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Madurastatins are a group of pentapeptides containing an oxazoline moiety, and, in a few cases, an imidazolidinone ring as an additional structural feature. In our search for new potential antiparasitic metabolites from natural sources, we studied the acetone extracts from a culture of Actinomadura sp. CA-135719. The LC/HRMS analysis of this extract identified the presence of the known madurastatins C1 (1), D1 (4), and D2 (5) together with additional members of the family that were identified as the new madurastatins H2 (2) and 33-epi-D1 (3) after isolation and spectroscopic analysis. The planar structures of the new compounds were established by HRMS, ESI-qTOF-MS/MS, and 1D and 2D NMR data, and their absolute configuration was proposed using Marfey's and bioinformatic analyses of the biosynthetic gene cluster (BGC). A revision of the absolute configuration of madurastatins D1 and D2 is proposed. Additionally, madurastatins containing imidazolidinone rings are proved to be artifacts originating during acetone extraction of the bacterial cultures. [ABSTRACT FROM AUTHOR]

Genome analysis of strain Streptomyces sp. CA-278952 revealed a biosynthetic gene cluster encoding a putative lipopeptide with a sequence containing an Asp-Gly-Glu-Ala motif. We envisioned that this motif could mimic the canonical Asp-X-Asp-Gly sequence found in previously reported calcium-dependent lipopeptide antibiotics. Chemical investigation of the producing strain led to the discovery of three novel lipodepsipeptides, dilarmycins A-C. The calcium-dependent antibacterial activity of the new compounds was confirmed against the Gram-positive pathogens methicillin-resistant Staphylococcus aureus and vancomycin-resistant Enterococcus .