzyme is also inactive with the standard set of hydroxycinnamic acids tested including caffeic acid, 4-coumaric acid, ferulic acid, and sinapic acid. Substrate specificity is corroborated by in silico modelling that suggests a perfect fit for the substrate piperic acid to the active site of the piperic acid CoA ligase. The CoA ligase gene shows its highest expression levels in immature green fruits, is also expressed in leaves and flowers, but not in roots. Virus-induced gene silencing provided some preliminary indications that the production of piperoyl-CoA is required for the biosynthesis of piperine in black pepper fruits.