3 Tetrazolylpyridopyrimidin 4 one derivatives useful as an antiallergy agent are produced by reacting a cyano derivative of pyridopyrimidin 4 one compound with hydrazoic acid, followed by hydrolysis, or with a salt of hydrazoic acid, reacting the resulting product with an acid or {HEAD ~ a base}, followed by {TAIL ~ hydrolysis} 
3 Tetrazolylpyridopyrimidin 4 one derivatives useful as an antiallergy agent are produced by reacting a cyano derivative of pyridopyrimidin 4 one compound with hydrazoic acid , followed by hydrolysis , or with a salt of hydrazoic acid , reacting the resulting product with an acid or { HEAD ~ a base } , followed by { TAIL ~ hydrolysis }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH REL REL TAIL TAIL TAIL TAIL TAIL