Studies on cytokinins ofnon-vV6-adenine type, as well as those of 7V6-adenine type are important to unveil the essential structures required for cytokinin activity. Besides A^TV'-disubstituted ureas, well-known cytokinins of non-N6-adenine type,1'2* some azanaphthalenes have been shown to be slightly active in tobacco callus tests.3>4) However, the cytokinin activity of pyrido[3,4-^/]pyrimidines, one of the triazanaphtalenes, has not been studied at all. Therefore, this report deals with the synthesis and cytokinin activity of some new 4-and 2,4-substituted pyrido[3,4-^pyrimidines. 4-Substituted-aminopyridopyrimidines are usually prepared from the pyridopyrimidin-4(3//)-ones via the 4chloro or 4-mercapto derivatives by two-step synthesis.5) Chlorodehydroxylation of la with POC13 and triethyl
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