Indole alkaloids with antibacterial activity from aqueous fraction of Alstonia scholaris

Design, synthesis and antiviral activity of indole derivatives containing quinoline moiety

A series of indole derivatives containing quinoline structures were designed and synthesized. The synthesized compounds were characterized by NMR and HRMS. And W14 was performed by single crystal X-ray diffraction experiments. The antiviral activity studies showed that some of the target compounds possessed significant activity against tobacco mosaic virus (TMV). In particular, W20 had significant activity. The results of in vivo anti-TMV activity assay showed that W20 possessed the best curative and protective activities with EC50 values of 84.4 and 65.7 μg/mL, which were better than ningnanmycin (NNM) 205.1 and 162.0 μg/mL, respectively. The results of Microscale thermophoresis (MST) showed that W20 had a strong binding affinity for the tobacco mosaic virus coat protein (TMV-CP) with a dissociation constant (Kd) of 0.00519 μmol/L, which was superior to that of NNM (1. 65320 μmol/L). The molecular docking studies were in accordance with the experimental results. In addition, the determination of malondialdehyde (MDA) content in tobacco leaves showed that W20 improved the disease resistance of tobacco. Overall, this study shows that indole derivatives containing quinoline can be used as new antiviral agents for plant viruses for further research.

Monoterpenoid indole alkaloids from Alstonia scholaris and their Toxoplasma gondii inhibitory activity

Nine previously unreported various types of monoterpenoid indole alkaloids, together with seven known analogues were isolated from the stem barks of Alstonia scholaris through a silica gel free methodology. The structures of 1-9 were elucidated by spectroscopic data analysis, electronic circular dichroism calculations, and single-crystal X-ray diffraction. Compound 1 is a modified echitamine-type alkaloid with a novel 6/5/5/7/6/6 hetero hexacyclic bridged ring system, and 8 and 9 exist as a zwitterion and trifluoroacetate salt, respectively. The anti-Toxoplasma activity of all isolates on infected Vero cells were evaluated, which revealed that compound 14 at 0.24 μM displayed potent activity. This study expanded the structural diversity of alkaloids of A. scholaris, and presented their potential application in anti-Toxoplasma drug development.

Pharmacological investigation of indole alkaloids from Alstonia scholaris against chronic glomerulonephritis

BACKGROUND

As one of the most commonly used folk medicines in "Dai" ethno-medicine system, Alstonia scholaris (l.) R. Br. has also been used for treat "water related diseases", such as chronic kidney disease. However, few study was reported for it on the intervention of chronic glomerulonephritis (CGN).

PURPOSE

To investigate the effect and potential mechanism of indole alkaloids from A. scholaris leaves in ICR mice with adriamycin nephropathy, as well as providing experimental evidence for the further application.

METHODS

ICR Mice were selected for injections of adriamycin (ADR) to induce the CGN model and administered total alkaloids (TA) and four main alkaloids continuously for 42 and 28 days, respectively. The pharmacological effects were indicated by serum, urine, and renal pathological observations. The targets and pathways of indole alkaloids on CGN intervention were predicted using the network pharmacology approach, and the immortalized mice glomerular podocyte (MPC5) cells model stimulated by ADR was subsequently selected to further verify this by western blotting and RT-qPCR methods.

RESULTS

TA and four major compounds dramatically reduced the levels of urinary protein, serum urea nitrogen (BUN), and creatinine (CRE) in ADR - induced CGN mice, while increasing serum albumin (ALB) and total protein (TP) levels as well as ameliorating kidney damage. Moreover, four alkaloids effected on 33 major target proteins and 153 pathways in the CGN, among which, PI3K-Akt as the main pathway, an important pathway for kidney protection by network pharmacology prediction, and then the four target proteins - HRAS, CDK2, HSP90AA1, and KDR were screened. As a result, Val-and Epi can exert a protective effect on ADR-stimulated MPC5 cells injury at a concentration of 50 μM. Furthermore, the proteins and RNA expression of HRAS, HSP90AA1, and KDR were down-regulated, and CDK2 was up-regulated after the intervention of Val-and Epi, which were supported by Western blotting and RT-qPCR. Additionally, Val-and Epi inhibited ROS production in the MPC5 cells model.

CONCLUSION

This study is the first to confirm the potential therapeutic effect of alkaloids from A. scholaris on CGN. TA with major bioactive components (vallesamine and 19‑epi-scholaricine) could exert protective effects against the ADR-induced CGN by regulating four key proteins: HRAS, CDK2, HSP90AA1, and KDR of the PI3K-Akt pathway.

Potential Plant-Based New Antiplasmodial Agent Used in Papua Island, Indonesia

Resistance to antimalarial medicine remains a threat to the global effort for malaria eradication. The World Health Organization recently reported that artemisinin partial resistance, which was defined as delayed parasite clearance, was detected in Southeast Asia, particularly in the Greater Mekong subregion, and in Africa, particularly in Rwanda and Uganda. Therefore, the discovery of a potential new drug is important to overcome emerging drug resistance. Natural products have played an important role in drug development over the centuries, including the development of antimalarial drugs, with most of it influenced by traditional use. Recent research on traditional medicine used as an antimalarial treatment on Papua Island, Indonesia, reported that 72 plant species have been used as traditional medicine, with Alstonia scholaris, Carica papaya, Andrographis paniculata, and Physalis minima as the most frequently used medicinal plants. This review aimed to highlight the current research status of these plants for potential novel antiplasmodial development. In conclusion, A. paniculata has the highest potential to be developed as an antiplasmodial, and its extract and known bioactive isolate andrographolide posed strong activity both in vitro and in vivo. A. scholaris and C. papaya also have the potential to be further investigated as both have good potential for their antiplasmodial activities in vivo. However, P. minima is a less studied medicinal plant; nevertheless, it opens the opportunity to explore the potential of this plant.

Chemistry, bioactivity, biosynthesis, and total synthesis of stemmadenine alkaloids

Covering: up to July 2022Stemmadenine alkaloids are a restrictive sub-group of monoterpene indole alkaloids, represented by two congeners: stemmadenine and vallesamine. Their skeleton is defined by the cleavage of the C-3-C-7 bond of the Strychnos group's pentacyclic scaffold in monoterpene indole alkaloids. The parent alkaloid stemmadenine acts as a key intermediate in the biosynthesis of several major monoterpene indole alkaloid families, including regular Strychnos alkaloids, Aspidosperma alkaloids, and Iboga alkaloids. In this review, a complete coverage of the stemmadenine alkaloids, from the early reports till the present day at 2022, are presented, and their diverse biological activities are briefly described. Moreover, the biosynthetic proposal for stemmadenine and the proposed biogenetic conversion of stemmadenine-type alkaloids into vallesamine-type congeners are discussed in detail. Moreover, the successful synthetic strategies to access the strained stemmadenine scaffolds are fully reviewed.

Synthesis, Antibacterial Activity, and Mechanisms of Novel Indole Derivatives Containing Pyridinium Moieties

The development of effective antibacterial agents equipped with novel action modes and unique skeletons starting from natural compounds serves as an important strategy in the modern pesticide industry. Disclosed here are a series of novel indole derivatives containing pyridinium moieties and their antibacterial activity evaluation against two prevalent phytopathogenic bacteria, Xanthomonas oryzae pv. oryzicola (Xoc) and X. oryzae pv. oryzae (Xoo). A three-dimensional (3D)-QSAR model was adopted to discover higher activity like title compounds based on the Xoc antibacterial activity of the tested compounds. Compound 43 was consequently designed, and it displayed higher antibacterial activity as expected with the half-maximal effective concentration EC₅₀ values of 1.0 and 1.9 μg/mL for Xoo and Xoc, respectively, which were better than those of the commercial drug thiodiazole copper (TC) (72.9 and 87.5 μg/mL). Under greenhouse conditions, the results of a rice in vivo pot experiment indicated that the protective and curative activities of compound 43 against rice bacterial leaf streak (BLS) and rice bacterial blight (BLB) were 45.0 and 44.0% and 42.0 and 39.3%, respectively, which were better than those of the commercial agent thiodiazole copper (38.0 and 37.9%, 38.6 and 37.0%) as well. Scanning electron microscopy images, defense enzyme activity tests, and proteomic techniques were utilized in a preliminary mechanism study, suggesting that compound 43 shall modulate and interfere with the physiological processes and functions of pathogenic bacteria.

Antibacterial and Antifungal Alkaloids from Asian Angiosperms: Distribution, Mechanisms of Action, Structure-Activity, and Clinical Potentials

The emergence of multidrug-resistant bacteria and fungi requires the development of antibiotics and antifungal agents. This review identified natural products isolated from Asian angiosperms with antibacterial and/or antifungal activities and analyzed their distribution, molecular weights, solubility, and modes of action. All data in this review were compiled from Google Scholar, PubMed, Science Direct, Web of Science, ChemSpider, PubChem, and a library search from 1979 to 2022. One hundred and forty-one antibacterial and/or antifungal alkaloids were identified during this period, mainly from basal angiosperms. The most active alkaloids are mainly planar, amphiphilic, with a molecular mass between 200 and 400 g/mol, and a polar surface area of about 50 Å2, and target DNA and/or topoisomerase as well as the cytoplasmic membrane. 8-Acetylnorchelerythrine, cryptolepine, 8-hydroxydihydrochelerythrine, 6-methoxydihydrosanguinarine, 2'-nortiliacorinine, pendulamine A and B, rhetsisine, sampangine, tiliacorine, tryptanthrin, tylophorinine, vallesamine, and viroallosecurinine yielded MIC ≤ 1 µg/mL and are candidates for the development of lead molecules.

Indole alkaloids of Alstonia scholaris (L.) R. Br. alleviated nonalcoholic fatty liver disease in mice fed with high-fat diet

Alstonia scholaris (L.) R. Br (Apocynaceae) is a well-documented medicinal plant for treating respiratory diseases, liver diseases and diabetes traditionally. The current study aimed to investigate the effects of TA on non-alcoholic fatty liver disease (NAFLD). A NAFLD model was established using mice fed a high-fat diet (HFD) and administered with TA (7.5, 15 and 30 mg/kg) orally for 6 weeks. The biochemical parameters, expressions of lipid metabolism-related genes or proteins were analyzed. Furthermore, histopathological examinations were evaluated with Hematoxylin-Eosin and MASSON staining. TA treatment significantly decreased the bodyweight of HFD mice. The concentrations of low-density lipoprotein (LDL), triglyceride (TG), aspartate aminotransferase (AST) and alanine aminotransferase (ALT) were also decreased significantly in TA-treated mice group, accompanied by an increase in high-density lipoprotein (HDL). Furthermore, TA alleviated hepatic steatosis injury and lipid droplet accumulation of liver tissues. The liver mRNA levels involved in hepatic lipid synthesis such as sterol regulatory element-binding protein 1C (SREBP-1C), regulators of liver X receptor α (LXRα), peroxisome proliferator activated receptor (PPAR)γ, acetyl-CoA carboxylase (ACC1) and stearyl coenzyme A dehydrogenase-1 (SCD1), were markedly decreased, while the expressions involved in the regulation of fatty acid oxidation, PPARα, carnitine palmitoyl transterase 1 (CPT1A), and acyl coenzyme A oxidase 1 (ACOX1) were increased in TA-treated mice. TA might attenuate NAFLD by regulating hepatic lipogenesis and fatty acid oxidation.

The clinical population pharmacokinetics, metabolomics and therapeutic analysis of alkaloids from Alstonia scholaris leaves in acute bronchitis patients

BACKGROUND

Capsule of alkaloids from leaf of Alstonia scholaris (CALAS) is a new investigational botanical drug (No. 2011L01436) for respiratory disease. Clinical population pharmacokinetics (PK), metabolomics and therapeutic data are essential to guide dosing in patients. Previous research has demonstrated the potential therapeutic effect of CALAS on acute bronchitis. Further clinical trial data are needed to verify its clinical efficacy, pharmacokinetics behavior, and influence of dosage and other factors.

PURPOSE

To verify the clinical efficacy and explore the potential biomarkers related to CALAS treatment for acute bronchitis.

MATERIALS AND METHODS

Oral CALAS was assessed in a randomized, double-blind, placebo-controlled trial. Fifty-five eligible patients were randomly assigned to four cohorts to receive 20, 40 or 80 mg, of CALAS three times daily for seven days, or placebo. Each CALAS cohort included 15 subjects, and the placebo group included 10 subjects. A population PK model of CALAS was developed using plasma with four major alkaloid components. Metabolomics analysis was performed to identify biomarkers correlated with the therapeutic effect of CALAS, and efficacy and safety were assessed based on clinical symptoms and adverse events.

RESULTS

The symptoms of acute bronchitis were alleviated by CALAS treatment without serious adverse events or clinically significant changes in vital signs, electrocardiography or upper abdominal Doppler ultrasonography. Moreover, one compartment model with first-order absorption showed that an increase in aspartate transaminase will reduce the clearance (CL) of scholaricine, and picrinine CL was inversely proportional to body mass index, while 19-epischolaricine and vallesamine CL increased with aging. The serum samples from acute bronchitis patients at different time points were analyzed using UPLC-QTOF in combination with the orthogonal projection to latent structures-discriminant analysis, which indicated higher levels of lysophosphatidylcholines, lysophosphatidylethanolamines and amino acids with CALAS treatment than with placebo.

CONCLUSION

This is the first study to evaluate the clinical efficacy and explored the potential biomarkers related to CALAS therapeutic mechanism of acute bronchitis by means of clinical trial combined the metabolomics study. This exploratory study provides a basis for further research on clinical efficacy and optimal dosing regimens based on pharmacokinetics behavior. Additional acute bronchitis patients and CALAS PK samples collected in future studies may be used to improve model performance and maximize its clinical value.

Samarium(ii) iodide-mediated reactions applied to natural product total synthesis

Natural product synthesis remains a field in which new synthetic methods and reagents are continually being evaluated. Due to the demanding structures and complex functionality of many natural products, only powerful and selective methods and reagents will be highlighted in this proceeding. Since its introduction by Henri Kagan, samarium(ii) iodide (SmI2, Kagan's reagent) has found increasing use in chemical synthesis. Over the years, many reviews have been published on the application of SmI2 in numerous reductive coupling procedures as well as in natural product total synthesis. This review highlights recent advances in SmI2-mediated synthetic strategies, as applied in the total synthesis of natural products since 2004.

The safety and tolerability of alkaloids from Alstonia scholaris leaves in healthy Chinese volunteers: a single-centre, randomized, double-blind, placebo-controlled phase I clinical trial

CONTEXT

Capsule of alkaloids from the leaf of Alstonia scholaris (L.) R.Br. (Apocynaceae) (CALAS) is a new investigational botanical drug (No. 2011L01436) for bronchitis, post-infectious cough and asthma.

OBJECTIVE

To observe the clinical safety and tolerability of CALAS.

MATERIALS AND METHODS

Subjects were assigned to eight cohorts, and each received randomly CALAS or placebo in one of single ascending dose (SAD) of 8, 40, 120, 240, 360, 480, or in one of multiple ascending dose (MAD) of 40 or 120 mg, three times daily for 7 days. Each cohort contained two placebo subjects.

RESULTS

Sixty-two enrolled volunteers completed the study and no serious adverse events and clinically significant changes in vital signs, electrocardiography, and upper abdominal Doppler ultrasonography were observed. The ratios of treatment-emergent adverse events (TEAEs) were reported in 11/46 (23.91%) of CALAS groups and 3/16 (18.75%) of the placebo group (p > 0.05), respectively, based on the results of SAD and MAD. All TEAEs were mild, transient, and disappeared without any intervention. The TEAEs possibly related to CALAS treatment were as followings: hiccups (4/46: 8%), dry mouth and nausea (3/46: 6%), increased sleep (2/46: 4%), abdominal distension (1/46: 2%), bilirubin elevated (1/46: 2%).

DISCUSSION AND CONCLUSIONS

CALAS is safe and well-tolerated with no unexpected or clinically relevant safety concerns up to a single dose of 360 mg and three times daily for 7 days up to 120 mg in healthy Chinese volunteers, supporting further Phase II studies.

Research Progress on Antibacterial Activities and Mechanisms of Natural Alkaloids: A Review

Alkaloids are nitrogen-containing heterocyclic compounds typically isolated from plants. They represent one of the most important types of natural products because of their large number and structural diversity and complexity. Based on their chemical core structures, alkaloids are classified as isoquinolines, quinolines, indoles, piperidine alkaloids, etc. In-depth analyses of alkaloids have revealed their antibacterial activities. To date, due to the widespread use of antibiotics, the problem of drug-resistant bacterial infections has been gradually increasing, which severely affects the clinical efficacy of antibacterial therapies and patient safety. Therefore, significant research efforts are focused on alkaloids because they represent a potentially new type of natural antibiotic with a wide antibacterial spectrum, rare adverse reactions, and a low tendency to produce drug resistance. Their main antibacterial mechanisms include inhibition of bacterial cell wall synthesis, change in cell membrane permeability, inhibition of bacterial metabolism, and inhibition of nucleic acid and protein synthesis. This article reviews recent reports about the chemical structures and the antibacterial activities and mechanisms of alkaloids. The purpose is to solve the problem of bacterial resistance and to provide a certain theoretical basis and research ideas for the development of new antibacterial drugs.

Pharmacological effects of indole alkaloids from Alstonia scholaris (L.) R. Br. on pulmonary fibrosis in vivo

ETHNOPHARMACOLOGICAL RELEVANCE

Alstonia scholaris (L.) R. Br. (Apocynaceae) is a Dai folk medicine for the treatment of lung diseases in China.

AIM OF THE STUDY

The present study investigated the anti-pulmonary fibrosis effects of total alkaloids (TA) and the potential active ingredients and its possible mechanism.

MATERIALS AND METHODS

After intratracheal instillation of bleomycin (BLM, 5 mg/kg), mice were divided into ten groups, and orally treated with the corresponding samples once daily for 28 days. The effect of indole alkaloids was determined through analysis of cytokines, as well as histopathological examinations and gene expressions.

RESULTS

Severe lung fibrosis was observed in the BLM-treated mice on day 28. However, the administration of TA significantly ameliorated the pathological changes in the lungs, decreased the content of Krebs von den Lungen-6, lactate dehydrogenase, transforming growth factor-β (TGF-β), hydroxyproline, type I collagen, and malonaldehyde, and enhanced the activity of superoxide dismutase in the serum and lung tissues. In addition, the enhanced TGF-β and matrix metalloproteinase-1 (MMP-1) expressions in BLM-induced mice were obviously weakened by indole alkaloids, as well as the ratio of matrix metalloproteinase-1 to tissue inhibitor of metalloproteinase-1 was decreased. Moreover, picrinine and scholaricine yielded markedly better values in the aforementioned indices than those in other samples, indicating that they may be the active ingredients of alkaloids.

CONCLUSIONS

TA exerted protective effects against BLM-induced pulmonary fibrosis by reducing collagen deposition through TGF-β/MMP-1 pathway.

Anti-microbial Effects In Vitro and In Vivo of Alstonia scholaris

Alstonia scholaris could be used as a traditional medicinal plant in China for the treatment of acute respiratory, which might be caused by respiratory tract infections. The investigation tested the anti-infective effects of total alkaloids extract (TA) from leaves of A. scholaris, and as a result, TA inhibited herpes simplex virus type 1 (HSV-1), respiratory syncytial virus (RSV) and influenza A virus (H1N1) in vitro respectively. In addition, the survival days of mice were prolonged, and the lung weights and mortality of mice were decreased significantly, after oral administrated TA in H1N1 and beta-hemolytic streptococcus infectious models in vivo respectively. The finding supported partly the traditional usage of A. scholaris in the treatment of respiratory infections.

Anti-Foc RT4 Activity of a Newly Isolated Streptomyces sp. 5-10 From a Medicinal Plant (Curculigo capitulata)

Fusarium wilt of banana caused by Fusarium oxysporum f. sp. cubense (Foc) is a disastrous soil-borne fungal disease. Foc tropical race 4 (Foc TR4) can infect almost all banana cultivars. Until now, there is a shortage of safety and effective control methods and commercial banana cultivars with a resistance against Foc TR4. Biocontrol using environmentally friendly microbes is a promising strategy for the management of Foc TR4. Here, a strain 5-10, newly isolated from a medicinal plant (Curculigo capitulata), exhibited a high antifungal activity against Foc TR4. Combing the morphological characteristics and molecular identification, strain 5-10 was classified as a Streptomyces genus. The sequenced genome revealed that more than 39 gene clusters were involved in the biosynthesis of secondary metabolites. Some multidrug resistance gene clusters were also identified such as mdtD, vatB, and vgaE. To improve the anti-Foc TR4 activity of the strain 5-10 extracts, an optimization method of fermentation broth was established. Antifungal activity increased by 72.13% under the fermentation system containing 2.86 g/L of NaCl and 11.57% of inoculation amount. After being treated with the strain 5-10 extracts, the Foc TR4 hyphae shrinked, deformed, and ruptured. The membrane integrity and cell ultrastructure incurred irreversible damage. Streptomyces sp. 5-10 extracts play a fungicidal role in Foc TR4. Hence, Streptomyces sp. 5-10 will be a potential biocontrol agent to manage fungal diseases by exploring the microbial fertilizer.

Chemical Diversity and Bioactivities of Monoterpene Indole Alkaloids (MIAs) from Six Apocynaceae Genera

By the end of the twentieth century, the interest in natural compounds as probable sources of drugs has declined and was replaced by other strategies such as molecular target-based drug discovery. However, in the recent times, natural compounds regained their position as extremely important source drug leads. Indole-containing compounds are under clinical use which includes vinblastine and vincristine (anticancer), atevirdine (anti-HIV), yohimbine (erectile dysfunction), reserpine (antihypertension), ajmalicine (vascular disorders), ajmaline (anti-arrhythmic), vincamine (vasodilator), etc. Monoterpene Indole Alkaloids (MIAs) deserve the curiosity and attention of researchers due to their chemical diversity and biological activities. These compounds were considered as an impending source of drug-lead. In this review 444 compounds, were identified from six genera belonging to the family Apocynaceae, will be discussed. These genera (Alstonia, Rauvolfia, Kopsia, Ervatamia, and Tabernaemontana, and Rhazya) consist of 400 members and represent 20% of Apocynaceae species. Only 30 (7.5%) species were investigated, whereas the rest are promising to be investigated. Eleven bioactivities, including antibacterial, antifungal, anti-inflammatory and immunosuppressant activities, were reported. Whereas cytotoxic effect represents 47% of the reported activities. Convincingly, the genera selected in this review are a wealthy source for future anticancer drug lead.

Indole alkaloids from leaves of Alstonia scholaris (L.) R. Br. protect against emphysema in mice

ETHNOPHARMACOLOGICAL RELEVANCE

Alstonia scholaris (L.) R. Br. (Apocynaceae) is a medicinal plant in China traditionally used to treat pulmonary diseases, including bronchitis, whooping cough, asthma and chronic obstructive pulmonary disease.

AIM OF THE STUDY

To provide experimental data supporting clinical adaptation of total indole alkaloids ( TA) from A. scholaris leaves for treating emphysema.

MATERIALS AND METHODS

An emphysema model was induced by a single intratracheal instillation of porcine pancreatic elastase followed by administration of TA and four main alkaloid components (scholaricine, 19-epischolaricine, vallesamine, and picrinine) for 30 consecutive days. Cytokine levels, histopathological parameters and protein expression in lung tissues were examined.

RESULTS

Administering the TA, picrinine, scholaricine, 19-epischolaricine and vallesamine for 30 days effectively inhibited inflammatory cell accumulation and invasion in the lung tissue and relieved pulmonary tissue injury. Oxygen saturation was enhanced, and interleukin (IL)-1β, monocyte-chemo attractive peptide 1, IL-11, matrix metalloproteinase-12, transforming growth factor-β and vascular endothelial growth factor levels were significantly reduced, likely by suppressing overactivation of alveolar macrophages and pulmonary fibrosis. The elastin content was markedly elevated, and fibronectin was reduced. Bcl-2 expression was significantly increased, and nuclear factor-κB and β-catenin levels were decreased.

CONCLUSIONS

TA can be potentially used as an effective novel drug for pulmonary emphysema and exerts its effects through not only inhibiting inflammation of the airway wall and airflow resistance but also promoting lung elastic recoil and protease/anti-protease balance.

Acute and Sub-chronic Toxicity of Indole Alkaloids Extract from Leaves of Alstonia scholaris (L.) R. Br. in Beagle Dogs

Alstonia scholaris (L.) R. Br., an evergreen tropical plant rich in indole alkaloids with significant physiological activity, is traditionally used to treat respiratory diseases in China. This study was conducted to establish the toxicity profile of the alkaloid extract (TA) of A. scholaris leaves in non-rodents. After oral administration of a single dose (4 g/kg.bw), a number of transient symptoms, such as unsteady gait, drooling, emesis, and reddening of peri-oral mucosa, were observed, but no treatment-related mortality. A sub-chronic toxicity study with a range of doses of TA (20, 60 and 120 mg/kg.bw) was conducted for a 13-week treatment period, followed by 4-week recovery observation. Except for emesis and drooling in majority of animals in 120 mg/kg.bw treatment group, no clinical changes were observed in TA-treated animals. Data from electrocardiography, bone marrow, urine, fecal, hematology and clinical chemistry analyses were comparable between TA-treated and control animals. No significant differences in the relative organ weights and histopathological characteristics were evident between the TA-treated and control groups. Accordingly, the non-observed-adverse-effect-level (NOAEL) of TA was established as 120 mg/kg.bw. Our results add further knowledge to the safety database for indole alkaloid extracts from A. scholaris with potential utility as novel drug candidates.

Natural indole-containing alkaloids and their antibacterial activities

As the growth in resistance to bacterial infection treatments poses a grave threat to global health in the 21st century, there is a constant need to explore novel antibacterial agents that have the ability to overcome drug resistance. Indole-containing alkaloids are widely distributed in nature, and a variety of indole-containing alkaloids have already been applied in clinical practice, proving that indole-containing alkaloids are fascinating and privileged scaffolds for the development of novel drugs. Moreover, indole-containing alkaloids could exert their antibacterial activity through the inhibition of efflux pumps, the biofilm, filamentous temperature-sensitive protein Z, and methicillin-resistant Staphylococcus aureus pyruvate kinase; so, indole-containing alkaloids constitute an important source of novel antibacterial agents. This review is an endeavor to highlight the advances in the development of indole-containing alkaloids with antibacterial potential, covering articles published in the recent 10 years.

Genotoxicity and Safety Pharmacology Studies of Indole Alkaloids Extract from Leaves of Alstonia scholaris (L.) R. Br

Indole alkaloids extract (IAAS) was prepared from leaves of Alstonia scholaris (L.) R. Br., an evergreen tropical plant widely distributed throughout the world. This plant has been used historically by the Dai ethnic people of China to treat respiratory diseases. This study evaluated the genotoxicity and safety pharmacology of IAAS to support clinical use. The bacterial reverse mutation (Ames) test, in vitro mammalian chromosomal aberration test, and in vivo mammalian erythrocyte micronucleus (MN) test were performed to evaluate genotoxicity. Mice were administered IAAS (240, 480, or 960 mg/kg bw) once orally to observe adverse central nervous system effects. Furthermore, beagle dogs were administered IAAS (10, 30, 60 mg/kg bw) once via the duodenum to evaluate its effects on the cardiovascular and respiratory systems. IAAS with or without S9-induced metabolic activation showed no genotoxicity in the Ames test up to 500 μg/plate, in the mammalian chromosomal aberration test up to 710 μg/mL, or in the MN test up to 800 mg/kg bw. No abnormal neurobehavioral effects were observed in mice following treatment with up to 960 mg/kg bw of IAAS. Moreover, blood pressure, heart rate, electrocardiogram parameters, and depth and rate of breathing in anesthetized beagle dogs did not differ among the IAAS doses or from the vehicle group. These data indicated that IAAS did not induce mutagenicity, clastogenicity, or genotoxicity, and no pharmaco-toxicological effects were observed in the respiratory, cardiovascular, or central nervous systems. Our results increased understanding of safety considerations associated with IAAS, and may indicate that IAAS is a possible drug candidate.

Acute and Chronic Toxicity of Indole Alkaloids from Leaves of Alstonia scholaris (L.) R. Br. in Mice and Rats

Alstonia scholaris (L.) R. Br. (Apocynaceae) is an evergreen tree that has been used to treat lung diseases. In this study, the toxicity profile of indole alkaloids from leaves of A. scholaris was investigated. In acute toxicity tests, mice were administered total alkaloids (TA) and five indole alkaloids. In a chronic toxicity test, rats were continuously administered TA (50, 100, and 300 mg/kg bw) for 13 weeks, followed by a 4-week recovery. A single administration of TA affected the behavior of mice, and at 12.8 g/kg bw, prone position, shortness of breath, wheezing, and convulsion were observed. The half-lethal dose (LD50) in mice was 5.48 g/kg bw, almost 2740 times the clinical dose in humans. Among the five indole alkaloids, the maximum tolerance dose in mice ranged from 0.75 to 4 g/kg bw. The TA-treated rats did not die and showed no adverse effects or dose-dependent changes in weight or food and water consumption, despite fluctuations in hematological and biochemical parameters compared with historical data. Furthermore, both gross and histopathological observations revealed no abnormalities in any organ. With daily oral administration to rats, the non-observed-adverse-effect-level of TA was 100 mg/kg bw. The results indicate that TA is safe for clinical use.

Nepenthe-Like Indole Alkaloids with Antimicrobial Activity from Ervatamia chinensis

Two monoterpenoid indole alkaloid erchinines A (1) and B (2), possessing unique 1,4-diazepine fused with oxazolidine architecture and three hemiaminals, were isolated from Ervatamia chinensis. Their structures were elucidated on the basis of intensive spectroscopic analysis, and a plausible biosynthetic pathway from ibogaine was proposed. Both compounds exhibited significant antimicrobial activity against Trichophyton rubrum and Bacillus subtilis, and their activities were comparable to the first line antifungal drug griseofulvin and antibiotic cefotaxime.

Immune-inhibitive phenyl-C1 substituent aporphine alkaloids from Thalictrum cirrhosum

Five new phenyl-C₁ substituent aporphine alkaloids, 6aR-2'-methoxycarbonyl-thaliadin (1), 6aR-2'-carboxyl-thaliadin (2), 6aR-3-methoxy-hernandalinol (3), 6aS-1,3,10-trimethoxy-natalamine (4), and 3-methoxy-2'-methoxycarbonyl-oxohernandalincin (5), together with sixteen known isoquinoline alkaloids (6-21) were isolated from the whole herb of Thalictrum cirrhosum (Levl.). Their structures were elucidated by extensive spectroscopic measurements, and six isoquinoline alkaloids showed significant inhibitory activity on concanavalin A-stimulated splenocytes proliferation with IC₅₀ values 36-44 μM by the immunosuppressive bioassay.

Effects of indole alkaloids from leaf of Alstonia scholaris on post-infectious cough in mice

ETHNOPHARMACOLOGICAL RELEVANCE

Leaf of Alstonia scholaris (L.) R. Br. (Apocynaceae), a wide used ethic-medicine in many Asia and Africa counties, has also been recorded as the common traditional Chinese medicine for treatment of illnesses in respiratory system by Dai people.

AIM OF THE STUDY

To provide experimental data of clinical adaption of total indole alkaloids (TA) from leaf of A. scholaris for treating post-infectious cough in phase II clinical trial.

MATERIALS AND METHODS

To model post-infectious cough, all animals except control group were instilled intra-tracheal with lipopolysaccharide (LPS) (80 μg/50 µL/mouse), followed by subsequent exposure to cigarette smoke (CS) for 30 min per day for a total of 30 days. Mice were orally given TA at dose of 10, 25, 50 mg/kg, and four main alkaloids (Sch: scholaricine, Epi: 19-epischolaricine, Val: vallesamine, Pic: picrinine) once daily. Cellular infiltration was assessed in the broncho-alveolar lavage fluid (BALF). Expression of interleukin-6 (IL-6) and C-reactive protein (CRP) in the serum was determined, the superoxide dismutase (SOD) activity as well as malondialdehyde (MDA) content in the serum and homogenate were examined. Finally, histopathological examination in the lungs was assessed by H. E. staining.

RESULTS

After administration of TA and four major alkaloids respectively, the symptoms of cough in mice were obviously attenuated. Total white blood cells (WBC) and neutrophils (NEU) amounts in BALF were reduced obviously and the pathological damage of lung was also attenuated. There was also significant reduction in IL-6, CRP, MDA and a marked improvement in SOD.

CONCLUSIONS

The efficacy of indole alkaloids against post-infectious cough (PIC) was shown in the down-regulation of inflammatory cells, cytokines, and the balance of antioxidants. What's more, the pharmacological effects of TA were better than single indole alkaloid, which might be related to the synergic effect of four major alkaloids.

New pyrazinoquinazoline alkaloids Isolated from a culture of Stenotrophomonas maltophilia QB-77

Two new pyrazinoquinazoline alkaloids, epi-fiscalin D (1) and epi-fiscalin E (2), as well as three known analogues, norquinadoline A (3), quinadoline A (4), and fiscalin C (5), were isolated from ethyl acetate extract of the fermentation broth of Stentrophomonas maltophilia QB-77. The structures of new compounds were elucidated on the basis of extensive spectroscopic data analysis including UV, HRESIMS, and 1D and 2D NMR experiments. All the isolated compounds were tested for their in vitro cytotoxicity against five human cancer cell lines (SMMC-7721, MCF-7, HL-60, SW480, and A-549) and antibacterial activities against Bacillus subtilis, Escherichia coli, and Staphylococcus aureus.

Antibacterial Indole Alkaloids with Complex Heterocycles from Voacanga africana

Voacafricines A and B, two unique monoterpenoid indole alkaloids each bearing five fused heterocycles, were obtained from the fruits of Voacanga africana. Their structures were elucidated by extensive spectroscopic methods and computational studies. A plausible biogenetic pathway was proposed from a common precursor, 19- epi-voacristine. Both compounds exhibited potent activity against Staphylococcus aureus and Salmonella typhi, and their activities were superior to those of the well-known antibacterial drugs berberine and fibrauretine.

Cytotoxic monoterpenoid indole alkaloids from Alstonia yunnanensis Diels

The ethanol extract of the aerial parts of Alstonia yunnanensis Diels afforded five new monoterpenoid indole alkaloids, alstiyunnanenines A-E (1-5), along with one known compound, alstoniascholarine I (6). The structures of the isolated compounds were established based on 1D and 2D (¹H-¹H COSY, HMQC, and HMBC) NMR spectroscopy, in addition to high resolution mass spectrometry. The isolated compounds were tested in vitro for cytotoxic potential using eight tumor cell lines. As a result, alkaloids 4-6 exhibited cytotoxicities against all tested tumor cell lines, especially against osteosarcoma cell lines (SOSP-9607, MG-63, Saos-2, M663) with IC₅₀ values<6μM.

Indole Glycosides from Aqueous Fraction of Strychnos nitida

Three new indole glycosides 22-deoxystrictosamide (1), 22-deoxystrictosamide N b-oxide (2) and vincosamide 2'-O-β-D-xylopyranoside-11-O-β-D-glucopyranoside (3), together with four known analogues were isolated from aqueous fraction of Strychnos nitida. Their structures were elucidated on the basis of extensive analysis of spectroscopic data. All the alkaloids were tested for their cytotoxic activity, but they did not show any exciting result.

Catalytic Asymmetric Total Synthesis of (-)-Actinophyllic Acid

Described herein is a catalytic asymmetric total synthesis of (-)-actinophyllic acid, with the key step being a chiral phosphine-catalyzed [3 + 2] annulation between an imine and an allenoate to form a pyrroline intermediate in 99% yield and 94% ee. The synthesis also features CuI-catalyzed coupling between a ketoester and a 2-iodoindole to shape the tetrahydroazocine ring; intramolecular alkylative lactonization; SmI2-mediated intramolecular pinacol coupling between ketone and lactone subunits to assemble the complex skeleton of (-)-actinophyllic acid; and an unprecedented regioselective dehydroxylation.

Alstoscholarisines H-J, Indole Alkaloids from Alstonia scholaris: Structural Evaluation and Bioinspired Synthesis of Alstoscholarisine H

Alstoscholarisines H-J (1-3), new monoterpenoid indole alkaloids with an unprecedented skeleton created via the formation of a C-3/N-1 bond, were isolated from Alstonia scholaris. Their structures were established by extensive spectroscopic analyses and the assessment of single-crystal X-ray diffraction data. The total synthesis of alstoscholarisine H was achieved via the regioselective nucleophilic addition of pyridinium through a bioinspired iminium ion intermediate followed by Pictet-Spengler-like cyclization.

Gold-catalyzed formation of indole derivatives from 2-alkynyl arylazides and oxygen-containing heterocycles

Gold-catalyzed ring-opening reactions of oxygen-containing heterocycles.

Catalytic synthesis and antimicrobial activity of N-(3-chloro-2-oxo-4-phenylazetidin-1-yl)-4-(1H-indol-3-yl)-6-methyl-2-thioxo-1,2,3,4-tetrahydropyrimidine-5-carboxamides

In continuation of our work towards synthesizing bio-active molecules we developed and optimized the methodology for novel

Monoterpenoid Indole Alkaloids from Inadequately Dried Leaves of Alstonia scholaris

Six new indole alkaloids, named alstoniascholarines L-Q (1-6), together with nineteen known analogues were isolated from the inadequately dried leaves of Alstonia scholaris. Their structures were elucidated on the basis of extensive analysis of spectroscopic data and by comparison of their physical and spectroscopic data with the literature values. In addition, the new alkaloids were tested for their cytotoxic and neurite outgrowth-promoting activities.