Purine nucleosides

Calf intestine adenosine deaminase. Substrate specificity

“…The absence of an absorption in the 1700-1900-cnr1 region of the infrared spectrum forces the assignment of the 1680-cm-1 band to carbonyl stretching mode, since there is no reported instance of an aromatic secondary amide (i.e., positions 7 and 8 of VI) existing in the enol form. This appearance of the C-8 carbonyl absorption at unusually long wavelength is further evidence for the unique electronic configuration of (VI) proposed by Rizkalla et al (1969). While it would be interesting to speculate that the electronic changes in this ring system are solely responsible for the lack of binding of l-methyl-8oxoadenosine (VI) to the enzyme, this cannot be done since we have presented some evidence to indicate that steric factors also play a role in the binding of 8-substituted adenosine derivatives to the enzyme.…”

Structure of 7-methyl-8-oxo-7,8-dihydroguanosine monohydrate

“…Certain ribonucleosides of guanine substituted at C8 have been shown to stimulate the immune system, and have been extensively studied as modulators of B-cell activation (Weigle, 1987). Tlae most studied derivatives include 8-bromoguanosine [(1), first prepared in our laboratory by Holmes & Robins (1964)], 8-mercaptoguanosine [(2) (Holmes & Robins, 1964)] and 7-methyl-8-oxo-7,8-dihydroguanosine [(3), first reported from our laboratory by Rizkalla, Robins & Broom (1969)]. These lowmolecular-weight compounds have been shown to act as intracellular mitogens in murine splenic B lymphocytes (Goodman & Weigle, 1984) and to augment the proliferation and differentiation of murine T cells in the presence of other stimulating signals (Ahmad & Mond, 1986;Feldbush & Ballas, 1985).…”

Copper/H2O2-Mediated Oxidation of 2′-Deoxyguanosine in the Presence of 2-Naphthol Leads to the Formation of Two Distinct Isomeric Adducts

“…54 Next, a possible N7 adduct for 1a/1b was ruled out by mechanistic and 13 C NMR chemical shift considerations. For a ring nitrogen to act as the nucleophile, it must be unprotonated; 55 however, the pK a of N7 of dOG (11.3) is much higher than that of N1 (8.6), so if arylation occurs through this mechanism, N1 should be the preferred site of reaction. 30,55 Another way to deprotonate N7 is through oxidation of dOG to dOG ox , but this product is electrophilic and adds nucleophiles at C5, as previously discussed.…”