Quinolinic acid is an endogenous N-methyl-D-aspartate (NMDA) receptor agonist synthesized from L-tryptophan via the kynurenine pathway.

25-Dimethylpyrazine is present in asparagus wheat bread crispbread Swiss cheeses black or green tea soya malt raw shrimp and squid. 25-Dimethylpyrazine is used as flavor additive and odorant in foods.

Oxalic acid is a strong dicarboxylic acid occurring in many plants and vegetables. It is produced in the body by metabolism of glyoxylic acid or ascorbic acid. It is not metabolized but excreted in the urine. It is used as an analytical reagent and general reducing agent.