Yeppoonic acids A – D: 1,2,4-trisubstituted arene carboxylic acid co-metabolites of conglobatin from an Australian Streptomyces sp.

Streptomyces sp. MST-91080 was isolated from a soil sample collected in Queensland, Australia. From this strain, yeppoonic acids A – D were purified and spectroscopically characterised. The yeppoonic acids are a family of diene enecarboxylic acids on a 1,2,4-trisubstituted benzene scaffold, structurally related to other Streptomyces secondary metabolites MF-EA-705α/β, NFAT-133 and the lorneic acids. Yeppoonic acids B and C show strong cytotoxicity against the NS-1 mouse myeloma cell line (IC₅₀ 2.3 µg ml^–1 and 3.8 µg ml^–1, respectively) and moderate activity against the DU 145 human prostate cancer cell line (IC₅₀ 32.8 µg ml^–1 and 49.6 µg ml^–1, respectively).