β-Carboline alkaloids from the roots of Peganum harmala L

This study reports the isolation of four new β-carboline alkaloids (1-4) and six previously identified alkaloids (5-10) from the roots of Peganum harmala L. Among these compounds, 1 and 2 were characterized as rare β-carboline-quinazoline dimers exhibiting axial chirality. Compound 3 possessed a unique 6/5/6/7 tetracyclic ring system with an azepine ring, and compound 4 was a novel annomontine β-carboline. The structures of these compounds were elucidated by spectroscopic data and quantum mechanical calculations. The biosynthetic pathways of 1-3 were proposed. Additionally, the cytotoxicity of some isolates against four cancer cell lines (HL-60, A549, MDA-MB-231, and DU145) was evaluated. Notably, compound 4 exhibited significant cytotoxicity against HL-60, A549, and DU145 cells with IC50 values of 12.39, 12.80, and 30.65 μmol·L-1, respectively. Furthermore, compound 2 demonstrated selective cytotoxicity against HL-60 cells with an IC50 value of 17.32 μmol·L-1.

Progress toward a biomimetic synthesis of pegaharmaline A

Efforts towards a biomimetic synthesis of the alkaloid pegaharmaline A began with attempted validation of the putative biosynthesis described in the isolation report. The reaction between vasicinone-derived pyrroloquinazoline 1 and tryptamines 2 and 9 proceeded under aqueous conditions at ambient temperature, forming the 1,6,10-triazaspiro[4.5]dec-7-anes 7 and 8. Alternative pyrroloquinazoline precursors were subsequently investigated; the reaction between dehydrodimethylisovasicinone (10) and tryptamine (9) led to the ring-opened product 13 that could not be converted into pegaharmaline A scaffold under Bischler-Napieralski conditions. The Pictet-Spengler reaction between a model isovasicinone (22) and tryptamine (9) was successful, but the resulting tetrahydro-β-carboline could not be converted into the natural product. These studies suggest an alternative biosynthetic pathway is potentially operating, while structural revision of the natural product cannot be ruled out at this time. As vasicinones and tryptamines are widely distributed throughout Nature, the novel scaffolds reported herein may be undiscovered natural products.

(±)-Pheharmines A–B, two pairs of racemic alkaloids with a morpholino[4,3,2-hi]β-carboline core, from the roots of Peganum harmala

Two pairs of unprecedented β-carboline-phenylpropanoid alkaloids, (±)-pheharmines A–B (1–4), characterized by a morpholino[4,3,2-hi]β-carboline core with two chiral centers, were isolated from the roots of Peganum harmala.

Pseudosterins A-C, Three 1-Ethyl-3-formyl-β-carbolines from Pseudostellaria heterophylla and Their Cardioprotective Effects

Pseudostellaria heterophylla is used in China not only as a functional food but also as an herb to tonify the spleen, enhance immunity, and treat palpitation. Our previous investigation showed that a fraction enriched in glycosides obtained from the roots of P. heterophylla possessed pronounced protective effects on H9c2 cells against CoCl₂-induced hypoxic injury. However, the active compounds responsible for the observed effects were still unknown. In the current investigation, pseudosterins A–C (1–3), three new alkaloids with a 1-ethyl-3-formyl-β-carboline skeleton, together with polydatin, have been isolated from the active fraction. Their structures were elucidated on the basis of spectroscopic analysis and quantum chemical calculations. The four compounds showed cardioprotective effects against sodium hydrosulfite-induced hypoxia-reoxygenation injury in H9c2 cells, with the three alkaloids being more potent. This is also the first report of alkaloids with a β-carboline skeleton isolated from P. heterophylla as cardioprotective agents.

A comprehensive overview of β-carbolines and its derivatives as anticancer agents

β-Carboline alkaloids are a family of natural and synthetic products with structural diversity and outstanding antitumor activities. This review summarizes research developments of β-carboline and its derivatives as anticancer agents, which focused on both natural and synthetic monomers as well as dimers. In addition, the structure-activity relationship (SAR) analysis of β-carboline monomers and dimers are summarized and mechanism of action of β-carboline and its derivatives are also presented. A few possible research directions, suggestions and clues for future work on the development of novel β-carboline-based anticancer agents with improved expected activities and lesser toxicity are also provided.

Peganum spp.: A Comprehensive Review on Bioactivities and Health-Enhancing Effects and Their Potential for the Formulation of Functional Foods and Pharmaceutical Drugs

The genus Peganum includes four species widely distributed in warm temperate to subtropical regions from the Mediterranean to Mongolia as well as certain regions in America. Among these species, Peganum harmala L., distributed from the Mediterranean region to Central Asia, has been studied and its phytochemical profile, traditional folk use, and application in pharmacological and clinical trials are well known. The review is aimed at presenting an insight into the botanical features and geographical distribution of Peganum spp. along with traditional folk uses. This manuscript also reviews the phytochemical profile of Peganum spp. and its correlation with biological activities evidenced by the in vitro and in vivo investigations. Moreover, this review gives us an understanding of the bioactive compounds from Peganum as health promoters followed by the safety and adverse effects on human health. In relation to their multipurpose therapeutic properties, various parts of this plant such as seeds, bark, and roots present bioactive compounds promoting health benefits. An updated search (until December 2020) was carried out in databases such as PubMed and ScienceDirect. Chemical studies have presented beta-carboline alkaloids as the most active constituents, with harmalol, harmaline, and harmine being the latest and most studied among these naturally occurring alkaloids. The Peganum spp. extracts have shown neuroprotective, anticancer, antimicrobial, and antiviral effects. The extracts are also found effective in improving respiratory disorders (asthma and cough conditions), dermatoses, and knee osteoarthritis. Bioactivities and health-enhancing effects of Peganum spp. make it a potential candidate for the formulation of functional foods and pharmaceutical drugs. Nevertheless, adverse effects of this plant have also been described, and therefore new bioproducts need to be studied in depth. In fact, the design of new formulations and nanoformulations to control the release of active compounds will be necessary to achieve successful pharmacological and therapeutic treatments.

β-Carbolines as potential anticancer agents

β-Carbolines are indole alkaloids having a tricyclic pyrido[3,4-b]indole ring in their structure. Since the isolation of first β-carboline from Peganum harmala in 1841, the isolation and synthesis of various β-carboline derivatives surged in the following centuries. β-Carboline derivatives due to their widespread availability from natural sources, structural flexibility, quick reactivity and interaction with varied anticancer targets such as DNA (intercalation, groove binding, etc.), enzymes (GPX4, topoisomerases, kinases, etc.) and proteins (tubulin, ABCG2/BRCP1, etc.) have established themselves as promising lead compounds for the synthesis of various anticancer active agents. The current review covers the synthesis and isolation, anticancer activity, mechanism of action and SAR of various β-carboline containing molecules, its derivatives and congeners.

Racemic indole alkaloids from the seeds of Peganum harmala

Five pairs of new 2-oxoindole alkaloids, (±)-peganumalines A-E (1-5), and a new indole alkaloid, peganumaline F (6), along with two known analogues, were isolated from the seeds of Peganum harmala. Their structures and absolute configurations were elucidated through spectroscopic analyses and quantum chemistry calculations. Notably, (±)-peganumalines A (1) represent a pair of rare 2-oxoindole dimeric alkaloid enantiomer with the hitherto unknown carbon skeleton. All isolates were tested for antiproliferative and antibacterial activities.

A review on traditional uses, phytochemistry, pharmacology, pharmacokinetics and toxicology of the genus Peganum

ETHNOPHARMACOLOGICAL RELEVANCE

The plants of the genus Peganum have a long history as a Chinese traditional medicine for the treatment of cough, hypertension, diabetes, asthma, jaundice, colic, lumbago, and many other human ailments. Additionally, the plants can be used as an amulet against evil-eye, dye and so on, which have become increasingly popular in Asia, Iran, Northwest India, and North Africa.

AIM OF THE REVIEW

The present paper reviewed the ethnopharmacology, phytochemistry, analytical methods, biological activities, metabolism, pharmacokinetics, toxicology, and drug interaction of the genus Peganum in order to assess the ethnopharmacological use and to explore therapeutic potentials and future opportunities for research.

MATERIALS AND METHODS

Information on studies of the genus Peganum was gathered via the Internet (using Google Scholar, Baidu Scholar, Elsevier, ACS, Pudmed, Web of Science, CNKI and EMBASE) and libraries. Additionally, information was also obtained from some local books, PhD and MS's dissertations.

RESULTS

The genus Peganum has played an important role in traditional Chinese medicine. The main bioactive metabolites of the genus include alkaloids, flavonoids, volatile oils, etc. Scientific studies on extracts and formulations revealed a wide range of pharmacological activities, such as cholinesterase and monoamine oxidase inhibitory activities, antitumor, anti-hypertension, anticoagulant, antidiabetic, antimicrobial, insecticidal, antiparasidal, anti-leishmaniasis, antioxidant, and anti-inflammatory.

CONCLUSIONS

Based on this review, there is some evidence for extracts' pharmacological effects on Alzheimer's and Parkinson's diseases, cancer, diabetes, hypertension. Some indications from ethnomedicine have been confirmed by pharmacological effects, such as the cholinesterase, monoamine oxidase and DNA topoisomerase inhibitory activities, hypoglycemic and vasodilation effects of this genus. The available literature showed that most of the activities of the genus Peganum can be attributed to the active alkaloids. Data regarding many aspects of the genus such as mechanisms of actions, metabolism, pharmacokinetics, toxicology, potential drug interactions with standard-of-care medications is still limited which call for additional studies particularly in humans. Further assessments and clinical trials should be performed before it can be integrated into medicinal practices.

Structurally Diverse Alkaloids from the Seeds of Peganum harmala

Investigation of the alkaloids from Peganum harmala seeds yielded two pairs of unique racemic pyrroloindole alkaloids, (±)-peganines A-B (1-2); two rare thiazole derivatives, peganumals A-B (3-4); six new β-carboline alkaloids, pegaharmines F-K (5-10); and 12 known analogues. Their structures, including stereochemistry, were elucidated through spectroscopic analyses, quantum chemistry calculations, and single-crystal X-ray diffraction. Notably, the incorporation of pyrrole and indole moieties in peganines A-B, thiazole fragments in peganumals A-B, and a C-1 α,β-unsaturated ester motif in pegaharmine F (5) are all rare, and their presence in the genus Peganum were demonstrated for the first time. All isolates were tested for antiproliferative activities against the HL-60, PC-3, and SGC-7901 cancer cell lines, and compounds 9, 11, 12, and 13 exhibited moderate cytotoxicity against HL-60 cancer cell lines with IC₅₀ values in the range of 4.36-9.25 μM.

In(OTf)3 assisted synthesis of β-carboline C-3 tethered imidazo[1,2-a]azine derivatives

Synthesis of β-carboline based natural products and synthetic derivatives is one of the frontier areas of research owing to their medicinal properties.

A Series of β-Carboline Alkaloids from the Seeds of Peganum harmala Show G-Quadruplex Interactions

In this study, we screened 17 medicinal plants for binding activity to G-quadruplex d(TTGGGTT)4 by (1)H NMR spectroscopy and found that the crude extract of Peganum harmala L. seeds showed the most potential binding activity. Subsequently, (1)H NMR- and bioassay-guided isolation of the extract of P. harmala L. was performed to obtain four pairs of partially racemized β-carboline alkaloids, pegaharmines A-D (1-4). Their structures and absolute configurations were determined by extensive NMR analyses, X-ray crystallography, ECD calculations, and CD exciton chirality approaches. Interestingly, pegaharmine D (4), which showed the strongest G-quadruplex interaction, exhibited significant cytotoxic activity against three cancer cell lines. This work contributed a practical strategy for the discovery of novel G-quadruplex ligands from natural products and provided potential insights for using β-carboline alkaloids as anticancer lead compounds specifically targeting G-quadruplexes.

Synthesis of S-(-)-5,6-Dihydrocanthin-4-ones via a Triple Cooperative Catalysis-Mediated Domino Reaction

An enantioselective synthesis of S-(-)-5,6-dihydrocanthin-4-ones via a triple cooperative catalysis-mediated domino reaction having a broad substrate scope is reported. The reaction between substituted 1-formyl-9H-β-carbolines and terminal alkynes in the presence of catalytic amounts of Jorgensen-Hayashi catalyst, copper iodide, and Hunig base proceeded via a multicascade route, affording the title compounds in good yields and excellent ees with interesting mechanistic features. These compounds were assessed for in vitro antiplasmodial activity against P. falciparum strains. Additionally, 5,6-dihydrocanthin-4-ones are demonstrated to be a versatile precursor to different fused β-carboline derivatives via simple synthetic transformations.

Racemic alkaloids from Macleaya cordata: structural elucidation, chiral resolution, and cytotoxic, antibacterial activities

Three pairs of new enantiomeric natural alkaloids (±)-macleayins C-E (1–3), together with five pairs of known racemic alkaloids (4–8), were isolated from the aerial parts of Macleaya cordata.