Korormicin (1) is an antibiotic produced by the marine bacterium Pseudoalteromonas sp. F-420 from the Palauan sea, with stereochemistry 5S,3'R,9'S,10'R. It specifically inhibits Gram-negative marine bacteria by targeting Na+-translocating NADHquinone reductase (Nqr), acting as a noncompetitive inhibitor for ubiquinone-1 with an inhibition constant of 82pM. Gly140 on NqrB (a subunit of the Nqr complex) is essential for its binding, and this residue is conserved in Gram-negative pathogens with the nqr operon, suggesting korormicin could be used against such bacteria. During a fermentation study of strain F-420, minor compounds derived from 1 were detected in the HPLC chromatogram during purification of 1. This report describes the isolation of derivatives 1a (7.30mg), 1b (13.25mg), 1c (3.89mg), 2 (10.69mg), and 3 (12.78mg) via processes including fermentation (Marine Broth 2216 supplemented with 1% maltose and 0.16% NaHCO3, 30℃, 20 hours), extraction (aqueous ethanol with ultrasonic disruption), purification (solvent extraction, silica gel column chromatography, size-exclusion chromatography, reversed-phase HPLC), and characterization using MS, NMR, IR, UV spectroscopy, and optical rotation. Structural analysis via 1H and 13C NMR, IR, UV, HMBC, and FAB-MS showed that the planar structures of these derivatives were very similar to that of 1.