Formation of 2-pentylpyridine from the thermal interaction of amino acids and 2,4-decadienal

To study the mechanism of 2-pentylpyridine formation in model systems, 2,4-decadienal was reacted with five amino acids (glycine, aspartic acid, asparagine, glutamic acid, and glutamine) at 180 degrees C for 1 h (pH 7.5). In addition to 2-pentylpyridine, 3-pentylpyridine was also tentatively identified from the thermal reactions. The relative yields of alkylpyridine formation from the reactions were asparagine > glutamine > aspartic acid > glutamic acid > glycine. When amide-N-15-labeled glutamine and asparagine were heated with 2,4-decadienal, the relative contribution of amide nitrogens to the formation of alkylpyridine was determined. Approximately half of nitrogen atoms in 2-pentylpyridine formed were contributed by the amide nitrogens of asparagine, whereas almost all of them came from the amide nitrogens in glutamine. The results above may indicate that both free ammonia and a-amino groups bound in amino acids can contribute to the formation of alkylpyridines, but free ammonia does so more effectively.