Triacetic acid lactone
Triacetic acid lactone (TAL; 4-hydroxy-6-methyl-2-pyrone) is an organic compound derived enzymatically from glucose. It is a light yellow solid that is soluble in organic solvents. Structure Triacetic acid lactone consists of two main tautomers. The tautomer on the left, featuring a 4-hydroxy group, the C4 carbon, is dominant. Triacetic acid lactone is classified as a 2-pyrone compound owing to the ketone group on the C2 carbon in its dominant form. Synthesis Triacetic acid lactone is synthesized either from dehydroacetic acid, another 2-pyrone derivative, or from glucose by enzymatic catalysis. In its original synthesis, triacetic acid lactone was obtained by treatment of dehydroacetic acid with sulfuric acid at 135 °C. Dehydroacetic acid undergoes ring-opening and hydration to form "tetracetic acid". Upon cooling, triacetic acid reverts to a lactone ring similar to the dehydroacetic acid structure, and the triacetic acid lactone is recovered by crystallization in cold water. Biosynthesis The microbial synthesis of triacetic acid lactone requires the enzyme 2-pyrone synthase (2-PS). This enzyme has been examined in two hosts Escherichia coli and Saccharomyces cerevisiae. The Saccharomyces cerevisiae host being used during the synthesis produces a higher yield (70%) compared with the Escherichia coli host, which produces a yield of 40% of