Synthesis, azido-tetrazole equilibrium studies and biological activity of 1-(2-azido-6-chloropyrid-4-yl)-3-phenylurea, a photoaffinity labeling reagent for cytokinin-binding proteins.

1-(2-Azido-6-chloropyrid-4-yl)-3-phenylurea was synthesized using known methods. Azido-tetrazole equilibrium for this compound was studied in various solvents, and the azide tautomer was found to be largely predominant. However, in water solution, it is suspected to exist in the tetrazole form in a significant amount. Like other 2,6-disubstituted pyridylurea analogs, it exhibits high cytokinin activity, and it is easily photolysable. Thus it appears to be a good candidate as a photoaffinity labeling reagent for cytokinin-binding proteins, receptors in particular. In the absence of the 6-chloro substituent, the tetrazole form was the only existing tautomer. The corresponding compound does not exhibit cytokinin activity and is not photolysable.