[Synthesis of 5-azido-3-nitro-omega-bromo-acetophenone- a photochemically active bifunctional reagent for the cross-linking of biopolymers].

The photochemically activatable heterobifunctional reagent 5-azido-3-nitro-omega-bromo-acetophenone (3) was synthesized by condensation of 3,5-dinitrobenzoyl chloride with diethyl malonate, acid-catalyzed decarboxylation of the formed malonester derivative 1 to 3,5-dinitro-acetophenone (2a), selective reduction of one nitro group in 2a to 5-amino-3-nitro-acetophenone (2b) and diazotization to 2c. Nucleophilic displacement of the diazonium group in 2c by sodium azide forms 5-azido-3-nitro-acetophenone (2d) which gives 3 after bromination. Compound 3 is photochemically labile and forms an highly reactive nitrene during ultraviolet irradiation. Since compound 3 is able to alkylate amino- or mercapto-groups of amino acids or nucleosides via its bromoacetyl residue, the bifunctional reagent 3 should cross link proteins or nucleic acids after nitrene generation.