Abstract
Titration of α-keto-δ-aminovaleric acid indicates the presence of two ionizable groups in the molecule with p K′ 1.77 and 5.99. The first p K′ corresponds to the COOH group. The second p K′ is attributed to the ionization of the pyrrolinium structure of Δ 1-pyrroline-2-carboxylic acid, the cyclic form of α-keto-δ-aminovaleric acid. This interpretation is supported by infrared spectroscopy of the solid compound isolated at pH 2.0 and 7.0. The existence of a pyrrolinium structure for Δ 1-pyrroline-2-carboxylic acid is also supported by the results of ultraviolet spectra. The influence of pH on the condensation reaction of Δ 1-pyrroline-2-carboxylic acid with o-aminobenzaldehyde, the nature of the derivatives formed in solutions of different pH by reduction with borohydride, and the increased susceptibility to N-acetylation of the form existing at low pH, are consistent with these structural deductions. The molecular extinctions of the colored compounds resulting from the reaction of pyrroline-2-carboxylic (α-keto-δ-aminovaleric) acid with acid ninhydrin and with o-aminobenzaldehyde were determined.
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