Lactoquinomycin C and D, two new medermycin derivatives from the marine-derived sp. SS17A.

Lactoquinomycin C () and Lactoquinomycin D (), two new medermycin derivatives together with six known compounds (-) were isolated from the rice solid fermentation of the marine-derived sp. SS17A. The intriguing structural features of the Lactoquinomycin D () which contains 5,14-epoxidation is relatively rare in medermycin derivatives. Compounds and exhibited no cytotoxicity against PC-3 and HCT-116 cancer cell lines, whereas compound showed stronger cytotoxicity with IC values of 0.02 and 0.04 μM, respectively. A structure-activity relationship was observed for the cytotoxicity of the medermycin derivatives with a γ-lactone unit is required for significant cytotoxicity based on compounds -.