Resolution of Ibuprofen Catalyzed with Free and Immobilized Lipases

Design, synthesis and characterization of captopril prodrugs for enhanced percutaneous absorption

Most drugs are designed primarily for oral administration, but the activity and stability profiles desirable for this route often make them unsuitable for transdermal delivery. We were therefore interested in designing analogues of captopril, a model drug with poor percutaneous penetration, for which the sustained steady-state blood plasma level associated with transdermal delivery (and which is unattainable orally) would be particularly beneficial. Quantitative structure—permeability relationships (QSPRs) predicted that ester and thiol prodrug derivatives of captopril would have lower maximal transdermal flux (Jm) than the parent drug, since the increases in permeability coefficient (kp) of prodrugs would be outweighed by the reductions in aqueous solubility. Therefore, the aim of this study was to synthesize a series of prodrugs of captopril and to determine if a QSPR model could be used to design therapeutically viable prodrugs. Molecules with the highest predicted kp values were synthesized and characterized, and Jm measured in Franz diffusion cells from saturated aqueous donor across porcine skin (fresh and frozen). In-vitro metabolism was also measured. Captopril and the prodrugs crossed the skin relatively freely, with Jm being highest for ethyl to butyl esters. Substantial first-order metabolism of the prodrugs was observed, suggesting that their enhanced percutaneous absorption was complemented by their metabolic performance. The results suggested that QSPR models provided excellent enhancements in drug delivery. This was not seen at higher lipophilicities, suggesting that issues of solubility need to be considered in conjunction with any such use of a QSPR model.

Synthesis and hydrolytic behaviour of glycerol-1,2-diibuprofenate-3-nitrate, a putative pro-drug of ibuprofen and glycerol-1-nitrate

Nitroxylated derivatives of non-steroidal anti-inflammatory drugs appear to offer protection against the gastrotoxicity normally associated with non-steroidal anti-inflammatory drugs, ostensibly via local production of nitric oxide. A diester of ibuprofen and glycerol-1-mononitrate has been prepared via the condensation of ibuprofen with 3-bromopropan-1,2-diol, followed by silver-(I)-nitrate-mediated nitroxylation. The release of ibuprofen from this diester has been studied in a simulated gastric fluid model with direct analysis by reverse-phase HPLC, using an acetonitrile-water (80%:20%) mobile phase containing trifluoroacetic acid (0.005%). n-Propyl ibuprofen was found to undergo pH-dependent hydrolysis, ranging from negligible hydrolysis at pH 5 to 52% hydrolysis at pH 3, over a 2-h period in this model. The ibuprofen-glycerol mononitrate diester was subjected to the most vigorous model hydrolytic conditions and was found to undergo 50 % hydrolysis during the study period. This study shows that pro-drugs of ibuprofen and glycerol mononitrate can be obtained, and can undergo degradation to the parent drugs under conditions simulating those likely to be encountered in the stomach.

Chiral high performance liquid chromatography resolution of ibuprofen esters

Two cellulose-based chiral stationary phases (Chiralcel OD and Chiralcel OJ) were compared on their ability to resolve various aliphatic ibuprofen esters. Chiralcel OJ with hexane as the mobile phase allows for the separation of most of the esters. Observed changes in resolution depending on the solute nature (basicity of the solute, esterified alcohol chain length, presence of a double bond) are discussed. An example of the application of this method for following the kinetic resolution of racemic ibuprofen is presented.