Xiapyrroles A–F: N-Alkylpyrrole Alkaloids from the Marine-Derived Actinomycete Streptomyces xiamenensis 1310KO-148

Six new N-alkylpyrrole alkaloids (1–6) were isolated from the marine-derived actinomycete Streptomyces xiamenensis 1310KO-148 from a sponge sample. The structures of xiapyrroles A–F (1–6) were elucidated by detailed analysis of extensive spectroscopic data, including 1D, 2D NMR, and HRESIMS data. The absolute configurations of 2, 3, 4, and 6 were determined by a comparison of their calculated and experimental electronic circular dichroism (ECD) spectra. The position of the hydroxamate group in 6 was confirmed through NO-methylation and NOESY data analysis. All compounds (1–6) were tested for their anti-inflammatory effects in LPS-stimulated RAW 264.7 cells, a mouse macrophage cell line. The treatment of RAW 264.7 cells with 30 μM of 1–6 showed no significant cytotoxic effects. However, 1 dose-dependently suppressed the LPS-induced production of NO (IC₅₀ = 29.5 μM) and interleukin-6 (IL-6) (IC₅₀ = 10.9 μM). Compound 1 exhibited no potential cytotoxicity against six solid cancer cell lines and eight blood cancer cell lines at a concentration of 30 μM.