Abstract
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.
Highlights
Marine actinomycetes are remarkable sources of novel secondary metabolites with wide chemical diversity [1]
The investigation of chemical components for Streptomyces species isolated from diverse marine environments has led to the discovery of diverse bioactive secondary metabolites, such as enzyme inhibitors, anticancer agents, and antibiotics [2,12,13,14,15]
Merochlorin A reportedly achieves minimum inhibitory concentration (MIC) values of 1–4 μg/mL against methicillin-resistant Staphylococcus aureus (MRSA), whereas merochlorins E and F exhibit stronger antibacterial activity against pathogenic Gram-positive strains, with MIC values of 1−2 μg/mL. The observation of this activity suggested that the gemdimethylmethylcyclohexane ring in merochlorins E and F plays an important role in the antibacterial activity [18,19]
Summary
Marine actinomycetes are remarkable sources of novel secondary metabolites with wide chemical diversity [1]. The investigation of chemical components for Streptomyces species isolated from diverse marine environments has led to the discovery of diverse bioactive secondary metabolites, such as enzyme inhibitors, anticancer agents, and antibiotics [2,12,13,14,15]. Merochlorin A reportedly achieves MIC values of 1–4 μg/mL against MRSA, whereas merochlorins E and F exhibit stronger antibacterial activity against pathogenic Gram-positive strains, with MIC values of 1−2 μg/mL. The observation of this activity suggested that the gemdimethylmethylcyclohexane ring in merochlorins E and F plays an important role in the antibacterial activity [18,19]. We describe the isolation and structural characterization of merochlorins G–J (1–4) and 10, as well as their antibacterial activity against Gram-positive bacteria
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