Interconversion and Hydrolysis of Monomethyl and Monoisopropyl Esters of Adenosine 2'- and 3'-Monophosphates: Kinetics and Mechanisms

Article abstract of DOI:10.1021/jo00011a032

First-order rate constants for mutual isomerization and hydrolytic cleavage of the monomethyl and monoisopropyl esters of adenosine 2'- and 3'-monophosphates (2'- and 3'-AMP) have been determined by HPLC over a wide pH range.Both reactions preceed at comparable rates under acidic conditions, exhibiting a second-order dependence of rate on hydronium ion concentration at 1 < pH < 2, and a first-order dependence in more acidic solutions.Moreover, hydrolytic depurination takes place at pH < 3.In the pH range 4 to 9 a pH-independent phosphate migration prevails.By contrast, in alkaline solutions the methyl esters are hydrolysed to a mixture of 2'- and 3'-AMP, the reaction rate being proportional to the hydroxide ion concentration at -> < 0.1 mol dm^-3.No sign of mutual isomerization was detected under these conditions.With the isopropyl esters alkaline degradation of the adenine moiety is considerably faster than the phosphodiester hydrolysis.Mechanisms of phosphate migration and phosphodiester hydrolysis under various conditions have been discussed.