Redox Activity of Some NADP Analogues and EPR Spectra of Radical Intermediates (A Review)

Data on the redox activity of several NADP/NADPH analogues and the magnetic resonance parameters of the intermediates, recorded using EPR, are summarized. Recent data on phosphorylated acridine derivatives are included, along with descriptions and simulations of their EPR spectra and calculations of their magnetic resonance parameters. The unpaired electron in the radicals is shown to be localized on the N-heterocyclic moiety, with the radicals being C-centred. Substituents in the heterocycle, either at nitrogen or carbon (C9 or similar), are shown not to significantly affect the magnetic resonance parameters. C9 phosphorylated acridanes, both mono- and bis-derivatives, have been shown to be capable of forming relatively stable radical intermediates in redox reactions. The EPR spectra of these intermediates were specially recorded and simulated for this review in order to compare them with data from previous studies. The obtained mono- and bisphosphorylated acridanes exhibit high stability in the catalytic hydrogen evolution reaction with TON values 6.9 and 5.5, respectively.