Isolation, structure elucidation, and antibacterial evaluation of the metabolites produced by the marine-sourced Streptomyces sp. ZZ820

New indole alkaloids streptoprenylindoles A–C ( 1 – 3 ) and diterpenoids 18-acetyl-cyclooctatin ( 8 ), 5,18-dedihydroxy-cyclooctatin ( 9 ), and 5-dehydroxy-cyclooctatin ( 10 ) were isolated from the culture of marine-derived Streptomyces sp. ZZ820, along with known 3-cyanomethyl-6-[3-methyl-2-butenyl]indole ( 4 ), N -(2-(1 H -indol-3-yl)ethylacetamide ( 5 ), 1-acetyl-β-carboline ( 6 ), indole-3-methylethanoate ( 7 ), cyclooctatin ( 11 ), and chromomycin A 3 ( 12 ). Their structures were elucidated by a combination of extensive spectroscopic analyses, ECD calculation, and the Mosher's method. Streptoprenylindoles A ( 1 ) and B ( 2 ) are enantiomers that were separated through the preparation of their Mosher esters. Three new diterpenoids ( 8 – 10 ) showed antibacterial activities against methicillin-resistant Staphylococcus aureus (MRSA) and Escherichia coli with MIC values of 24.11–55.12 μM, while chromomycin A 3 ( 12 ) showed potent antibacterial activities against MRSA (MIC: 0.59 μM) and E. coli (MIC 0.04 μM).