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Abstract

Lactimidomycin (1) was described in the literature as an exquisitely potent cell migration inhibitor. Encouraged by this claim, we developed a concise and scalable synthesis of this bipartite glutarimide-macrolide antibiotic, which relies on the power of ring-closing alkyne metathesis (RCAM) for the formation of the unusually strained 12-membered head group. Subsequent deliberate digression from the successful path to 1 also brought the sister compound isomigrastatin (2) as well as a series of non-natural analogues of these macrolides into reach. A careful biological re-evaluation of this compound collection showed 1 and progeny to be potently cytotoxic against a panel of cancer cell lines, even after one day of compound exposure; therefore any potentially specific effects on tumor cell migration were indistinguishable from the acute effect of cell death. No significant cell migration inhibition was observed at sub-toxic doses. Although these findings cannot be reconciled with some reports in the literature, they are in accord with the notion that lactimidomycin is primarily a ribosome-binder able to effectively halt protein biosynthesis at the translation stage.