Isolation of Scalimides A-L: ß-Alanine-Bearing Scalarane Analogs from the Marine Sponge Spongia sp.

A chemical investigation of a methanol extract of Spongia sp., a marine sponge collected from the Philippines, identified 12 unreported scalarane-type alkaloids-scalimides A-L (1-12)-together with two previously described scalarin derivatives. The elucidation of the structure of the scalaranes based on the interpretation of their NMR and HRMS data revealed that 1-12 featured a ß-alanine-substituted E-ring but differed from each other through variations in their oxidation states and substitutions occurring at C16, C24, and C25. Evaluation of the antimicrobial activity of 1-12 against several Gram-positive and Gram-negative bacteria showed that 10 and 11 were active against Micrococcus luteus and Bacillus subtilis, respectively, with MIC values ranging from 4 to 16 µg/mL.

Cytoprotective Polyketides from Sponge-Derived Fungus Lopadostoma pouzarii.

The new polyketides lopouzanones A and B, as well as the new 1-O-acetyl and 2-O-acetyl derivatives of dendrodochol B, were isolated from the sponge-derived marine fungus Lopadostoma pouzarii strain 168CLC-57.3. Moreover, six known polyketides, gliorosein, balticolid, dendrodolide G, dihydroisocoumarine, (-)-5-methylmellein, and dendrodochol B, were identified. The structures of the isolated compounds were determined by a combination of NMR and ESIMS techniques. The absolute configurations of the lopouzanones A and B were determined using the Mosher's method. The cytotoxicity of the isolated compounds against human prostate cancer cells PC-3 and normal rat cardiomyocytes H9c2 was investigated. Gliorosein showed weak DPPH radical-scavenging activity and in vitro cardioprotective effects toward rotenone toxicity and CoCl2-mimic hypoxia.

Transcriptional and toxic responses to saxitoxin exposure in the marine copepod Tigriopus japonicus.

Saxitoxin (STX) is a highly toxic marine neurotoxin produced by phytoplankton and a growing threat to ecosystems worldwide due to the spread of toxic algae. Although STX is an established sodium channel blocker, the overall profile of transcriptional levels in STX-exposed organisms has yet to be described. Here, we describe a toxicity assay and transcriptome analysis of the copepod Tigriopus japonicus exposed to STX. The half-maximal lethal concentration of STX was 12.35 µM, and a rapid mortality slope was evident at concentrations between 12 and 13 µM. STX induced changes in swimming behavior among the copepods after 10 min of exposure. In transcriptome analysis, gene ontology revealed that the genes involved in nervous system and gene expression were highly enriched. In addition, the congenital neurological disorder and nuclear factor erythroid 2-related factor 2-mediated oxidative stress pathways were identified to be the most significant in network analysis and toxicity pathway analysis, respectively. This study provides valuable information about the effects of STX and related transcriptional responses in T. japonicus.

Phytochemical characterization and bioactivity toward breast cancer cells of unhydrolyzed and acid-hydrolyzed extracts of Fagonia indica.

Phytochemicals from the genus, Fagonia, have been attracting increasing attention due to their potential beneficial effects on human health. Fagonia species contain various types of phytochemicals such as flavonoids, alkaloids, saponins, terpenoids, coumarins and tannins. In this study, we investigated the phytochemical composition of unhydrolyzed and acid-hydrolyzed extracts of Fagonia indica and their bioactivity toward breast cancer MCF-7 cells in vitro. The results revealed that F. indica contains phytochemicals consistent with the reported phytochemical composition of this Fagonia species, with greater amounts of aglycones detected in the hydrolyzed extract. The crude extract of F. indica without acid hydrolysis was found to be ineffective in inhibiting the growth of MCF-7 cells at doses below 1000 µg/mL. However, after acid hydrolysis (to mimic gastro-intestinal hydrolysis), the F. indica extract became growth-inhibitory to MCF-7 cells as low as 10 µg/mL and the cytotoxicity increased with increasing dose and time of treatment. The results suggest that F. indica extracts contain phytochemicals in glycosidic forms whose aglycones are active as anti-proliferative agents toward breast cancer cells in vitro.

Inhibitory Effects of Nitrogenous Metabolites from a Marine-Derived Streptomyces bacillaris on Isocitrate Lyase of Candida albicans.

Two nitrogenous metabolites, bacillimide (1) and bacillapyrrole (2), were isolated from the culture broth of the marine-derived actinomycete Streptomyces bacillaris. Based on the results of combined spectroscopic and chemical analyses, the structure of bacillimide (1) was determined to be a new cyclopenta[c]pyrrole-1,3-dione bearing a methylsulfide group, while the previously reported bacillapyrrole (2) was fully characterized for the first time as a pyrrole-carboxamide bearing an alkyl sulfoxide side chain. Bacillimide (1) and bacillapyrrole (2) exerted moderate (IC50 = 44.24 µM) and weak (IC50 = 190.45 µM) inhibitory effects on Candida albicans isocitrate lyase, respectively. Based on the growth phenotype using icl-deletion mutants and icl expression analyses, we determined that bacillimide (1) inhibits the transcriptional level of icl in C. albicans under C2-carbon-utilizing conditions.

Crystal structure of AmpC BER and molecular docking lead to the discovery of broad inhibition activities of halisulfates against ß-lactamases.

AmpC BER is an extended-spectrum (ES) class C ß-lactamase with a two-amino-acid insertion in the H10 helix region located at the boundary of the active site compared with its narrow spectrum progenitor. The crystal structure of the wild-type AmpC BER revealed that the insertion widens the active site by restructuring the flexible H10 helix region, which is the structural basis for its ES activity. Besides, two sulfates originated from the crystallization solution were observed in the active site. The presence of sulfate-binding subsites, together with the recognition of ring-structured chemical scaffolds by AmpC BER, led us to perform in silico molecular docking experiments with halisulfates, natural products isolated from marine sponge. Inspired by the snug fit of halisulfates within the active site, we demonstrated that halisulfate 3 and 5 significantly inhibit ES class C ß-lactamases. Especially, halisulfate 5 is comparable to avibactam in terms of inhibition efficiency; it inhibits the nitrocefin-hydrolyzing activity of AmpC BER with a Ki value of 5.87 µM in a competitive manner. Furthermore, halisulfate 5 displayed moderate and weak inhibition activities against class A and class B/D enzymes, respectively. The treatment of ß-lactamase inhibitors (BLIs) in combination with ß-lactam antibiotics is a working strategy to cope with infections by pathogens producing ES ß-lactamases. Considering the emergence and dissemination of enzymes insensitive to clinically-used BLIs, the broad inhibition spectrum and structural difference of halisulfates would be used to develop novel BLIs that can escape the bacterial resistance mechanism mediated by ß-lactamases.

Investigation of the Fungal Diversity of the Federated States of Micronesia and the Construction of an Updated Fungal Inventory.

The Federated States of Micronesia (FSM) is an island country in the western Pacific and is a known biodiversity hotspot. However, a relatively small number of fungi (236 species) have been reported till July 2021. Since fungi play major ecological roles in ecosystems, we investigated the fungal diversity of FSM from various sources over 2016 and 2017 and constructed a local fungal inventory, which also included the previously reported species. Fruiting bodies were collected from various host trees and fungal strains were isolated from marine and terrestrial environments. A total of 99 species, of which 78 were newly reported in the FSM, were identified at the species level using a combination of molecular and morphological approaches. Many fungal species were specific to the environment, host, or source. Upon construction of the fungal inventory, 314 species were confirmed to reside in the FSM. This inventory will serve as an important basis for monitoring fungal diversity and identifying novel biological resources in FSM.

Oxygenated Theonellastrols: Interpretation of Unusual Chemical Behaviors Using Quantum Mechanical Calculations and Stereochemical Reassignment of 7α-Hydroxytheonellasterol.

A total of eight new oxygenated 4-exo-methylene sterols, 1-8, together with one artifact 9 and six known sterols 11-16, were isolated from the marine sponge Theonella swinhoei collected from the Bohol province in Philippines. Structures of sterols 1-8 were determined from 1D and 2D NMR data. Among the sterols, 8α-hydroxytheonellasterol (4) spontaneously underwent an allylic 1,3-hydroxyl shift to produce 15α-hydroxytheonellasterol (9) as an artifact; this was rationalized by quantum mechanical calculations of the transition state. In addition, the 1,2-epoxy alcohol subunit of 8α-hydroxy-14,15-ß-epoxytheonellasterol (5) was assigned using the Gauge-Independent Atomic Orbital (GIAO) NMR chemical shift calculations and subsequent DP4+ analysis. Finally, comparison of the 13C chemical shifts of isolated 7α-hydroxytheonellasterol (6) with the reported values revealed significant discrepancies at C-6, C-7, C-8, and C-14, leading to reassignment of the C-7 stereochemistry in the known structure.

Enantioselective total synthesis of (+)-ieodomycin A, (+)-ieodomycin B, and their three stereoisomers.

We describe a divergent and enantioselective total synthesis of (+)-ieodomycin A and (+)-ieodomycin B with three stereoisomers. The main advantage of the present synthesis is the late-stage elaboration of the side chain, which would afford a wide range of structurally diverse analogs with interesting bioactivities.

Triterpene Glycosides Isolated from the Edible Sea Cucumber Bohadschia vitiensis and Their Antagonistic Activity against Transient Receptor Potential Ankyrin 1.

Transient receptor potential ankyrin 1 (TRPA1) is a cation channel that plays a critical role in the occurrence and transmission of pain. By screening 393 marine invertebrate extracts for their antagonistic activity against TRPA1, it was found that the extract of the edible sea cucumber Bohadschia vitiensis had a remarkable potency. Bioassay-guided separation of the extract resulted in the isolation of six triterpene glycosides, including a novel analog. All six isolated compounds exhibited high inhibitory potency against TRPA1 (IC50 values ranging from 0.60 to 3.26 µM), which is comparable to that of a previously developed synthetic antagonist (A-967079). The discovery of TRPA1 antagonists, originated from this edible sea cucumber, opens the door for the elaboration of the valuable triterpene scaffold for the development of novel safe analgesics.

Phenazine Derivatives with Anti-Inflammatory Activity from the Deep-Sea Sediment-Derived Yeast-Like Fungus Cystobasidium laryngis IV17-028.

Three new phenazine derivatives (1-3), along with known compounds (4-7) of saphenic acid derivatives, were isolated from a deep-sea sediment-derived yeast-like fungus Cystobasidium larynigs collected from the Indian Ocean. The structures of the new compounds (1-3) were determined by analysis of spectroscopic data, semi-synthesis and comparison of optical rotation values. All the isolated compounds (1-7), except for 2, showed nitric oxide (NO) production inhibitory effect against lipopolysaccharide (LPS)-induced murine macrophage RAW 264.7 cells without cytotoxicity at concentrations up to 30 µg/mL. This is the first report on the yeast-like fungus Cystobasidium laryngis producing phenazines and anti-inflammatory activity of 1-7 including saphenic acid (4).

Cytotoxic Furan- and Pyrrole-Containing Scalarane Sesterterpenoids Isolated from the Sponge Scalarispongia sp.

Three furan-containing scalarane sesterterpenoids (1⁻3) and a novel pyrrole-containing analog (4) were isolated from the sponge Scalarispongia species. Compound 3, reported in the literature as a synthetic derivative of furoscalarol 2, was for the first time isolated from a natural source. During the separation performed using a silica column in the presence of methanol, 16-methoxy derivatives (5, 6) were obtained from the unintended reaction of 2. The isolated natural products 3 and 4 and the artifact 5 showed moderate to high cytotoxicity against six human cancer cell lines, whereas compound 6, the C-16 epimer of 5, showed no cytotoxicity at a concentration of 60 µΜ.

Synthesis, Molecular Engineering, and Photophysical Properties of Fluorescent Thieno[3,2- b]pyridine-5(4 H)-ones.

We describe a synthetic approach for a set of fluorescent thieno[3,2- b]pyridine-5(4 H)-one derivatives and their photophysical properties. These fluorophores are prepared by a series of reactions employing the Suzuki-Miyaura cross-coupling reaction and a regioselective aza-[3 + 3] cycloaddition of 3-aminothiophenes with α,ß-unsaturated carboxylic acids. Our findings revealed that the photophysical properties are chemically tunable by an appropriate choice of functional group on the thieno[3,2- b]pyridine-5(4 H)-one scaffold.

Bromopyrrole Alkaloids from the Sponge Agelas kosrae.

Two new sceptrin derivatives (1,2) and eight structurally-related known bromopyrrole-bearing alkaloids were isolated from the tropical sponge Agelas kosrae. By a combination of spectroscopic methods, the new compounds, designated dioxysceptrin (1) and ageleste C (2), were determined to be structural analogs of each other that differ at the imidazole moiety. Dioxysceptrin was also found to exist as a mixture of α-amido epimers. The sceptrin alkaloids exhibited weak cytotoxicity against cancer cells. Compounds 1 and 2 also moderately exhibited anti-angiogenic and isocitrate lyase-inhibitory activities, respectively.

Streptoglycerides A-D with a Rare 6/5/5 Tricyclic Ring Skeleton from a Marine Actinomycete Streptomyces species.

Four novel secondary metabolites possessing a unique 6/5/5 tricyclic ring system, streptoglycerides A-D (1-4), were isolated from a marine actinomycete Streptomyces sp. derived from a mangrove sample collected on Kosrae Island. Their structures and absolute configurations were elucidated by spectroscopic data and electronic circular dichroism data. Streptoglyceride C (3) showed a weak inhibitory effect on the production of nitric oxide in BV-2 microglia cells.

Cyclopeptides from the Sponge Stylissa flabelliformis.

Three new cyclopeptides, phakellistatins 20-22 (1-3), as well as 10 known cyclopeptides of the same structural class were isolated from the tropical sponge Stylissa flabelliformis. By a combination of chemical and spectroscopic methods, the structures of the new compounds were determined to be an epimeric mixture of cycloheptapeptides (1) and two epimeric cyclodecapeptides (2 and 3) related to the phakellistatins. The cyclopeptides were evaluated for in vitro cytotoxicity against a variety of cancer cell lines, and compounds 2 and 3 exhibited significant activity.

Radiosensitization by Marine Sponge Agelas sp. Extracts in Hepatocellular Carcinoma Cells with Autophagy Induction.

Although radiation therapy is an effective treatment modality in many cancers, there is an urgent need to develop therapeutic drugs capable of overcoming radioresistance or minimizing normal tissue toxicity. A wide variety of marine-derived bioactive compounds have been screened for anti-cancer drug discovery, but little is known regarding radiation therapy applications. In this study, six different extracts of marine sponges collected from the Micronesian sea were screened for anti-cancer and radiosensitizing activity. Two extracts derived from Agelas sponges collected off the coast of Kosrae and Chuuk, the Federated States of Micronesia significantly decreased clonogenic survival of hepatocellular carcinoma (HCC) cells after exposure to ionizing radiation (IR). The Agelas extracts augmented IR-induced apoptosis and accumulation of reactive oxygen species (ROS). Endoplasmic reticulum (ER) stress was increased via unfolded protein response stimulation, which induced autophagy. N-acetylcysteine, a ROS scavenger, diminished ER stress and autophagy induction effects. This result indicated that Agelas extracts may sensitize HCC cells to IR via ROS overproduction in vitro. Our findings suggest that the Agelas sp. may have potential utility in radiosensitizer development.

Suppression of RANKL-Induced Osteoclastogenesis by the Metabolites from the Marine Fungus Aspergillus flocculosus Isolated from a Sponge Stylissa sp.

A new α-pyrone merosesquiterpenoid possessing an angular tetracyclic carbon skeleton, ochraceopone F (1), and four known secondary metabolites, aspertetranone D (2), cycloechinulin (3), wasabidienone E (4), and mactanamide (5), were isolated from the marine fungus Aspergillus flocculosus derived from a sponge Stylissa sp. collected in Vietnam. The structures of Compounds 1-5 were elucidated by analysis of 1D and 2D NMR spectra and MS data. All the isolated compounds were evaluated for anti-proliferation activity and their suppression effects on receptor activator of nuclear factor κB ligand (RANKL)-induced osteoclast differentiation using tartate-resisant acid phosphatase (TRAP). Compounds 1-5 had no anti-proliferative effect on human cancer cell lines up to 30 µg/mL. Among these compounds, aspertetranone D (2) and wasabidienone E (4) exhibited weak osteoclast differentiation inhibitory activity at 10 µg/mL. However, mactanamide (5) showed a potent suppression effect of osteoclast differentiation without any evidence of cytotoxicity.

Three New Cytotoxic Steroidal Glycosides Isolated from Conus pulicarius Collected in Kosrae, Micronesia.

Three new sulfated steroidal glycosides (3-5), along with known cholesterol derivatives (1,2), were isolated from the visceral extract of the cone snail Conus pulicarius. The structure of each new compound was elucidated by nuclear magnetic resonance spectroscopy and high-resolution mass spectrometry. The three new compounds exhibited significant in vitro cytotoxicity (GI50 values down to 0.49 µM) against the K562 human leukemia cell line.