A novel synthesis of carbon-labelled quinolone-3-carboxylic acid antibacterials

3-Iodoquinolones were prepared from the corresponding quinolone-3-carboxylic acids by Hunsdiecker-type iododecarboxylation reactions with lead tetraacetate and iodine. Cyanation of the iodo compounds with mixtures of potassium [13C]cyanide and copper (1) iodide, gave [3-13C]cyanoquinolones which on acidic hydrolysis afforded quinolone-[3-13C]carboxylic acids. In this way, nalidixic acid, an immediate precursor of norfloxacin, and quinolone WIN57273 were labelled with carbon-13 in the metabolically stable carboxylic acid fragment. (author)