Semisynthetic derivatives of the fungal metabolite eupenifeldin via targeting the tropolone hydroxy groups

Eupenifeldin (1) is a fungal secondary metabolite possessing bis-tropolone moieties that demonstrates nanomolar cytotoxic activity against a number of cancer cell types. As a potential anticancer lead, this meroterpenoid was used to access 29 semisynthetic analogues via functionalization of the reactive hydroxy groups of the bis-tropolones. A series of ester (2–6), carbonate (7–8), sulfonate (9–16), carbamate (17–20), and ether (21–30) analogues of 1 were generated via 22 reactions. Most of these compounds were disubstituted, produced via functionalization of both of the tropolonic hydroxy moieties, although three mono-functionalized analogues (6, 8, and 24) and one tri-functionalized analogue (3) were also obtained. The cytotoxic activities of 1–30 were evaluated against human melanoma and ovarian cancer cell lines (i.e., MDA-MB-435 and OVCAR3, respectively). Ester and carbonate analogues of 1 (i.e., 2–8) maintained cytotoxicity at the nanomolar level, and the greatest improvement in aqueous solubility came from the monosuccinate analogue (6), which was acylated on the secondary hydroxy at the 11 position.