Three prenylated indole alkaloids (1-3), including two new penicimutamides D-E (1-2), were isolated from a diethyl sulfate mutant of the marine-derived fungus Penicillium purpurogenum G59. The structures of 1-3, and their absolute configurations, were determined by spectroscopic methods, including X-ray crystallography and CD analyses. HPLC-UV and HPLC-MS analyses showing that 1-3 were only produced in the mutant evidenced that the silent biosynthetic pathways that produce 1-3 in the parental strain are activated by DES mutagenesis.