A cytotoxic alkaloidal meroterpenoid, saccharoquinoline (1), has been isolated from the fermentation broth of the marine-derived bacterium Saccharomonospora sp. CNQ-490. The planar structure of 1 was elucidated by 1D, 2D NMR, and MS spectroscopic data analyzes, while the relative configuration of 1 was defined through the interpretation of NOE spectroscopic data. Saccharoquinoline (1) is composed of a drimane-type sesquiterpene unit in combination with an apparent 6,7,8-trihydroxyquinoline-2-carboxylic acid. This combination of biosynthetic pathways was observed for the first time in natural microbial products. Saccharoquinoline (1) was found to have cytotoxicity against the HCT-116 cancer cell line by inducing G1 arrest, which leads to cell growth inhibition.

Antartin (1), a new zizaane-type sesquiterpene, was isolated from Streptomyces sp. SCO736. The chemical structure of 1 was assigned from the interpretation of 1D and 2D NMR in addition to mass spectrometric data. The relative stereochemistry of 1 was determined by analysis of NOE data, while the absolute stereochemistry was decided based on a comparison of experimental and calculated electronic circular dichroism (ECD) spectra. Antartin (1) showed cytotoxicity against A549, H1299, and U87 cancer cell lines by causing cell cycle arrest at the G1 phase.

A cyclic depsipeptide, nobilamide I (1), along with the known peptide A-3302-B/TL-119 (2), was isolated from the saline cultivation of the marine-derived bacterium Saccharomonospora sp., strain CNQ-490. The planar structure of 1 was elucidated by interpretation of 1D and 2D NMR and MS spectroscopic data. The absolute configurations of the amino acids in 1 were assigned by using the C₃ Marfey’s analysis and comparing them with those of 2 based on their biosynthetic pathways. Nobilamide I (1) decreased cell motility by inhibiting epithelial–mesenchymal transition markers in A549 (lung cancer), AGS (gastric cancer), and Caco2 (colorectal cancer) cell lines. In addition, 1 modulated the expression of the matrix metalloproteinase (MMP) family (MMP2 and MMP9) in the three cell lines.

Four new chlorinated meroterpenoids, merochlorins G−J (1−4), and 10, a dihydronaphthalenedione precursor, along with known merochlorins A (5) and C−F (6−9), were obtained from cultivation of the bacterium strain Streptomyces sp. CNH-189, which was isolated from marine sediment. The planar structures of compounds 1−4 and 10 were elucidated by interpretation of MS, UV, and NMR spectroscopic data. The relative configurations of compounds 1−4 were determined via analysis of nuclear Overhauser effect (NOE) spectroscopic data, after which their absolute configurations were established by comparing the experimental electronic circular dichroism (ECD) spectra of compounds 1−4 to those of previously reported possible enantiomer models and DP4 calculations. Compound 3 displayed strong antibacterial activities against Bacillus subtilis, Kocuria rhizophila, and Staphylococcus aureus, with MIC values of 1, 2, and 2 μg/mL, respectively, whereas compound 1 exhibited weak antibacterial effects on these three strains, with a 16−32 μg/mL MIC value range.

Mycousfurans (1 and 2), two new usnic acid congeners, along with (−)-mycousnine (3), (−)-placodiolic acid (4), and (+)-usnic acid (5), were isolated using high-performance liquid chromatography-ultraviolet (HPLC-UV)-guided fractionation of extracts of Mycosphaerella sp. isolated from a marine sediment. The planar structures of 1 and 2 were elucidated using 1D and 2D NMR spectra. The relative configurations of the stereogenic carbons of 1 and 2 were established via analysis of their nuclear Overhauser spectroscopy (NOESY) spectra, and their absolute configurations were determined using a comparison of experimental and calculated electronic circular dichroism (ECD) spectra. Compounds 1 and 2 were found to have antibacterial activity, showing moderate activity against Kocuria rhizophila and Staphylococcus aureus.

Analysis of the chemical components from the culture broth of the marine bacterium Saccharomonospora sp. CNQ-490 has yielded three novel compounds: saccharobisindole (1), neoasterric methyl ester (2), and 7-chloro-4(1H)-quinolone (3), in addition to acremonidine E (4), pinselin (5), penicitrinon A (6), and penicitrinon E (7). The chemical structures of the three novel compounds were elucidated by the interpretation of 1D, 2D nuclear magnetic resonance (NMR), and high-resolution mass spectrometry (HRMS) data. Compound 2 generated weak inhibition activity against Bacillus subtilis KCTC2441 and Staphylococcus aureus KCTC1927 at concentrations of 32 μg/mL and 64 μg/mL, respectively, whereas compounds 1 and 3 did not have any observable effects. In addition, compound 2 displayed weak anti-quorum sensing (QS) effects against S. aureus KCTC1927 and Micrococcus luteus SCO560.