Abstract
Kinetic ..cap alpha.. deuterium isotope effects have been measured for acid-catalyzed hydrolysis of inosine and adenosine. For inosine hydrolysis, values of k/sub H/k/sub D/ follow: in 1.0 M HCl, 1.21 and 1.20 at 25 and 50/sup 0/C, respectively; in 0.1 M HCl, 1.19 and 1.18 at 25 and 50/sup 0/C, respectively. For adenosine hydrolysis, k/sub H/k/sub D/ is 1.23 in 0.1 M HCl at 25/sup 0/C. The values require that the transition states for hydrolysis of both the monocation and dication of inosine and the dication of adenosine have marked oxocarbonium ion character. Detailed mechanisms which accord with this and other experimental observations include (1) a classical Al mechanism in which the C--N bond is largely cleaved in the transition state; (2) a mechanism involving some form of nucleophilic participation by solvent in which bond cleavage is advanced relative to bond formation in the transition state; or (3) complete C--N bond cleavage with rate-determining diffusion apart of oxocarbonium ion and purine base. 53 references, 1 figure, 2 tables.
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