Labradorins with Antibacterial Activity Produced by Pseudomonas sp.

The urgent need for new antibacterial drugs has led to renewed interest in microorganisms, which historically have been the main source of previously discovered antibiotics. The present study describes the discovery of two new antibacterial oxazolylindole type alkaloids, labradorins 5 () and 6 (), which were isolated and characterized from two isolates of sp., along with four previously known tryptophane derived alkaloids. The structures of and were determined by NMR spectroscopy and MS, and confirmed by synthesis. During bioassay-guided isolation using several human bacterial pathogens, and displayed activity towards and . The minimal inhibitory concentrations (MIC) of compounds and against were 12 μg·mL and 50 μg·mL, respectively, whereas the MICs against were >50 μg·mL. The CC values of compound towards a liver cell line (HEP-G2) and a T-cell line (MT4) were 30 μg·mL and 20 μg·mL, respectively, and for compound were >100 μg·mL and 20 μg·mL, respectively. Due to the limited potency of compounds and , along with their toxicity, the compounds do not warrant further development towards new antibiotics.