Initial efforts toward the optimization of arylomycins for antibiotic activity.

While most clinically used antibiotics were derived from natural products, the isolation of new broad-spectrum natural products has become increasingly rare and narrow-spectrum agents are typically deemed unsuitable for development because of intrinsic limitations of their scaffold or target. However, it is possible that the spectrum of a natural product antibiotic might be limited by specific resistance mechanisms in some bacteria, such as target mutations, and the spectra of such "latent" antibiotics might be reoptimized by derivatization, just as has been done with clinically deployed antibiotics. We recently showed that the spectrum of the arylomycin natural product antibiotics, which act via the novel mechanism of inhibiting type I signal peptidase, is broader than previously believed and that resistance in several key human pathogens is due to the presence of a specific Pro residue in the target peptidase that disrupts interactions with the lipopeptide tail of the antibiotic. To begin to test whether this natural resistance might be overcome by derivatization, we synthesized analogues with altered lipopeptide tails and identified several with an increased spectrum of activity against S. aureus. The data support the hypothesis that the arylomycins are latent antibiotics, suggest that their spectrum may be optimized by derivatization, and identify a promising scaffold upon which future optimization efforts might focus.