Synthesis and properties of a naphthalene-containing artificial redox coenzyme

An analogue of the reactive triazine dye C.I. Reactive Blue 2 containing nicotinamide, Blue N-3, was shown previously to be coenzymically active with horse liver alcohol dehydrogenase (HLADH). 1,2 Blue N-3 contains an anthraquinone chromophore which is believed to mimic the adenine group of the natural coenzyme NAD +, 3 but which gives rise to a strong absorption in the visible region of the spectrum. This, together with its relatively low solubility in water, has hindered the development of a simple spectrophotometric assay for monitoring its coenzymic activity and kinetics. Based on the knowledge that modifications to the adenine moiety of the natural coenzyme NAD + do not greatly affect its coenzymic activity, 4 the blue anthraquinone chromophore of Blue N-3 was replaced with a terminal naphthalene group to yield the analogue Nap 1 ( Figure 1). This modification resulted in a markedly reduced molar extinction coefficient at 630 nm, increased water solubility, and an improved coenzymic performance. This paper describes the synthesis of Nap 1 and the characterization of its UV-visible absorption properties, pH stability, alcohol substrate specificity, electrochemical reversibility, and kinetic properties. These characteristics are compared and contrasted with those of Blue N-3 and NAD +.