Chlokamycins B–D: Chlorohydrin-Containing Polycyclic Tetramate Macrolactams with Cytotoxic Activity from the Marine Sponge-Derived Streptomyces xiamenensis 1310KO-148

Chemical investigation of the marine sponge-derived <i>Streptomyces xiamenensis</i> 1310KO-148 afforded six polycyclic tetramate macrolactams (PTMs), including three known compounds (<b>1</b>-<b>3</b>) and three previously undescribed chlorohydrin-containing analogues, chlokamycins B-D (<b>4</b>-<b>6</b>). Their planar structures were elucidated by extensive analysis of 1D and 2D NMR spectra and HR-ESIMS data, while the relative configurations were assigned using NOESY correlations. The absolute configurations were further confirmed by electronic circular dichroism (ECD) calculations. Compounds <b>3</b>-<b>6</b> exhibited significant cytotoxic activity against 14 human cancer cell lines (GI₅₀ = 2.68-24.92 μM) and antibacterial activity against <i>Staphylococcus aureus</i> (MIC = 16.00-32.00 μg/mL) and <i>Micrococcus luteus</i> (MIC = 4.00-32.00 μg/mL) among six tested bacterial strains.