Pyridopyrimidines biologically interesting

G. Reactive Methyl Groups Pyridopyrimidines of Biological Interest... 

The field of pyridopyridazines, although potentially a rich one, has been little explored compared with that of the pyridopyrimidines. This is due partly to the difficulty of preparation of several of the member systems, to the relatively small number of different syntheses utilized for those systems which have been explored, and the relative lack of interesting biological activity, or pharmaceutical and other uses found with them. 

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