Ultraviolet‐and Γ‐ray‐induced Reactions of Nucleic Acid Constituents With Alcohols. On the Selectivity of These Reactions for Purines

Photochemistry of carboxylic acid derivatives

“…to cyclic compounds such as 1,3-dimethyluracil (eq 148), 160 although in the latter systems a different mechanism sometimes competes161 which leads to alkoxy-substituted products (eq 149). Ethers (eq 150) 162 and hydrocarbons (eq 151)163 can be added in a similar way; with these a competitive reaction leads to «-substituted products, and the results of deuterium-labeling (147) studies suggest that the ß carbon in the excited state abstracts a hydrogen atom to give these alternative products, since the use of perdeuteriocyclohexane163 leads to an «-substituted product with one deuterium in the ß position.…”

“…The need for electron-rich alkenes is indicative of electron-transfer involvement, and the radical cation of 1,1-diphenylethylene is implicated172 in forming a triphenyltetrahydronaphthalene as by-product in some reactions (eq 160). In the reaction between benzoic acid and 2,3-+ Ph2C=CH2 (Ar = p-NC-C6H4) (160) dimethylbut-2-ene there is evidence for biradical formation173 because the major product arises by a 1,5-hydrogen transfer in the biradical (eq 161). Such a process is possible because of the OH group of the acid, and the whole reaction is a "reverse" Norrish type 2 process going through a hydroxy 1,4-biradical.…”

Ultraviolet- an .gamma.-ray-Induced reactions of nucleic acid constituents. Reactions of purines with ethers and dioxolane

“…All guanosine photoproducts do not possess the absorption band of the H-8 proton in the nmr, thus indicating that the hydrogen atom at C-8 was substituted. The absorption of the sugar moiety in the photoproduct is very similar to that of the starting nucleotide, except for the anomeric proton.lb The 4 H, -CH2CH2-), 5.95 (s, 3 , N-7 CH3), 6.45 (s, 3 , N-3 CH3), 6.64 (s, 3 H, N-l CH3) A 4.82 (m, 1 H, caffeine CH-O), 5.7 (m, 1 H, -CHCH2OH) 6 (d, 3 H, N-7 CH3; J = 3.6 Hz), 6.28 (m, 2 H, -CH2OH), 6.46 (s, 3…”

Light-induced free radical alkylation of polynucleotides and their enzymatic digestion

“…Our results indicate that the photoalkylation reactions can be applied for the modification of polynucleotides, and that the modified polynucleotides are sensitive to RNase. The 2-propanol-modified moieties consist either of uracil residues which underwent addition of the alcohol across the 5,6-double bond (6)(7)(8) or adenine or guanine residues, which were alkylated at the C-8 position. With irradiated poly(G) and 2-propanol, T1-RNase hydrolyzed the polynucleotide,under standard conditions, in the normal pattern, and the digestion resulted in a mixture of Guo-2'(3')-P and 8-a-hydroxyisopropyl-Guo-2'(3')-P. These results indicate that alkylation at the C-8 position of guanine residue with the a-hydroxyisopropyl group does not lead to the inability of Tl-RNase to rupture the phosphodiester bonds of the alkylated guanine moiety.…”

“…It is noteworthy that uracil and its derivatives also react photochemically with some organic compounds, e.g. alcohols, to yield the corresponding 6-substituted-5,6-dihydro-uracils (6)(7)(8). These reactions can further be utilized to extend the use of photochemistry as a probe of polynucleotide structure and interaction.…”