1,3-Dihydro-2H-imidazol-2-one5918-93-431 % similar 3-Amino-1,2,4-triazole61-82-531 % similar Isocytosine108-53-230 % similar 4,6-Difluoro-2-pyrimidinamine675-11-630 % similar 2-Amino-5-bromopyrimidine7752-82-130 % similar