Concise Total Synthesis of the Potent Translation and Cell Migration Inhibitor Lactimidomycin

An efficient total synthesis of the antiproliferative macrolide and cell migration inhibitor lactimidomycin (3) is reported, which relies on the performance of ring closing alkyne metathesis (RCAM). The strained 12-membered 1,3-enyne 21 as the key intermediate was forged with the aid of [(Ph3SiO)3Mo≡CPh]·OEt2 (27) as the most effective member of a new generation of powerful alkyne metathesis catalysts. 21 was elaborated to the target by a ruthenium catalyzed trans-hydrosilylation/proto-desilylation sequence and a highly diastereoselective Mukaiyama aldol reaction controlled by oxazaborolidinone 29 as strategic operations

Total Syntheses and Biological Reassessment of Lactimidomycin, Isomigrastatin and Congener Glutarimide Antibiotics

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