Damxungmacin A and B, Two New Amicoumacins with Rare Heterocyclic Cores Isolated from Bacillus subtilis XZ-7

Two new amicoumacins, named Damxungmacin A (1) and B (2), were isolated from the culture broth of a soil-derived bacterium Bacillus subtilis XZ-7. Their chemical structures were elucidated by spectroscopic studies (UV, IR, NMR and HR-ESI-MS). Compound 1 possessed a 1,4-diazabicyclo[2.2.1]heptane-2-one ring system in its structure, which was reported for the first time, while 2 had a 1-acetylmorpholine-3-one moiety, which was naturally rare. Compound 1 exhibited moderate to weak cytotoxic activities against three human tumor cell lines (A549, HCT116 and HepG2) with IC₅₀ values of 13.33, 14.34 and 13.64 μM, respectively. Meanwhile, compound 1 showed weak antibacterial activities against some strains of Staphylococcus epidermidis, while compound 2 at 16 μg/mL did not show antibacterial activity.