Acetomycin, a γ-butyrolactone isolated from Streptomyces ramulosus, was first reported in 1958 by Ettlinger et al. at ETH Zurich. Acetomycin is potently active in vitro against HCT-8 human colon adenocarcinoma cells and L1210 murine leukemia cells. Acetomycin is inactive in vivo giving rise to the design and synthesis of esterase-resistant analogues.