Three new secondary metabolites, actinoflavosides B–D (1–3), were discovered in the culture broth of two actinomycete strains (JML48 and JMS33) that were isolated from tidal mudflat sediment in Muan, Republic of Korea. The planar structures of the actinoflavosides were elucidated by MS, UV, and NMR analyses. The stereochemistry of an aminosugar, 2,3,6-trideoxy-3-amino-ribopyranoside in the actinoflavosides was determined by J-based configuration analysis using values obtained from DQF-COSY experiments and modified Mosher’s method. Actinoflavosides B–D (1–3) displayed antibacterial activity against Pseudomonas aeruginosa, and actinoflavoside D (3) significantly increased IL-2 production in mouse splenocytes.

In this study, metagenomic analysis was employed to investigate the bacterial communities in the Muan tidal mudflat of the Republic of Korea. We used metagenomic analysis to identify the microbial community in tidal soil dominated by Proteobacteria. From this environment, the bacterial strain, Saccharomonospora sp. CMS18, was isolated and yielded two previously unknown compounds, penipaline D (3) and N-acetyl-dimethylallyltryptophan (4). The chemical structures of the isolated compounds along with 6-dimethylallyl-indole (1), 6-dimethylallyltryptophan (2), penipaline D (3), and N-acetyl-dimethylallyltryptophan (4) were structurally investigated using HR-ESI-MS and NMR spectroscopy. The isolated compound 6-dimethylallyl-indole (1) demonstrated broad-spectrum antifungal activity, with IC₅₀ value of 0.04 mM against Candida glabrata and 0.35 mM against both Candida albicans and Cryptococcus neoformans. Additionally, it exhibited additive interaction with caspofungin against C. albicans.