Isomerization through Cleavage and Recombination of Imidazolide Linkage in the Condensed Tricyclic System Related to Hypermodified Bases of Phenylalanine Transfer Ribonucleic Acids

概要

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1-Benzyl-4,6-dimethyl-4,9-dihydro-1H-imidazo[1,2-α]purin-9-one bearing an alkyl, a 1-alkenyl, a hydroxymethyl, a methoxymethyl, or a formyl group at the 7-position (3a-e) underwent rearrangement through fission and recyclization of the pyrimidine ring, attaining equilibrium with the corresponding positional isomer 4a-e in MeONa-MeOH at 25℃, whereas 7-methoxycarbonyl and 7-halogeno compounds 3f-i were irreversibly converted into the rearranged products 4f-i under identical conditions. The position of equilibrium appears to be affected by the electronic factor of the substitutent rather than the steric one. The pseudo-first-order rate constants measured for the reactions of 3a, b, d, f-i suggest that the reaction is accelerated by the electron-withdrawing substituent. However, the reactions of this series of compounds do not always obey the Hammett equation.On the other hand, a linear free energy relationship (ρ=+3.2) was observed for the rates of rearrangement of a 6-demethyl series of compounds 9a, b, d, f, g, when σ^0_P values were employed. The deviations from this relationship for the reactions with the 7-hydroxymethyl compound 9c and the 7-carbamoyl compound 9e are explicable in terms of the accelerative effect through intramolecular hydrogen bonding with the carbonyl oxygen at the 9-position.
公益社団法人日本薬学会の論文
1999-10-15