A1 Refereed original research article in a scientific journal
pH- and buffer-independent cleavage and mutual isomerization of uridine 2 '- and 3 '-alkyl phosphodiesters: implications for the buffer catalyzed cleavage of RNA
Authors: Kosonen M, Yousefi-Salakdeh E, Stromberg R, Lonnberg H
Publisher: ROYAL SOC CHEMISTRY
Publication year: 1998
Journal:: Royal Society of Chemistry. Journal: Perkin Transactions 2
Journal name in source: JOURNAL OF THE CHEMICAL SOCIETY-PERKIN TRANSACTIONS 2
Journal acronym: J CHEM SOC PERK T 2
Issue: 7
First page : 1589
Last page: 1595
Number of pages: 7
ISSN: 0300-9580
DOI: https://doi.org/10.1039/a801670d
Abstract
Concurrent isomerization of the ethyl, 2-ethoxyethyl, 2,2-dichloroethyl and 2,2,2-trichloroethyl esters of uridine 3'-phosphate to their 2'-counterparts and cleavage to uridine 2',3'-cyclic phosphate have been studied over a wide pH-range (H-0 -0.2 to pH 9) at 363.2 K, The buffer-independent pa-rate profiles obtained show involvement of four distinct kinetic terms in the cleavage reaction, viz. dependence of rate on [H+][SH], [SH], [S-] and [S-][H+](-1) (S- denotes the diester monoanion). The beta(lg) values (lg = leaving group) for the partial reactions are -0.04 +/- 0.04, -0.19 +/- 0.12, -0.59 +/- 0.12 and -1.10 +/- 0.05, respectively. The isomerization, in turn, shows dependence of rate on [H+][SH], [SH] and [S-], the beta(rg) values (rg = remnant group) being -0.23 +/- 0.04, -0.23 +/- 0.11 and -0.03 +/- 0.01. The mechanisms of various partial reactions are evaluated by comparing these values with those of specific and buffer catalyzed reactions of the corresponding 3'-phosphotriesters, regarded as mimetics of the neutral ionic form of diesters, Furthermore, the mechanistic significance of the dissimilar competition between the cleavage and isomerization with diesters and triesters is discussed.
Concurrent isomerization of the ethyl, 2-ethoxyethyl, 2,2-dichloroethyl and 2,2,2-trichloroethyl esters of uridine 3'-phosphate to their 2'-counterparts and cleavage to uridine 2',3'-cyclic phosphate have been studied over a wide pH-range (H-0 -0.2 to pH 9) at 363.2 K, The buffer-independent pa-rate profiles obtained show involvement of four distinct kinetic terms in the cleavage reaction, viz. dependence of rate on [H+][SH], [SH], [S-] and [S-][H+](-1) (S- denotes the diester monoanion). The beta(lg) values (lg = leaving group) for the partial reactions are -0.04 +/- 0.04, -0.19 +/- 0.12, -0.59 +/- 0.12 and -1.10 +/- 0.05, respectively. The isomerization, in turn, shows dependence of rate on [H+][SH], [SH] and [S-], the beta(rg) values (rg = remnant group) being -0.23 +/- 0.04, -0.23 +/- 0.11 and -0.03 +/- 0.01. The mechanisms of various partial reactions are evaluated by comparing these values with those of specific and buffer catalyzed reactions of the corresponding 3'-phosphotriesters, regarded as mimetics of the neutral ionic form of diesters, Furthermore, the mechanistic significance of the dissimilar competition between the cleavage and isomerization with diesters and triesters is discussed.
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