New Spirotetronate Antibiotics, Lobophorins H and I, from a South China Sea-Derived Streptomyces sp. 12A35

Strain 12A35 was isolated from a deep-sea sediment collected from the South China Sea and showed promising antibacterial activities. It was identified as Streptomyces sp. by the 16S rDNA sequence analysis. Bioassay-guided fractionation using HP20 adsorption, flash chromatography over silica gel and octadecylsilyl (ODS) and semi-preparative HPLC, led to the isolation and purification of five metabolites from the fermentation culture of 12A35. Two new spirotetronate antibiotics, lobophorins H (1) and I (2), along with three known analogues, O-β-kijanosyl-(1→17)-kijanolide (3), lobophorins B (4) and F (5) were characterized by 1D, 2D-NMR and MS data. These compounds exhibited significant inhibitory activities against Bacillus subtilis. Compounds 1 and 5 exhibited moderate activities against Staphylococcus aureus. In particular, the new compound lobophorin H (1) showed similar antibacterial activities against B. subtilis CMCC63501 to ampicillin.