Inhibitors of cyclic AMP phosphodiesterase in Picrasma quassioides Bennet, and inhibitory activities of related beta-carboline alkaloids

β-Carboline alkaloids from Picrasma quassioides and their 3D-QSAR study on anti-inflammation in LPS-induced RAW 264.7 cells

Two new β-carboline alkaloids (1-2), 1-pyrrolidone propionyl-β-carboline (1) and 1-(3-hydroxy-2-oxopiperidine-1-ethyl)-4,8-dimethoxyl-β-carboline (2), named kumujantine W and J respectively, together with ten known compounds (3-12) were isolated from the stems of Picrasma quassioides (D. Don) Benn. Their structures were elucidated from spectral data including 1D and 2D NMR, UV, IR, HR-ESI-MS spectroscopic analysis and ECD calculations as well as by comparison to the reference databases or literature. The anti-inflammatory effects of these alkaloids (1-12) and six other β-carboline alkaloids (13-18) in LPS-induced RAW 264.7 cells were evaluated by measuring nitric oxide (NO) concentrations. Among them, compounds 1, 3, 6, 15, and 17 could inhibit the secretion of NO, displaying significant anti-inflammatory activity without affecting cell viability in vitro, and 3D-QSAR analysis further revealed the influence of groups on the activity in β-carboline alkaloids.

Anthranilamides with quinoline and β-carboline scaffolds: design, synthesis, and biological activity

In the present study, we report the design and synthesis of novel amide-type hybrid molecules based on anthranilic acid and quinoline or β-carboline heterocyclic scaffolds. Three types of biological screenings were performed: (i) in vitro antiproliferative screening against a panel of solid tumor and leukemia cell lines, (ii) antiviral screening against several RNA viruses, and (iii) anti-quorum sensing screening using gram-negative Chromobacterium violaceum as the reporter strain. Antiproliferative screening revealed a high activity of several compounds. Anthranilamides 12 and 13 with chloroquine core and halogenated anthranilic acid were the most active agents toward diverse cancer cell lines such as glioblastoma, pancreatic adenocarcinoma, colorectal carcinoma, lung carcinoma, acute lymphoblastic, acute myeloid, chronic myeloid leukemia, and non-Hodgkin lymphoma, but also against noncancerous cell lines. Boc-protected analogs 2 and 3 showed moderate activities against the tested cancer cells without toxic effects against noncancerous cells. A nonhalogenated quinoline derivative 10 with N-benzylanthranilic acid residue was equally active as 12 and 13 and selective toward tumor cells. Chloroquine and quinoline anthranilamides 10-13 exerted pronounced antiviral effect against human coronaviruses 229E and OC43, whereas 12 and 13 against coronavirus OC43 (EC₅₀ values in low micromolar range; selectivity indices from 4.6 to > 10.4). Anthranilamides 14 and 16 with PQ core inhibited HIV-1 with EC₅₀ values of 9.3 and 14.1 µM, respectively. Compound 13 displayed significant anti-quorum/biofilm effect against the quorum sensing reporter strain (IC₅₀ of 3.7 μM) with no apparent bactericidal effect.

Alkaloids from Picrasma quassioides: An overview of their NMR data, biosynthetic pathways and pharmacological effects

Picrasma quassioides, a member of the Simaroubaceae family, is the subject of research in numerous pharmacological and chemical studies. This plant mainly contains alkaloids, quassinoids and terpenoids. These molecules exhibit various pharmacological benefits, such as anti-inflammatory, anticancer, and anti-viral effects, on the cardiovascular system. Alkaloids make up the majority of these molecules. This review describes 127 alkaloid substances from P. quassioides. These alkaloids can be divided into the following classes: β-carbolines, canthinones and alkaloid dimers. A compilation of their nuclear magnetic resonance spectroscopy data and possible biosynthetic pathways of these compounds and the pharmacological effects of P. quassioides are also included.

Pharmacological effects of Picrasma quassioides (D. Don) Benn for inflammation, cancer and neuroprotection (Review)

Picrasma quassioides (D. Don) Benn is an Asian shrub with a considerable history of traditional medicinal use. P. quassioides and its extracts exhibit good therapeutic properties against several diseases, including anti-inflammatory, antibacterial and anticancer effects. However, the composition of compounds contained in P. quassioides is complex; although various studies have examined mixtures or individual compounds extracted from it, studies on the application of P. quassioides extracts remain limited. In the present review, the structures and functions of the compounds identified from P. quassioides and their utility in anti-inflammatory, anticancer and neuroprotectant therapies was discussed. The present review provided up-to-date information on pharmacological activities and clinical applications for P. quassioides extracts.

Genus Picrasma: A comprehensive review on its ethnopharmacology, phytochemistry and bioactivities

ETHNOPHARMACOLOGICAL RELEVANCE

The genus Picrasma belongs to the Simaroubaceae family and contains six species which are mainly distributed in tropical and subtropical regions of Asia and America. The barks, roots, stems, branches, or leaves of several Picrasma species have been applied as folk medicines to treat fever, sore throat, dysentery, eczema, nausea, loss of appetite, diabetes mellitus, cancer, and hypertension.

AIM OF THE STUDY

A systematic summary on the botanic characterization, ethnopharmacological uses, phytochemistry, bioactivities and toxicity of species belonging to Picrasma was presented to facilitate the exploitation of the therapeutic potential of these plants.

MATERIALS AND METHODS

The literatures about Picrasma were retrieved from a series of scientific search engines including Web of Science, SciFinder, PubMed, CNKI, Google Scholar, Elsevier, Wiley, ACS publications, and SpringerLink between 1970 and 2020. Plant names were validated by "The Plant List" (www.theplantlist.org).

RESULTS

As ethnopharmacological uses, Picrasma species are valuable folk medicines to treat fever, inflammation, dysentery, eczema, cancer, diabetics, skin infection, and so on. Up to now, a total of 361 compounds including 126 alkaloids, 132 quassinoids, 67 triterpenoids, and 36 miscellaneous compounds were reported from Picrasma species. Quassinoids and alkaloids are the principal constituents in the genus. The extracts and phytochemical constituents of Picrasma species demonstrate a wide range of bioactivities including cytotoxic, anti-inflammatory, antimicrobial, and other activities.

CONCLUSIONS

Picrasma species are widely used as traditional medicines, have diverse chemical constituents with obvious biological activities. Nevertheless, further studies are required on the Picrasma species to assert the ethnopharmacological uses, clarify their bioactive constituents, determine pharmacological actions, and toxicity. Therefore, the present review may provide a critical clue for future studies and further exploitations on Picrasma species.

Natural Molecules as Talented Inhibitors of Nucleotide Pyrophosphatases/Phosphodiesterases (PDEs)

BACKGROUND

Phosphodiesterases (PDEs) are a wide group of enzymes with multiple therapeutic actions, including vasorelaxation, cardiotonic, antidepressant, anti-inflammatory, antithrombotic, anti-spasmolytic, memory-enhancing, and anti-asthmatic. PDEs with eleven subtypes from PDE-1 to PDE-11 typically catalyze the cleavage of the phosphodiester bond and, hence, degrades either cyclic adenosine monophosphate (cAMP) or cyclic guanosine monophosphate (cGMP).

OBJECTIVE

Several selective or non-selective inhibitors of the PDE subtypes are used clinically, i.e. sildenafil, rolipram, cysteine, etc. Recently, interest in plant-based pharmacologically bioactive compounds having potent PDEs inhibitory potential has increased. Purposely, extensive research has been carried out on natural products to explore new inhibitors of various PDEs. Therefore, this review summarizes the published data on natural PDEs inhibitors and their potential therapeutic applications.

METHODS

For this purpose, natural compounds with PDE inhibitory potential have been surveyed through several databases, including PubMed, Web of Sciences (WoS), Scopus, and Google Scholar.

RESULTS

According to a detailed literature survey, the most promising class of herbal compounds with PDE-inhibiting property has been found to belong to phenolics, including flavonoids (luteolin, kaempferol, icariin, etc.). Many other encouraging inhibitors from plants have also been identified, such as coumarins (23, 24) (licoarylcoumarin and glycocoumarin,), saponins ( agapanthussaponins), lignans (31, 33) [(±)-schizandrin and kobusin], terpenes (28, 29, 31) (perianradulcin A, quinovic acid, and ursolic acid), anthraquinones (18, 19) (emodin and chrysophanol), and alkaloids (Sanjoinine-D) (36).

CONCLUSION

In this review, studies have revealed the PDE-inhibitory potential of natural plant extracts and their bioactive constituents in treating various diseases; however, further clinical studies comprising synergistic use of different therapies (synthetic & natural) to acquire multi-targeted results might also be a promising option.

Recent Advances in the Synthesis of β-Carboline Alkaloids

β-Carboline alkaloids are a remarkable family of natural and synthetic indole-containing heterocyclic compounds and they are widely distributed in nature. Recently, these alkaloids have been in the focus of interest, thanks to their diverse biological activities. Their pharmacological activity makes them desirable as sedative, anxiolytic, hypnotic, anticonvulsant, antitumor, antiviral, antiparasitic or antimicrobial drug candidates. The growing potential inherent in them encourages many researchers to address the challenges of the synthesis of natural products containing complex β-carboline frameworks. In this review, we describe the recent developments in the synthesis of β-carboline alkaloids and closely related derivatives through selected examples from the last 5 years. The focus is on the key steps with improved procedures and synthetic approaches. Furthermore the pharmacological potential of the alkaloids is also highlighted.

Pharmacokinetic and bioavailability study of 5-hydroxy-4-methoxycanthin-6-one, a typical canthinone alkaloid, in rats using ultra-high performance liquid chromatography/electrospray ionization tandem mass spectrometry

5-methoxycanthin-6-one, a major canthinone alkaloid isolated from Picrasma quassioides, exhibited significant pharmacological activities. In this study, a rapid and sensitive LC-MS/MS method was established and validated for the determination of 5-hydroxy-4-methoxycanthin-6-one in rat plasma. Small quantities (20 μL) of plasma sample were used for sample preparation. 5-Hydroxy-4-methoxycanthin-6-one and an internal standard (IS, caffeine) were separated using an ACQUITY HSS T3 column (50 × 2.1 mm, 1.7 μm; Waters, Milford, MA, USA). The mobile phase was composed of 0.1% formic acid in water and acetonitrile. Precursor-to-product ion transitions were m/z 267.0 → 168.2 and m/z 195.0 → 138.1 for quantitative monitoring of 5-hydroxy-4-methoxycanthin-6-one and IS, respectively. The assay was linear over the concentration range of 0.5-500 ng/mL (r > 0.99) with the lower limit of quantification 0.5 ng/mL. Other parameters, including intra- and inter-day precision and accuracy, carryover, stability, extraction recovery, matrix effect, and dilution effect, were within acceptable limits. The validated method was successfully applied to pharmacokinetic study in rats after intravenous (5 mg/kg) and oral (10, 25, 50 mg/kg) administration of 5-hydroxy-4-methoxycanthin-6-one. The result indicated that 5-hydroxy-4-methoxycanthin-6-one was quickly absorbed into the blood and reached the highest concentration at ~33.0-42.0 min, with moderate elimination half-life (0.85-2.11 h) and low bioavailability (16.62-24.42%) after oral administration. The study provided valuable information that can be used as a reference for studying other canthinone alkaloids.

Effects of Picrasma quassioides and its active constituents on Alzheimer's disease in vitro and in vivo

Alzheimer disease (AD), a prevalent neurodegenerative disorder, is one of the leading causes of dementia. However, there is no effective drug for this disease to date. Picrasma quassioides (D.Don) Benn, a Chinese traditional medicine, was used mainly for the treatment of inflammation, fever, microbial infection and dysentery. In this paper, we reported that the EtOAc extract of Picrasma quassioides stems showed potential neuroprotective activities in l-glutamate-stimulated PC12 and Aβ_25-35-stimulated SH-SY5Y cell models, as well as improved memory and cognitive abilities in AD mice induced by amyloid-β peptide. Moreover, it was revealed that the anti-AD mechanism was related to suppressing neuroinflammatory and reducing Aβ_1-42 deposition using ELISA assay kits. To clarify the active components of the EtOAc extract of Picrasma quassioides stems, a systematic phytochemistry study led to isolate and identify six β-carboline alkaloids (1-6), seven canthin-6-one alkaloids (7-13), and five quassinoids (14-18). Among them, four β-carbolines (1-3, and 6) and six canthin-6-ones (7-11, and 13) exhibited potential neuroprotective activities in vitro. Based on these date, the structure-activity relationships of alkaloids were discussed. Furthermore, molecular docking experiments showed that compounds 2 and 3 have high affinity for both of dual-specificity tyrosine phosphorylation-regulated kinase 1A (DYPKIA) and butyrylcholinesterase (BuChE).

Identification of β-carboline and canthinone alkaloids as anti-inflammatory agents but with different inhibitory profile on the expression of iNOS and COX-2 in lipopolysaccharide-activated RAW 264.7 macrophages

A compound library, which consists of 75 natural β-carboline-type or canthinone-type alkaloids from Simaroubaceae plants and their chemical synthetic analogues, was screened for the anti-inflammatory activity by inhibition of the overproduction of inflammatory mediator nitric oxide (NO) in lipopolysaccharide (LPS)-activated RAW 264.7 macrophage cells. Six compounds, namely, benzalharman (23), kumujian (27), 1-ethyl-1,2,3,4-tetrahydro-β-carboline-3-carboxylic acid (37), 1-acetophenone-1,2,3,4-tetrahydro-β-carboline-3-carboxylic acid (42), cathin-6-one (46), and 9-methoxy-cathin-6-one (57), exhibited significant inhibitory activity on the overproduction of NO with good dose dependency. Further investigation demonstrated that all of the six compounds down-regulated the high expression of inducible nitric oxide synthase (iNOS) protein. Among them, two canthinone-type alkaloids (46 and 57) potently down-regulated cyclooxygenase-2 (COX-2) protein expression in a dose-dependent manner and also inhibited the overproduction of inflammatory mediator prostaglandin E₂ (PGE₂). However, the β-carboline-type alkaloids (23, 27, 37, and 42) exhibited no obvious inhibition on the overproduction of PGE₂ and the expression of COX-2 protein. The results suggested that β-carboline-type alkaloids and canthinone-type alkaloids may exert an anti-inflammatory effect through different mechanism.

A comprehensive review on the potential therapeutic benefits of phosphodiesterase inhibitors on cardiovascular diseases

Phosphodiesterases are a group of enzymes that hydrolyze cyclic nucleotides, which assume a key role in directing intracellular levels of the second messengers' cAMP and cGMP, and consequently cell function. The disclosure of 11 isoenzyme families and our expanded knowledge of their functions at the cell and molecular level stimulate the improvement of isoenzyme selective inhibitors for the treatment of various diseases, particularly cardiovascular diseases. Hence, future and new mechanistic investigations and carefully designed clinical trials could help reap additional benefits of natural/synthetic PDE inhibitors for cardiovascular disease in patients. This review has concentrated on the potential therapeutic benefits of phosphodiesterase inhibitors on cardiovascular diseases.

Pharmacokinetics and tissue distribution of 4,5-dimethoxycanthin-6-one and its major metabolites in rats

4,5-Dimethoxycanthin-6-one and 5-hydroxy-4-methoxycanthin-6-one are the active ingredients of P. quassiodes. In the present work, a LC-MS/MS method was developed for the determination of 4,5-dimethoxycanthin-6-one and its major metabolites 5-hydroxy-4-methoxycanthin-6-one (M1) and 4-hydroxy-5-methoxycanthin-6-one (M2) in rat plasma and tissues, and applied to study their pharmacokinetics and tissue distribution after intramuscular administration of 4,5-dimethoxycanthin-6-one to rats. By protein precipitation with methanol for plasma samples and liquid-liquid extraction with ethyl acetate for tissue samples, the analytes were separated on an ODS C₁₈ column with a mobile phase consisted of methanol and water (0.1% formic acid), and quantified by a MS detector in positive multiple reaction monitoring (MRM) mode. MS transitions were m/z 281.0→167.1 for 4,5-dimethoxycanthin-6-one, m/z 267.0→168.1 for M1 and M2, m/z 251.0→195.1 for 3-methylcanthin-2,6-dione (IS). The pharmacokinetic results indicate that 4,5-dimethoxycanthin-6-one is absorbed rapidly (T_max=5.4-6.4min), distributed rapidly and widely in the order of liver>kidney≈lung≈large intestine≈small intestine, and eliminated quickly (t_1/2z=64.9-77.7min) following the intramuscular administration. Furthermore, M1 and M2 were detected only in rat plasma and liver at the indicated times after the intramuscular administration.

Metabolic profile of 5-hydroxy-4-methoxycanthin-6-one, a typical canthinone alkaloid, in rats determined by liquid chromatography-quadrupole time-of-flight tandem mass spectrometry together with multiple data processing techniques

Picrasma quassioides (D. Don) Benn. is a traditional Chinese medicine used clinically to treat gastrointestinal disorders and as a vermifuge. 5-Hydroxy-4-methoxycanthin-6-one (CAN), a major canthinone alkaloid found in P. quassioides, has significant pharmacological activities. In the present study, a method using liquid chromatography-quadrupole time-of-flight tandem mass spectrometry together with multiple data processing techniques, including extracted ion chromatogram, multiple mass defect filter, precursor/product ion scanning and neutral loss scanning was developed to screen and characterize the phase I and II metabolites of CAN in plasma, bile, urine and feces of rats after a single oral dose of 20mg/kg. A total of 17 metabolites were tentatively or conclusively identified. Pathways for the metabolism of CAN have been proposed, and include hydroxylation, N-decarbonylation, methylation, oxidation and sequential conjugation. A previously unknown metabolically active site at the C4-C6 position and a novel N-decarbonylation-oxidation metabolic pathway for the prototypical canthinone alkaloid, CAN, were discovered. Our results provide valuable information about the in vivo metabolism of CAN that can also be used as a comprehensive guide for the biotransformation of other canthinone alkaloids.

Evaluation of canthinone alkaloids as cerebral protective agents

Considerable attention has been paid to cerebral protective drugs as a potential therapy for dementia. Screening of a natural compound library here resulted in identification of five canthinone alkaloids, viz., picrasidine L (1), picrasidine O (2), eurycomine E (3), 3-ethyl-canthin-5,6-dione (4), and 3-ethyl-4-methoxy-canthin-5,6-dione (5), as novel cerebral protective agents. The structure-activity relationship indicated that C-4, C-9, and N-3 substitutions greatly affected their cerebral protective effect. Among these, compound 2 exhibited a cerebral protective effect through suppressing neuronal hyperexcitability due to an increase in the excitatory neurotransmitter glutamic acid. Furthermore, compound 2 did not affect heart rate and mean systolic blood pressure. This investigation suggests that compound 2 has potential for further development as a cerebral protective drug.

The pharmacokinetics and bioavailability of three canthinone alkaloids after administration of Kumu injection to rats

ETHNOPHARMACOLOGICAL RELEVANCE

Kumu injection (KMI) is made from the branches and stems of Picrasma quassiodes (D. Don) Benn. and has been used clinically for the treatment of upper respiratory tract infection, acute tonsillitis, enteritis and bacillary dysentery. 3-methylcanthin-2,6-dione, 5-hydroxy-4-methoxycanthin-6-one, 4,5-dimethoxycanthin-6-one are the active ingredients of KMI because of its therapeutic effects.

AIM OF THE STUDY

To develop a LC-MS/MS method for simultaneous determination of three active canthinone alkaloids (4,5-dimethoxycanthin-6-one, 5-hydroxy-4-methoxycanthin-6-one and 3-methylcanthin-2,6-dione) in rat plasma and for the pharmacokinetic study of them after administered of KMI to rats.

MATERIALS AND METHODS

Rats were divided into 5 groups (n=5 per group), 3 groups administered intramuscularly with a single dose of KMI at 0.30, 0.45 and 0.90mL/kg respectively, and the other 2 groups administered intragastically or intravenously a single dose of KMI at 0.9mL/kg respectively. The concentrations of 4,5-dimethoxycanthin-6-one, 5-hydroxy-4-methoxycanthin-6-one and 3-methylcanthin-2,6-dione in plasma were determined by the established LC-MS/MS method at different time points and the pharmacokinetic parameters were estimated by non-compartmental analysis.

RESULTS

Pharmacokinetic results indicated that all of the alkaloids were absorbed rapidly and 3-methylcanthin-2,6-dione was eliminated fastest in rats. After intramuscular administration of KMI to rats, the absolute bioavailability is excellent, and the pharmacokinetic profiles are characterized by the first order kinetics.

CONCLUSION

The established method is suitable for the quantitation of the three alkaloids in rat plasma. And this pharmacokinetic study suggested that intramuscular injection of KMI was suitable in clinical usage.

Identification of in vivo and in vitro metabolites of 4,5-dimethoxycanthin-6-one by HPLC-Q-TOF-MS/MS

4,5-Dimthexycanthin-6-one and 5-hydroxy-4-methoxycanthin-6-one are the main active ingredients of Picrasma quassioides, which is a widely used herbal medicine for the treatment of gastroenteritis, snakebite, infection and hypertension in China. In the present study, the in vitro metabolites of 4,5-dimethoxycanthin-6-one in rat, mouse, dog and human liver microsomes, as well as the in vivo metabolites in rat plasma and urine following a single oral dose of 4,5-dimethoxycanthin-6-one, were identified by high-performance liquid chromatography combined with triple TOF mass spectrometry (HPLC-TOF/MS/MS). The metabolites were elucidated based on an accurate mass measurement, the MS/MS fragmentation patterns, the retention times of the parent drug and its metabolites, and the relevant drug biotransformation rules. After incubation in liver mcrosomes for 50 min, 4,5-dimethoxycanthin-6-one produced 8 phase I metabolites including 2 mono-demethylated metabolites (M1, M2), 3 mono-hydroxylated metabolites (M3-M5), and 3 mono-demethylated and mono-hydroxylated metabolites (M6-M8) in rat and mouse liver microsomes, 7 phase I metabolites (without M7) in dog and human liver microsomes. After a single oral administration of 4,5-dimethoxycanthin-6-one to rats, there were 3 phase I metabolites (M1, M2 and M5) detected in rat plasma and 5 phase I metabolites (M1-M5) in rat urine. Phase II metabolites were not detected in rat plasma and urine. Among these metabolites, mono-demethylated metabolites (M1 and M2) were the major metabolites of 4,5-dimethoxycanthin-6-one, mono-hydroxylated metabolites (M3-M5) were the minor metabolites of 4,5-dimethoxycanthin-6-one.

Quality Evaluation of Traditional Chinese Medicine Compounds in Xiaoyan Lidan Tablets: Fingerprint and Quantitative Analysis Using UPLC-MS

XiaoyanLidan tablets (XYLDTs) are traditional Chinese medicines frequently used for syndromes of the liver and gallbladder, cholecystitis and cholangitis. To evaluate the consistency of the quality of commercial XYLDT preparations, we established a simple and reliable ultra-performance liquid chromatography (UPLC) method with a photodiode array (PDA) detector and mass spectrometry (MS), including a fingerprint analysis and quantification of the main pharmacologically-active markers. In the UPLC-PDA detection-based fingerprint analysis of XYLDTs, approximately 39 peaks were found in the XYLDT chromatogram, 26 of which were attributed to Picrasmaquassioides, nine to Andrographis and four to Isodonserra. Subsequently, the structures of these bioactive markers were identified through ESI-MS analyses. Using the chemometricmethods of similarity analysis and principal component analysis, the five significant herbal componentswere determined as 4-methoxy-5-hydroxycanthin-6-one, andrographolide, dehydroandrographolide, neoandrographolide and rosmarinic acid, and these components were qualitatively assessed. Our experimental results demonstrated that combining the fingerprint analysis with UPLC-MS and multi-ingredient determination is useful for rapid pharmaceutical quality evaluation. Moreover, the combined approach can potentially differentiate the origin, determine the authenticity and assess the overall quality of the formulae.

Preparative separation of alkaloids from Picrasma quassioides (D. Don) Benn. by conventional and pH-zone-refining countercurrent chromatography

Two high-speed countercurrent chromatography (HSCCC) modes were compared by separation of major alkaloids from crude extract of Picrasma quassioides. The conventional HSCCC separation was performed with a two-phase solvent system composed of petroleum ether-ethyl acetate-methanol-water (5:5:4.5:5.5, v/v/v/v) with 200 mg loading. pH-Zone-refining CCC was performed with two-phase solvent system composed of petroleum ether-ethyl acetate-n-butanol-water (3:2:7:9, v/v/v/v) where triethylamine (10 mM) was added to the upper organic stationary phase and hydrochloric acid (5 mM) was added to the lower aqueous phase with 2 g loading. From 2 g of crude extract, 87 mg of 5-methoxycanthin-6-one (a), 38 mg of 1-methoxy-β-carboline (b), 134 mg of 1-ethyl-4,8-dimethoxy-β-carboline (c), 74 mg of 1-ethoxycarbonyl-β-carboline (d), 56 mg of 1-vinyl-4,8-dimethoxy-β-carboline (e) and 26 mg of 1-vinyl-4-dimethoxy-β-carboline (f) were obtained with purities of over 97.0%. The results indicated that pH-zone-refining CCC is an excellent separations tool at the multigram level.

In vitro and in vivo anti-inflammatory effects of 4-methoxy-5- hydroxycanthin-6-one, a natural alkaloid from Picrasma quassioides

In the present study, we evaluated the anti-inflammatory effect of 4-methoxy-5- hydroxycanthin-6-one (CAN), a natural alkaloid isolated from Picrasma quassioides. CAN significantly inhibited the production of NO and the release of TNF-α induced by LPS in macrophage RAW 264.7. Western blot showed that CAN can downregulate the expression of iNOS protein. After oral administration, CAN (3, 9, and 27 mg/kg) reduced the development of carrageenan-induced paw edema and complete Freund's adjuvant (CFA)-induced chronic arthritis in rats. The observed results indicated that pre-treatment with CAN might be an effective therapeutic intervention against inflammatory diseases including chronic arthritis.

Antihypertensive effects of extract from Picrasma quassiodes (D. Don) Benn. in spontaneously hypertensive rats

ETHNOPHARMACOLOGICA RELEVANCE: Picrasma quassiodes (D. Don) Benn. (PQB) is a widely used herbal medicine used for gastroenteritis, snakebite, infection and hypertension in China. The aim of the study was to investigate the possible antihypertensive mechanisms on spontaneously hypertensive rats (SHR) of the extract from Picrasma quassiodes (D. Don) Benn.

MATERIALS AND METHODS

In the in vivo study, extract from Picrasma quassiodes (D. Don) Benn. at the dose of 50, 100, 200mg/kg and captopril (12.5mg/kg) were administrated to different group of SHR rats by gavage for six consecutive weeks after the blood pressures were firstly measured. At the end of the study, rats serum nitric oxide (NO) was measured by the nitrate reductase method; superoxide dismutase (SOD) and malondialdehyde (MDA) activities were measured by the colorimetric method; the expression of aorta endothelial nitric oxide synthase (eNOS) was measured by immunohistochemical analysis.

RESULTS

The results showed that the oral administration of PQB could lower the systolic blood pressure (SBP) of SHR rats. In addition, the serum level of NO in SHR treated with PQB (100 and 200mg/kg) was increased dramatically (P<0.05, P<0.01), but administration with captopril had no significant effect. The expression of aorta eNOS was markedly increased when treated with PQB. The serum SOD levels were increased with treatment of PQB (100 and 200mg/kg; P<0.05, P<0.01). All the effects of these parameters were comparable to that of the SHR control group.

CONCLUSIONS

Our results disclosed that PQB is effective to lower blood pressure of SHR, its antihypertensive effect is probably associated with lowering oxidative stress by reducing SOD activity, preserving endothelial function and increasing the expression of eNOS to regulate NO and directly relax artery.

Ultrasonic microwave-assisted extraction coupled with high-speed counter-current chromatography for the preparation of nigakinones from Picrasma quassioides (D.Don) Benn

INTRODUCTION

Nigakinones are the main effective compounds of Picrasma quassioides (D. Don) Benn and are widely used in traditional Chinese medicine, therefore a rapid and efficient separation and purification method is necessary.

OBJECTIVE

To develop a new method based on ultrasonic microwave-assisted extraction (UMAE) and high-speed counter-current chromatography (HSCCC) for the rapid separation and purification of nigakinone and methylnigakinone from P. quassioides (D.Don) Benn.

METHODOLOGY

Response surface methodology (RSM) was used to optimise the extraction conditions of UMAE: 10.0 g of original sample was extracted with 210 mL of 90% (v/v) aqueous methanol at 60°C for 13 min, ultrasonic power was 100 W and microwave power was dynamically adjusted to the given temperature. After extraction, the extract was introduced into the HSCCC and separated with a hexane:ethyl acetate:methanol:2% acetic acid (9:11:9:11, v/v/v/v) solvent system.

RESULTS

About 2.1 mg nigakinone with purity of 96.8% was obtained in one step within 200 min, methylnigakinone was also obtained with a purity of 75.6%. Their chemical structures were identified with ESI-MS and ¹H-NMR.

CONCLUSION

UMAE coupled with HSCCC was found to be a promising and feasible alternative method to separate and purify alkaloids from natural herbs such as P. quassiodes.

Fingerprinting and simultaneous determination of alkaloids in Picrasma quassioides from different locations by high performance liquid chromatography with photodiode array detection

A simple and sensitive method was developed and validated for profiling and simultaneous quantitation of seven alkaloids (6-hydroxy-β-carboline-1-carboxylic acid, β-carboline-1-carboxylic acid, β-carboline-1-propanoic acid, 3-methylcanthin-5,6-dione, 5-hydroxy-4-methoxycanthin-6-one, 1-methoxycarbony-β-carboline, and 4,5-dimethoxycanthin-6-one) in Picrasma quassioide grown in different locations by high-performance liquid chromatography with photodiode array detection. The analysis was conducted on a Phenomenex Gemini C(18) column at 35°C with mobile phase of 25 mM aqueous ammonium acetate (pH 4.0, adjusted by glacial acetate acid) and acetonitrile. A common fingerprint chromatograph under 254 nm consisting of 27 peaks was constructed for the evaluation of the similarities among 31 P. quassioide samples. Samples from Guangdong and Guangxi Provinces were found to be within group linkage and showed significant difference from that of Jiangxi Province origin by using principal component analysis and hierarchical clustering analysis. In addition, the seven alkaloids were identified by electrospray ionization mass spectrometry and comparing with reference standards and literature data. All of them were determined simultaneously using the established HPLC method. This rapid and effective analytical method could be employed for quality assessment of P. quassioide, as well as pharmaceutical products containing this herbal material.

Preparative isolation and purification of alkaloids from Picrasma quassiodes (D. Don) Benn. by high-speed countercurrent chromatography

By using a two-phase solvent system composed of n-hexane-ethyl acetate-methanol-water (2:2:2:2, v/v/v/v), a high-speed counter-current chromatography technique was successfully used for isolation and purification of three alkaloids from Picrasma quassiodes (D. Don) Benn. for the first time. A total of 22.1 mg of 3-methylcanthin-2,6-dione, 4.9 mg of 4-methoxy-5-hydroxycanthin-6-one and 1.2 mg of 1-mthoxycarbonyl-β-carboline were obtained from 100 mg of crude extract of Picrasma quassiodes (D. Don) Benn. in less than 5 h, with purities of 89.30%, 98.32% and 98.19%, respectively. The target compounds were identified by ESI-MS, (1)H NMR and (13)C NMR.

Three-step synthesis of Ethyl Canthinone-1-carboxylates from ethyl 4-bromo-6-methoxy-1,5-naphthyridine-3-carboxylate via a Pd-catalyzed Suzuki-Miyaura coupling and a Cu-catalyzed amidation reaction [corrected]

Ethyl canthin-6-one-1-carboxylate (1b) and nine analogues 1c-k were prepared from readily prepared ethyl 4-bromo-6-methoxy-1,5-naphthyridine-3-carboxylate (2b) via a three-step non-classical approach that focused on construction of the central pyrrole (ring B) using Pd-catalyzed Suzuki-Miyaura coupling followed by Cu-catalyzed C-N coupling. Furthermore, treatment of the ethyl canthinone-1-carboxylate 1b with NaOH in DCM/MeOH (9:1) gave the canthin-6-one-1-carboxylic acid (6) in high yield. All compounds are fully characterized.

Beta-carboline alkaloids from the stems of Picrasma quassioides

Five new beta-carboline alkaloids, 6,12-dimethoxy-3-(2-hydroxylethyl)-beta-carboline (1), 3,10-dihydroxy-beta-carboline (2), 6,12-dimethoxy-3-(1-hydroxylethyl)-beta-carboline (3), 6,12-dimethoxy-3-(1,2-dihydroxylethyl)-beta-carboline (4), and 6-methoxy-3-(2-hydroxyl-1-ethoxylethyl)-beta-carboline (5), and two new natural products, 6-methoxy-12-hydroxy-3-methoxycarbonyl-beta-carboline (6) and 3-hydroxy-beta-carboline (7) were isolated from the stems of Picrasma quassioides along with 16 known beta-carboline alkaloids (8-23). The structures of new compounds were determined by extensive spectroscopic analyses, and the 1D and 2D NMR data of compounds 6, 7 and 10 were reported for the first time. The bioassays showed that only compounds 14 and 16 could enhance the differentiation of 3T3-L1 preadiocytes accompanied by secretion of adiponectin proteins among these 23 compounds.

Quassidines A-D, bis-beta-carboline alkaloids from the stems of Picrasma quassioides

Four new bis-beta-carboline alkaloids, quassidines A-D (1-4), together with a known alkaloid, picrasidine C (5), were isolated from the stems of Picrasma quassioides. Quassidine A (1) is the first reported bis-beta-carboline alkaloid possessing a novel cyclobutane moiety. The structures of the new compounds were determined on the basis of their 1D and 2D NMR and X-ray diffraction data. A possible biogenetic pathway for these alkaloids was proposed, and all compounds were evaluated for anti-inflammatory activity. Only quassidine A (1) showed weak activity.

Chapter 1 Allelochemical Properties or the Raison D'être of Alkaloids

This chapter provides evidence that alkaloids are not waste products or functionless molecules as formerly assumed, but rather defense compounds employed by plants for survival against herbivores and against microorganisms and competing plants. These molecules were developed during evolution through natural selection in that they fit many important molecular targets, often receptors, of cells, which are seen in molecules that mimic endogenous neurotransmitters. The chapter discusses that microorganisms and herbivores rely on plants as a food source. Since both have survived, there must be mechanisms of adaptations toward the defensive chemistry of plants. Many herbivores have evolved strategies to avoid the extremely toxic plants and prefer the less toxic ones. Many herbivores have potent mechanisms to detoxify xenobiotics, which allow the exploitation of at least the less toxic plants. In insects, many specialists evolved that are adapted to the defense chemicals of their host plant, in that they accumulate these compounds and exploit them for their own defense. Alkaloids function as defense molecules against insect predators in the examples studied, and this is further support for the hypothesis that the same compound also serves for chemical defense in the host plant. It needs more experimental data to understand fully the intricate interconnections between plants, their alkaloids, and herbivores, microorganisms, and other plants.

Studies on Ailanthus altissima cell suspension cultures. The effect of basal media on growth and alkaloid production

Time-course experiments have been carried out to investigate the relationship between growth and alkaloid accumulation in A. altissima cell suspension cultures. Results indicate that the type of basal medium, viz. Murashige and Skoog, Linsmaier and Skoog, Schenk and Hildebrandt or Gamborg's B5, has a significant influence on both growth and alkaloid production.