Double Schiff Base Adducts of 2,3-Butanedione with Glycine: Formation of Pyrazine Rings with the Participation of Amino Acid Carbon Atoms

Abstract

The 1,2-dicarbonyl compounds are well-known for their ability to undergo a one-to-one interaction with amino acids and generate aroma-active pyrazines through the Strecker reaction. An earlier publication reported the generation of tetrahydropyrazine moiety from the double addition of amino acids to 1,2-dicarbonyl compounds. To evaluate the potential of this intermediate to undergo oxidation and form pyrazines, a model system composed of glycine and 2,3-butanedione was evaluated under pyrolytic conditions at 250 °C, as well as under pressurized high-temperature conditions at 120 °C. These studies have indicated the unexpected formation of 2,3-dimethylpyrazine and 2,3,5-trimethylpyrazine in addition to the expected tetramethylpyrazine. Isotope-labeling studies using [¹³C-1]glycine (98%), [¹³C-2]glycine (99%), and [¹⁵N]glycine (98%) have shown that, as expected, tetramethylpyrazine was completely unlabeled, whereas 51% of 2,3-dimethylpyrazine incorporated two ¹³C-2 atoms from glycine, 20% incorporated one atom, and 29% was unlabeled. Furthermore, the label incorporation pattern in the major mass spectral fragment at m/z 67 indicated that the C-2 atoms originating from glycine reside in the ring system of 2,3-dimethylpyrazine. The formation of doubly labeled 2,3-dimethylpyrazine was rationalized through proposition of the double addition of glycine to 2,3-butanedione, and the formation of singly labeled isotopomer was justified by sequential Schiff base formation of 2-amino-butan-3-one first with the Strecker aldehyde and then followed by glycine. This pathway can also generate the double-labeled pyrazine. Finally, the unlabeled pyrazine was proposed to form through the Strecker reaction of 2,3-butanedione and its degradation product glyoxal with glycine. The proposed pathways were also consistent with the observed label distribution patterns of 2,3,5-trimethylpyrazine.

Brown Carbon Formation Potential of the Biacetyl–Ammonium Sulfate Reaction System

“…While BA can react with glycine to form tetramethylpyrazine, its reaction with AS does not favorably produce a species able to reduce the imine-substituted BA (m/z 86) needed for pyrazine formation. 63 Light Absorbance. The reacted BA + AS system exhibits light absorbance similar to that of other small carbonyls, 44 with absorbance peaks at approximately 190, 224, and 280 nm.…”

“…The presence of the α-diketone in BA leads to a decreased number of imidazole derivatives and an increased presence of oxazole derivatives compared to other carbonyl + AS systems. , Additionally, no pyrazines were identified in the BA + AS system. While BA can react with glycine to form tetramethylpyrazine, its reaction with AS does not favorably produce a species able to reduce the imine-substituted BA ( m / z 86) needed for pyrazine formation …”

Processing of bottom-fermented gluten-free beer-like beverages based on buckwheat and quinoa malt with chemical and sensory characterization

“…Their formation most probably occurred from amino acids and vicinal diketones. A recent publication has reported the unexpected formation of 2,3‐dimethylpyrazine and 2,3,5‐trimethylpyrazine in addition to the expected tetramethylpyrazine in a model system composed of glycine and 2,3‐butanedione . Furans are derivatives of furan and can be found in heat‐treated commercial foods formed by thermal degradation of natural food constituents .…”

Thermal generation or aroma

“…Recently, Yaylayan has also shown that under some conditions, part of the glycine carbon skeleton can be found in the pyrazine ring (Guerra and Yaylayan, 2012 dicarbonyl/amino acid soup, there are many permutations and combinations of carbonyl-amine condensations that can lead to the formation of pyrroles and pyrazines. For example, the dicarbonyls, rather than undergoing a Strecker degradation, can form a double Schiff base with glycine that can cyclise leaving two glycine-based carbons in the pyrazine ring.…”