咖啡因

丙酮酸

8-(1-hydroxyethyl)-1,3-dimethyl-7H-purine-2,6-dione

1,3,7-trimethyl-2,6-dioxo-2,3,6,7-tetrahydro-1H-purine-8-carboxylic acid amide

8-acetyl-1,3-dimethyl-3,7-dihydro-purine-2,6-dione