A Novel Prodrug Strategy for β-Dicarbonyl Carbon Acids: Syntheses and Evaluation of the Physicochemical Characteristics of C-Phosphoryloxymethyl (POM) and Phosphoryloxymethyloxymethyl (POMOM) Prodrug Derivatives

The C-phosphoryloxymethyl (POM) and phosphoryloxymethyloxymethyl (POMOM) prodrugs resulting from derivatization at the reactive α-carbon of β-dicarbonyl carbon acid drugs represent a unique approach for improving their chemical stability and aqueous solubility. This work evaluates the physicochemical and in vitro enzymatic bioconversion lability of selected prodrugs of phenylbutazone and phenindione. The POM and POMOM prodrug derivatives of phenylbutazone are highly water soluble (≥250mg/mL), chemically stable with projected shelf-lives of 4.5 years (pH 3.5, 25°C) and 1.1 years (pH 6.0, 25°C), respectively. Interestingly, both prodrug derivatives do not display a pH-dependency typical of many phosphate monoesters, although the similarities of their apparent thermodynamic activation parameters indicate a hydrolysis mechanism similar to other phosphates. These prodrugs undergo alkaline phosphatases catalyzed bioconversion to their respective carbon acids with an expected faster rate exhibited by the POMOM derivatives. Additionally, in marked contrast to the oxidative instability of phenindione, its POM prodrug is stable. The results from these studies reaffirm the rationale of transiently “masking” the reactive α-carbon/proton bond by covalently incorporating a POM or POMOM promoiety. This prodrug strategy presents a twofold advantage, enhancement of aqueous solubility and prevention of oxidative instability, two intrinsic formulation limitations found for β-dicarbonyl carbon acid drugs.