A1 Vertaisarvioitu alkuperäisartikkeli tieteellisessä lehdessä
GENERAL AND SPECIFIC ACID-BASE CATALYSIS OF THE HYDROLYSIS AND INTERCONVERSION OF RIBONUCLEOSIDE 2'-PHOSPHOTRIESTERS AND 3'-PHOSPHOTRIESTERS - KINETICS AND MECHANISMS OF THE REACTIONS OF 5'-O-PIVALOYLURIDINE 2'-DIMETHYLPHOSPHATES AND 3'-DIMETHYLPHOSPHATES
Tekijät: KOSONEN M, LONNBERG H
Kustantaja: ROYAL SOC CHEMISTRY
Julkaisuvuosi: 1995
Lehti:: Royal Society of Chemistry. Journal: Perkin Transactions 2
Tietokannassa oleva lehden nimi: JOURNAL OF THE CHEMICAL SOCIETY-PERKIN TRANSACTIONS 2
Lehden akronyymi: J CHEM SOC PERK T 2
Numero: 6
Aloitussivu: 1203
Lopetussivu: 1209
Sivujen määrä: 7
ISSN: 0300-9580
DOI: https://doi.org/10.1039/p29950001203
Tiivistelmä
Kinetics of the hydrolysis and interconversion of 5'-O-pivaloyluridine 2'- and 3'-dimethylphosphates in the pH range 0-9 have been studied. At pH < 2, both reactions are first order in hydronium ion concentration, the hydrolysis being three times as fast as the interconversion. The interconversion, however, becomes hydroxide-ion-catalysed at pH as low as 2.5, whereas the hydrolysis remains pH independent to pH 7, and becomes then base-catalysed. Both reactions are susceptible to general-base catalysis, the Brosted beta values based on carboxylate ions being 0.75. These observations suggest that the monocationic, phosphorane intermediate, obtained by the attack of 2'-OH on the phosphotriester monocation, is decomposed to the hydrolysis and isomerization products at a comparable rate. By contrast, the monoanionic phosphorane, obtained by the attack of 2'-O- on the neutral phosphotriester, predominantly gives isomerization products; the methoxide ion leaves 10(5) times less readily than the sugar oxyanions, 2'-O- or 3'-O-. Accordingly, the pH-independent hydrolysis appears to consist of consecutive specific base/acid catalysis. The buffer-catalysed reactions are Suggested to proceed by general-base-catalysed attack of 2'-OH on neutral phosphotriester, followed by general-acid-catalysed decomposition of the phosphorane intermediate to either hydrolysis or isomerization products. The mechanisms of the hydrolysis and isomerization of the internucleosidic phosphodiester bonds are discussed on these bases.
Kinetics of the hydrolysis and interconversion of 5'-O-pivaloyluridine 2'- and 3'-dimethylphosphates in the pH range 0-9 have been studied. At pH < 2, both reactions are first order in hydronium ion concentration, the hydrolysis being three times as fast as the interconversion. The interconversion, however, becomes hydroxide-ion-catalysed at pH as low as 2.5, whereas the hydrolysis remains pH independent to pH 7, and becomes then base-catalysed. Both reactions are susceptible to general-base catalysis, the Brosted beta values based on carboxylate ions being 0.75. These observations suggest that the monocationic, phosphorane intermediate, obtained by the attack of 2'-OH on the phosphotriester monocation, is decomposed to the hydrolysis and isomerization products at a comparable rate. By contrast, the monoanionic phosphorane, obtained by the attack of 2'-O- on the neutral phosphotriester, predominantly gives isomerization products; the methoxide ion leaves 10(5) times less readily than the sugar oxyanions, 2'-O- or 3'-O-. Accordingly, the pH-independent hydrolysis appears to consist of consecutive specific base/acid catalysis. The buffer-catalysed reactions are Suggested to proceed by general-base-catalysed attack of 2'-OH on neutral phosphotriester, followed by general-acid-catalysed decomposition of the phosphorane intermediate to either hydrolysis or isomerization products. The mechanisms of the hydrolysis and isomerization of the internucleosidic phosphodiester bonds are discussed on these bases.
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