Abstract
An actinomycete strain (H12-15) isolated from a sea sediment in a mangrove district was identified as Streptomyces antibioticus on the basis of 16S rDNA gene sequence analysis as well as the investigation of its morphological, physiological, and biochemical characteristics. Two novel benzamido nonacyclic dilactones, namely neoantimycins A (1) and B (2), together with the known antimycins A1ab (3a,b), A2a (4), and A9 (5), were isolated from the culture broth of this strain. Compounds 1 and 2 are the first natural modified ATNs with an unusual benzamide unit. The structures of these new compounds, including their absolute configuration, were established on the basis of HRMS, NMR spectroscopic data, and quantum chemical ECD calculations. Their cytotoxicities against human breast adenocarcinoma cell line MCF-7, the human glioblastoma cell line SF-268, and the human lung cancer cell line NCI-H460 were also tested. All compounds exhibited mild cytotoxic activity. However, Compounds 1 and 2 showed no activity against C. albicans at the test concentration of 1 mg/mL via paper disc diffusion, while the known antimycins showed obvious antifungal activity.
Highlights
Marine-derived microorganisms are emerging as virtually unlimited sources for new structural classes of bioactive natural substances [1,2]
ANTs are produced by a polyketide synthase (PKS)/hybrid non-ribosomal peptide synthetase (NRPS)
During our ongoing research on bioactive secondary metabolites from Streptomyces [17,18,19], two novel nonacyclic dilactone fused with benzamide, neoantimycins A and B (1,2), and three known
Summary
Marine-derived microorganisms are emerging as virtually unlimited sources for new structural classes of bioactive natural substances [1,2]. More than 50% of all known antibiotics have been originated from actinomycete bacteria, especially Streptomyces species [3]. A (ANTs) including deacyl antimycins have been reported [4,5,6,7,8], which exhibited antifungal [9], anticancer [10], anti-inflammatory [11], and insecticidal [12] activities. Natural ANTs possess a unique nine-membered dilactone core conjugated with a 3-formyl aminosalicylic acid (FAS) moiety [16]. During our ongoing research on bioactive secondary metabolites from Streptomyces [17,18,19], two novel nonacyclic dilactone fused with benzamide, neoantimycins A and B (1,2), and three known
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