Abstract
Three new napyradiomycins (1–3) were isolated from the culture broth of a marine-derived actinomycete strain SCSIO 10428, together with six known related analogues napyradiomycin A1 (4), 18-oxonapyradiomycin A1 (5), napyradiomycin B1 (6), napyradiomycin B3 (7), naphthomevalin (8), and napyradiomycin SR (9). The strain SCSIO 10428 was identified as a Streptomyces species by the sequence analysis of its 16S rRNA gene. The structures of new compounds 1–3, designated 4-dehydro-4a-dechloronapyradiomycin A1 (1), 3-dechloro-3-bromonapyradiomycin A1 (2), and 3-chloro-6,8-dihydroxy-8-α-lapachone (3), respectively, were elucidated by comparing their 1D and 2D NMR spectroscopic data with known congeners. None of the napyradiomycins 1–9 showed antioxidative activities. Napyradiomycins 1–8 displayed antibacterial activities against three Gram-positive bacteria Staphylococcus and Bacillus strains with MIC values ranging from 0.25 to 32 μg mL−1, with the exception that compound 3 had a MIC value of above 128 μg mL−1 against Staphylococcus aureus ATCC 29213. Napyradiomycins 2, 4, 6, and 7 exhibited moderate cytotoxicities against four human cancer cell lines SF-268, MCF-7, NCI-H460, and HepG-2 with IC50 values below 20 μM, while the IC50 values for other five napyradiomycins 1, 3, 5, 8 and 9 were above 20 μM.
Highlights
In the past decade, marine-derived actinomycetes have emerged as a valuable source for drug discovery [1,2]
The neighbor-joining tree was constructed based on the 16S rRNA gene sequences of strain SCSIO 10428 and other closely related Streptomyces species (Figure S1)
Compounds 1–3 were elucidated as new compounds, designated 4-dehydro-4a-dechloronapyradiomycin A1 (1), 3-dechloro-3-bromonapyradiomycin A1 (2), and 3-chloro-6,8-dihydroxy-8-α-lapachone (3), respectively, on the basis of the analysis of MS, 1D and 2D NMR data and the comparison with known compounds
Summary
Marine-derived actinomycetes have emerged as a valuable source for drug discovery [1,2]. A number of structurally unique natural products with antitumor [3,4], antiinfective [5], and antimalarial bioactivities [6], have been discovered from marine-derived actinomycetes. Our recent efforts on marine-derived actinomycetes led to the isolation of structurally diverse novel natural products with antibacterial, antitumor, and antimalarial bioactivities [7,8,9,10,11,12,13,14,15,16,17]. In the course of our continuous searching for new bioactive natural products from marine-derived actinomycetes, crude fermentation extracts of the actinomycetal strain SCSIO 10428 were found to exhibit significant antimicrobial activities and to be lethal to brine shrimp (Artemia salina). We report the isolation, structure elucidation, and biological activities of these nine compounds
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