Igidamycins A–C, Rare Sugar-Bearing Anthracycline Glycosides from a Marine Actinomycete, <i>Streptomyces</i> sp.

Genome-guided mining of marine <i>Streptomyces</i> sp. GCU-142 led to the identification of three unprecedented sugar-bearing anthracycline glycosides, igidamycins A-C (<b>1</b>-<b>3</b>). The structures of <b>1</b>-<b>3</b> were assigned by spectroscopic analysis including NMR, HR-MS, and UV spectroscopy. Their configurations were determined by ROESY NMR data, the modified Mosher's method, l-cysteine methyl ester derivatization, and TD-DFT ECD calculations. Bioinformatic analysis suggested a plausible biosynthetic pathway of igidamycins, integrating type II polyketide assembly, extensive sugar tailoring, and late-stage nitration. Notably, igidamycin A (<b>1</b>), bearing a nitro group at C-6, exhibited potent antibacterial activity against various Gram-positive pathogens. In contrast, the non-nitrated congeners (<b>2</b> and <b>3</b>) were inactive, highlighting a key role of the nitro functionality in its antibacterial potency.