The prompt appearance of multiantibiotic-resistant bacteria necessitates finding alternative treatments that can attenuate bacterial infections while minimizing the rate of antibiotic resistance development. Streptococcus pneumoniae, a notorious human pathogen, is responsible for severe antibiotic-resistant infections. Its pathogenicity is influenced by a cell-density communication system, termed quorum sensing (QS). As a result, controlling QS through the development of peptide-based QS modulators may serve to attenuate pneumococcal infections. Herein, we set out to evaluate the impact of the introduction of bulkier, nonproteogenic side-chain residues on the hydrophobic binding face of CSP1 to optimize receptor-binding interactions in both of the S. pneumoniae specificity groups. Our results indicate that these substitutions optimize the peptide-protein binding interactions, yielding several pneumococcal QS modulators with high potency. Moreover, pharmacological evaluation of lead analogs revealed that the incorporation of nonproteogenic amino acids increased the peptides' half-life towards enzymatic degradation while remaining nontoxic. Overall, our data convey key considerations for SAR using nonproteogenic amino acids, which provide analogs with better pharmacological properties.
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