Discovery of Brominated Alboflavusins With Anti-MRSA Activities.

As methicillin-resistant (MRSA) is becoming a serious pathogenic threaten to human health worldwide, there is an urgent need to discover new antibiotics for the treatment of MRSA infections. Alboflavusins (AFNs) are a group of halogenated cyclohexapeptides with anti-MRSA activities. In this study, two novel brominated AFN congeners (compounds and ) were isolated from the wild-type strain sp. 313 that was fermented in the production medium supplemented with NaBr; two new (compounds and ) and a known (compound ) dehelogenated AFN congeners were isolated from Δ, in which the tryptophan halogenase gene was inactivated. The structures of these compounds were assigned by careful NMR and MS analyses. The anti-MRSA activities of varied AFN congeners were assessed against different MRSA strains, which revealed that compounds and with bromine displayed effective activities against the tested MRSA strains. Especially, compound showed good anti-MRSA activity, while compounds , , and without halogen exhibited weak anti-MRSA activities, outlining the influence of halogen substitution to the bioactivities of AFNs.