Streptoindoles A–D, novel antimicrobial indole alkaloids from the marine-associated actinomycete Streptomyces sp. ZZ1118

Abstract

Six indole alkaloids, including the new streptoindoles A–D (1–4) and the known N-acetyltryptamine (5) and (3S)-bacilsubteramide A (6), were isolated from a culture of the marine-sourced actinomycete Streptomyces sp. ZZ1118 in rice medium. Streptoindoles A (1) and B (2) were enantiomers and separated by using a chiral HPLC column. Structures of the isolated compounds were determined based on their HRESIMS data, extensive NMR spectroscopic analyses, ECD calculations, optical rotation calculations, and a single crystal X-ray diffraction experiment. Streptoindoles A (1) and B (2) showed antimicrobial activities in inhibiting the growth of methicillin-resistant Staphylococcus aureus (MRSA), Escherichia coli, and Candida albicans with MIC values in a range from 7 to 25 μg/mL. Streptoindole C (3) had antimicrobial activities against E. coli and C. albicans with a MIC value of 7 μg/mL, while streptoindole D (4) showed antibacterial activity (MIC: 25 μg/mL) against MRSA.