Three New Diketopiperazines from the Previously Uncultivable Marine BacteriumGallaecimonas mangroviHK-28 Cultivated by iChip

Thein situapplication of iChip cultivation in mangrove sediment from Hainan province, China, led to the isolation of a novel bacterial speciesGallaecimonas mangroviHK-28. The extract ofG. mangroviHK-28 exhibited antibiotic activity against the aquatic pathogenVibrio harveyi, and its chemical constituents were further investigated by bioactivity-guided isolation. Three new diketopiperazines, gallaecimonamides A-C, were accordingly isolated from the AcOEt extract of the fermentation broth ofG. mangroviHK-28. The planar structures of gallaecimonamides A-C were determined using HR-ESI-MS together with 1D- and 2D-NMR. The absolute configurations of gallaecimonamides A-C were assigned by optical rotation, NOESY experiment and TDDFT ECD calculations. Thein vitroantibacterial and antimalarial activities of gallaecimonamides A-C were assessed. Gallaecimonamide A was found to display antibacterial activity againstV. harveyiwith a MIC value of 50 mu m. However, gallaecimonamides B and C showed no antibacterial activity againstV. harveyi(MIC >300 mu m). In addition, all the isolates did not exhibit any inhibitory activities againstV. parahaemolyticus(MIC>300 mu m) andPlasmodium falciparumW2 (EC50>100 mu g/mL).