Isolation and characterization of phytotoxic compounds produced by Streptomyces sp. AMC 23 from red mangrove (Rhizophora mangle).

Natural products produced by microorganisms have been utilized as sources of new drugs possessing a wide range of agrochemical and pharmacological activities. During our research on Actinomycetes from Brazilian mangroves, the ethyl acetate extract of Streptomyces sp. AMC 23 isolated from the red mangrove (Rhizophora mangle) rhizosphere produced a highly active compound against the microalga Chlorella vulgaris, often used to assess the phytotoxic activity. As a result, the bioassay-guided fractionation led to the isolation of the mixture of the known compounds bafilomycin B1 and bafilomycin B2. The chemical structures of bafilomycin B1 and bafilomycin B2 were established based on their spectroscopic data by infrared (IR), mass spectrometry (MS), (1)H nuclear magnetic resonance (NMR), gradient-enhanced heteronuclear multiple quantum coherence (gHMQC), and gradient-enhanced heteronuclear multiple-bond connectivity (gHMBC) as well as comparison with reference data from the literature. Moreover, it was also possible to identify other bafilomycins using non-chromatographic-dependent techniques (Tandem mass spectrometry). Additionally, this is the first report on the phytotoxic activity of bafilomycin B1.