Methyl scanning approach for enhancing the biological activity of the linear peptidic natural product, efrapeptin C

Efrapeptin C ( 1a ) is a large peptidic natural product comprising a 15-mer linear sequence and exerts potent anticancer activity by inhibiting mitochondrial F o F 1 -ATP synthase. Residues 1-6 and 9-15 of 1a fold into two 3 10 -helical domains and interact with ATP synthase, while the central β-Ala-7-Gly-8 region functions as a flexible linker of the two domains. To enhance the function of 1a by minimally modifying its structure, we envisioned attaching one small methyl group to the β-Ala-7-Gly-8 and designed six methylated analogues 1b-1g , differing only in the position and configuration of the methyl group. We enabled the first solid-phase total synthesis of 1a and unified syntheses of 1b-1g . The growth inhibitory activities of 1a-1g against MCF-7 cells varied significantly: 1f with ( S )-β 3 -hAla-7 and its epimer 1g with ( R )-β 3 -hAla-7 were 4-fold more and 5-fold less potent, respectively, than 1a . Remarkably, the most potent 1f had the most stabilized 3 10 -helical conformation and the highest hydrophobicity, which likely contributed to its effective transfer to the target protein within mitochondria. Moreover, 1f exhibited higher proteolytic stability than 1a . Therefore, the present methyl scanning approach provides a new strategy for changing the original properties of linear peptidic natural products to develop new pharmaceuticals. Efrapeptin C is a linear peptidic natural product that exerts potent anticancer activity. The methyl scanning approach led to the discovery of a fully synthetic efrapeptin analogue with superior bioactivity and proteolytic stability.