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.

Cytotoxicity of dioncophylline A and related naphthylisoquinolines in leukemia cells, mediated by NF-κB inhibition, angiogenesis suppression, G2/M cell cycle arrest, and autophagy induction.

BACKGROUND: Inhibition of NF-κB activity represents a strategy to treat acute myeloid leukemia, one of the most lethal leukemia types. Naphthylisoquinolines (NIQs) are cytotoxic alkaloids from lianas of the families Ancistrocladaceae and Dioncophyllaceae, which are indigenous to tropical rainforests. PURPOSE: Uncovering therapeutic possibilities and underlying molecular mechanisms of dioncophylline A and its derivatives towards NF-κB related cellular processes. METHODS: Resazurin-based cell viability assay was performed for dioncophylline A and three derivatives on wild-type CCRF-CEM and multidrug-resistant CEM/ADR5000 cells. Transcriptome analysis was executed to discover cellular functions and molecular networks associated with dioncophylline A treatment. Expression changes obtained by mRNA microarray hybridization were confirmed using qRT-PCR. Molecular docking was applied to predict the affinity of the NIQs with NF-κB. To validate the in silico approach, NF-κB reporter assays were conducted on HEK-Blue™ Null1 cells. Cell death mechanisms and cell cycle arrest were studied using flow cytometry. The potential activity on angiogenesis was evaluated with the endothelial cell tube formation assay on HUVECs using fluorescence microscopy. Intracellular NF-κB location in HEK-Blue™ Null1 cells was visualized with immunofluorescence. Finally, the anti-tumor activity of dioncophylline A was studied by a xenograft zebrafish model in vivo. RESULTS: Our study demonstrated that dioncophylline A and its derivatives exerted potent cytotoxicity on leukemia cells. Using Ingenuity Pathway Analysis, we identified the NF-κB network as the top network, and docking experiments predicted dioncophylline A and two of its derivatives sharing the same binding pocket with the positive control compound, triptolide. Dioncophylline A showed the best inhibitory activity in NF-κB reporter assays compared to its derivatives, caused autophagy rather than apoptosis, and induced G2/M arrest. It also prevented NF-κB translocation from the cytoplasm to the nucleus. Tube formation as an angiogenesis marker was significantly suppressed by dioncophylline A treatment. Finally, the remarkable anti-tumor activity of dioncophylline A was proven in zebrafish in vivo. CONCLUSION: Taken together, we report for the first time the molecular mechanism behind the cytotoxic effect of dioncophylline A on leukemia cells. Dioncophylline A showed strong cytotoxic activity, inhibited NF-κB translocation, significantly affected the NF-κB in silico and in vitro, subdued tube formation, induced autophagy, and exerted antitumor activity in vivo. Our findings enlighten both the cellular functions including the NF-κB signaling pathway and the cytotoxic mechanism affected by dioncophylline A.

Ancistrocladinium A Induces Apoptosis in Proteasome Inhibitor-Resistant Multiple Myeloma Cells: A Promising Therapeutic Agent Candidate.

The N,C-coupled naphthylisoquinoline alkaloid ancistrocladinium A belongs to a novel class of natural products with potent antiprotozoal activity. Its effects on tumor cells, however, have not yet been explored. We demonstrate the antitumor activity of ancistrocladinium A in multiple myeloma (MM), a yet incurable blood cancer that represents a model disease for adaptation to proteotoxic stress. Viability assays showed a potent apoptosis-inducing effect of ancistrocladinium A in MM cell lines, including those with proteasome inhibitor (PI) resistance, and in primary MM cells, but not in non-malignant blood cells. Concomitant treatment with the PI carfilzomib or the histone deacetylase inhibitor panobinostat strongly enhanced the ancistrocladinium A-induced apoptosis. Mass spectrometry with biotinylated ancistrocladinium A revealed significant enrichment of RNA-splicing-associated proteins. Affected RNA-splicing-associated pathways included genes involved in proteotoxic stress response, such as PSMB5-associated genes and the heat shock proteins HSP90 and HSP70. Furthermore, we found strong induction of ATF4 and the ATM/H2AX pathway, both of which are critically involved in the integrated cellular response following proteotoxic and oxidative stress. Taken together, our data indicate that ancistrocladinium A targets cellular stress regulation in MM and improves the therapeutic response to PIs or overcomes PI resistance, and thus may represent a promising potential therapeutic agent.

Molecular determinants of the response of cancer cells towards geldanamycin and its derivatives.

Geldanamycin is an ansamycin-derivative of a benzoquinone isolated from Streptomyces hygroscopicus. It inhibits tyrosine kinases and heat shock protein 90 (HSP90). Geldanamycin and 11 derivatives were subjected to molecular docking to HSP90, and 17-desmethoxy-17-N,N-dimethylamino-geldanamycin (17-DMAG) was the compound with the highest binding affinity (-7.73 ± 0.12 kcal/mol) and the lowest inhibition constant (2.16 ± 0.49 µM). Therefore, 17-DMAG was selected for further experiments in comparison to geldanamycin. Multidrug resistance (MDR) represents a major problem for successful cancer therapy. We tested geldanamycin and 17-DMAG against various drug-resistant cancer cell lines. Although geldanamycin and 17-DMAG inhibited the proliferation in all cell lines tested, multidrug-resistant P-glycoprotein-overexpressing CEM/ADR5000 cells were cross-resistant, ΔEGFR-overexpressing tumor cells and p53 knockout cells were sensitive to these two compounds. COMPARE and hierarchical cluster analyses were performed, and 60 genes were identified to predict the sensitivity or resistance of 59 NCI tumor cell lines towards geldanamycin and 17-DMAG. The distribution of cell lines according to their mRNA expression profiles indicated sensitivity or resistance to both compounds with statistical significance. Moreover, bioinformatic tools were used to study possible mechanisms of action of geldanamycin and 17-DMAG. Galaxy Cistrome analyses were carried out to predict transcription factor binding motifs in the promoter regions of the candidate genes. Interestingly, the NF-ĸB DNA binding motif (Rel) was identified as the top transcription factor. Furthermore, these 60 genes were subjected to Ingenuity Pathway Analysis (IPA) to study the signaling pathway interactions of these genes. Interestingly, IPA also revealed the NF-ĸB pathway as the top network among these genes. Finally, NF-ĸB reporter assays confirmed the bioinformatic prediction, and both geldanamycin and 17-DMAG significantly inhibited NF-κB activity after exposure for 24 h. In conclusion, geldanamycin and 17-DMAG exhibited cytotoxic activity against different tumor cell lines. Their activity was not restricted to HSP90 but indicated an involvement of the NF-KB pathway.

Ancistrobrevinium A, the first N-methylated, cationic naphthylisoquinoline alkaloid, from the tropical liana Ancistrocladus abbreviatus (Ancistrocladaceae).

Ancistrobrevinium A (1) is the first N-methylated and non-hydrogenated, and thus cationic naphthylisoquinoline alkaloid. It was discovered in the root bark extract of the phytochemically productive West African liana Ancistrocladus abbreviatus (Ancistrocladaceae). Its constitution was elucidated by HR-ESI-MS and 1D and 2D NMR. Due to the steric hindrance in the proximity of the linkage between the naphthalene and isoquinoline parts, the biaryl axis is rotationally hindered. It thus constitutes a stable element of chirality - the only one in the new alkaloid since, different from most other naphthylisoquinoline alkaloids, it has no stereogenic centers. The axial configuration of 1 was assigned by electronic circular dichroism (ECD) investigations, which gave a positive couplet, indicating a 'positive chirality', here corresponding to a P-configuration. Ancistrobrevinium A (1) showed a weak cytotoxic activity against A549 lung cancer cells (IC50 = 50.6 µM).

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.

Jozibrevine D from Ancistrocladus ileboensis, the fifth alkaloid in a series of six possible atropo-diastereomeric naphthylisoquinoline dimers, showing antiparasitic and antileukemic activities.

A new dimeric naphthylisoquinoline alkaloid, jozibrevine D (4e), was isolated from the Central-African liana Ancistrocladus ileboensis. It is a Dioncophyllaceae-type metabolite, being R-configured at C-3 and lacking an oxygen function at C-6 in both isoquinoline moieties. The two identical monomers of jozibrevine D are symmetrically linked via the sterically constrained 3',3''-positions of the naphthalene units so that the central biaryl linkage is rotationally hindered and the alkaloid is, thus, C2-symmetric. With the two outer biaryl bonds being chiral, too, 4e possesses three consecutive stereogenic axes. The absolute stereostructure of the new compound was assigned by 1D and 2D NMR, ruthenium-mediated oxidative degradation, and electronic circular dichroism (ECD) spectroscopy. Jozibrevine D (4e) is the fifth discovered isomer in a series of six possible natural atropo-diastereomeric dimers. It shows potent, and selective, antiprotozoal activity against P. falciparum (IC50 = 0.14 µM), and it also exhibits good cytotoxic activities against drug-sensitive acute lymphoblastic CCRF-CEM leukemia cells (IC50 = 11.47 µM) and their multidrug-resistant CEM/ADR5000 subline (IC50 = 16.61 µM).

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.

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

[This corrects the article DOI: 10.1039/D2RA05758A.].

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.

The Stereoselective Total Synthesis of Axially Chiral Naphthylisoquinoline Alkaloids.

The naphthylisoquinoline (NIQ) alkaloids are a thrilling class of natural biaryls─structurally, biosynthetically, and pharmacologically. A common feature of these metabolites is the biaryl bond between their naphthalene and isoquinoline moieties, which in most cases is rotationally hindered, leading to the phenomenon of axial chirality. Depending on their individual structures, including the respective axial configurations, NIQs show promising bioactivities. Their total synthesis is a challenging but rewarding goal, with the stereocontrolled construction of the biaryl linkage as the key step.The position of the biaryl axis and its configuration determine the overall molecular shape and thus the choice of the best possible method for efficient asymmetric aryl-aryl bond formation. The axis in NIQs can cover a broad range of steric hindrance, from freely rotating to configurationally stable. For dioncophylline B (1) and dioncophylline F (2a/b), with only two ortho-substituents next to the axis, the synthesis is easy to accomplish by direct coupling of the intact naphthalene moiety with the isoquinoline unit, and no atropo-selectivity is required.Naphthylisoquinolines with a configurationally stable biaryl axis are the focus of the present Account. They are more difficult to synthesize because, in addition to the problem of decreased chemical yields with increasing steric hindrance at the axis, the synthesis needs to proceed stereoselectively. Within this class of NIQs, 5,8'-coupled representatives, such as korupensamine A (3a), have received considerable synthetic attention because the rotational barrier is high enough for the existence of atropisomerism without being too excessive, and they show potent bioactivities. Their synthesis, as systematically presented herein, thus occupies a central role in this report. For their aryl-aryl bond formation, both intra- and intermolecular approaches can be successfully applied. Axial stereoinformation is introduced by internal asymmetric induction from stereogenic elements already present in the isoquinoline or its precursors, from chiral auxiliary elements artificially introduced, or by external asymmetric induction using chiral catalysts.To overcome even higher steric hindrance, as in ancistrocladine (4a), innovative approaches were developed. A most successful strategy is the "lactone concept" developed by the Bringmann group, which allows the directed synthesis of any desired atropisomer in high chemical and optical yields, thus permitting the atropo-divergent preparation of the two isomers from a single joint precursor. In this approach, the two formal tasks of stereoselective biaryl synthesis, which are usually done simultaneously─the C-C linkage and the asymmetric induction─are achieved consecutively. The coupling step is performed intramolecularly after prefixation of the coupling partners by an ester bridge. The resulting biaryl lactone already possesses the biaryl axis but is still configurationally unstable; it can then, with internal or external asymmetric induction, be cleaved atropo-divergently with high stereoselectivities. Besides its unique concept, the procedure excels by its broad applicability; among all presented methods, it has been used for the synthesis of the largest number of NIQs, more than 20 representatives, including those with the highest steric hindrance.This Account gives comprehensive insight into the plethora of conceptual approaches for the efficient formation of the hindered biaryl bond of NIQs.

Spirombandakamine A3 and Cyclombandakamines A8 and A9, Polycyclic Naphthylisoquinoline Dimers, with Antiprotozoal Activity, from a Congolese Ancistrocladus Plant.

Spirombandakamine A3 (7) is only the third known naphthylisoquinoline dimer with a spiro-fused novel molecular framework and the first such representative to possess a relative trans-configuration at the two chiral centers in both tetrahydroisoquinoline subunits. It was found in the leaves of a botanically as yet unidentified Congolese Ancistrocladus plant, which is morphologically closely related to the Central African taxon Ancistrocladus ealaensis. Likewise isolated were the new cyclombandakamines A8 (8) and A9 (9), which belong to another most recently discovered type of unusual oxygen-bridged naphthylisoquinoline dimers and two previously described "open-chain" analogues, mbandakamines C (10) and D (11). The full absolute stereostructures of these compounds were assigned by combining spectroscopic, chemical, and chiroptical methods. Preliminary biomimetic investigations indicated that both spirombandakamine- and cyclombandakamine-type dimers result from the oxidation of their open-chain mbandakamine-type congeners. The new dimeric alkaloids 7-9 displayed potent growth-inhibitory activity against Plasmodium falciparum, the protozoal pathogen causing malaria, and moderate effects on Trypanosoma brucei rhodesiense, the parasite responsible for African sleeping sickness.

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.

Naphthylisoquinoline alkaloids and their synthetic analogs as potent novel inhibitors against Babesia canis in vitro.

Babesia canis is the predominant and clinically relevant canine Babesia species in Europe. Transmitted by vector ticks, the parasite enters red blood cells and induces a severe, potentially fatal hemolytic anemia. Here, we report on the antibabesial activities of three extracts of the West African tropical plant species Triphyophyllum peltatum (Dioncophyllaceae) and Ancistrocladus abbreviatus (Ancistrocladaceae) and of 13 genuine naphthylisoquinoline alkaloids isolated thereof. Two of the extracts and eight of the alkaloids were found to display strong activities against Babesia canis in vitro. Among the most potent compounds were the C,C-coupled dioncophyllines A (1a) and C (2) and the N,C-linked alkaloids ancistrocladium A (3) and B (4), with half-maximum inhibition concentration (IC50) values of 0.48 µM for 1a, 0.85 µM for 2, 1.90 µM for 3, and 1.23 µM for 4. Structure-activity relationship (SAR) studies on a small library of related genuine analogs and non-natural synthetic derivatives of 1a and 2 revealed the likewise naturally occurring alkaloid N-methyl-7-epi-dioncophylline A (6b) to be the most potent (IC50, 0.14 µM) among the investigated compounds. Although none of the tested naphthylisoquinolines showed 100 % inhibition of parasite infection - as displayed by imidocarb dipropionate (IC50, 0.07 µM), which was used as a positive control - the antibabesial potential of the dioncophyllines A (1a) and C (2) and related compounds such as 6b, its atropo-diastereomer 6a (IC50, 1.45 µM), and 8-O-(p-nitrobenzyl)dioncophylline A (14) (IC50, 0.82 µM) is to be considered as high. The SAR results showed that N-methylation and axial chirality exert a strong impact on the antibabasial activities of the naphthylisoquinolines presented here, whereas dimerization, as in jozimine A2 (5) (IC50, 140 µM), leads to a significant decrease of activity against B. canis. Alkaloids displaying good to high activities against B. canis like the dioncophyllines 1a, 2, 6a, and 6b were found to cause only a small degree of hemolysis (< 0.7 %), whereas compounds with moderate to weak antibabesial activities such as 6-O-methyl-4'-O-demethylancistrocladine (15a) (IC50, 14.0 µM) and its atropo-diastereomer 6-O-methyl-4'-O-demethylhamatine (15b) (IC50, 830 µM) caused a high degree of hemolysis (7.3 % for 15a and 11.2 % for 15b). In this respect, the most effective anti-Babesia naphthylisoquinolines are also the safest ones.

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

Ancistrosecolines A-F (8-13) are the first seco-type naphthylisoquinoline alkaloids discovered in Nature. In all these novel compounds, the tetrahydroisoquinoline ring is cleaved, with loss of C-1. They were isolated from the root bark of Ancistrocladus abbreviatus (Ancistrocladaceae), along with 1-nor-8-O-demethylancistrobrevine H (14), which is the first naturally occurring naphthylisoquinoline lacking the otherwise generally present methyl group at C-1. The stereostructures of the new alkaloids were established by HRESIMS, 1D and 2D NMR, oxidative degradation, and experimental and quantum-chemical ECD investigations. Ancistrosecolines A-F (8-13) and 1-nor-8-O-demethylancistrobrevine H (14) are typical Ancistrocladaceae-type metabolites, i.e., oxygenated at C-6 and S-configured at C-3, belonging to the subclasses of 7,1'- and 7,8'-coupled alkaloids. The biaryl linkages of 8-14 are rotationally hindered due to bulky ortho-substituents next to the axes. Owing to the constitutionally unsymmetric substitution patterns on each side of the axis, this C-C single bond represents an element of chirality in 1-nor-8-O-demethylancistrobrevine H (14) and in ancistrosecolines A-D (8-11). In ancistrosecolines E (12) and F (13), however, the likewise rotationally hindered biaryl axes do not constitute chiral elements, due to a symmetric substitution pattern, with its identical two methoxy functions at C-6 and C-8 in the phenyl subunit. And these two methoxy groups are, for the first time, not constitutionally heterotopic, but diastereotopic to each other. Ancistrosecoline D (11) exhibits strong cytotoxicity against HeLa cervical cancer cells. As visualized by Hoechst nuclei staining and by real-time imaging experiments, 11 induced massive nuclei fragmentation in HeLa cells, leading to apoptotic cell death.

Ealamines A-H, a Series of Naphthylisoquinolines with the Rare 7,8'-Coupling Site, from the Congolese Liana Ancistrocladus ealaensis, Targeting Pancreatic Cancer Cells.

From the twigs and leaves of the Central African liana Ancistrocladus ealaensis (Ancistrocladaceae), a series of ten 7,8'-coupled naphthylisoquinoline alkaloids were isolated, comprising eight new compounds, named ealamines A-H (4a, 4b, 5-10), and two known ones, 6-O-demethylancistrobrevine A (11) and yaoundamine A (12), which had previously been found in related African Ancistrocladus species. Only one of the new compounds within this series, ealamine H (10), is a typical Ancistrocladaceae-type alkaloid, with 3S-configuration at C-3 and an oxygen function at C-6, whereas seven of the new alkaloids are the first 7,8'-linked "hybrid-type" naphthylisoquinoline alkaloids, i.e., 3R-configured and 6-oxygenated in the tetrahydroisoquinoline part. The discovery of such a broad series of 7,8'-coupled naphthyltetrahydroisoquinolines is unprecedented, because representatives of this subclass of alkaloids are normally found in Nature quite rarely. The stereostructures of the new ealamines were assigned by HRESIMS, 1D and 2D NMR, oxidative degradation, and experimental and quantum-chemical ECD investigations, and-in the case of ealamine A (4a)-also confirmed by X-ray diffraction analysis. Ealamines A-D exhibited distinct-and specific-antiplasmodial activities, and they displayed pronounced preferential cytotoxic effects toward PANC-1 human pancreatic cancer cells in nutrient-deprived medium, without causing toxicity under normal, nutrient-rich conditions, with ealamine C (5) as the most potent agent.

A Near-Complete Series of Four Atropisomeric Jozimine A2-Type Naphthylisoquinoline Dimers with Antiplasmodial and Cytotoxic Activities and Related Alkaloids from Ancistrocladus abbreviatus.

Three new naphthylisoquinoline dimers, jozibrevines A-C (1a-c), were isolated from the West African shrub Ancistrocladus abbreviatus, along with the known dimer jozimine A2 (1d). The two molecular moieties of 1a-d are coupled via the sterically constrained 3',3″-positions of their two naphthalene units, so that the central biaryl linkage is rotationally hindered. With the two outer axes also being chiral, 1a-d possess three consecutive stereogenic axes. The four isolated dimers all have the same constitutions and identical absolute configurations at the four stereogenic centers, but differ by their axial chirality. They belong to the extremely small class of Dioncophyllaceae-type naphthylisoquinoline dimers, i.e., being devoid of oxygen functions at C-6 and bearing the R-configuration at C-3 in their isoquinoline portions. Besides these dimers, the plant produces predominantly typical Ancistrocladaceae-type monomeric compounds, i.e., with the S-configuration at C-3 and an oxygen function at C-6, such as the new ancistrobrevines K (5) and L (6). Furthermore, a new hybrid-type (i.e., mixed Ancistrocladaceae/Dioncophyllaceae-type) alkaloid was identified, named ancistrobrevine M (7), which is 3R-configured and 6-oxygenated. Remarkable was the discovery of its "inverse hybrid-type" counterpart, dioncoline A (8). It is the as yet only known 3S-configured naphthylisoquinoline lacking an O-functionality at C-6. The new jozibrevines A-C (1a-c) exhibited pronounced antiplasmodial activities in the submicromolar range, with 1a being the most potent compound (IC50, 0.012 µM). Furthermore, jozimine A2 (1d) showed cytotoxicity against human colon carcinoma (HT-29), fibrosarcoma (HT1080), and multiple myeloma (MM.1S) cancer cells, displaying IC50 values of 12.0, 9.0, and 5.0 µM, respectively, whereas jozibrevines A (1a) and B (1b) were nontoxic in this concentration range.

An Unusually Broad Series of Seven Cyclombandakamines, Bridged Dimeric Naphthylisoquinoline Alkaloids from the Congolese Liana Ancistrocladus ealaensis.

A series of seven unusual dimeric naphthylisoquinoline alkaloids was isolated from the leaves of the tropical liana Ancistrocladus ealaensis J. Léonard, named cyclombandakamine A (1), 1-epi-cyclombandakamine A (2), and cyclombandakamines A3-7 (3-7). These alkaloids have a chemically thrilling structural array consisting of a twisted dihydrofuran-cyclohexenone-isochromene system. The 1'″-epimer of 4, cyclombandakamine A1 (8), had previously been discovered in an unidentified Ancistrocladus species related to A. ealaensis. Both lianas produce the potential parent precursor, mbandakamine A (9), but only A. ealaensis synthesizes the corresponding cyclized form, along with a broad series of slightly modified analogs. The challenging isolation required, besides multi-dimensional chromatography, the use of a pentafluorophenyl stationary phase. Featuring up to six stereocenters and two types of chiral axes, their structures were elucidated by means of 1D and 2D NMR, HRESIMS, in combination with oxidative chemical degradation experiments as well as chiroptical (electronic circular dichroism spectroscopy) and quantum chemical calculations. Compared to the 'open-chain' parent compound 9, these dimers displayed rather moderate antiplasmodial activities.

Dimeric naphthylisoquinoline alkaloids: polyketide-derived axially chiral bioactive quateraryls.

Covering: up to April 2019Dimeric naphthylisoquinoline (NIQ) alkaloids are an emerging group of structurally, biosynthetically, and pharmacologically intriguing natural products, as yet isolated from African and Asian lianas belonging to the genus Ancistrocladus Wall. (Ancistrocladaceae) exclusively. These metabolites and their monomers are the only known di- and tetrahydroisoquinoline alkaloids that do not originate from aromatic amino acids, but from polyketide precursors. Stereochemically, dimeric NIQs are characterized by the presence of several stereogenic centers and up to three consecutive chiral axes. The most recent highlight is the discovery of dimers that witness a new biosynthetic follow-up chemistry: by oxidative cyclization, leading to bridged, cage-like molecular architectures. Depending on their individual structures, the dimers show promising biological activities, including antiviral, antiprotozoal, and antitumor properties, most of them quite different from those of the monomers. This is the first review on these multi-facetted dimeric alkaloids, dealing with their isolation, their structural diversity, their biosynthetic origin, their pharmacological properties, and their total synthesis.

Antiprotozoal dimeric naphthylisoquinolines, mbandakamines B3 and B4, and related 5,8'-coupled monomeric alkaloids, ikelacongolines A-D, from a Congolese Ancistrocladus liana.

From the leaves of a botanically and phytochemically as yet unexplored Ancistrocladus liana discovered in the rainforests of the Central region of the Democratic Republic of the Congo in the vicinity of the town of Ikela, six new naphthylisoquinoline alkaloids were isolated, viz., two constitutionally unsymmetric dimers, the mbandakamines B3 (3) and B4 (4), and four related 5,8'-linked monomeric alkaloids, named ikelacongolines A-D (5a, 5b, 6, and 7). The dimers 3 and 4 are structurally unusual quateraryls comprising two 5,8'-coupled monomers linked via a sterically strongly constrained 6',1''-connection between their naphthalene units. These compounds contain seven elements of chirality, four stereogenic centers and three consecutive chiral axes. They were identified along with two known related compounds, the mbandakamines A (1) and B2 (2), which had so far only been detected in two Ancistrocladus species indigenous to the Northwestern Congo Basin. In addition, five known monomeric alkaloids, previously found in related Central African Ancistrocladus species, were isolated from the here investigated Congolese liana, three of them belonging to the subclass of 5,8'-coupled naphthylisoquinoline alkaloids, whereas two compounds exhibited a less frequently occurring 7,8'-biaryl linkage. The stereostructures of the new alkaloids were established by spectroscopic (in particular HRESIMS, 1D and 2D NMR), chemical (oxidative degradation), and chiroptical (electronic circular dichroism) methods. The mbandakamines B3 (3) and B4 (4) displayed pronounced activities in vitro against the malaria parasite Plasmodium falciparum and the pathogen of African sleeping sickness, Trypanosoma brucei rhodesiense.