9H-carbazole derivatives from a Streptomyces species under potassium iodide stress and their anti-inflammatory properties.

By continuously activating silent gene cluster of the marine-derived Streptomyces strain OUCMDZ-5511 under high salt stress, three new iodinated 9H-carbazole derivatives (1-3) and a novel oxazole-fused chlorinated 9H-carbazole derivative (4), along with five previously reported analogues (5-9), were obtained from the cultures grown with 7.5% potassium iodide (KI). The structures of these previously undocumented compounds were elucidated as 4-iodo-3-methoxy-9H-carbazole (1), 4-iodo-3-methoxy-9H-carbazole-6-ol (2), 4-iodo-3-methoxy-9H-carbazole-8-ol (3), and 10-chloro-9-methoxy-6H-oxazolo[5,4-c]carbazole (4), using MS and NMR spectroscopic techniques. Notably, compound 3 demonstrated a more potent anti-inflammatory effect than the positive control in a CuSO4-induced inflammation zebrafish model, likely by modulating the Myd88/NF-κB signaling pathway to exert its anti-inflammatory activity.