Fig. 3. (A) LC-ESI-MS full scan spectrum of the bacillomycin D C14. (B) ESI-MS/MS spectrum analysis of the precursor ion [M + H]⁺ at m/z 1031.54. (C) The theoretical b-ion and y-ion fragments dissociated from ring-opening reactions between Glu and Pro. (D) Structure of bacillomycin D C14.