Pyrrole-Containing Alkaloids from a Marine-Derived Actinobacterium Streptomyces zhaozhouensis and Their Antimicrobial and Cytotoxic Activities

Two new alkaloids, streptopyrroles B and C (1 and 2), were discovered through a chemical investigation of the ethyl acetate (EtOAc) extract from a marine-derived actinomycete, Streptomyces zhaozhouensis, along with four known analogs (3-6). The structures of the new compounds were elucidated by spectroscopic analysis (HR-ESIMS, 1D, and 2D NMR) and a comparison of their experimental data with literature values. The new compounds were evaluated for their antimicrobial activity by standard broth dilution assay, and the tested compounds showed significant activity against Gram-positive bacteria with minimum inhibitory concentration (MIC) values ranging from 0.7 to 2.9 mu M, and kanamycin was used as a positive control with MIC values ranging from <0.5 to 4.1 mu M. Additionally, 1, 3, and 5 were evaluated for their cytotoxicity against six tumor cell lines by sulforhodamine B (SRB) assay, and these compounds displayed cytotoxic activities against all the tested cell lines, with concentration causing 50% cell growth inhibition (GI(50)) values ranging from 4.9 to 10.8 mu M, while a positive control, adriamycin, showed GI(50) values of 0.13-0.17 mu M.

Automated summary

Two new alkaloids, streptopyrroles B and C, were discovered from an extract of a marine-derived actinomycete. Their structures were determined through spectroscopic analysis and comparison with literature values. The compounds showed significant antimicrobial activity against Gram-positive bacteria and cytotoxic activities against tumor cell lines.