3-甲基尿酸

6-硫代-7,9-二氢-3H-嘌呤-2,8-二酮

1,8-二氢蝶啶-2,4,7-三酮

1,3,6,8-tetrahydro-2,4,5,7-pyrimido<5,4-g>pteridinetetrone

1,3,8,9-tetramethylpurine-2,6-dione