Applying molecular networking for targeted isolation of depsipeptides.

LC-HRMS/MS molecular networking enabled the targeted isolation of three new neoantimycin analogs (1, 3, 5) and two known ones (2, 4) from the culture broth of RJ8. After derivatization into C1-hydroxyl form compounds (6-10) respectively, the absolute structures of 1-5 were clearly determined by analyzing the hydrolyzed components from 6-10. Compounds 2 and 3 were confirmed to be a pair of epimers with different stereochemistry at C-2, and so were 4 and 5. This is the first report of the isolation and characterization of epimers of NATs. The most abundant eight compounds we obtained were subjected to a cytotoxicity assay, 1 and 6 exhibited excellent cytotoxicity with the lowest IC value in the picomolar range against six human carcinoma cell lines while 7 and 8 showed potent cytotoxicity against PC-9 and PC-9/GR cell lines.