Purmedermycin A (1) and purmedermycin B (2), which were isolated from Streptomyces sp. SS17A, feature a rearranged and reconstructed C/D/E ring formed by the fusion of a tryptophan unit and medermycin or menoxymycin B, respectively, making them the first of a new type of medermycin. Their structures were determined by extensive spectroscopic analysis and ECD calculations. Compound 1 exhibited cytotoxicity against PC-3 and HCT-116 cancer cell lines with IC₅₀ values of 1.33 and 4.51 μM, respectively.