Photolysis of 2-azidopyridines. the behavior of 1-(2-azido-6-chloropyrid-4-yl)-3-phenylurea,a photoaffinity labeling reagent for probing cytokinin-binding proteins

The photolysis of l-(2-azido-6-chloropyrid-4-yl)-3-phenylurea ( 1 ) was studied under various conditions. In alcohols or in hexane, complex mixtures of products were obtained. Methoxide anions or diethylamine gave rise in high yield to 1,3-diazepines resulting from ring enlargement of the intermediate nitrene with addition of one molecule of the nucleophile, and nucleophilic substitution of the chlorine atom. A similar reaction was observed in water, when Pyrex filtered light was used. However, with unfiltered light produced by a powerful lamp, the main reaction was photodechlorination. The reagent 1 is expected to bind covalently to cytokinin-binding proteins through different ways upon photolysis.