Five new sesterterpenes, 14,15-dehydro-6-epi-ophiobolin K (1), 14,15-dehydro- ophiobolin K (2), 14,15-dehydro-6-epi-ophiobolin G (3), 14,15-dehydro-ophiobolin G (4) and 14,15-dehydro-(Z)-14-ophiobolin G (5), together with four known ophiobolins (6–9) were isolated from the marine fungus Aspergillus flocculosus derived from the seaweed Padina sp. collected in Vietnam. The five new ophiobolins were first isolated as ophiobolin derivatives consisting of a fully unsaturated side chain. Their structures were elucidated via spectroscopic methods including 1D, 2D NMR and HR-ESIMS. The absolute configurations were determined by the comparison of chemical shifts and optical rotation values with those of known ophiobolins. All compounds (1–9) were then evaluated for their cytotoxicity against six cancer cell lines, HCT-15, NUGC-3, NCI-H23, ACHN, PC-3 and MDA-MB-231. All the compounds showed potent cytotoxicity with GI₅₀ values ranging from 0.14 to 2.01 μM.

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 hydroxylated rhamnolipids, dokdolipids A−C (1−3) were obtained from the marine actinomycete Actinoalloteichus hymeniacidonis, which was isolated from a sediment sample collected off the coasts of Dokdo island, Republic of Korea. The structures of the isolated compounds were elucidated on the basis of 1D and 2D NMR and mass spectrometric data analyses. Their absolute configurations were assigned using the modified Mosher’s method and specific rotation values, as well as acid hydrolysis, chemical derivatizations and subsequent HPLC analysis to determine the configuration of the sugar moieties. All new compounds were evaluated for their cytotoxicity against six cancer cell lines, HCT-15, NUGC-3, NCI-H23, ACHN, PC-3 and MDA-MB-231. Compounds 1−3 displayed moderate cytotoxicity against all the cell lines tested with IC₅₀ values ranging from 13.7−41.5 µM.

Two new phomaligols, deketo-phomaligol A (1) and phomaligol E (2), together with six known compounds (3–8) were isolated from the culture broth of the marine-derived fungus Aspergillus flocculosus. Compound 1 was first isolated as a phomaligol derivative possessing a five-membered ring. The structures and absolute configurations of the new phomaligols were determined by detailed analyses of mass spectrometry (MS), nuclear magnetic resonance (NMR) data, optical rotation values and electronic circular dichroism (ECD). In addition, the absolute configurations of the known compounds 3 and 4 were confirmed by chemical oxidation and comparison of optical rotation values. Isolated compounds at a concentration of 100 μM were screened for inhibition of nitric oxide (NO) production in lipopolysaccharide (LPS)-induced BV-2 microglial cells. Among the compounds, 4 showed moderate anti-neuroinflammatory effects with an IC₅₀ value of 56.6 μM by suppressing the production of pro-inflammatory mediators in activated microglial cells without cytotoxicity.

Melanoma is an aggressive skin cancer with a high risk of cancer-related deaths, and inducing apoptosis in melanoma cells is a promising therapeutic strategy. This study investigates the anti-tumor potential of a novel lucknolide derivative LA-UC as a therapeutic candidate for melanoma. Lucknolide A (LA), a tricyclic ketal-lactone metabolite isolated from marine-derived Streptomyces sp., was chemically modified by introducing a 10-undecenoyl group to synthesize LA-UC. LA-UC preferentially inhibited the proliferation of melanoma cells, including B16F10, while exerting minimal effects on normal melanocytes or other tumor cell types, indicating the selective action of LA-UC against melanoma cells. LA-UC decreased G2/M checkpoint proteins, including cyclin B1 and Cdc2, while activating caspase-3 and caspase-9, resulting in G2/M cell cycle arrest and inducing apoptotic cell death in B16F10 cells. The addition of a pan-caspase inhibitor confirmed the caspase-dependent mechanism of LA-UC-induced cell death. Additionally, LA-UC elevated mitochondrial ROS levels, leading to mitochondrial membrane disruption, upregulation of pro-apoptotic proteins, and DNA damage in melanoma cells. The ROS scavenger N-acetylcysteine reduced LA-UC-induced mitochondrial ROS accumulation, mitochondrial membrane disruption, DNA damage, and apoptosis. Collectively, these findings suggest that LA-UC induces G2/M cell cycle arrest and caspase-dependent apoptosis in B16F10 cells through excessive mitochondrial ROS generation, membrane impairment, and DNA damage, highlighting its potential as a promising therapeutic candidate for melanoma treatment.