Regiospecific one-pot, combinatorial synthesis of new substituted pyrimido[4,5- c]pyridazines as potential monoamine oxidase inhibitors

New 3-aryl-6-methylpyrimido[4,5- c ]pyridazine-5,7(6 H ,8 H) -diones and 3-aryl-6-ethyl-7-thioxo-7,8-dihydropy-rimido[4,5- c ]pyridazin-5(6 H) -ones were efficiently synthesized via a regiospecific one-pot reaction of N -methylbarbituric acid and N -ethyl-2-thiobarbituric acid with various arylglyoxal monohydrates in the presence of hydrazine dihydrochlo- ride in ethanol at 50 °C. The target compounds were obtained in high yields and were regioisomerically pure after recrystallization. These new heterocycles may act as potential MAO B inhibitors.