Synthesis and Properties of a pH-Insensitive Fluorescent Nitric Oxide Cheletropic Trap (FNOCT)

The synthesis and properties of the new fluorescent nitric oxide cheletropic trap (FNOCT) 14, designed for the trapping and quantification of nitric oxide (NO) production in chemical and biological systems, is described (Scheme 3). The dicarboxylic acid 14 and the corresponding bis[(acetyloxy)methyl] ester derivative 15 of the FNOCT contain a 2-methoxy-substituted phenanthrene group as fluorophoric unit. The fluorescence of the reduced NO adduct of this FNOCT (λexc 320 nm, λem 380 nm) is pH-independent. Trapping experiments were carried out in aqueous buffer solution at pH 7.4 with nitric oxide being added as a bolus as well as being released from the NO donor compound MAHMA NONOate (= (1Z)-1-{methyl[6-(methylammonio)hexyl]amino}diazen-1-ium-1,2-diolate), indicating a trapping efficiency of ca. 50%. In a biological application, nitric oxide was scavenged from a culture of lipopolysaccharide-stimulated rat alveolar macrophages. Under the applied conditions, a production of 11.1 ± 1.5 nmol of NO per hour and per 105 cells was estimated.