(a) Pyridoxal catalysis of Eq. 26.53 involves the following transformations. (Running these reactions in the reverse direction with a different a-keto acid completes Eq. 26.53.)

Using bases (B;) and acids (⁺BH) as needed, provide curved-arrow mechanisms for these reactions. Your mechanism should show the important intermediates. As part of your mechanism, explain the significance of the pyridinium ion in the catalysis of this reaction sequence.

(b) Using bases (B;) and acids (⁺BH) as needed, provide a curved-arrow mechanism for the conversion of the a-amino acid serine into formaldehyde and glycine.

Transcribed Image Text:

CHIN-CHCH₂R CO₂ (from Eq. 26.56) CH₂- =C-CH₂R CO₂ H₂O CH,NH, + O₂C-C-CH₂R an a-keto acid pyridoxamine phosphate