Abstract
Model systems of D-glucose and ammonia with metal ions, oxygen, antioxidants, and sodium hydroxide were reacted at 100°C (solution temp.) for 2_??_18 hr to investigate pyrazine formation pathways. Pyrazines identified in these model systems were unsubstituted-, 2-methyl-, 2, 5-dimethyl-, 2, 6-dimethyl-, 2-ethyl-, 2, 3-dimethyl-, 2-ethyl-5-methyl-, 2-ethyl-6-methyl-, 2, 3, 5-trimethyl-, 2-ethyl-3-methyl-, 2-vinyl-, 2-ethyl-3, 5-dimethyl-, 2-ethyl-3, 6-dimethyl- and ethyl vinyl-. Results show that a-amino carbonyl compounds acted as inter-mediates to form various pyrazines. For example, 2-methylpyrazine may be formed from the condensation of α-amino-α-hydroxy acetaldehyde and α-amino acetone following the elimination of a water molecule.
We propose that the formation of a pyrazine ring from dihydropyrazine is due to the dehydration of hydroxy dihydropyrazine rather than the dehydrogenation of dihydropyrazine. This explains the formation of an alkyl group (e. g., an ethyl group) from the sugar moiety.
We propose ten α-amino carbonyl intermediates from the alkylpyrazines which we obtained, and their formation schemes are discussed.
