MUTUAL ISOMERIZATION OF URIDINE 2'-ALKYLPHOSPHATE AND 3'-ALKYLPHOSPHATE AND CLEAVAGE TO A 2',3'-CYCLIC PHOSPHATE - THE EFFECT OF THE ALKYL GROUP ON THE HYDRONIUM-ION-CATALYZED AND HYDROXIDE-ION-CATALYZED REACTIONS

Isopropyl, ethyl, 2-ethoxyethyl, 2-chloroethyl, 2,2-dichloroethyl and 2,2,2-trichloroethyl esters of uridine 3'-phosphate have been prepared . In aqueous acid the compounds undergo concurrent isomerization to 2' -alkylphosphates and cleavage to uridine 2',3'-cyclic phosphate, but i n aqueous alkali only cleavage to the cyclic phosphate takes place. Bu ffer-independent rate constants for these reactions have been determin ed. The hydroxide-ion-catalyzed reaction to the 2',3'-cyclic monophosp hate is exceptionally susceptible to the polar nature of the leaving g roup, the beta(1g) value being -1.28 +/- 0.05. By contrast, the hydron ium-ion-catalyzed isomerization and cleavage are both rather insensiti ve to the electron-withdrawing ability of the alkyl group, the beta an d beta(1g) values being -0.18 +/- 0.02 and -0.12 +/- 0.05, respectivel y. The transition state structures of the reactions are discussed on t he basis of these structural-effects.