Pyridopyrimidines: Part IX - Synthesis and antibacterial activity of 2-methylthio-6-phenylazo-5,7-dimethylpyrido[2,3-d]pyrimidin-4(3H)-ones

2-Amino-3-carbethoxy-5-phenylazo-4,6-dimethylpyridine 2, obtained by diazo coupling of 2-amino-3-carbethoxy-4,6-dimethyl-pyridine 1 and phenyl diazoni um chloride, has been reacted with various aryl isothiocyanates 3 to get N- 1-substituted N-2-[3-carbethoxy-5-phenylazo-4,6-dimehyl-2-pyridyl]thioureas 4. Cyclization of pyridyl thioureas 4 using two different reaction conditi ons affords 3-substituted 2-thioxo-6-phenylazo-5,7-dimethylpyrido[2,3-d]pyr imidin-4(3H)-ones 5, which are S-methylated by dimethyl sulfate under alkal ine condition to yield the title 2-methylthio-6-phenylazo-5,7-dimethylpyrid o[2,3-d]pyrimidines 6. All the newly synthesized compounds 4, 5 and 6 have been screened for their antibacterial activity.