The reactions of hydrated electrons (e(aq) (-)) with 8-bromo-2'-deoxyinosine (8) and 8-bromoinosine (12) have been investigated by radiolytic methods coupled with product studies and have been addressed computationally by means of BB1K-HMDFT calculations. Pulse radiolysis revealed that one-electron reductive cleavage of the C--Br bond gives the C8 radical 9 or 13 followed by a fast radical translocation to the sugar moiety. Selective generation of a C5' radical occurs in the 2'-deoxyribo derivative, whereas in the ribo analogue the reaction is partitioned between the C5' and C2' positions with similar rates. Both C5' radicals undergo cyclizations, 10-->11 and 14-->15, with rate constants of 1.4 x 10(5) and of 1.3 x 10(4) s(-1), respectively. The redox properties of radicals 10 and 11 have also been investigated. A synthetically useful photoreaction has also been developed as a one-pot procedure that allows the conversion of 8 to 5',8-cyclo-2'-deoxyinosine in a high yield and a diastereoisomeric ratio (5'R)/(5'S) of 4:1. The present results are compared with data previously obtained for 8-bromoadenine and 8-bromoguanine nucleosides. Theory suggests that the behavior of 8-bromopurine derivatives with respect to solvated electrons can be attributed to differences in the energy gap between the pi*- and sigma*-radical anions.

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Sorbitylfurfural (Furalglucitol), widely used in the cosmetic industry as antioxidant and antiinflammatory agent, reacts with hydroxyl radical in neutral aqueous solution with a rate constant almost at the diffusional limit, k 1 = 7.3 × 109 M-1 s-1. Despite the unselective character of the OH radical, addition to the 5‘ position in the furanic ring seems to provide the dominant path. The consequent allylic radical undergoes the cleavage of the C−O bond (k 2 = 1.7 × 106 s-1) in β position to form a pseudo-seven-atom ring via a hydrogen bond between the attacking OH group and the furanic oxygen. A 1,6 H-shift between the two oxygen atoms (k3 = 1.4 × 105 s-1) then precedes a disproportionation reaction which leads to the final products (k4 = 2.0 × 107 M-1 s-1). The proposed mechanism is based on the UV−vis spectra of intermediates and final products obtained after pulse and gamma radiolysis, on nonlinear kinetic fittings of absorbance versus time curves, on quantum-mechanical calculations of electronic transitions and reaction enthalpies. The two most important final products have been isolated and characterized as sorbityl-but-2-enal derivatives by LC-MS.

Here, we show that two tautomers are produced by the protonation of the guanine-electron adduct. The fate of electron adducts of a variety of substituted guanosines was investigated by radiolytic methods and addressed computationally by means of time-dependent DFT (TD-B3LYP/6-311G**//B1B95/6-31+G**) calculations. The reaction of e(aq-) with guanosine and 1-methylguanosine produces two transient species, whereas the reaction with N2-ethylguanosine and N2,N2-diethylguanosine produces only one. The two short-lived intermediates, which show a substantial difference in their UV-visible spectra, are recognized to be two purine tautomers (i.e., iminic 18 and aminic 19 forms). The tautomerization 18 --> 19 occurs with a rate constant of ca. 1.5 x 106 s(-1) , and theory suggests that it is a water-assisted process.

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