Peganumine A, a β-carboline dimer with a new octacyclic scaffold from Peganum harmala

Bioinspired total synthesis and biological activity of Pegaharine A

BACKGROUND

Phytopathogens cause various diseases by parasitizing crops, reducing crop yield and resulting in substantial economic losses in agricultural production. A novel type isolated from the perennial herbaceous Peganum harmala L. seeds, β-carboline alkaloids pegaharine A (PA), has become a hot topic in developing plant-originated green pesticides owing to their significant physiological activities.

RESULTS

A scalable bioinspired total synthesis of PA is accomplished in the present work. The systematical biological assay study showed that PA exhibited moderate inhibitory activity against nine tested plant pathogenic fungi and showed significant inhibitory activity in vitro against the three tested plant pathogenic bacteria. Most noteworthy is the inhibitory rates of PA on Xanthomonas oryzae pv. oryzae (Xoo), X. oryzae pv. oryzicola (Xoc) and X. axonopodis pv. citri (Xac) of 93.6%, 92.1% and 86.1%, respectively, which are better than the control drug, bismerthiazol (63.4%, 61.2% and 53.7% at 100 μg mL-1 concentration). Furthermore, the EC50 value of PA against Xoo, Xoc and Xac was 52.2, 60.0 and 65.1 μg mL-1 , respectively, superior to 72.9, 64.2 and 70.1 μg mL-1 of the control drug. Moreover, the anti-Xoo mechanistic studies revealed that PA exerted its antibacterial effects by increasing the permeability of the bacterial membrane, reducing the extracellular polysaccharide content and inducing morphological changes in bacterial cells.

CONCLUSION

A novel β-carboline alkaloid, PA, was prepared by biomimetic total synthesis. Its significant antibacterial activity was closely related to the permeation of bacterial cell membranes, which was confirmed by anti-Xoo mechanistic studies. More importantly, the structure could be regarded as a model for developing novel bactericides. © 2023 Society of Chemical Industry.

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.

Recent developments in the total synthesis of natural products using the Ugi multicomponent reactions as the key strategy

The total syntheses of selected natural products using different versions of the Ugi multicomponent reaction is reviewed on a case-by-case basis. The revision covers the period 2008-2023 and includes detailed descriptions of the synthetic sequences, the use of state-of-the-art chemical reagents and strategies, as well as the advantages and limitations of the transformation and some remedial solutions. Relevant data on the isolation and bioactivity of the different natural targets are also briefly provided. The examples clearly evidence the strategic importance of this transformation and its key role in the modern natural products synthetic chemistry toolbox. This methodology proved to be a valuable means for easily building molecular complexity and efficiently delivering step-economic syntheses even of intricate structures, with a promising future.

Alkaloid diversity expansion of a talent fungus Penicillium raistrichii through OSMAC-based cultivation

Introduction

Alkaloidal natural products are attractive for their broad spectrum of pharmaceutical bioactivities. In the present work, the highly productive saline soil derived fungus, Penicillium raistrichii, was subjected to the strategy of OSMAC (one strain many compounds) with changes of cultivation status. Then, the work-flow led to the expansion of the alkaloid chemical diversity and subsequently induced the accumulation of four undescribed alkaloids, named raistrimides A-D (1-4), including three β-carbolines (1-3), one 2-quinolinone (4), and one new natural product, 2-quinolinone (5), along with five known alkaloid chemicals (6-10).

Methods

A set of NMR techniques including 1H, 13C, HSQC and HMBC, along with other spectroscopic data of UV-Vis, IR and HRESIMS, were introduced to assign the plain structures of compounds 1-10. The absolute configuration of 1-3 were elucidated by means of X-ray crystallography or spectroscopic analyses on optical rotation values and experimental electronic circular dichroism (ECD) data. In addition, it was the first report on the confirmation of structures of 6, 7 and 9 by X-ray crystallography data. The micro-broth dilution method was applied to evaluate antimicrobial effect of all compounds towards Staphylococcus aureus, Escherichia coli, and Candida albicans.

Results and discussion

The results indicated compounds 1, 3 and 4 to be bioactive, which may be potential for further development of anti-antimicrobial agents. The finding in this work implied that OSMAC strategy was a powerful and effective tool for promotion of new chemical entities from P. raistrichii.

Inspired by bis-β-carboline alkaloids: Construction and antitumor evaluation of a novel bis-β-carboline scaffold as potent antitumor agents

Bis-β-carboline alkaloids are widely distributed in natural products and represent a promising drug-like scaffold for discovering drugs and bioactive molecules. In this study, we utilized the structural simplification strategy to construct a novel bis-β-carboline scaffold via "one-pot" condensation-Mannich reaction. The simplified bis-β-carboline derivatives were obtained in good yield. Antitumor evaluation revealed most compounds, especially 3m, displayed potent antitumor activity (IC₅₀ values for 3m: 0.96 μM ∼ 1.52 μM). More importantly, 3m displayed valuable antitumor properties including anti-migration and anti-invasion activity against cancer cells, antiangiogenic and vascular-disrupting properties. Mechanistic studies revealed 3m potently inhibited both Top1 and Top2 activity, thus interfering with DNA synthesis in cancer cells. Taken together, this study developed a new synthetic methodology to construct a novel bis-β-carboline scaffold, which represents a promising lead structure for antitumor drug discovery.

Therapeutic significance of molecular hybrids for breast cancer research and treatment

Worldwide, breast cancer is still a leading cause of cancer death in women. Indeed, over the years, several anti-breast cancer drugs have been developed; however, the complex heterogeneous nature of breast cancer disease reduces the applicability of conventional targeted therapies with the upsurge in side effects and multi-drug resistance. Molecular hybrids generated by a combination of two or more active pharmacophores emerged as a promising approach in recent years for the design and synthesis of anti-breast cancer drugs. The hybrid anti-breast cancer molecules are well known for their several advantages compared to the parent moiety. These hybrid forms of anti-breast cancer molecules demonstrated remarkable effects in blocking different pathways contributing to the pathogenies of breast cancer and improved specificity. In addition, these hybrids are patient compliant with reduced side effects and multi-drug resistance. The literature revealed that molecular hybrids are applied to discover and develop novel hybrids for various complex diseases. This review article highlights the recent progress (∼2018-2022) in developing molecular hybrids, including linked, merged, and fused hybrids, as promising anti-breast cancer agents. Furthermore, their design principles, biological potential, and future perspective are discussed. The provided information will lead to the development of novel anti-breast cancer hybrids with excellent pharmacological profiles in the future.

Antitumor potential of tricyclic pyridone analogues from an entomopathogenic fungus, Fusarium avenaceum SYKC02-P-1

Two new tricyclic pyridone analogues, fusapyridons C (1) and D (2), were isolated along with structurally related known compounds 3 - 5 from the entomopathogenic fungus, F. avenaceum SYKC02-P-1. The structures of compounds 1 and 2 were elucidated by analyzing the spectral data of UV, 1 D and 2 D NMR as well as HRESIMS. The absolute configurations of fusapyridons C and D were established by means of single crystal X-ray diffraction and electronic circular dichroism calculation. And antitumor testing of all the isolates showed that compounds 4 and 5 exhibited significant inhibitory activity against the human prostate cancer cells (PC-3 cell lines) with IC₅₀ values of 2.76 and 1.86 μM, respectively.

Catalytic Enantioselective Pictet-Spengler Reaction of α-Ketoamides Catalyzed by a Single H-Bond Donor Organocatalyst

The asymmetric Pictet–Spengler reaction (PSR) with aldehydes is well known. However, PSR involving ketones as electrophilic partners is far‐less developed. We report herein the first examples of catalytic enantioselective PSR of tryptamines with α‐ketoamides. A new class of easily accessible prolyl‐urea organocatalysts bearing a single H‐bond donor function catalyzes the title reaction to afford 1,1‐disubstituted tetrahydro‐β‐carbolines in excellent yields and enantioselectivities. The kinetic isotope effect using C2‐deuterium‐labelled tryptamine indicates that the rearomatization of the pentahydro‐β‐carbolinium ion intermediate might be the rate‐ and the enantioselectivity‐determining step.

Chemical Constituents of the Aerial Part of Valeriana officinalis var. latifolia Miq. With COX-2 Inhibitory Activity

Twelve compounds, including a new iridoid (1) and 11 known compounds, were obtained from the aerial part of Valeriana officinalis var. latifolia Miq. Their structures were assigned by spectroscopic and mass spectrometric methods. All isolates were screened in vitro for cyclooxygenase-2 (COX-2) inhibitory activity. Two compounds (9 and 10) exhibited significant COX-2 inhibitory activity, with IC50 values ranging from 0.67 to 6.77 μM. The possible recognition mechanism between compound 9 and COX-2 was predicted by molecular docking analysis.

(±)-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.

Recent applications of asymmetric organocatalytic annulation reactions in natural product synthesis

The past two decades have witnessed remarkable growth of asymmetric organocatalysis, which is now a firmly established synthetic tool, serving as a powerful platform for the production of chiral molecules. Ring structures are ubiquitous in organic compounds, and, in the context of natural product synthesis, strategic construction of ring motifs is often crucial, fundamentally impacting the eventual fate of the whole synthetic plan. In this review, we provide a comprehensive and updated summary of asymmetric organocatalytic annulation reactions; in particular, the application of these annulation strategies in natural product synthesis will be highlighted.

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.

Unified Synthesis of Polycyclic Alkaloids by Complementary Carbonyl Activation*

A complementary dual carbonyl activation strategy for the synthesis of polycyclic alkaloids has been developed. Successful applications include the synthesis of tetracyclic alkaloids harmalanine and harmalacinine, pentacyclic indoloquinolizidine alkaloid nortetoyobyrine, and octacyclic β-carboline alkaloid peganumine A. The latter synthesis features a protecting-group-free assembly and an asymmetric disulfonimide-catalyzed cyclization. Furthermore, formal syntheses of hirsutine, deplancheine, 10-desbromoarborescidine A, and oxindole alkaloids rhynchophylline and isorhynchophylline have been achieved. Finally, a concise synthesis of berberine alkaloid ilicifoline B was completed.

Alkaloids of Peganum harmala: Anticancer Biomarkers with Promising Outcomes

BACKGROUND

Cancer is a serious and growing global health issue worldwide. In the cancerous cells, the normal cell cycle has been disrupted via a series of irreversible changes. Recently, the investigations on herbal medicine and clarifying the phytochemicals potential in treat cancer has been increased. The combination of phytochemicals with conventional cancer treatment approaches can improve outcomes via advancing cell death, restraining cell proliferation and invasion, sensitizing cancerous cells, and promoting the immune system. Therefore, phytochemicals can be introduced as relevant complementary medicaments in cancer therapy. Peganum harmala L. (Zygophyllaceae) as a valuable medicinal herb, possesses various alkaloid ingredient.

OBJECTIVE

Pointing to the importance of new avenues for cancer management and P. harmala convincing effect in this field, this review strived to collect a frame to epitome possible scopes to develop novel medicines in cancer treatment.

METHODS

Keywords "Peganum harmala" and cancer, or chemotherapy, or anti-neoplasm were searched through the "Scopus" database up to 29th of February 2020. Papers linking to agriculture, chemistry, environmental, and genetics sciences were omitted and, papers centered on cancer were selected.

RESULTS AND DISCUSSION

In the current study, 42 related papers to cancer treatment and 22 papers on alkaloid bioactive components are collected from 72 papers. The β-carboline alkaloids derived from P. harmala, especially harmine, demonstrate notable anticancer properties by targeting apoptosis, autophagy, abnormal cell proliferation, angiogenesis, metastasis, and cytotoxicity. Based on the collected information, P. harmala holds significant anticancer activity. Considering the mechanism of the various anticancer drugs and their acting similarity to P. harmala, the alkaloids derived from this herb, particularly harmine, can introduce as a novel anticancer medicine solely or in adjuvant cancer therapy.

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.

Design, Synthesis, Antiproliferative Evaluation, and Molecular Docking Studies of N-(3-Hydroxyindole)-Appended β-Carbolines/Tetrahydro-β-Carbolines Targeting Triple-Negative and Non-Triple-Negative Breast Cancer

The present manuscript pertains to the design and synthesis of a series of 3-hydroxyindole-substituted β-carbolines/tetrahydro-β-carbolines with an aim to explore their antiproliferative structure-activity relationship against breast cancer. The conjugate with an optimum combination of a flexible tetrahydro-β-carboline core, a tertiary alcoholic group along with a chloro substituent on the indole ring, proved to be the most active compound. It displayed IC50 values of 13.61 and 22.76 μM against MCF-7 (ER+) and MDA-MB-231 (ER-) cells, respectively. The docking studies were found to be consistent with experimental results owing to the stronger binding affinity of the synthesized conjugates via hydrophobic and H-bonding interactions.

β-Carboline Alkaloids from the Seeds of Peganum harmala and Their Anti-HSV-2 Virus Activities

Pegaharines A-G (1-6), six novel β-carboline alkaloids representing three types of skeleton, were isolated from the seeds of Peganum harmala. Compound 1 is a peculiar β-carboline alkaloid characterized by the unprecedented carbon skeleton of an azepine-indole system. Compounds 3-6 represent the first examples of heterodimers constructed from rare tetracyclic β-carboline and classic tricyclic β-carboline alkaloids. Compounds 1 and 2 were characterized by X-ray crystallography. Compound 4 exhibited strong antiviral activity against HSV-2, with an IC₅₀ value of 2.12 ± 0.14 μM.

Norcolocynthenins A and B, two cucurbitane 3-nor-Triterpenoids from Citrullus colocynthis and their cytotoxicity

Two novel cucurbitane 3-nor-triterpenoids, named norcolocynthenins A (1) and B (2), were isolated from the fruits of Citrullus colocynthis. The structures including their absolute configurations were determined by extensive spectroscopic analyses and theoretical calculations. Compound 1 features an unprecedented 5/6/6/5-fused ring system while compound 2 possesses a rare lactone moiety at modified ring A. Compounds 1 and 2 showed significant cytotoxic activity against human cancer cell lines of HL-60 (IC₅₀ = 8.32, 6.49 μM) and PC-3 (IC₅₀ = 31.26, 13.42 μM). The plausible biosynthetic pathway of compounds 1 and 2 via a key enzymatic Baeyer-Villiger reaction is proposed.

Triterpenoids with anti-proliferative effects from the seeds of Peganum harmala L

Three undescribed lupane-type triterpenoids (1-3), three undescribed oleanane-type triterpenoids (4-6), and ten known pentacyclic triterpenoids (7-16) were isolated from the seeds of Peganum harmala L. (Zygophyllaceae). Their structures were elucidated using various spectroscopic methods (IR, HR-ESI-MS, 1D, and 2D NMR). All the triterpenoids were screened for anti-proliferative activity against HeLa, HepG2, and SGC-7901 cells using the MTT method. Except compounds 1, 2, and 13, all the other triterpenoids exhibited potent cytotoxic activities against tumour cells. Compounds 3, 6, and 15 inhibited the proliferation of HeLa cells in a dose-dependent manner, as observed by the colony formation assay. When HeLa cells were treated with different doses of compounds 3, 6, and 15, the cell nuclei changed shape to a crescent form and were condensed and fragmented, as observed by Hoechst 33258 staining. Additionally, these three triterpenoids induced the apoptosis in HeLa cells, which was detected by Western blot analysis.

Recent applications of the Wittig reaction in alkaloid synthesis

The Wittig reaction is the chemical reaction of an aldehyde or ketone with a triphenyl phosphonium ylide (the Wittig reagent) to afford an alkene and triphenylphosphine oxide. Noteworthy, this reaction results in the synthesis of alkenes in a selective and predictable fashion. Thus, it became as one of the keystone of synthetic organic chemistry, especially in the total synthesis of natural products, where the selectivity of a reaction is paramount of importance. A literature survey disclosed the existence of vast numbers of related reports and comprehensive reviews on the applications of this important name reaction in the total synthesis of natural products. However, the aim of this chapter is to underscore, the applications of the Wittig reaction in the total synthesis of one the most important and prevalent classes of natural products, the alkaloids, especially those showing important and diverse biological activities.

The base-free van Leusen reaction of cyclic imines on water: synthesis of N-fused imidazo 6,11-dihydro β-carboline derivatives

Construction of imidazoles has been demonstrated on water under base-free conditions. The reaction of dihydro β-carboline imines and p-toluenesulfonylmethyl isocyanides furnished the corresponding substituted N-fused imidazo 6,11-dihydro β-carboline derivatives in very good yields under ambient conditions. The use of deuterium oxide (D2O) as a solvent enabled the incorporation of deuterium isotopes in the imidazole ring.

IBX-mediated oxidative addition of isocyanides to cyclic secondary amines: total syntheses of alangiobussine and alangiobussinine

The present study describes a robust and general method for the synthesis of C(1)-carboxamides through IBX-mediated oxidative addition of isocyanides to tryptolines and 1,2,3,4-tetrahydroisoquinolines. In this transformation, IBX plays a dual role of an oxidant and Lewis acid to activate imine facilitating isocyanide addition. Detailed mechanistic investigations were performed by isotopic labeling and real-time NMR experiments. The method was utilized for the gram scale syntheses of two alkaloids alangiobussine and alangiobussinine in 63% and 45% overall yield, respectively.

Enantiomeric β-carboline dimers from Picrasma quassioides and their anti-hepatoma potential

Four pairs of enantiomeric β-carboline alkaloids, (+/-)-kumudine A-D, along with their biosynthesis-related compound kumudine E, were obtained from the stems of Picrasma quassioides. Their structures, including the absolute configurations, were determined via extensive spectroscopic data combined with electronic circular dichroism (ECD) spectroscopic analyses and quantum mechanical ECD calculations. (+/-)-Kumudine A possessed a scaffold of β-carboline-phenylpropanoid adduct, which were the first examples of this type of β-carboline alkaloid from nature. The cytotoxicity assay against hepatocellular carcinoma Hep3B and HepG2 cells was evaluated by SRB assay, which showed that (-)-Kumudine B had stronger effect than its enantiomer (+)-Kumudine B in Hep3B cells. Moreover, further flow cytometry analysis also supported the enantioselectivity between (+)-Kumudine B and (-)-Kumudine B, suggesting that the compounds caused death of hepatoma cells through apoptosis induction.

An AcOH-mediated metal free approach towards the synthesis of bis-carbolines and imidazopyridoindole derivatives and assessment of their photophysical properties

A concise, atom-economical and environmentally sustainable tandem strategy has been formulated to access highly fluorescent (Φ_F up to 40%) target molecules via the formation of three C–N bonds in a single operation.

2,7-Diazabicyclo[2.2.1]heptanes: novel asymmetric access and controlled bridge-opening

Organocatalysed asymmetric Michael additions of substituted triketopiperazines to enones afford products in high yield and enantiomeric ratio (er). Further modification delivers products possessing natural product (NP) scaffolds including diazabicyclo[2.2.1]heptane, prolinamide and harmicine.

Diastereoselective approach to rationally design tetrahydro-β-carboline–isatin conjugates as potential SERMs against breast cancer

A series of tetrahydro-β-carboline–isatin conjugates, with varying substituents as well as stereochemistry at C-1 and C-5 position of tetrahydro-β-carboline (THβC) and isatin ring, were prepared and assayed for anti-proliferative efficacy on Estrogen Responsive ER(+) (MCF-7) and ER(−ve) MDA-MB-231 cell-lines. The synthesized scaffolds displayed selective anti-proliferative efficacy against MCF-7 cell-line with the most active conjugate 8b exhibiting an IC₅₀ value of 37.42 μM, comparable to that of peganumine A, a tetrahydro-β-carboline analogue, isolated from Peganum harmala. The synthesized compound 8b was also more potent than the standard drug tamoxifen (IC₅₀ = 50 μM against MCF-7). The observed activities were further corroborated via docking studies in ER-α (PDB ID: 3ERT).

A series of tetrahydro-β-carboline–isatin conjugates was prepared and assayed for anti-proliferative activities on Estrogen Responsive ER(+) and non-responsive ER(−ve) cell-lines.

Application of the Asymmetric Pictet-Spengler Reaction in the Total Synthesis of Natural Products and Relevant Biologically Active Compounds

Tetrahydroisoquinolines are the framework of numerous natural products predominantly alkaloids, an important and one of the most wide spread families of naturally occurring compounds in the plant kingdom. Tetrahydroisoquinolines are commonly constructed through an old reaction, the so-called Pictet−Spengler Reaction (PSR). In this reaction, a β-aryl ethylamine undergoes an acid mediated condensation with a suitable aldehyde or ketone, followed by ring closure. In this review, we aim to highlight the applications of the asymmetric variant of this old name reaction in the total synthesis of natural products, chiefly, alkaloids, which exhibit significant biological properties.

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 C-H Oxidation/Two-Fold Cyclization Approach to Imidazopyridoindole Scaffold under Mild Oxidizing Conditions

An expeditious one-step synthesis of the imidazopyridoindole scaffold was achieved through the C-H oxidation/two-fold cyclization reaction of methyl ketone and tryptamine derivatives. Mild oxidizing conditions were employed to realize the efficient oxidation of C(sp³)-H bonds, while suppressing overoxidation of the intermediate and ensuring the cross-trapping of two in situ generated acylimine intermediates.

A new polyketide glycoside from the rhizospheric Clonostachys rogersoniana associated with Panax notoginseng

A new polyketide glycoside rogerson A (1), along with two known compounds, rogerson B (2) and (22E)-5α,8α-epidioxyergosta-6,22-dien-3β-ol (3), was obtained from the solid fermentation of Clonostachys rogersoniana, which was isolated from the rhizosphere soil of Panax notoginseng. Rogerson B (2) was isolated for the first time from a natural source. Their structure was determined by extensive analyses of NMR and MS studies. Compounds 1 and 2 were tested for its cytotoxicity against five human cancer cell lines.