We synthesized various 4-[[3, 4-(methylenedioxy) benzylyllaminolquinazolines substituted at the 5-to 8-positions and evaluated their inhibitory activities toward cyclic GMP phosphodiesterase (cGMP-PDE) from porcine aorta. Monosubstitution at the &position wae essential for the inhibitory activity, and the preferred Substituents were compact and hydrophobic: methoxy (3b, ICs0= 0.23 pM), methyl (3c, 0.10 pM), chloro (3d, 0.019 pM), ...