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

[Image: see text] Unambiguous assignments have been made for each individual pK(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 pK(a) value of the similar amine and guanidine functional groups, which decorate aminoglycoside antibiotics.