A1 Vertaisarvioitu alkuperäisartikkeli tieteellisessä lehdessä
Hydrolytic reactions of the phosphorodithioate analogue of uridylyl(3 ',5 ')uridine: Kinetics and mechanisms for the cleavage, desulfurization, and isomerization of the internucleosidic linkage
Tekijät: Ora M, Jarvi J, Oivanen M, Lonnberg H
Kustantaja: AMER CHEMICAL SOC
Julkaisuvuosi: 2000
Lehti:: Journal of Organic Chemistry
Tietokannassa oleva lehden nimi: JOURNAL OF ORGANIC CHEMISTRY
Lehden akronyymi: J ORG CHEM
Vuosikerta: 65
Numero: 9
Aloitussivu: 2651
Lopetussivu: 2657
Sivujen määrä: 7
ISSN: 0022-3263
DOI: https://doi.org/10.1021/jo991632a
Tiivistelmä
The hydrolytic reactions of the phosphorodithioate analogue of uridylyl(3',5')uridine [3',5'-Up(s)(2)U] were followed by HPLC over a wide pH range at 363.2 K. Under acidic and neutral conditions, three reactions compete: (i) desulfurization to a mixture of the (R-P)- and (S-P)-diastereomers of the corresponding 3',5'- and 2',5'-phosphoromonothioates [3',5'- and 2',5'-Up(s)U], which are subsequently desulfurized to a mixture of uridylyl(3',5')- and -(2',5')uridine [3',5'- and 2',5'-UpU], (ii) isomerization to 2',5'-Up(s)(2)U, and (iii) cleavage to uridine, in all likelihood via a 2',3'-cyclic phosphorodithioate (2',3'-cUMPS(2)). Under alkaline conditions (pH > 8), only a hydroxide ion catalyzed hydrolysis to uridine via 2',3'-cUMPS(2) takes place. At pH 3-7, all three reactions are pH-independent, the desulfurization being approximately 1 order of magnitude faster than the cleavage and isomerization. At pH < 3, all the reactions are hydronium ion catalyzed. On going to very acidic solutions, the cleavage gradually takes over the desulfurization and isomerization. Accordingly, the cleavage overwhelmingly predominates at pH < 0. The overall hydrolytic stability of 3',5'-Up(s)(2)U is comparable to that of (S-P)- and (R-P)-3',5'-Up(s)U land to that of 3',5'-UpU, except at pH < 2. The rate of the hydroxide ion catalyzed hydrolysis of 3',5'-Up(s)(2)U is 37% and 53% of that of(S-P)- and (R-P)-3',5'-Up(s)U, respectively. The reactions, however, differ with the respect of the product accumulation. While the phosphoromonothioates produce a mixture of 2'- and 3'-thiophosphates as stable products, 3',5'-Up(s)(2)U is hydrolyzed to uridine without accumulation of the corresponding dithiophosphates. At pH i 3, where the hydrolysis is hydronium ion catalyzed, the kinetic thio-effect of the second thio substitution is small: under very acidic conditions (H-0 -0.69), (S-P)-3',5'-Up(s)U reacts 1.6 times as fast as 3',5'-Up(s)(2)U, but the reactivity difference decreases on going to less acidic solutions. In summary, the hydrolytic stability of 3',5'-Up(s)(2)U closely resembles that of the corresponding phosphoromonothioate. While replacing one of the nonbridging phosphate oxygens of 3',5'-UpU with sulfur stabilizes the phosphodiester bond under acidic conditions by more than 1 order of magnitude, the replacement of the remaining nonbridging oxygen has only a minor influence on the overall hydrolytic stability.
The hydrolytic reactions of the phosphorodithioate analogue of uridylyl(3',5')uridine [3',5'-Up(s)(2)U] were followed by HPLC over a wide pH range at 363.2 K. Under acidic and neutral conditions, three reactions compete: (i) desulfurization to a mixture of the (R-P)- and (S-P)-diastereomers of the corresponding 3',5'- and 2',5'-phosphoromonothioates [3',5'- and 2',5'-Up(s)U], which are subsequently desulfurized to a mixture of uridylyl(3',5')- and -(2',5')uridine [3',5'- and 2',5'-UpU], (ii) isomerization to 2',5'-Up(s)(2)U, and (iii) cleavage to uridine, in all likelihood via a 2',3'-cyclic phosphorodithioate (2',3'-cUMPS(2)). Under alkaline conditions (pH > 8), only a hydroxide ion catalyzed hydrolysis to uridine via 2',3'-cUMPS(2) takes place. At pH 3-7, all three reactions are pH-independent, the desulfurization being approximately 1 order of magnitude faster than the cleavage and isomerization. At pH < 3, all the reactions are hydronium ion catalyzed. On going to very acidic solutions, the cleavage gradually takes over the desulfurization and isomerization. Accordingly, the cleavage overwhelmingly predominates at pH < 0. The overall hydrolytic stability of 3',5'-Up(s)(2)U is comparable to that of (S-P)- and (R-P)-3',5'-Up(s)U land to that of 3',5'-UpU, except at pH < 2. The rate of the hydroxide ion catalyzed hydrolysis of 3',5'-Up(s)(2)U is 37% and 53% of that of(S-P)- and (R-P)-3',5'-Up(s)U, respectively. The reactions, however, differ with the respect of the product accumulation. While the phosphoromonothioates produce a mixture of 2'- and 3'-thiophosphates as stable products, 3',5'-Up(s)(2)U is hydrolyzed to uridine without accumulation of the corresponding dithiophosphates. At pH i 3, where the hydrolysis is hydronium ion catalyzed, the kinetic thio-effect of the second thio substitution is small: under very acidic conditions (H-0 -0.69), (S-P)-3',5'-Up(s)U reacts 1.6 times as fast as 3',5'-Up(s)(2)U, but the reactivity difference decreases on going to less acidic solutions. In summary, the hydrolytic stability of 3',5'-Up(s)(2)U closely resembles that of the corresponding phosphoromonothioate. While replacing one of the nonbridging phosphate oxygens of 3',5'-UpU with sulfur stabilizes the phosphodiester bond under acidic conditions by more than 1 order of magnitude, the replacement of the remaining nonbridging oxygen has only a minor influence on the overall hydrolytic stability.
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