Cytotoxic aaptamine derivatives from the South China Sea sponge Aaptos aaptos

Anticancer potential of active alkaloids and synthetic analogs derived from marine invertebrates

In recent years, the number of cancers has soared, becoming one of the leading causes of human death. At the same time, marine anticancer substances have been the focus of marine drug research. Marine alkaloids derived from marine invertebrates like sponges are an important class of secondary metabolites, which have good bioactivities of blocking the cancer cell cycle, inducing autophagy and apoptosis of cancer cells, inhibiting cancer cell invasion and proliferation. They show potential as anticancer drug candidates. Therefore, in this review, we focus on the detailed introduction of bioactive alkaloids and their synthetic analogs from marine invertebrates, such as 4-chloro fascapysin and other 41 kinds of marine alkaloids or marine alkaloid synthetic analogs. They have significant anticancer activities on breast cancer, cervical cancer, colorectal cancer, prostate cancer, lung cancer, liver cancer, and so on. It provides new candidate compounds for anticancer drug research and provides a reference basis for marine drug resources research.

Uncommon Epoxyquinols Pyrrolocytosporin A and Cytosporin E2 from the Fungus Eutypella sp. D-1

Two uncommon epoxyquinols, pyrrolocytosporin A (1) and cytosporin E2 (2), along with the known cytosporin Y1 (3), were isolated from the solid defined medium of the Arctic-derived fungus Eutypella sp. D-1. Their structures were established through comprehensive analyses of spectroscopic and electronic circular dichroism data. Structurally, compound 1 represented the first nitrogen-containing epoxyquinol characterized by a pyrrole fused cytosporin framework, while compound 2 contained an uncommon cyclic carbonate functionality. The antibacterial, immunosuppressive, anti-inflammatory, and cytotoxic activities of all compounds were evaluated. Among the three metabolites, only compound 1 exhibited inhibitory effects on nitric oxide production induced by lipopolysaccharide with an IC50 value of 6.55 μM. Additionally, only compound 2 displayed inhibitory activity against ConA-induced T-cell proliferation with an IC50 value of 9.85 μM.

Sponge-derived alkaloid AP-7 as a sensitizer to cisplatin in the treatment of multidrug-resistant NSCLC via Chk1-dependent mechanisms

Multidrug resistance is a substantial obstacle in treating non-small cell lung cancer (NSCLC) with therapies like cisplatin (DDP)-based adjuvant chemotherapy and EGFR-tyrosine kinase inhibitors (TKIs). Aaptamine-7 (AP-7), a benzonaphthyridine alkaloid extracted from Aaptos aaptos sponge, has been shown to exhibit a broad spectrum of anti-tumor activity. However, the anti-cancer activity of AP-7 in combination with DDP and its molecular mechanisms in multidrug-resistant NSCLC are not yet clear. Our research indicates that AP-7 bolsters the growth inhibition activity of DDP on multidrug-resistant NSCLC cells. AP-7 notably disrupts DDP-induced cell cycle arrest and amplifies DDP-induced DNA damage effects in these cells. Furthermore, the combination of AP-7 and DDP downregulates Chk1 activation, interrupts the DNA damage repair-dependent Chk1/CDK1 pathway, and helps to overcome drug resistance and boost apoptosis in multidrug-resistant NSCLC cells and a gefitinib-resistant xenograft mice model. In summary, AP-7 appears to enhance DDP-induced DNA damage by impeding the Chk1 signaling pathway in multidrug-resistant NSCLC, thereby augmenting growth inhibition, both in vitro and in vivo. These results indicate the potential use of AP-7 as a DDP sensitizer in the treatment of multidrug-resistant NSCLC.

Synthesis of Novel Benzo[b][1,6]naphthyridine Derivatives and Investigation of Their Potential as Scaffolds of MAO Inhibitors

In this work, 2-alkyl-10-chloro-1,2,3,4-tetrahydrobenzo[b][1,6]naphthyridines were obtained and their reactivity was studied. Novel derivatives of the tricyclic scaffold, including 1-phenylethynyl (5), 1-indol-3-yl (8), and azocino[4,5-b]quinoline (10) derivatives, were synthesized and characterized herein for the first time. Among the newly synthesized derivatives, 5c-h proved to be MAO B inhibitors with potency in the low micromolar range. In particular, the 1-(2-(4-fluorophenyl)ethynyl) analog 5g achieved an IC₅₀ of 1.35 μM, a value close to that of the well-known MAO B inhibitor pargyline.

Marine Sponge Aaptos suberitoides Extract Improves Antiproliferation and Apoptosis of Breast Cancer Cells without Cytotoxicity to Normal Cells In Vitro

The anticancer effects and mechanisms of marine sponge Aaptos suberitoides were rarely assessed, especially for methanol extract of A. suberitoides (MEAS) to breast cancer cells. This study evaluated the differential suppression effects of proliferation by MEAS between breast cancer and normal cells. MEAS demonstrated more antiproliferation impact on breast cancer cells than normal cells, indicating oxidative stress-dependent preferential antiproliferation effects on breast cancer cells but not for normal cells. Several oxidative stress-associated responses were highly induced by MEAS in breast cancer cells but not normal cells, including the generations of cellular and mitochondrial oxidative stress as well as the depletion of mitochondrial membrane potential. MEAS downregulated cellular antioxidants such as glutathione, partly contributing to the upregulation of oxidative stress in breast cancer cells. This preferential oxidative stress generation is accompanied by more DNA damage (γH2AX and 8-hydroxy-2-deoxyguanosine) in breast cancer cells than in normal cells. N-acetylcysteine reverted these MEAS-triggered responses. In conclusion, MEAS is a potential natural product for treating breast cancer cells with the characteristics of preferential antiproliferation function without cytotoxicity to normal cells in vitro.

Microwave-assisted one-pot two-step imine formation-hetero-Diels-Alder-detosylation/aromatization sequence: direct access to dibenzo[b,h][1,6]naphthyridines

A microwave-assisted, copper-catalyzed, one-pot, two-step reaction is established to access functionalized [1,6]naphthyridines in high yields (up to 96%) starting from 2-(N-propargylamino)benzaldehydes and arylamines. This rapid and operationally simple sequential reaction allowed the construction of two new heterocyclic rings and three new (2 C-C and 1 C-N) bonds in a single synthetic operation. This reaction tolerated various electron-donating and electron-withdrawing substituents well and delivered the desired products in a shorter reaction time under microwave irradiation. This reaction proceeds through a sequential imine formation, intramolecular [4 + 2] hetero-Diels-Alder reaction, and air oxidation, followed by detosylation-aromatization steps.

FeCl3-Catalyzed Synthesis of 6-Thioxo-hexahydroindeno[1',2':4,5]imidazo[1,5-a]pyridin-12(6H)-ones via an Interesting [1,2] Oxygen Shift Pathway

An iron-catalyst mediated one-pot multicomponent route for the synthesis of novel 6-thioxo-hexahydroindeno[1',2':4,5]imidazo[1,5-a]pyridin-12(6H)-one scaffolds has been developed using ninhydrin, l-proline, and aryl isothiocyanates in ethanol medium. This methodology offers an interesting [1,2] oxygen shift mechanism pathway via a number of ring-opening and ring-closing cascade steps to provide diverse substituted hexahydroindeno-imidazo[1,5-a]pyridinones in excellent to good yields. The stereochemistry of the proline ring is lost during the course of the reaction. This protocol is well acceptable toward both electron-accepting and electron-donating functionalities at the ortho-, meta-, and para-positions of the isothiocyanate moiety. Nonhazardous conditions, step economic, and easy operational process are the advantages of this methodology.

Aaptamine derivatives with CDK2 inhibitory activities from the South China Sea sponge Aaptos suberitoides

Three new aaptamines (1-3) together with two known derivatives (4-5) were isolated from the South China Sea sponge Aaptos suberitoides. The structures of all compounds were unambiguously elucidated by spectroscopic analyses as well as the comparison with literature data. All the compounds were evaluated for their cytotoxic activities against five human cancer cell lines including H1299, H520, SCG7901, CNE-2 and SW680 cells. As a result, compounds 3-5 showed moderate cytotoxicities against H1299 and H520 cells with IC₅₀ values ranging from 12.9 to 20.6 μg/mL. Besides, compounds 3-5 also showed potent inhibitory activities toward cyclin-dependent kinase-2 (CDK2) with IC₅₀ values of 14.3, 3.0 and 6.0 μg/mL, respectively. In addition, compounds 3-5 significantly induced G1 arrests of H1299 cells at low concentrations. Drug affinity responsive target stability (DARTS) experiments were carried out and further demonstrated that compound 3 could effectively bind with CDK2 protein and protect it from the degradation by pronase.

Review on marine sponge alkaloid, aaptamine: A potential antibacterial and anticancer drug

In recent years, biological macromolecules have piqued the interest of researchers owing to their vast variety of biological uses. As a result, the marine sponge is a multicellular heterotrophic parazoan with chemicals for defence against predator assaults, biofouling and microbial diseases. These priceless molecules are known as secondary metabolites, and they are essential for survival in a highly competitive environment. So far, over 5,000 marine natural compounds have been extracted from marine sponges, making them an excellent option for drug formulation. One among them is, aaptamine, a marine alkaloid with a benzo[de][1,6]-napthyridine framework extensively distributed in marine sponges. Due to this reason, aaptamine has been intensively researched for various biological purposes, including cancer and protease inhibition, offering fresh insights into novel treatments. Keeping this in mind, we reviewed the biological significance of the marine sponge alkaloid aaptamine.

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.

Antioxidant and UV-radiation absorption activity of aaptamine derivatives - potential application for natural organic sunscreens

Antioxidant and UV absorption activities of three aaptamine derivatives including piperidine[3,2-b]demethyl(oxy)aaptamine (C1), 9-amino-2-ethoxy-8-methoxy-3H-benzo[de][1,6]naphthyridine-3-one (C2), and 2-(sec-butyl)-7,8-dimethoxybenzo[de]imidazo[4,5,1-ij][1,6]-naphthyridin-10(9H)-one (C3) were theoretically studied by density functional theory (DFT). Direct antioxidant activities of C1-C3 were firstly evaluated via their intrinsic thermochemical properties and the radical scavenging activity of the potential antioxidants with the HOO˙/HO˙ radicals via four mechanisms, including: hydrogen atom transfer (HAT), single electron transfer (SET), proton loss (PL) and radical adduct formation (RAF). Kinetic calculation reveals that HOO˙ scavenging in water occurs via HAT mechanism with C1 (k app, 7.13 × 106 M-1 s-1) while RAF is more dominant with C2 (k app, 1.40 × 105 M-1 s-1) and C3 (k app, 2.90 × 105 M-1 s-1). Antioxidant activity of aaptamine derivatives can be classified as C1 > C3 > C2. Indirect antioxidant properties based on Cu(i) and Cu(ii) ions chelating activity were also investigated in aqueous phase. All three studied compounds show spontaneous and favorable Cu(i) ion chelating activity with ΔG 0 being -15.4, -13.7, and -15.7 kcal mol-1, whereas ΔG 0 for Cu(ii) chelation are -10.4, -10.8, and -2.2 kcal mol-1 for C1, C2 and C3, respectively. In addition, all compounds show UVA and UVB absorption; in which the excitations are determined mostly as π-π* transition. Overall, the results suggest the potential applications of the aaptamines in pharmaceutics and cosmetics, i.e. as a sunscreen and antioxidant ingredient.

Marine Natural Products: A Potential Source of Anti-hepatocellular Carcinoma Drugs

Hepatocellular carcinoma (HCC) has high associated morbidity and mortality rates. Although chemical medication represents a primary HCC treatment strategy, low response rates and therapeutic resistance serve to reduce its efficacy. Hence, identifying novel effective drugs is urgently needed, and many researchers have sought to identify new anti-cancer drugs from marine organisms. The marine population is considered a "blue drug bank" of unique anti-cancer compounds with diverse groups of chemical structures. Here, we discuss marine-derived compounds, including PM060184 and bryostatin-1, with demonstrated anti-cancer activity in vitro or in vivo. Based on the marine source (sponges, algae, coral, bacteria, and fungi), we introduce pharmacological parameters, compound-induced cytotoxicity, effects on apoptosis and metastasis, and potential molecular mechanisms. Cumulatively, this review provides insights into anti-HCC research conducted to date in the field of marine natural products and marine-derived compounds, as well as the potential pharmacological mechanisms of these compounds and their status in drug development.

Four new aaptamine alkaloids from marine sponge Aaptos aaptos

Four new aaptamine alkaloids, named as 9-methoxy-N-demethylaaptanone (1), 3,5-dicarbomethoxy-1,​6-​naphthyridine (2), aaptosvanphongs A and B (3 and 4), and three known aaptamine alkaloids as 2-methoxy-3-oxoaaptamine (5), 8,9,9-trimethoxy-9H-benzo[de][1,6]-naphthyridine (6), and demethyl(oxy)aaptamine (7) were isolated from the sponge Aaptos by various chromatographic methods. Their structures were established by extensive spectroscopic analyses (HR-ESI-MS, 1 D and 2 D NMR) and by comparison of the spectral data with those reported in the literature. Compounds 1-7 significantly showed cytotoxic effects against SK-LU-1, MCF-7, HepG2, and SK-Mel-2 cell lines with IC₅₀ values in range from 7.7 ± 0.8 to 51.4 ± 1.8 µM. Among them, compound 7 exhibited the most cytotoxic activity with corresponding IC₅₀ values of 9.2 ± 1.0, 7.8 ± 0.6, 8.4 ± 0.8, and 7.7 ± 0.8 µM.

Leucandioxoles A and B, two 1,3-benzodioxole derivatives from the South China Sea sponge Leucandra sp

Two new 1,3-benzodioxole derivatives, leucandioxoles A and B (1-2), together with two known related compounds (3-4), have been isolated from the South China Sea sponge Leucandra sp. The structures of all compounds were clearly elucidated on the basis of spectroscopic analyses and compared with the literatures. The cytotoxicity against A549, Hep G2, MDA-MB-231, and HeLa cell lines of 1-4 were evaluated. Only compound 1 exhibited moderate activity against MDA-MB-231 cells with the IC₅₀ value of 7.98 ± 0.74 μM.

Aromatic Ring Substituted Aaptamine Analogues as Potential Cytotoxic Agents against Extranodal Natural Killer/T-Cell Lymphoma

A chemical modification study was conducted on the marine natural product aaptamine (1), isolated from the marine sponge Aaptos aaptos. Thirty new derivatives substituted by various aromatic rings at the 3- and 7-positions of aaptamine were prepared by bromination, followed by the Suzuki coupling reaction. Sixteen compounds displayed cytotoxicities to four cancer cell lines (IC₅₀ < 10 μM). In particular, compound 5i demonstrated a significant antiproliferative effect on the extranodal natural killer/T-cell lymphoma (ENKT) cell line SNK-6 with an IC₅₀ value of 0.6 μM. Additionally, compound 5i showed cytotoxicities to multiple lymphoma cell lines, including Ramos, Raji, WSU-DLCL2, and SU-DHL-4 cells.

Synthesis of imidazo[1,5-a]pyridines via cyclocondensation of 2-(aminomethyl)pyridines with electrophilically activated nitroalkanes

Imidazo[1,5-a]pyridines were efficiently prepared via the cyclization of 2-picolylamines with nitroalkanes electrophilically activated in the presence of phosphorous acid in polyphosphoric acid (PPA) medium.

Aaptodines A-D, Spiro Naphthyridine-Furooxazoloquinoline Hybrid Alkaloids from the Sponge Aaptos suberitoides

LC-MS-oriented fractionation of the sponge Aaptos suberitoides resulted in the isolation of four heptacyclic alkaloids, aaptodines A-D (1-4), which contain 9,10-dihydrofuro[2,3-f][1,3]oxazolo[5,4-h]quinolone and 7,8-dihydrocyclopenta[de][1,6]naphthyridine subunits with a spiro carbon atom. The structures were determined on the basis of NMR spectroscopic and single-crystal X-ray diffraction data analysis aided by electronic circular dichroism calculations and Mosher's method. A biosynthetic pathway for the formation of aaptodines A-D is postulated. Aaptodine D exhibits potent inhibition against osteoclast formation.

A Review of the Secondary Metabolites From the Marine Sponges of the Genus Aaptos

Marine sponges, which belong to the phylum Porifera (Metazoa), are considered the single best source of marine natural products. Among them, members of the genus Aaptos are attractive targets for marine natural product research owing to their abundant biogenetic ability to produce aaptamine derivatives. Apart from aaptamine alkaloids, there are also reports of other compounds from Aaptos sponges. This work reviews the secondary metabolites isolated from Aaptos species from 1982 to 2020, with 46 citations referring to 62 compounds (47 for aaptamines and 15 for others). The emphasis is placed on the structure of the organic molecules, relevant biological activities, chemical ecology aspects, and biosynthesis studies, which are described in the classifications of aaptamines and other compounds in the order of the published year.

3-(Phenethylamino)demethyl(oxy)aaptamine as an anti-dormant mycobacterial substance: Isolation, evaluation and total synthesis

3-(Phenethylamino)demethyl(oxy)aaptamine (1) was re-discovered from the marine sponge of Aaptos sp. as an anti-dormant mycobacterial substance through the bioassay-guided separation. Compound 1 showed potent anti-microbial activity against Mycobacterium bovis BCG with a minimum inhibitory concentration of 0.75 µg/mL under both aerobic conditions and hypoxic conditions inducing dormant state. Compound 1 was also effective against pathogenic M. tuberculosis strains including clinical multidrug-resistant strains. Furthermore, the successful total syntheses of 1 and its analog 3-aminodemethyl(oxy)aaptamine (2) afford sufficient quantities for further biological studies.

Towards 20,20-difluorinated bryostatin: synthesis and biological evaluation of C17,C27-fragments

The syntheses of compounds corresponding to 20,20-difluorinated C17–C27 fragments of bryostatin are reported together with preliminary PKC binding data.

N-Me-trichodermamide B isolated from Penicillium janthinellum, with antioxidant properties through Nrf2-mediated signaling pathway

A new trichodermamide-like alkaloid, N-Me-trichodermamide B (compound 1), was isolated from a marine fungus Penicillium janthinellum HDN13-309. The structure and absolute configuration of compound 1 were determined by extensive NMR analysis and the modified Mosher's method. This new alkaloid exhibited cellular protection from the H₂O₂-induced oxidative damage, and the mechanism study revealed that this antioxidant activity was regulated through Nrf2-mediated signaling pathway in HaCaT human keratinocytes. In addition, the inhibitor of p38 abrogated compound 1-induced phosphorylation of p38, up-expression of HO-1, and the nuclear localization of Nrf2. As a result, it suggested that this new alkaloid-induced antioxidant signaling pathway might be initiated through activation of p38.

Influence of Aaptamine Alkaloids on the Growth of Seedling Roots of Agricultural Plants

The effect of spongean alkaloids aaptamine (1), isoaaptamine (2), 9-demethylaaptamine (3), aaptanone (4), N-demethylaaptanone (5), and semisynthetic 4- N-methylaaptanone (6) was studied on the growth of seedlings roots of soy { Glycine max (L.) Merr.}, maize ( Zea mays L.), wheat ( Triticum aestivum L.), buckwheat ( Fagopyrum esculentum Moench), and barley ( Hordeum vulgare L.). It was shown that a stimulatory effect depends on the chemical structure of the compounds and species of crop plants. The structural motif of aaptamines 1–3 is essential for a stimulating activity on the growth of seedling roots of soy, maize, and wheat. The oxygenated 1,6-naphthyridine core of aaptanones 5 and 6 is important for their growth stimulating activity on barley roots.

Leucanone A and naamine J, glycerol ether lipid and imidazole alkaloid from the marine sponge Leucandra sp

Chemical investigation on CH₂Cl₂ extract of the marine sponge Leucandra sp. afforded two new compounds named leucanone A (1) and naamine J (2), together with eight known compounds (3-10). Their structures were elucidated on the basis of NMR spectroscopic analyses, and comparing with the literature. The cytotoxic activities of the compounds were evaluated against four cancer cell lines, and compound 2 showed mild cytotoxic activities against MCF-7, A549, HeLa, and PC9 cancer cell lines with IC₅₀ values in the range of 20.1-45.3 μM.

Muscarine, imidazole, oxazole and thiazole alkaloids

Covering: July 2012 to June 2015. Previous review: Nat. Prod. Rep., 2013, 30, 869-915The structurally diverse imidazole-, oxazole-, and thiazole-containing secondary metabolites are widely distributed in terrestrial and marine environments, and exhibit extensive pharmacological activities. In this review the latest progress involving the isolation, biological activities, and chemical and biogenetic synthesis studies on these natural products has been summarized.

Ag(i)-Catalyzed one-pot synthesis of 4-fluorobenzo[b][1,6] naphthyridines and 4-fluoroisoquinolines via iminofluorination of alkynes with Selectfluor

Ag(i)-Catalyzed one-pot synthesis of 4-fluorobenzo[b][1,6]naphthyridines is described from o-alkynylquinolinyl aldehydes through imines.

N-Demethylaaptanone, A new Congener of Aaptamine Alkaloids from the Vietnamese Marine Sponge Aaptos aaptos

A new compound, N-demethylaaptanone (5), having an oxygenated 1,6-naphthyridine core, has been isolated from the Vietnamese marine sponge Aaptos aaptos, along with the known metabolites, aaptamine (1), isoaaptamine (2), 9-demethylaaptamine (3), and aaptanone (4). The structure of N-demethylaaptanone was determined as 9-hydroxy-8-methoxy-4 H-benzo[ de][1,6]-naphthyridine-5,6-dione from spectroscopic data.

Marine natural products

This review covers the literature published in 2014 for marine natural products (MNPs), with 1116 citations (753 for the period January to December 2014) referring to compounds isolated from marine microorganisms and phytoplankton, green, brown and red algae, sponges, cnidarians, bryozoans, molluscs, tunicates, echinoderms, mangroves and other intertidal plants and microorganisms. The emphasis is on new compounds (1378 in 456 papers for 2014), together with the relevant biological activities, source organisms and country of origin. Reviews, biosynthetic studies, first syntheses, and syntheses that lead to the revision of structures or stereochemistries, have been included.

Ligand-free palladium-catalyzed facile construction of tetra cyclic dibenzo[b,h][1,6]naphthyridine derivatives: domino sequence of intramolecular C–H bond arylation and oxidation reactions

A ligand-free Pd-catalyzed approach has been developed for the synthesis of dibenzo-fused naphthyridines.

Three new aaptamine derivatives from the South China Sea sponge Aaptos aaptos

Three new aaptamine derivatives (1-3), together with six known related compounds (4-9), have been isolated from the South China Sea sponge Aaptos aaptos. The structures of all compounds were unambiguously elucidated on the basis of spectroscopic analyses. Compounds 1, 4, 5, 7, and 9 showed cytotoxic activities against HeLa, K562, MCF-7, and U937 cell lines with IC50 values in the range of 0.90-12.32 μM.

Aaptamine derivatives with antifungal and anti-HIV-1 activities from the South China Sea sponge Aaptos aaptos

Five new alkaloids of aaptamine family, compounds (1–5) and three known derivatives (6–8), have been isolated from the South China Sea sponge Aaptos aaptos. The structures of all compounds were unambiguously elucidated by spectroscopic analyses, as well as by comparison with the literature data. Compounds 1–2 are characterized with triazapyrene lactam skeleton, whereas compounds 4–5 share an imidazole-fused aaptamine moiety. These compounds were evaluated in antifungal and anti-HIV-1 assays. Compounds 3, 7, and 8 showed antifungal activity against six fungi, with MIC values in the range of 4 to 64 μg/mL. Compounds 7–8 exhibited anti-HIV-1 activity, with inhibitory rates of 88.0% and 72.3%, respectively, at a concentration of 10 μM.