Targeted Isolation of N‑Acetylcysteine-Containing Angucycline Derivatives from Streptomyces sp. MC16 and Their Antiproliferative Effects

Liquid chromatography-mass spectrometry (LC-MS/MS)-based molecular networking analysis was applied to sp. MC16. The automatic classification of the MolNetEnhancer module revealed that its major constituent was an angucycline derivative. By targeted isolation of unique clusters in the molecular network, which showed different patterns from typical angucycline compounds, two new -acetylcysteine-attached angucycline derivatives ( and ) were isolated. The structures were elucidated based on intensive NMR analysis and high-resolution electrospray ionization mass spectrometry (HR-ESI-MS). All isolated compounds (-) were tested for their inhibitory effects on the proliferation of A431, A549, and HeLa cell lines. Antibiotics 100-1 () and vineomycinone B () showed moderate inhibitory effects on these three cell lines with IC values ranging from 18.5 to 59.0 μM, while compounds and with an additional -acetylcysteine residue showed weak inhibitory effects only on the HeLa cell line with IC values of 54.7 and 65.2 μM, respectively.