Multinuclear Nuclear Magnetic Resonance Spectroscopy Is Used to Determine Rapidly and Accurately the Individual pKa Values of 2-Deoxystreptamine, Neamine, Neomycin, Paromomycin, and Streptomycin

Unambiguous assignments have been made for each individual p K a value of the amino group and guanidine substituents on 2-deoxystreptamine, neamine, neomycin, paromomycin, and streptomycin by pH-titration evaluation of their 1 H, 13 C, and 15 N (by 1 H- 15 N heteronuclear multiple-bond correlation (HMBC) spectra) NMR chemical shifts (δ X s) as the reporter nuclei. These data require minor revisions of the literature data in terms of the assignment order for neomycin and paromomycin. In situ titrations and NMR spectroscopy are shown to be a powerful combination for rapidly (minutes) obtaining each distinct p K a value of the similar amine and guanidine functional groups, which decorate aminoglycoside antibiotics.