Phocoenamicins B and C, New Antibacterial Spirotetronates Isolated from a Marine Micromonospora sp.

Phocoenamicins B and C ( and ), together with the known spirotetronate phocoenamicin (), were isolated from cultures of sp. The acetone extract from a culture of this strain, isolated from marine sediments collected in the Canary Islands, displayed activity against methicillin-resistant (MRSA), H37Ra and . Bioassay-guided fractionation of this extract using SP207ss column chromatography and preparative reversed-phased HPLC led to the isolation of the new compounds and belonging to the spirotetronate class of polyketides. Their structures were determined using a combination of HRMS, 1D and 2D NMR experiments and comparison with the spectra reported for phocoenamicin. Antibacterial activity tests of the pure compounds against these pathogens revealed minimal inhibitory concentration (MIC) values ranging from 4 to 64 µg/mL for MRSA, and 16 to 32 µg/mL for H37Ra, with no significant activity found against and vancomycin-resistant (VRE) at concentrations below 128 µg/mL, and weak activity detected against grown on agar plates.