(+)-
Negamycin (1), a natural dipeptidic
antibiotic bearing a
hydrazide structure, exhibits a readthrough activity toward the
nonsense mutation of the
dystrophin gene and restores
dystrophin expression in muscles of
Duchenne muscular dystrophy model mdx mice. Herein to develop more potent readthrough compounds, we performed a structure-activity relationship (SAR) study of 3-epi-deoxynegamycin (2), which is also another natural readthrough compound with little antimicrobial activity, focusing on the main
carbon chain length. We found that one
carbon atom shorter derivative 9b shows a higher readthrough activity than 1 and 2. Further derivatization at the
carboxylic acid part of 9b demonstrates that its meta-chlorobenzyl
ester derivative 17e, which has a higher ClogP value, exhibits a more potent readthrough activity than 9b. Interestingly, in the cell-free
protein expression system, the readthrough activity of 17e drastically decreases compared to that in the cell-based assay. These results suggest that benzyl
ester-type derivatives enhance the hydrophobicity and function as
prodrugs to produce active compound 9b in living cell systems.