Vibrational and NMR spectra of phenylpyruvic acid and its salts in aqueous solution

Synthesis of aromatic 13C/2H-α-ketoacid precursors to be used in selective phenylalanine and tyrosine protein labelling

“…18d NMR spectra of compounds 1-3 in D 2 O show mainly the keto forms, whereas in DMSO-d 6 the enol forms predominate, which is in accordance with literature data. 23…”

Temperature-variable NMR Study of the keto-enol Tautomerism of Phenylpyruvic Acid

“…Many spectroscopic studies, ultra violet (UV), infrared (IR), Raman and nuclear magnetic resonance (NMR) studies, have been reported on the keto-enol tautomerism [3][4][5][6][7][8][9][10][11][12] and conformation 6,9,10,12,13 of PA and PPA. These many investigations have revealed that these compounds exist as equilibrium mixtures consisting of the keto and enol forms.…”

“…7 Next, Hanai et al investigated the IR, Raman, and NMR spectra of PPA in the solid state, organic solvents and those its solid salts. [8][9][10] It was revealed that PPA takes the enol form in the solid state, and that the keto form is more stable in an aqueous solution. Carpy et al assigned the structures of the two tautomeric forms of PPA in DMSO solvent by 1 H and 13 C NMR spectroscopy, and found by X-ray crystallography of the single crystal that the crystalline form takes the keto isomer.…”