Nucleoside2′,3′/3′,5′-Bis(thio)phosphate Analogues Are Promising Antioxidants Acting Mainly via Cu+/Fe2+ Ion Chelation

We synthesized a series of adenine/guanine 2′,3′- or 3′,5′-bisphosphate and -bisphosphorothioate analogues, 1–6, as potential Cu+/Fe2+ chelators, with a view to apply them as biocompatible and water-soluble antioxidants. We found that electron paramagnetic resonance (EPR)-monitored inhibition of OH radicals production from H2O2, in an Fe2+-H2O2 system, by bisphosphate derivatives 1, 3, and 5 (IC50 = 36, 24, and 40 μM, respectively), was more effective than it was by ethylenediaminetetraacetic acid (EDTA), by a factor of 1.5, 2, and 1.4, respectively. Moreover, 2′-deoxyadenosine-3′,5′-bisphosphate, 1, was 1.8- and 4.7-times more potent than adenosine 5′-monophosphate (AMP) and adenosine 5′-diphosphate (ADP), respectively. The bisphosphorothioate derivatives 2, 4, and 6 (IC50 = 92, 50, and 80 μM, respectively), exhibited a dual antioxidant activity, acting as both metal-ion chelators and radical scavengers [2,2′-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS) assay data indicates IC50 = 50, 70, and 108 μM vs 27 μM for Trolox]. Only 2′-deoxyadenosine-3′,5′-bisphosphorothioate, 2, exhibited good inhibition of Cu+-induced H2O2 decomposition (IC50 = 78 vs 224 μM for EDTA). Nucleoside–bisphosphorothioate analogues (2, 4, and 6) were weaker inhibitors than the corresponding bisphosphate analogues (1, 3, and 5), due to intramolecular oxidation under Fenton reaction conditions. 1H- and 31P NMR monitored Cu+ titration of 2, showed that Cu+ was coordinated by both 3′,5′-bisphosphorothioate groups, as well as N7-nitrogen atom, while adenosine-2′,3′-bisphosphorothioate, 6, coordinated Cu+ only by 2′,3′-bisphosphorothioate groups. In conclusion, an additional terminal phosphate group on AMP/guanosine 5′-monophosphate (GMP) resulted in Fe2+-selective chelators highly potent as Fenton reaction inhibitors.