CN1C=NC2=C1C(=O)N(C(=O)N2C)C caffeine
CN1C2=C(C(=O)N(C1=O)C)NC=N2 theophylline
CC(=O)CC(C1=CC=CC=C1)C2=C(C3=CC=CC=C3OC2=O)O warfarin