Exchange of Carbon-Bound Hydrogen Atoms ortho to the Hydroxyl Group in Tyrosine

Abstract

The carbon-bound hydrogen atoms of tyrosine that exchange with solvent protons in strongly acid solutions at about 100°C are not the methylene hydrogen atoms but a pair on the aromatic ring. Of the two pairs of protons on the aromatic ring, observed in the proton magnetic resonance spectra, the pair at higher field undergoes exchange in 2.4 N DCI at 100°C. Other hydrogen atoms, attached either to aliphatic or aromatic carbon atoms, exhibit no noticeable exchange under the same conditions. From a chemical-shift analysis the exchanging protons are assigned as those ortho to the hydroxyl group on the aromatic ring.