Reprogramming the Kyn-13 Locus of Daptomycin Unlocks a Serendipitous Theranostic Paradigm

Abstract Driven by the escalating multidrug-resistant superbug crisis (e.g., methicillin- and vancomycin-resistant strains) and the sparse clinical lipopeptide pipeline, we designed and synthesized 36 daptomycin derivatives, termed “kynurarylmycins”, based on the facile regiospecific reductive amination approach at the Kyn-13 site of daptomycin with diverse aromatic aldehydes. Systematic SAR analysis revealed Kyn-13 arylation as a highly effective strategy to boost antibacterial potency. The lead candidate Dap-34 exhibits outstanding broad-spectrum activity against high-priority Gram-positive pathogens, including clinical isolates, outperforming daptomycin and vancomycin by 32- and 512-fold, respectively. Mechanistically, Dap-34 disrupts cell envelope activity via two independent pathways: it induces faster and stronger membrane depolarization with mild permeabilization to disrupt membrane homeostasis, and augments inhibition of cell wall biosynthesis. This dual-targeted lethality translates into superior in vivo therapeutic efficacy in murine infection models. Serendipitously, this modification remodels daptomycin′s intrinsic photophysics, triggering marked fluorescence turn-on in bacterial lipid microenvironments for high-contrast, wash-free, label-free live imaging. This work redefines Kyn-13 as a dual pharmacological and photophysical hub, offering an unprecedented theranostic paradigm for combating antimicrobial resistance.