Macromolecular prodrugs. IXX. Kinetics of hydrolysis of benzyl dextran carbonate ester conjugates in aqueous buffer solutions and human plasma.

Benzyl carbonate esters of dextran with varying degrees of substitution have been synthesized. The kinetics of the hydrolytic cleavage of the carbonate ester bond in aqueous solution within the pH range 0.44-10.46 (37 degrees C) has been investigated. The degradation reactions followed pseudo-first-order kinetics and a rate expression encompassing hydrogen ion-, hydroxide ion- and water-catalyzed hydrolysis of the dextran conjugates was derived. No influence of the degree of substitution on the reaction rates was observed. In alkaline solution a slightly enhanced lability of trifluorethyl benzyl carbonate ester compared to the benzyl dextran carbonate esters was observed, indicating a lack of any significant intramolecular catalytic effect in the hydrolysis of the dextran esters. Almost identical rates of liberation of benzyl alcohol were found in 80% human plasma and aqueous buffer of pH 7.4, indicating the lack of enzyme-mediated cleavage of the dextran carbonate ester bond.