Grisemycin, a Bridged Angucyclinone with a Methylsulfinyl Moiety from a Marine-Derived Streptomyces sp.

Grisemycin (1), the first sulfur angucyclinone with an unusual ether-bridged system, was isolated from a marine-derived Streptomyces griseus strain M268. Its novel, here cage-like, structure was determined by spectroscopic analysis and single-crystal X-ray diffraction. Compound 1 exhibited modestly selective activity against the HL-60 cell line with an IC50 value of 31.54 μM. Futhermore, the absolute stereochemistry of kiamycin (2), an 1,12-epoxybenz[a]anthracene, previously obtained from the same strain, was established by X-ray diffraction analysis.