Amylimycins A–C, New Bacillomycin D Analogs from Marine-Derived Bacillus amyloliquefaciens

Marine-derived microorganisms are a rich source of structurally diverse natural products with significant pharmaceutical potential. In this study, three new cyclic lipopeptides, amylimycins A–C (1–3), were isolated from a marine-derived Bacillus amyloliquefaciens strain. The chemical structures of these compounds were elucidated through comprehensive spectroscopic analyses and chiral derivatization using 1-fluoro-2,4-dinitrophenyl-5-alanine amide (FDAA). Amylimycins A–C (1–3) were identified as bacillomycin D analogs belonging to the iturin family, characterized by a cyclic heptapeptide core linked to a β-amino fatty acid moiety. Notably, these compounds featured uncommon branched β-amino fatty acid chains with varied chain lengths, representing a distinctive structural characteristic among bacillomycin D analogs. Amylimycins A–C (1–3) showed moderate antibacterial activity against the Gram-positive bacteria Bacillus subtilis and Staphylococcus epidermidis, while displaying weak to no activity against the Gram-negative strains Escherichia coli and Pseudomonas fluorescens.