Experimental Determination of the pKa Values of Clinically Relevant Aminoglycoside Antibiotics: Toward Establishing pKa-Activity Relationships

Investigating the relationship between individual pKa values and the efficacy of aminoglycosides is essential for the development of more effective and targeted therapies. In this work, we measured the pKa values for individual amino groups of the six clinically relevant aminoglycoside antibiotics gentamicin, tobramycin, amikacin, arbekacin, plazomicin, and apramycin using 15N-1H heteronuclear multiple-bond correlation and 1H NMR experiments. For arbekacin and plazomicin, the pKa values are reported for the first time. These pKa values were used to calculate the net charges of the aminoglycosides and the protonation levels of amino groups under various pH conditions. The results were analyzed in relation to the mode of interaction and inhibition to establish pKa relationships for rRNA binding, inhibitory activity, and the pH dependence of the uptake into bacterial cells.