Hygrolansamycins A-D, O-Heterocyclic Macrolides from Streptomyces sp. KCB17JA11

Six ansamycin derivatives were isolated from the culture broth of Streptomyces sp. KCB17JA11, including four new hygrolansamycins A-D (1-4) and known congeners divergolide O (5) and hygrocin C (6). Compounds 1-5 featured an unusual six-membered O-heterocyclic moiety. The isolation workflow was guided by a Molecular Networking-based dereplication strategy. The structures of 1-4 were elucidated using NMR and HRESIMS experiments, and the absolute configuration was established by the Mosher's method. Compound 2 exhibited mild cytotoxicity against five cancer cell lines with IC₅₀ values ranging from 24.60 ± 3.37 μM to 49.93 ± 4.52 μM.