Three new naphthoquinone-based meroterpenoids from <i>Streptomyces</i> sp. HBERC-16614 with antibacterial activities

Three new naphthoquinone-based meroterpenoids (<b>1</b>-<b>3</b>), including spironaphthomeroterpenoid (<b>1</b>), a novel naphthoquinone-based meroterpenoid with a rare [5, 6] spiro-ring skeleton, and naphthablins D and E (<b>2</b>-<b>3</b>), along with three known analogues (<b>4</b>-<b>6</b>) were isolated from <i>Streptomyces</i> sp. HBERC-16614. The structures of these compounds, including their absolute configurations, were established by extensive spectroscopic analysis and electronic circular dichroism (ECD) spectrum. The antibacterial activities of compounds (<b>1</b>-<b>6</b>) were evaluated against <i>Staphylococcus aureus</i>, <i>Streptococcus suis</i>, and <i>Escherichia coli</i>. Among them, compound <b>1</b> demonstrated potent antibacterial activity against <i>S. aureus</i>, with a minimum inhibitory concentration (MIC) value of 3.13 µg/mL.