Ancistrosecolines A-F, Unprecedented seco-Naphthylisoquinoline Alkaloids from the Roots of Ancistrocladus abbreviatus, with Apoptosis-Inducing Potential against HeLa Cancer Cells

Structural variety and pharmacological potential of naphthylisoquinoline alkaloids

Naphthylisoquinoline alkaloids are a fascinating class of natural biaryl compounds. They show characteristic mono- and dimeric scaffolds, with chiral axes and stereogenic centers. Since the appearance of the last comprehensive overview on these secondary plant metabolites in this series in 1995, the number of discovered representatives has tremendously increased to more than 280 examples known today. Many novel-type compounds have meanwhile been discovered, among them naphthylisoquinoline-related follow-up products like e.g., the first seco-type (i.e., ring-opened) and ring-contracted analogues. As highlighted in this review, the knowledge on the broad structural chemodiversity of naphthylisoquinoline alkaloids has been decisively driven forward by extensive phytochemical studies on the metabolite pattern of Ancistrocladus abbreviatus from Coastal West Africa, which is a particularly "creative" plant. These investigations furnished a considerable number of more than 80-mostly new-natural products from this single species, with promising antiplasmodial activities and with pronounced cytotoxic effects against human leukemia, pancreatic, cervical, and breast cancer cells. Another unique feature of naphthylisoquinoline alkaloids is their unprecedented biosynthetic origin from polyketidic precursors and not, as usual for isoquinoline alkaloids, from aromatic amino acids-a striking example of biosynthetic convergence in nature. Furthermore, remarkable botanical results are presented on the natural producers of naphthylisoquinoline alkaloids, the paleotropical Dioncophyllaceae and Ancistrocladaceae lianas, including first investigations on the chemoecological role of these plant metabolites and their storage and accumulation in particular plant organs.

Discovery of plant-derived anti-tumor natural products: Potential leads for anti-tumor drug discovery

Natural products represent a paramount source of novel drugs. Numerous plant-derived natural products have demonstrated potent anti-tumor properties, thereby garnering considerable interest in their potential as anti-tumor drugs. This review compiles an overview of 242 recently discovered natural products, spanning the period from 2018 to the present. These natural products, which include 69 terpenoids, 42 alkaloids, 39 flavonoids, 21 steroids, 14 phenylpropanoids, 5 quinolines and 52 other compounds, are characterized by their respective chemical structures, anti-tumor activities, and mechanisms of action. By providing an essential reference and fresh insights, this review aims to support and inspire researchers engaged in the fields of natural products and anti-tumor drug discovery.

New trends in the practical use of isoquinoline alkaloids as potential drugs applicated in infectious and non-infectious diseases

In the last years, traditional natural products have been the center of attention for the scientific community and exploration of their therapeutic abilities is proceeding permanently. Isoquinoline alkaloids have always attracted scientific interest due to either their positive or negative effects on human organism. The present review describes research on isoquinoline alkaloids isolated from different plant species. Alkaloids are one of the most important classes of plant derived compounds among these isoquinoline alkaloids possess varied biological activities such as anticancer, antineurodegenerative diseases, antidiabetic, antiinflammatory, antimicrobial, and many others. The use of plants against different disorders is entrenched in traditional medicine around the globe. Recent progress in modern therapeutics has stimulated the use of natural products worldwide for various ailments and diseases. The review provides a collection of information on the capabilities of some isoquinoline alkaloids, its potential for the treatment of various diseases and is designed to be a guide for future research on different biologically active isoquinoline alkaloids and plant species containing them. The authors are aware that they were not able to cover the whole area of the topic related to biological activity of isoquinoline alkaloids. This review is intended to suggest directions for further research and can also help other researchers in future studies.

Targeting Pancreatic Cancer with Novel Plumbagin Derivatives: Design, Synthesis, Molecular Mechanism, In Vitro and In Vivo Evaluation

Pancreatic tumors grow in an "austerity" tumor microenvironment characterized by nutrient deprivation and hypoxia. This leads to the activation of adaptive pathways in pancreatic cancer cells, promoting tolerance to nutrition starvation and aggressive malignancy. Conventional anticancer drugs are often ineffective against tumors that grow in such austerity condition. Plumbagin, a plant-derived naphthoquinone, has shown potent preferential cytotoxicity against pancreatic cancer cells under nutrient-deprived conditions. Therefore, we synthesized a series of plumbagin derivatives and found that 2-(cyclohexylmethyl)-plumbagin (3f) was the most promising compound with a PC₅₀ value of 0.11 μM. Mechanistically, 3f was found to inhibit the PI3K/Akt/mTOR signaling pathways, leading to cancer cell death under nutrient-deprived conditions. In vivo studies using pancreatic cancer xenograft mouse models confirmed the efficacy of 3f, demonstrating significant inhibition of tumor growth in a dose-dependent manner. Compound 3f represents a highly promising lead for anticancer drug development based on an antiausterity strategy.

Dioncophyllidine E: The first configurationally semi-stable, 7,3'-coupled naphthyldihydroisoquinoline alkaloid, from Ancistrocladus abbreviatus, with antiausterity activity against PANC-1 human pancreatic cancer cells

The discovery of a new naphthylisoquinoline alkaloid, dioncophyllidine E (4), from the tropical liana Ancistrocladus abbreviatus (Ancistrocladaceae) is described. Due to its rare 7,3'-coupling type, combined with the lack of an oxygen function at C-6, it is configurationally semi-stable at the biaryl axis, and thus occurs as a pair of slowly interconverting atropo-diastereomers, 4a and 4b. Its constitution was assigned mainly by 1D and 2D NMR. The absolute configuration at the stereocenter, C-3, was elucidated by oxidative degradation. The absolute axial configuration of the individual atropo-diastereomers was established by their HPLC resolution, combined with online electronic circular dichroism (ECD) investigations, providing nearly mirror-imaged LC-ECD spectra. These were assigned to the respective atropisomers by ECD comparison with a related, but configurationally stable alkaloid, ancistrocladidine (5). Dioncophyllidine E (4a/4b) exhibits a strong preferential cytotoxicity against PANC-1 human pancreatic cancer cells under nutrient-deprived conditions, with a PC₅₀ value of 7.4 µM, suggesting its potential as an agent against pancreatic cancer.

Korupensamine A, but not its atropisomer, korupensamine B, inhibits SARS-CoV-2 in vitro by targeting its main protease (Mpro)

By combining docking and molecular dynamics simulations, we explored a library of 65 mostly axially chiral naphthylisoquinoline alkaloids and their analogues, with most different molecular architectures and structural analogues, for their activity against SARS-CoV-2. Although natural biaryls are often regarded without consideration of their axial chirality, they can bind to protein targets in an atroposelective manner. By combining docking results with steered molecular dynamics simulations, we identified one alkaloid, korupensamine A, that atropisomer-specifically inhibited the main protease (M^pro) activity of SARS-CoV-2 significantly in comparison to the reference covalent inhibitor GC376 (IC₅₀ = 2.52 ± 0.14 and 0.88 ± 0.15 μM, respectively) and reduced viral growth by five orders of magnitude in vitro (EC₅₀ = 4.23 ± 1.31 μM). To investigate the binding pathway and mode of interaction of korupensamine A within the active site of the protease, we utilized Gaussian accelerated molecular dynamics simulations, which reproduced the docking pose of korupensamine A inside the active site of the enzyme. The study presents naphthylisoquinoline alkaloids as a new class of potential anti-COVID-19 agents.

Asian Ancistrocladus Lianas as Creative Producers of Naphthylisoquinoline Alkaloids

This book describes a unique class of secondary metabolites, the mono- and dimeric naphthylisoquinoline alkaloids. They occur in lianas of the paleotropical Ancistrocladaceae and Dioncophyllaceae families, exclusively. Their unprecedented structures include stereogenic centers and rotationally hindered, and thus likewise stereogenic, axes. Extended recent investigations on six Ancistrocladus species from Asia, as reported in this review, shed light on their fascinating phytochemical productivity, with over 100 such intriguing natural products. This high chemodiversity arises from a likewise unique biosynthesis from acetate-malonate units, following a novel polyketidic pathway to plant-derived isoquinoline alkaloids. Some of the compounds show most promising antiparasitic activities. Likewise presented are strategies for the regio- and stereoselective total synthesis of the alkaloids, including the directed construction of the chiral axis.

Naphthylisoindolinone alkaloids: the first ring-contracted naphthylisoquinolines, from the tropical liana Ancistrocladus abbreviatus, with cytotoxic activity

The West African liana Ancistrocladus abbreviatus is a rich source of structurally most diverse naphthylisoquinoline alkaloids. From its roots, a series of four novel representatives, named ancistrobrevolines A-D (14-17) have now been isolated, displaying an unprecedented heterocyclic ring system, where the usual isoquinoline entity is replaced by a ring-contracted isoindolinone part. Their constitutions were elucidated by 1D and 2D NMR and HR-ESI-MS. The absolute configurations at the chiral axis and at the stereogenic center were assigned by using experimental and computational electronic circular dichroism (ECD) investigations and a ruthenium-mediated oxidative degradation, respectively. For the biosynthetic origin of the isoindolinones from 'normal' naphthyltetrahydroisoquinolines, a hypothetic pathway is presented. It involves oxidative decarboxylation steps leading to a ring contraction by a benzilic acid rearrangement. Ancistrobrevolines A (14) and B (15) were found to display moderate cytotoxic effects (up to 72%) against MCF-7 breast and A549 lung cancer cells and to reduce the formation of spheroids (mammospheres) in the breast cancer cell line.

Plant isoquinoline alkaloids: Advances in the chemistry and biology of berberine

Alkaloids are one of the most important classes of plant bioactives. Among these isoquinoline alkaloids possess varied structures and exhibit numerous biological activities. Basically these are biosynthetically produced via phenylpropanoid pathway. However, occasionally some mixed pathways may also occur to provide structural divergence. Among the various biological activities anticancer, antidiabetic, antiinflammatory, and antimicrobial are important. A few notable bioactive isoquinoline alkaloids are antidiabetic berberine, anti-tussive codeine, analgesic morphine, and muscle relaxant papaverine etc. Berberine is one of the most discussed bioactives from this class possessing broad-spectrum pharmacological activities. Present review aims at recent updates of isoquinoline alkaloids with major emphasis on berberine, its detailed chemistry, important biological activities, structure activity relationship and implementation in future research.

N,C-Coupled naphthylisoquinoline alkaloids: a versatile new class of axially chiral natural products

Covering: up to April 2021During the past decades, a plethora of natural products with restricted rotation about a biaryl axis have been discovered, among them the naphthylisoquinoline (NIQ) alkaloids, mostly C,C-coupled and having remarkable bioactivities. Within this fascinating class of naturally occurring biaryl compounds, NIQ alkaloids bearing an N,C-heterobiaryl axis have attracted particular attention. They are structurally and biosynthetically unprecedented, with interesting stereochemical implications and biological activities. In contrast to existing articles and reviews about axially chiral - yet C,C-coupled - natural products, this is the first, comprehensive review on the new subclass of N,C-coupled NIQs, their isolation and structural elucidation, their N,C-axial chirality, their biosynthetic origin, their promising antiparasitic and antileukemic activities, and their total synthesis.

Organocatalyzed Cascade Aza-Michael/Aldol Reaction for Atroposelective Construction of 4-Naphthylquinoline-3-carbaldehydes

An organocatalyzed cascade aza-Michael/Aldol reaction of alkynals with N-(2-(1-naphthoyl)phenyl)benzenesulfonamides has been disclosed. In the presence of a secondary amine catalyst, this method enables the construction of a series of axially chiral 4-naphthylquinoline-3-carbaldehydes in yields of up to 97% with enantioselectivities of up to 96%. Several further transformations of the synthesized products were investigated to demonstrate their synthetic applications.

Ancistrobrevidines A-C and related naphthylisoquinoline alkaloids with cytotoxic activities against HeLa and pancreatic cancer cells, from the liana Ancistrocladus abbreviatus

From the leaves of Ancistrocladus abbreviatus (Ancistrocladaceae), six 5,1'-coupled naphthyldihydroisoquinoline alkaloids were isolated, ancistrobrevidines A-C (5-7), 5-epi-dioncophyllidine C₂ (10), 6-O-methylhamatinine (8), and 6-O-methylancistectorine A₃ (9); the two latter compounds were already known from related plants. Most strikingly, this series comprises alkaloids belonging to three different subclasses of naphthylisoquinolines. Ancistrobrevidine C (7) and the alkaloids 8 and 9, displaying the S-configuration at C-3 and an oxygen function at C-6, are three further representatives of the large subgroup of 5,1'-coupled Ancistrocladaceae-type compounds found in nature. 5-epi-Dioncophyllidine C₂ (10), lacking an oxygen function at C-6 and having the R-configuration at C-3, is only the third representative of a 5,1'-linked Dioncophyllaceae-type naphthylisoquinoline. Likewise rare are 5,1'-coupled hybrid-type alkaloids, which are 6-oxygenated and 3R-configured. The ancistrobrevidines A (5) and B (6) are the only second and third examples of such 5,1'-linked naphthylisoquinolines in Ancistrocladus species showing the landmarks of both, Ancistrocladaceae- and Dioncophyllaceae-type naphthylisoquinolines. In the roots of A. abbreviatus, two further unprecedented 5,1'-coupled alkaloids were discovered, ancistrobreviquinones A (11) and B (12), consisting of a 3,4-naphthoquinone portion coupled to a tetrahydroisoquinoline subunit. They are the very first quinoid naphthylisoquinolines possessing an ortho-diketone entity. Ancistrobrevidine C (7) exerted pronounced antiproliferative activities against HeLa cervical cancer cells and preferential cytotoxicity towards PANC-1 human pancreatic cancer cells under nutrient-deprived conditions following the antiausterity approach. Moreover, 7 suppressed the migration of PANC-1 cells and significantly inhibited colony formation under nutrient-rich conditions in a concentration-dependent manner, and induced dramatic alteration in cell morphology, leading to cell death.

Computational studies of biologically active alkaloids of plant origin: an overview

Computational studies nowadays constitute a crucial source of information for drug development, because they provide information on many molecular properties and also enable predictions of the properties of not-yet-synthesized compounds. Alkaloids are a vast group of natural products exhibiting a variety of biological activities, many of which are interesting for drug development. On the other hand, computational studies of biologically active alkaloids have so far mostly focused on few particularly relevant or “popular” molecules, such as quinine, caffeine, or cocaine, with only few works on the other molecules. The present work offers an overview of existing computational studies on alkaloid molecules, from the earliest ones to the most recent, and considering all the theoretical approaches with which studies have been performed (both quantum mechanics and molecular dynamics). The considered studies are grouped according to their objectives and outcomes, such as conformational analysis of alkaloid molecules, effects of selected solvents on their properties, docking studies aimed at better understanding of the interactions between alkaloid molecules and biological targets, studies focusing on structure activity relationships, and computational studies performed to confirm experimental results. It is concluded that it would be important that computational studies on many other alkaloid molecules are performed and their results made available, covering their different classes as well as the variety of their biological activities, to attain better understanding of the properties not only of individual molecules, but also of groups of related molecules and of the overall alkaloids family.