The reaction of an aromatic heterocycle with a proton is called a protonation. One of articles about this theory is 《Nucleosides and nucleotides. XXX. Syntheses of 8-substituted guanosine derivatives》. Authors are Ikehara, Morio; Muneyama, Kei.The article about the compound:8-Bromoguaninecas:3066-84-0,SMILESS:NC(N1)=NC(NC(Br)=N2)=C2C1=O).Computed Properties of C5H4BrN5O. Through the article, more information about this compound (cas:3066-84-0) is conveyed.
cf. CA 64, 14255f. 8-Bromoguanosine (I) was converted to 8-mercaptoguanosine by the method of Holmes and Robins (CA 60, 14584c), and was methylated with methyl iodide to afford 8-methylthioguanosine (II). In addition, 8-ethylthioguanosine was obtained directly by reaction of I with ethyl mercaptide in ethanol. II was oxidized either with N-chlorosuccinimide or with H2O2 (H2O2, in limited amount, being preferable) to afford 8-(methylsulfonyl)guanosine (III). When III was heated at 80° in 0.1N HCl 4 hrs., 8-methylsulfonylguanine (IV) (but not an N-oxide derivative) was obtained. Treatment of III with 0.1N NaOH at 100° 3 hrs. also gave IV. When III was kept at 30° 40 hrs. in dimethyl sulfoxide with excess Na tert-butoxide, a substance having λ (H)+ 256, 284 mμ; λ(OH)- 286 mμ was obtained, accompanied by a small amount of IV. The former compound contained S and D-ribose moieties, and it was deduced from its uv properties that the guanosine ring in III had been cleaved. Its absorption could be explained if a bathochromic shift of approx. 10-20 mμ, which is generally observed by the substitution of a methyl sulfonyl group at the 8-position of guanosine, was added to the absorption spectra of 4-aminoimidazolecarboxamide 1-p-riboside (λ(H+) 267, 240 mμ; λ(OH-) 267 mμ). The pKa value of III (8.3) is much higher than that of guanosine (9.2-9.5). The easy dissociation of N’-H of III would render the pyrimidine ring more susceptible to the nucleophilic attack of tert-butoxide. Under similar reaction conditions guanosine did not react with tert-butoxide. When III was treated with Na methoxide in methanol at 130-50°, 8-methoxyguanosine was obtained, the structure of which was confirmed by comparison with a sample obtained from I. 8-Dimethylaminoguanosine was prepared by heating I with dimethylamine in methanol at 120-30° 5 hrs. It is concluded that nucleophilic substitution occurred smoothly in I, as expected in the case of aromatic halo compound activated by ο- or p-electron attracting groups. However, in the case of III the strong electron-attracting nature of the methylsulfonyl group at position 8 caused a nucleophilic attack on N1 or N3, and the subsequent cleavage of the pyrimidine ring. Moreover, acidic hydrolysis easily cleaved III at the glycosidic linkage, whereas 8-hydroxypurine D-ribonucleoside is resistant to such cleavage. 14 references.
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Tetrahydrofuran – Wikipedia,
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