Detection of intact vancomycin–arginine as the active antibacterial conjugate in E. coli by whole-cell solid-state NMR

Abstract

The introduction of new and improved antibacterial agents based on facile synthetic modifications of existing antibiotics represents a promising strategy to deliver urgently needed antibacterial candidates to treat multi-drug resistant bacterial infections. Using this strategy, vancomycin was transformed into a highly active agent against antibiotic-resistant Gram-negative organisms in vitro and in vivo through the addition of a single arginine to yield vancomycin–arginine (V–R). Here, we report detection of the accumulation of V–R in E. coli by whole-cell solid-state NMR using ¹⁵N-labeled V–R. ¹⁵N CPMAS NMR revealed that the conjugate remained fully amidated without loss of arginine, demonstrating that intact V–R represents the active antibacterial agent. Furthermore, C{N}REDOR NMR in whole cells with all carbons at natural abundance ¹³C levels exhibited the sensitivity and selectivity to detect the directly bonded ¹³C–¹⁵N pairs of V–R within E. coli cells. Thus, we also present an effective methodology to directly detect and evaluate active drug agents and their accumulation within bacteria without the need for potentially perturbative cell lysis and analysis protocols.