Electrochemistry of purine derivatives. 2: Correlation of anodic differential pulse peak potentials with Hammett substituent constants.

Differential pulse voltammetry was used to measure anodic peak potentials at the glassy carbon electrode (in pH 2 to 11 aqueous buffer versus Ag/AgCl) for 14 purine bases and nucleosides. The tested compounds included the antiviral drugs 9-[(1,3-dihydroxy-2-propoxy)-methyl]guanine (1) and acyclovir (2) plus six analogues of 1. At pH 7, representative peak potential values were as follows: 1, 0.97 V; 2, 1.01 V; 6-amino-6-deoxy-1 1.00 V; guanosine, 1.03 V; 2'-deoxyguanosine, 1.03 V. The observed potentials at pH 7 and related literature values correlated with Hammett pi(para) substituent constants. For 24 purines, stepwise multiple linear regression provided the relationship: P7 = (1.08 +/- 0.055) + (1.13 +/- 0.13) sigma 8 + (0.338 +/- 0.061)sigma(2 + 6) + (0.281 +/- 0.043)D (with n = 24, r2 = 0.930, CV = 11.1, and F = 88) where P7 is the pH 7 oxidation potential, the subscripts refer to purine ring substitution position, and D is an indicator variable for substitution at purine N9 by furanoside or glycoside analogue moieties. The observed relationship permits predictions of anodic peak potentials for other purines the substitution patterns of which are known.