1,3,6-Trimethylpyrimido(4,5-d)pyrimidine-2,4,5,7(1H,3H,6H,8H)-tetrone 64467-32-9 Pyrimido(4,5-d)pyrimidine-2,4,5,7(1H,3H,6H,8H)-tetrone, 1,3,6-trimethyl-