Abstract

Siderophores are iron-chelating agents secreted by microorganisms under iron-limiting conditions, and have garnered increasing attention for their diverse biological activities. Guided by an iron-responsive metabolomic analysis, a new hydroxamate siderophore designated terragine H ( 1 ) was isolated from the fermentation broth of Streptomyces sp. D106, along with three known congeners legonoxamine D ( 2 ), terragine A ( 3 ) and legonoxamine A ( 4 ). The structure of 1 was elucidated by comprehensive NMR and MS analyses, revealing a linear scaffold characterized by a 4-methylhexanoyl side chain and a terminal succinimide moiety. The complete NMR assignment for legonoxamine D ( 2 ) is also reported, providing definitive structural validation for a metabolite previously characterized only by MS data. Bioassays revealed that all compounds possess iron-chelating capacity in the chrome azurol S assay, with 3 and 4 showing potency comparable to the clinical standard deferoxamine B. Compounds 1 – 3 also demonstrated significant antioxidant activity in the DPPH radical scavenging assay. Furthermore, compounds 1 and 3 exhibited moderate cytotoxicity against the MCF-7 tumor cell line.