pKa determination by ¹H NMR spectroscopy - an old methodology revisited.
pKa values of acids and protonated bases have an essential impact on organic synthesis, medicinal chemistry, and material and food sciences. In drug discovery and development, they are of utmost importance for the prediction of pharmacokinetic and pharmacodynamic properties. To date, various methods for the determination of pKa values are available, including UV-spectroscopic, potentiometric, and capillary electrophoretic techniques. An additional option is provided by nuclear magnetic resonance (NMR) spectroscopy. The underlying principle is the alteration of chemical shifts of NMR-active nuclei (e.g., (13)C and (1)H) depending on the protonation state of adjacent acidic or basic sites. When these chemical shifts are plotted against the pH, the inflection point of the resulting sigmoidal curve defines the pKa value. Although pKa determinations by (1)H NMR spectroscopy are reported for numerous cases, the potential of this approach is not yet fully evaluated. We therefore revisited this method with a diverse set of test compounds covering a broad range of pKa values (pKa 0.9-13.8) and made a comparison with four commonly used approaches. The methodology revealed excellent correlations (R(2)=0.99 and 0.97) with electropotentiometric and UV spectroscopic methods. Moreover, the comparison with in silico results (Epik and Marvin) also showed high correlations (R(2)=0.92 and 0.94), further confirming the reliability and utility of this approach.
Institute of Molecular Pharmacy, Pharmacenter, University of Basel, Klingelbergstrasse 50, CH-4056 Basel, Switzerland.
Jacqueline
J
Bezençon
Institute of Molecular Pharmacy, Pharmacenter, University of Basel, Klingelbergstrasse 50, CH-4056 Basel, Switzerland.
Matthias B
MB
Wittwer
Institute of Molecular Pharmacy, Pharmacenter, University of Basel, Klingelbergstrasse 50, CH-4056 Basel, Switzerland.
Brian
B
Cutting
Institute of Molecular Pharmacy, Pharmacenter, University of Basel, Klingelbergstrasse 50, CH-4056 Basel, Switzerland.
Martin
M
Smieško
Pharmaceuticals Division, Non-Clinical Safety, F. Hoffmann-La Roche Ltd., 4070 Basel, Switzerland.
Bjoern
B
Wagner
Pharmaceuticals Division, Non-Clinical Safety, F. Hoffmann-La Roche Ltd., 4070 Basel, Switzerland.
Manfred
M
Kansy
Institute of Molecular Pharmacy, Pharmacenter, University of Basel, Klingelbergstrasse 50, CH-4056 Basel, Switzerland. Electronic address: beat.ernst@unibas.ch.
Beat
B
Ernst
D003198:Computer Simulation; D015195:Drug Design; D055808:Drug Discovery / Q000379:methods; D006801:Humans; D006863:Hydrogen-Ion Concentration; D004364:Pharmaceutical Preparations / Q000737:chemistry*; D066244:Proton Magnetic Resonance Spectroscopy / Q000379:methods*; D015203:Reproducibility of Results
D004364:Pharmaceutical Preparations
(1)H NMR spectroscopy; Dissociation constant; Physicochemical properties; Site of protonation; pK(a) determination