Isomerization through Cleavage and Recombination of Imidazolide Linkage in the Condensed Tricyclic System Related to Hypermodified Bases of Phenylalanine Transfer Ribonucleic Acids
| Autor: | Shin-ichi Ohyama, Taisuke Itaya, Yoshihisa Shirasaki, Yukiko Ono, Tae Kanai, Nobuhiro Muramoto |
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| Rok vydání: | 1999 |
| Předmět: | |
| Zdroj: | Chemical and Pharmaceutical Bulletin. 47:1464-1472 |
| ISSN: | 1347-5223 0009-2363 |
| DOI: | 10.1248/cpb.47.1464 |
| Popis: | 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°C, 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 σ0P 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. |
| Databáze: | OpenAIRE |
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