Novel antibacterial alkaloids from the Mariana Trench-derived actinomycete Streptomyces sp. SY2255

Two novel alkaloids of streptoquinoneazaindole A (1) and streptoureipyrrole A (2), together with 36 known compounds (3–38), were isolated from the Mariana Trench-associated actinomycete Streptomyces sp. SY2255. Structures of the new compounds were determined based on their HRESIMS data, NMR spectroscopic analyses, and optical rotation calculations. Streptoquinoneazaindole A (1) has an unprecedent benzoquinone-pyridine-pyrrole skeleton, streptoureipyrrole A (2) is a rare pyrrole alkaloid, and 6-hydroxybenzothiazole (28) is reported as a natural product for the first time. Streptoquinoneazaindole A (1) showed antibacterial activities against methicillin-resistant Staphylococcus aureus and Escherichia coli with a MIC value of 25 μg/mL.