Marine microorganisms, particularly marine actinomycetes, have attracted considerable attention as one of the most important resources for new biologically active metabolites.1 For example, new compounds have been isolated from actinomycetes of sponge origin.2–4 Our group was engaged in the isolation of actinobacteria from marine sponges. We have recently discovered novel compounds, namely the anthracyclines tetracenoquinocin and 5-imino aranciamycin,5 a teleocidin JBIR-31,6 the tetrapeptides JBIR-34 and -35,7 and the isoprenoids JBIR-46–48.8,9 Our intention was to support the idea that new species are capable of producing unique metabolites. For this purpose, we isolated new species of Streptomyces from marine sponges and then searched for secondary metabolites in the cultures of isolated strains. In this study, we isolated a new species (SpD081030ME-02) of Streptomyces from a Demospongiae class of marine sponge, and purified a new compound termed JBIR-58 (1, Figure 1a) from the fermentation broth of Streptomyces sp. SpD081030ME-02. We report herein the fermentation, isolation, structure elucidation and, in brief, the biological activity of 1.