Evaluation of glycolamide esters and various other esters of aspirin as true aspirin prodrugs

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Abstract
A series of glycolamide, glycolate, (acyloxy)methyl, alkyl, and aryl esters of acetylsalicylic acid (aspirin) were synthesized and evaluated as potential prodrug forms of aspirin. N,N-Disubstituted glycolamide esters were found to be rapidly hydrolyzed in human plasma, resulting in the formation of aspirin as well as the corresponding salicyclate esters. These in turn hydrolyzed rapidly to salicylic acid. The largest amount of aspirin formed from the esters were 50 and 55% in case of the N,N-dimethyl- and N,N-diethylglycolamide esters, respectively. Similar results were obtained in blood with the N,N-dimethyl- and N,N-diethylglycolamide esters. Unsubstituted and monosubstituted glycolamide esters as well as most other esters previously suggested to be aspirin prodrugs were shown to hydrolyze exclusively to the corresponding salicylic acid esters. Lipophilicity parameters and water solubilities of the esters were determined, and structural factors favoring ester prodrug hydrolysis at the expense of deacetylation to yield salicylate ester are discussed. The properties of some N,N-disubstituted glycolamide esters of aspirin are highlighted with respect to their use as potential aspirin prodrugs.