Bioactive pyridoacridine alkaloids from the micronesian sponge Oceanapia sp

Chemical and Pharmacological Prospection of the Ascidian Cystodytes dellechiajei

Marine invertebrates are a traditional source of natural products with relevant biological properties. Tunicates are soft-bodied, solitary or colonial, sessile organisms that provide compounds unique in their structure and activity. The aim of this work was to investigate the chemical composition of the ascidian Cystodytes dellechiajei, selected on the basis of a positive result in biological screening for ligands of relevant receptors of the innate immune system, including TLR2, TLR4, dectin-1b, and TREM2. Bioassay-guided screening of this tunicate extract yielded two known pyridoacridine alkaloids, shermilamine B (1) and N-deacetylshermilamine B (2), and a family of methyl-branched cerebrosides (3). Compounds 2 and 3 showed selective binding to TREM2 in a dose-dependent manner. N-deacetylshermilamine B (2), together with its acetylated analogue, shermilamine B (1), was also strongly cytotoxic against multiple myeloma cell lines. TREM2 is involved in immunomodulatory processes and neurodegenerative diseases. N-deacetylshermilamine B (2) is the first example of a polycyclic alkaloid to show an affinity for this receptor.

Marine pyridoacridine, pyridoacridone and pyrroloacridine alkaloids

The families of pyridoacridine, pyridoacridone, and pyrroloacridine alkaloids are fascinating classes of natural products that have attracted the attention of chemists for over 80 years. Since the first purification of a brightly colored molecule isolated from the sea anemone Calliactis parasitica in 1940, over 110 examples of these alkaloids have been reported from marine organisms. While the paucity of numbers of protons relative to carbons and nitrogens in these molecules presents challenges in structure solution, the chemist is rewarded by their bright pigmented colors and typically diverse biological activities. In the past, several authors have proposed biosynthetic relationships within the pyridoacridine family of alkaloids, formulating a family tree derived from the reaction of dopaminequinone and kynuramine to tie together over 75 alkaloids. Inclusion of two additional quinones, and one homologous diamine, building blocks, for which there is biomimetic synthesis support, is suggestive of a more expansive connected biogenesis that encompasses not only pyridoacridines, but also pyridoacridone, and pyrroloacridine alkaloids. This review covers the isolation, structure elucidation, and proposed biosynthesis and biogenesis of pyridoacridine, pyridoacridone and pyrroloacridine marine alkaloids published to the end of 2022. Biomimetic or bio-inspired syntheses of the compound classes are described and new biological activities reported since 2004 are updated.

Kuanoniamine C Suppresses Adipogenesis and White Adipose Tissue Expansion by Modulating Mitochondrial Function

Obesity is characterized by the excessive accumulation of fat to adipose tissue, which is related to abnormal increasing white adipose tissue (WAT) in the body, and it upregulates the risk of multiple diseases. Here, kuanoniamine C, which is a pyridoacridine alkaloid, suppressed the differentiation of pre-adipose cells into white adipocytes via the modulation of mitochondrial function, and inhibited WAT expansion in the early phase of high-fat-diet-induced obesity model. Pharmacological analysis revealed that inhibition of mitochondrial respiratory complex II, which new target of kuanoniamine C, activated reactive oxygen species (ROS)-extracellular signal-regulated kinase (ERK)-β-catenin signaling, and this signaling was antagonized by insulin-, IBMX-, and dexamethasone-induced adipogenesis. Therefore, the kuanoniamine C might prevent abnormal WAT expansion even when eating a diet that is not calorie restricted.

Toward the Total Synthesis of Alpkinidine: Synthesis of Haloquinone CE Ring System Synthons and Attempted Nucleophilic Bisannulation

Model chemistry involving the bisannulation of 2,3-dichloro-1,4-naphthoquinone with the ester enolate derived from ethyl o-nitrophenylacetic acid, which rapid assembled the ABCD ring system of a pentacyclic pyrroloacridine, has been applied to the attempted synthesis of the marine natural product alpkinidine. The reaction of ethyl o-nitrophenylacetic acid with 6,7-dichloro-2-methylisoquinoline-1,5,8(2H)-trione, required to extend the model strategy to alpkinidine, was unfruitful, giving only complex mixtures. Efforts to direct the regiochemistry of the key Michael substitution step using 6-bromo-2-methylisoquinoline-1,5,8(2H)-trione afforded an adduct sharing the complete carbon skeleton of alpkinidine, but this could not be elaborated to the natural product.

Secondary Metabolites from Marine Sponges of the Genus Oceanapia: Chemistry and Biological Activities

In this review, we summarized the distribution of the chemically investigated Oceanapia sponges, including the isolation and biological activities of their secondary metabolites, covering the literature from the first report in 1989 to July 2019. There have been 110 compounds reported during this period, including 59 alkaloids, 33 lipids, 14 sterols and 4 miscellaneous compounds. Besides their unique structures, they exhibited promising bioactivities ranging from insecticidal to antibacterial. Their complex structural characteristics and diverse biological properties have attracted a great deal of attention from chemists and pharmaceuticals seeking to perform their applications in the treatment of disease.

Chemical Diversity and Bioactivity of Marine Sponges of the Genus Oceanapia: A Review

:

The marine sponges of the genus Oceanapia sp. is comprised of more than 50 species and are distributed in the seas around the tropical and subtropical regions. They are mainly found in the northern Indian oceans, Japan, and the south pacific coast. They are highly colored and known to be a rich source of various secondary metabolites, particularly, alkaloids. Several other secondary metabolites were also reported from this genus which include terpenes, sphingolipids, ceramides, cerebrosides, acetylenic acids, and thiocyanatins, etc. Many of these compounds isolated from this genus exhibited various biological properties including anticancer, antimicrobial, anti-HIV, ichthyotoxicity and nematocidal activities. Although several secondary metabolites have been reported from this genus, a dedicated review of the chemicals and biological activities of this genus is so far lacking. Keeping this in mind this review describes the various chemical entities isolated from the sponges of the genus Oceanapia detailing their chemical structures along with their reported biological properties.

Biological Activity of Naturally Derived Naphthyridines

Marine and terrestrial environments are rich sources of various bioactive substances, which have been used by humans since prehistoric times. Nowadays, due to advances in chemical sciences, new substances are still discovered, and their chemical structures and biological properties are constantly explored. Drugs obtained from natural sources are used commonly in medicine, particularly in cancer and infectious diseases treatment. Naphthyridines, isolated mainly from marine organisms and terrestrial plants, represent prominent examples of naturally derived agents. They are a class of heterocyclic compounds containing a fused system of two pyridine rings, possessing six isomers depending on the nitrogen atom's location. In this review, biological activity of naphthyridines obtained from various natural sources was summarized. According to previous studies, the naphthyridine alkaloids displayed multiple activities, i.a., antiinfectious, anticancer, neurological, psychotropic, affecting cardiovascular system, and immune response. Their wide range of activity makes them a fascinating object of research with prospects for use in therapeutic purposes.

Synthesis and Evaluation of the Tetracyclic Ring-System of Isocryptolepine and Regioiso-Mers for Antimalarial, Antiproliferative and Antimicrobial Activities

A series of novel quinoline-based tetracyclic ring-systems were synthesized and evaluated in vitro for their antiplasmodial, antiproliferative and antimicrobial activities. The novel hydroiodide salts 10 and 21 showed the most promising antiplasmodial inhibition, with compound 10 displaying higher selectivity than the employed standards. The antiproliferative assay revealed novel pyridophenanthridine 4b to be significantly more active against human prostate cancer (IC₅₀ = 24 nM) than Puromycin (IC₅₀ = 270 nM) and Doxorubicin (IC₅₀ = 830 nM), which are used for clinical treatment. Pyridocarbazoles 9 was also moderately effective against all the employed cancer cell lines and moreover showed excellent biofilm inhibition (9a: MBIC = 100 µM; 9b: MBIC = 100 µM).

The Ascidian-Derived Metabolites with Antimicrobial Properties

Among the sub-phylum of Tunicate, ascidians represent the most abundant class of marine invertebrates, with 3000 species by heterogeneous habitat, that is, from shallow water to deep sea, already reported. The chemistry of these sessile filter-feeding organisms is an attractive reservoir of varied and peculiar bioactive compounds. Most secondary metabolites isolated from ascidians stand out for their potential as putative therapeutic agents in the treatment of several illnesses like microbial infections. In this review, we present and discuss the antibacterial activity shown by the main groups of ascidian-derived products, such as sulfur-containing compounds, meroterpenes, alkaloids, peptides, furanones, and their derivatives. Moreover, the direct evidence of a symbiotic association between marine ascidians and microorganisms shed light on the real producers of many extremely potent marine natural compounds. Hence, we also report the antibacterial potential, joined to antifungal and antiviral activity, of metabolites isolated from ascidian-associate microorganisms by culture-dependent methods.

Oxoisoaporphines and Aporphines: Versatile Molecules with Anticancer Effects

Cancer is a disease that involves impaired genome stability with a high mortality index globally. Since its discovery, many have searched for effective treatment, assessing different molecules for their anticancer activity. One of the most studied sources for anticancer therapy is natural compounds and their derivates, like alkaloids, which are organic molecules containing nitrogen atoms in their structure. Among them, oxoisoaporphine and sampangine compounds are receiving increased attention due to their potential anticancer effects. Boldine has also been tested as an anticancer molecule. Boldine is the primary alkaloid extract from boldo, an endemic tree in Chile. These compounds and their derivatives have unique structural properties that potentially have an anticancer mechanism. Different studies showed that this molecule can target cancer cells through several mechanisms, including reactive oxygen species generation, DNA binding, and telomerase enzyme inhibition. In this review, we summarize the state-of-art research related to oxoisoaporphine, sampangine, and boldine, with emphasis on their structural characteristics and the relationship between structure, activity, methods of extraction or synthesis, and anticancer mechanism. With an effective cancer therapy still lacking, these three compounds are good candidates for new anticancer research.

Natural Products from Sponges

The sponge is one of the oldest multicellular invertebrates in the world. Marine sponges represent one of the extant metazoans of 700–800 million years. They are classified in four major classes: Calcarea, Demospongiae, Hexactinellida, and Homoscleromorpha. Among them, three genera, namely, Haliclona, Petrosia, and Discodemia have been identified to be the richest source of biologically active compounds. So far, 15,000 species have been described, and among them, more than 6000 species are found in marine and freshwater systems throughout tropical, temperate, and polar regions. More than 5000 different compounds have been isolated and structurally characterized to date, contributing to about 30% of all marine natural products. The chemical diversity of sponge products is high with compounds classified as alkaloids, terpenoids, peptides, polyketides, steroids, and macrolides, which integrate a wide range of biological activities, including antibacterial, anticancer, antifungal, anti-HIV, anti-inflammatory, and antimalarial. There is an open debate whether all natural products isolated from sponges are produced by sponges or are in fact derived from microorganisms that are inhaled though filter-feeding or that live within the sponges. Apart from their origin and chemoecological functions, sponge-derived metabolites are also of considerable interest in drug development. Therefore, development of recombinant microorganisms engineered for efficient production of sponge-derived products is a promising strategy that deserves further attention in future investigations in order to address the limitations regarding sustainable supply of marine drugs.

Structure-Dependent Activity of Natural GABA(A) Receptor Modulators

GABA(A) receptors are ligand-gated ion channels consisting of five subunits from eight subfamilies, each assembled in four hydrophobic transmembrane domains. This pentameric structure not only allows different receptor binding sites, but also various types of ligands, such as orthosteric agonists and antagonists, positive and negative allosteric modulators, as well as second-order modulators and non-competitive channel blockers. A fact, that is also displayed by the variety of chemical structures found for both, synthetic as well as nature-derived GABA(A)-receptor modulators. This review covers the literature for natural GABA(A)-receptor modulators until the end of 2017 and discusses their structure-activity relationship.

Marine Pyridoacridine Alkaloids: Biosynthesis and Biological Activities

Pyridoacridines are a class of strictly marine-derived alkaloids that constitute one of the largest chemical families of marine alkaloids. During the last few years, both natural pyridoacridines and their analogues have constituted excellent targets for synthetic works. They have been the subject of intense study due to their significant biological activities; cytotoxic, antibacterial, antifungal, antiviral, insecticidal, anti-HIV, and anti-parasitic activities. In the present review, 95 pyridoacridine alkaloids isolated from marine organisms are discussed in term of their occurrence, biosynthesis, biological activities, and structural assignment.

Pyridinoacridine alkaloids of marine origin: NMR and MS spectral data, synthesis, biosynthesis and biological activity

This review focuses on pyridoacridine-related metabolites as one biologically interesting group of alkaloids identified from marine sources. They are produced by marine sponges, ascidians and tunicates, and they are structurally comprised of four to eight fused rings including heterocycles. Acridine, acridone, dihydroacridine, and quinolone cores are features regularly found in these alkaloid skeletons. The lack of hydrogen atoms next to quaternary carbon atoms for two or three rings makes the chemical shift assignment a difficult task. In this regard, one of the aims of this review is the compilation of previously reported, pyridoacridine (13)C NMR data. Observations have been made on the delocalization of electrons and the presence of some functional groups that lead to changes in the chemical shift of some carbon resonances. The lack of mass spectra information for these alkaloids due to the compactness of their structures is further discussed. Moreover, the biosynthetic pathways of some of these metabolites have been shown since they could inspire biomimetic synthesis. The synthesis routes used to prepare members of these marine alkaloids (as well as their analogues), which are synthesized for biological purposes are also discussed. Pyridoacridines were found to have a large spectrum of bioactivity and this review highlights and compares the pharmacophores that are responsible for the observed bioactivity.

Significance of investigating allelopathic interactions of marine organisms in the discovery and development of cytotoxic compounds

Marine sessile organisms often inhabit rocky substrata, which are crowded by other sessile organisms. They acquire living space via growth interactions and/or by allelopathy. They are known to secrete toxic compounds having multiple roles. These compounds have been explored for their possible applications in cancer chemotherapy, because of their ability to kill rapidly dividing cells of competitor organisms. As compared to the therapeutic applications of these compounds, their possible ecological role in competition for space has received little attention. To select the potential candidate organisms for the isolation of lead cytotoxic molecules, it is important to understand their chemical ecology with special emphasis on their allelopathic interactions with their competitors. Knowledge of the ecological role of allelopathic compounds will contribute significantly to an understanding of their natural variability and help us to plan effective and sustainable wild harvests to obtain novel cytotoxic chemicals. This review highlights the significance of studying allelopathic interactions of marine invertebrates in the discovery of cytotoxic compounds, by selecting sponge as a model organism.

A mini review on pyridoacridines: Prospective lead compounds in medicinal chemistry

Natural products are increasingly being considered “critical and important” in drug discovery paradigms as a number of them such as camptothecin, penicillin, and vincristine serve as “lead molecules” for the discovery of potent compounds of therapeutic interests namely irinotecan, penicillin G, vinblastine respectively. Derived compounds of pharmacological interests displayed a wide variety of activity viz. anticancer, anti-inflammatory, antimicrobial, anti-protozoal, etc.; when modifications or derivatizations are performed on a parent moiety representing the corresponding derivatives. Pyridoacridine is such a moiety which forms the basic structure of numerous medicinally important natural products such as, but not limited to, amphimedine, ascididemin, eilatin, and sampangine. Interestingly, synthetic analogues of natural pyridoacridine exhibit diverse pharmacological activities and in view of these, natural pyridoacridines can be considered as “lead compounds”. This review additionally provides a brief but critical account of inherent structure activity relationships among various subclasses of pyridoacridines. Furthermore, the current aspects and future prospects of natural pyridoacridines are detailed for further reference and consideration.

Inhibition of marine biofouling by bacterial quorum sensing inhibitors

Seventy eight natural products from chemical libraries containing compounds from marine organisms (sponges, algae, fungi, tunicates and cyanobacteria) and terrestrial plants, were screened for the inhibition of bacterial quorum sensing (QS) using a reporter strain Chromobacterium violaceum CV017. About half of the natural products did not show any QS inhibition. Twenty four percent of the tested compounds inhibited QS of the reporter without causing toxicity. The QS inhibitory activities of the most potent and abundant compounds were further investigated using the LuxR-based reporter E. coli pSB401 and the LasR-based reporter E. coli pSB1075. Midpacamide and tenuazonic acid were toxic to the tested reporters. QS-dependent luminescence of the LasR-based reporter, which is normally induced by N-3-oxo-dodecanoyl-L-homoserine lactone, was reduced by demethoxy encecalin and hymenialdisin at concentrations >6.6 μM and 15 μM, respectively. Hymenialdisin, demethoxy encecalin, microcolins A and B and kojic acid inhibited responses of the LuxR-based reporter induced by N-3-oxo-hexanoyl-L-homoserine lactone at concentrations >0.2 μM, 2.2 μM, 1.5 μM, 15 μM and 36 μM, respectively. The ability to prevent microfouling by one of the compounds screened in this study (kojic acid; final concentrations 330 μM and 1 mM) was tested in a controlled mesocosm experiment. Kojic acid inhibited formation of microbial communities on glass slides, decreasing the densities of bacteria and diatoms in comparison with the control lacking kojic acid. The study suggests that natural products with QS inhibitory properties can be used for controlling biofouling communities.

Structures and antimicrobial activities of pyridoacridine alkaloids isolated from different chromotypes of the ascidian Cystodytes dellechiajei

Three new pentacyclic alkaloids were isolated from different chromotypes of the western Mediterranean ascidian Cystodytes dellechiajei. The purple color morph collected in Catalonia contained the known compounds kuanoniamine D (1), shermilamine B (2), N-deacetylkuanoniamine D (3), and styelsamine C (4) and a new alkaloid named N-deacetylshermilamine B (5). The green color morph collected in the Balearic Islands contained the known compounds 11-hydroxyascididemin (6) and 8,9-dihydro-11-hydroxyascididemin (7) and two new alkaloids named cystodimine A (8) and cystodimine B (9). The blue color morph collected in Catalonia yielded the known compound ascididemin (10). The structures of all compounds were elucidated on the basis of spectroscopic data, mainly 1D and 2D NMR data. The antimicrobial potential of the pyridoacridine alkaloids isolated from each color morph was evaluated and compared.

Naturally Occurring Nitrogen–Sulfur Compounds. The Benzothiazole Alkaloids

Several alkaloids contain both nitrogen and sulfur, and a subset of these interesting terrestrial and marine natural products – the benzothiazoles – forms the subject of the present short review. Benzothiazole alkaloids are relatively rare in Nature, but they range in structural complexity from benzothiazole itself and simple derivatives thereof, through the well-known firefly luciferin, to more complex molecules such as the thiazo-rifamycins and the dercitin-kuanoniamine family. Although the biosynthesis of benzothiazoles has not been studied in many cases, the evidence suggests that they are derived from cysteine addition to benzoquinone derivatives followed by ring contraction of the resulting benzothiazine adducts. The review also highlights the fact that little synthetic work has been done on benzothiazole-containing natural products.

Nordehydrocyclodercitin, a hexacyclic pyridoacridine alkaloid from the marine ascidian,Aplidiumsp

A new hexacyclic pyridoacridine alkaloid, nordehydrocyclodercitin (1), from an ascidian, Aplidium sp., cf. Aplidium cratiferum collected at Arab Reef, Great Barrier Reef, Australia is reported. Nordehydrocyclodercitin is structurally related to stellettamine (2) and cyclodercitin (3), which are sponge metabolites, and cycloshermilamine D (4) which was isolated from the marine tunicate Cystodytes violatinctus. The structure of nordehydrocyclodercitin was determined by interpretation of spectroscopic data, particularly those obtained from HMBC correlations, and by comparison with reported data for known related pyridoacridine alkaloids.

Anticancer activity evaluation of kuanoniamines A and C isolated from the marine sponge Oceanapia sagittaria, collected from the Gulf of Thailand

The pyridoacridine alkaloids kuanoniamines A and C were isolated together with 24 α-methylcholestanol, p-hydroxybenzaldehyde, p-hydroxybenzoic acid, phenylacetic acid and 3-formylindole from the ethyl acetate extract of the marine sponge Oceanapia sagittaria (Sollas), collected from the Gulf of Thailand. Kuanoniamines A and C were evaluated for their effect on the growth of five human tumour and a non-tumour cell lines, as well as on the proliferation of human lymphocytes. Kuanoniamine A was found to be a potent growth inhibitor of all the tumour and a non-tumour cell lines while kuanoniamine C was less potent but showed high selectivity toward the estrogen dependent (ER+) breast cancer cell line. Kuanoniamine A has shown to be a more potent inhibitor of DNA synthesis than kuanoniamine C. Kuanoniamine A was also found to cause an extensive reduction of the MCF-7 cells in G2/M phase as well as an increase in the apoptotic cells.

The nature and role of pigments of marine invertebrates

Marine animals, especially those from tropical waters, are often brilliantly coloured, and bright colouration is widespread in both sessile and non-sessile invertebrates. These spectacular natural colours are common in species inhabiting shallow waters, and appear not only in animals exposed to bright light, but also in those living in dark areas where colours are visible only with artificial illumination. Marine organisms also show variation in colour with depth and geographical location, and display great variety in colour patterning. These colour characteristics are the result of several different processes, and serve various purposes - the distribution and function of pigments seems to vary between invertebrate groups. In addition to playing an important role in how marine organisms interact, pigments may be involved in physiological processes. Although nitrogenous pigments predominate, marine organisms contain pigments belonging to all the major structural classes of natural products, as well as some that are unique to the marine environment. This review discusses the nature and significance of such pigments, the chemical and biological processes involved, the factors responsible for and affecting bright colourations, as well as their evolution and speculation as to their function.

Bioactive Marine Alkaloids

The chapter deals with bioactive marine alkaloids. The chemistry and biological activities of pyridoacridines, pyrroloacridines, indoles, β-carbolines, pyrroles, isoquinolines, and tyrosine derived alkaloids have been discussed and reviewed.

Marine natural products as prototype agrochemical agents

In the interest of identifying new leads that could serve as prototype agrochemical agents, 18 structurally diverse marine-derived compounds were examined for insecticidal, herbicidal, and fungicidal activities. Several new classes of compounds have been shown to be insecticidal, herbicidal, and fungicidal, which suggests that marine natural products represent an intriguing source for the discovery of new agrochemical agents.

Marine pyridoacridine alkaloids and synthetic analogues as antitumor agents

Pyrido[4,3,2-mn]acridines are of major interest as metabolites in sponges and ascidians. During the last few years, numerous additional compounds of this family were isolated, some of them being polycyclic structures already reported with different substituents (shermilamine or kuanoniamine-derivatives), others, such as neoamphimedine, arnoamines and styelsamines having original structures. The synthesis of these compounds and analogues have been performed in order to allow their biological evaluation. In most of the cases, the cytotoxicity of analogues was improved compared to the natural product, specially in ascididemin or meridine series. The pyridoacridines have not a sole mode of action, but it seems that the reductive DNA cleavage mediated by reactive oxygen species is a potential general mode of action.

Insect antifeedant activity of flavones and chromones against Spodoptera litura

The antifeedant polymethylated flavones 5-hydroxy-3,6,7,8,4'-heptamethoxyflavone, 5-hydroxy-3,6,7,8-tetramethoxyflavone, and 5,6-dihydroxy-3,7-dimethoxyflavone have been isolated from the cudweed, Gnaphalium affine D. Don (Compositae). These flavonoids and authentic analogues showed insect antifeedant activity against the common cutworm (Spodoptera litura F.). In a previous paper, it was suggested that there was no substituent on the B-ring of the flavonoid for the beneficial antifeedant activity against the common cutworm. These flavonoids having a phenyl group as the B-ring and the chromone as elimination of the B-ring from the flavonoids were used to test the hypothesis of the previously described B-ring effect. The known fact is that Sculletaria baicarensis (Rutaceae) produced the 2-phenyl flavone. Test compounds and their methylated derivatives were prepared from this material for the structure-activity relationship (SAR) study of insect antifeedant activity. In spite of the 2-phenyl flavonoids, some tested compounds did not show any insect antifeedant activity against the common cutworm, although these inactive flavonoids were deficient in the 6-substituent group on the A-ring of the flavonoid. This 6-position-substituted derivative almost showed strong insect antifeedant activity against common cutworm. Moreover, the tested flavonoids having a hydroxyl group as a substituent on any of the positions tended to increase the activity. These results suggested the importance of the 6-position substitution on the flavonoid; however, hydrophilic substituents decreased the activity. Baicalein (5,6,7-trihydroxyflavone) derivatives did not show any activity despite having the 6-substituent derivative. Although the activity of some chromones increased the activity of the flavone, the bulky B-ring was a disadvantage for the antifeedant activity. It was suggested that the charge on C(3) and C(5) of the flavonoid was important for the biological activity. Additionally, an adequate hydrogen bonding property, which is different from lipophilicity, was an advantage for the activity on the basis of a QSAR analysis.

Structures and cytotoxic properties of sponge-derived bisannulated acridines

A reinvestigation of sponge natural products from additional Indo-Pacific collections of Xestospongiacf. carbonaria and X. cf. exigua has provided further insights on the structures, biological activities, and biosynthetic origin of bisannulated acridines. These alkaloids include one known pyridoacridine, neoamphimedine (2), and three new analogues, 5-methoxyneoamphimedine (4), neoamphimedine Y (5), and neoamphimedine Z (6). A completely new acridine, alpkinidine (7), was also isolated. A disk diffusion soft agar assay, using a panel of five cancer cell lines (solid tumors and leukemias) and two normal cells, was used to evaluate the differential cytotoxicity (solid tumor selectivity) of the sponge semipure extracts and selected compounds including amphimedine (1), 2, 4, and 7. While all four compounds were solid tumor selective, 1 and 2 were the most potent and 4 was the most selective. The rationale used to characterize the new structures is outlined along with the related biosynthetic pathways envisioned to generate 2 and 7.

The pyridoacridine family tree: a useful scheme for designing synthesis and predicting undiscovered natural products

The pyridoacridine natural products represent a large and growing class and serve here to illustrate the wealth of information that can be extracted by comparing natural products on the basis of structure and occurrence.

Three new pyridoacridine type alkaloids from a singaporean ascidian

Two new pyridoacridine alkaloids, kuanoniamines E and F, and a new ring-opened pyridoacridine alkaloid, subarine, were isolated from a Singaporean ascidian. Also isolated were known pyridoacridine alkaloids ascididemin and kuanoniamines A and D. The structures of the alkaloids were determined by spectroscopic methods.

Anti-proliferative effects of new staurosporine derivatives isolated from a marine ascidian and its predatory flatworm

Nine indolocarbazole alkaloids of the staurosporine type, including three new derivatives, were evaluated for their potential as inhibitors of cell proliferation and macromolecule synthesis. Four derivatives were tested as inhibitors of cell proliferation with twelve human leukemia cell lines and demonstrated powerful antiproliferative activities, with 3-hydroxystaurosporine being the most potent. IC(50) values were determined using the cell line MONO-MAC-6 and with an IC(50) of 13 ng/ml, 3-hydroxystaurosporine turned out to be one of the most active staurosporine-type inhibitors described so far. All derivatives, except 3-hydroxy-3'-demethoxy-3'-hydroxystaurosporine and 4'-N-methylstaurosporine very strongly reduced RNA and DNA synthesis with 3-hydroxystaurosporine again being the strongest inhibitor. Analysis of structure-activity relationships demonstrated that hydroxylation of staurosporine at position 3 of the indolocarbazole moiety caused an increase in anti-proliferative activity, while hydroxylation at carbon 11 resulted in a decrease in activity. Our results suggest that not only the presence or absence of hydrophilic substitutions, but also the position of the alteration within the molecule, is important in the antiproliferative properties of the various staurosporine analogues.

A polyisoprenylated benzophenone from Cuban propolis

A novel polyisoprenylated benzophenone (1) has been isolated from an ethanol extract of Cuban propolis. Its structure has been determined using high-field 2D NMR techniques. Compound 1 showed significant antimicrobial and antifungal activity against a variety of bacteria and yeasts.

Evaluation of toxicity of some saponins on brine shrimp

Toxicity of several types of saponins (1-11) against brine shrimp (Artemia salina) were evaluated. As a result, it was found that most tested compounds were not toxic to brine shrimp at high enough concentration. The most toxic saponin (1) to brine shrimp showed also cytotoxicity towards HL-60 tumor cell line using MTT assay. Brine shrimp model may thus be used as bench-top assay in finding cytotoxic components from saponin-containing fractions of plant extracts.