Bis(indole) alkaloids, of the topsentin class (1—4) and hamacanthin class (5—9), isolated from the marine sponge Spongosorites sp. were investigated using several biological assays. In the evaluation of antimicrobial activity against various strains of bacteria and fungi, compounds of the hamacanthin class exhibited more potent antibacterial activity than those of the topsentin class. Deoxytopsentin (1) and hamacanthin A (5) also exhibited significant antibacterial activity against methicillin-resistant Staphylococcus aureus, with MIC values of less than 12.5 μg/ml. In the antifungal activity test, hamacanthins, especially hamacanthin A (5), showed potent inhibitory activity against medically important pathogenic fungi. In contrast, all of the topsentins (1—4) were inactive against fungal growth. These compounds (1—9) also exhibited moderate cytotoxicity against cancer cell lines at concentrations between 1.1 and >20 μg/ml.

Alterations in microbial culture conditions may trigger the production of diverse bioactive secondary metabolites. While applying various culture conditions and monitoring secondary metabolite profiles using LC/MS, hormaomycins B and C (1 and 2) were discovered from a marine mudflat-derived actinomycete, Streptomyces sp., collected in Mohang, Korea. The planar structures of the hormaomycins, which bear structurally-unique units, such as 4-(Z)-propenylproline, 3-(2-nitrocyclopropyl)alanine, 5-chloro-1-hydroxypyrrol-2-carboxylic acid and b-methylphenylalanine, were established as the first natural analogues belonging to the hormaomycin peptide class. The absolute configurations of 1 and 2 were deduced by comparing their CD spectra with that of hormaomycin. These hormaomycins exhibited significant inhibitory effects against various pathogenic Gram-positive and Gram-negative bacteria.