Proton magnetic resonance studies of alpha-keto acids.
Pulsed Fourier transform proton magnetic resonance was used to study alpha-ketoglutaramic, and several other alpha-keto acids in aqueous solutions as a function of pH. Most alpha-keto acids were found to exist in equilibrium with the hydrate (gem-doil). The equilibrium position favors the nonhydrated alphs-keto acid at neutral pH, but at low pH values (below the pKa of the alpha-carboxylic acid group) the hydrate predominates. We found evidence that alpha-ketoglutaric acid exists in a third equilibrium form which is assigned to the lactol. alpha-Ketoglutaramic acid (the alpha-keto acid analog of glutamine) which is known to exist predominantly in a cyclic form at pH 7.0 was shown to exist as a cyclic structure over a wide pH range. However, the cyclic form is an equilibrium mixture of 2-pyrrolidone-5-hydroxy-5-carboxylic and 1-pyrrolin-2-one-5-carboxylic acids.
D003903:Deuterium; D006038:Glyoxylates; D006863:Hydrogen-Ion Concentration; D007651:Keto Acids; D007656:Ketoglutaric Acids; D007700:Kinetics; D009682:Magnetic Resonance Spectroscopy; D008968:Molecular Conformation; D011773:Pyruvates; D013329:Structure-Activity Relationship; D014867:Water
D006038:Glyoxylates; D007651:Keto Acids; D007656:Ketoglutaric Acids; D011773:Pyruvates; D014867:Water; D003903:Deuterium