Hydrolysis and intramolecular transesterification of ribonucleoside 3′-phosphotriesters:: comparison of structural effects in the reactions of asymmetric and symmetric dialkyl esters of 5′-O-pivaloyl-3′-uridylic acid

beta(rg) values (rg = remnant group) for the O2'<----> O3' isomerization df asymmetric dialkyl esters of 5'-O-pivaloyluridine 3'-phosphate and beta(lg) values (lg = leaving group) for the cleavage of the more electronegative alkoxy group from these triesters under various conditions have been determined. The reactions Studied included hydronium ion, hydroxide ion, general acid and general base, and pH- and buffer-independent cleavage. The results are compared with the corresponding values obtained earlier with the symmetric 3'-triesters and the catalysis mechanisms are discussed.