New Shikimic Acid Derivatives From the Marine-Derived Actinomycete Streptomyces sp. G666 and Their Antimicrobial Activities

Analysis of an antimicrobial extract from the agar-based culture of the marine-derived actinomycete Streptomyces sp. G666 led to the isolation of three new shikimic acid derivatives, streptomine A-C (1-3), along with five known compounds (4-8). Their structures were established by their spectral data analyses, including MS and NMR. All the isolated compounds were evaluated for their antimicrobial activity against a panel of clinically significant microorganisms. Three new compounds 1-3 demonstrated selective antimicrobial activity against Gram-positive Enterococcus faecalis with MIC values ranging from 32 to 64 µg/mL. Compound 3 exhibited the highest inhibitory effect against E. faecalis with an MIC value of 32 µg/mL. Compound 4 selectively inhibited Escherichia coli with an MIC value of 128 µg/mL. In addition, compounds 1-3 moderately inhibited the yeast Candida albicans with the same MIC value of 16 µg/mL. Unfortunately, most of isolated compounds were inactive against Gram-negative bacteria E. coli, Pseudomonas aeruginosa, and Salmonella enterica.