Glycolamide esters as biolabile prodrugs of carboxylic acid agents: synthesis, stability, bioconversion, and physicochemical properties

Metal Template Assisted Proximal Arrangement of a Nucleophile and an Electrophile: Site-Selective Acylation of α-Hydroxyamides in Polyols

Site-selective acylation of α-hydroxyl groups in amides has been achieved in the presence of other primary hydroxyl groups with intrinsic high reactivity. In this methodology, a relatively stable pyridine aldoxime ester was exploited as an acyl donor to suppress undesired acylation. The catalytic activation of a pyridine aldoxime ester with a Lewis acid produced a cationic complex, which preferentially attracted the Lewis basic α-hydroxyamide via a template effect, to thus facilitate o-acylation.

Colon-targeting mutual prodrugs of 5-aminosalicylic acid and butyrate for the treatment of ulcerative colitis

The aim of this study was to design and synthesize four colon-targeting mutual prodrugs of 5-aminosalicylic acid (5-ASA) and butyrate, and evaluate their therapeutic effects on ulcerative colitis.

Cu(ii)-Mediated keto C(sp3)–H bond α-acyloxylation of N,N-dialkylamides with aromatic carboxylic acids

The first example of Cu(ii)-mediated oxidative coupling of aromatic carboxylic acids with the C(sp³)–H bond adjacent to the keto group of N,N-dialkylamides has been developed.

Active Site Mapping of an Aspartic Protease by Multiple Fragment Crystal Structures: Versatile Warheads To Address a Catalytic Dyad

Crystallography is frequently used as follow-up method to validate hits identified by biophysical screening cascades. The capacity of crystallography to directly screen fragment libraries is often underestimated, due to its supposed low-throughput and need for high-quality crystals. We applied crystallographic fragment screening to map the protein-binding site of the aspartic protease endothiapepsin by individual soaking experiments. Here, we report on 41 fragments binding to the catalytic dyad and adjacent specificity pockets. The analysis identifies already known warheads but also reveals hydrazide, pyrazole, or carboxylic acid fragments as novel functional groups binding to the dyad. A remarkable swapping of the S1 and S1' pocket between structurally related fragments is explained by either steric demand, required displacement of a well-bound water molecule, or changes of trigonal-planar to tetrahedral geometry of an oxygen functional group in a side chain. Some warheads simultaneously occupying both S1 and S1' are promising starting points for fragment-growing strategies.

Interspecies Differences in the Metabolism of a Multiester Prodrug by Carboxylesterases

The pentaethyl ester prodrug of the chelating agent diethylene triamine pentaacetic acid (DTPA) referred to as C2E5 is being developed as an orally bioavailable radionuclide decorporation agent. The predicted human efficacy obtained in these experimental animals is confounded by interspecies variations of metabolism. Therefore, in the present study, carboxylesterase-mediated metabolism of [(14)C]-C2E5 was compared in the S9 intestinal and hepatic fractions of human, dog, and rat and their respective plasma. Intestinal hydrolysis of C2E5, resulting in the formation of the tetraethyl ester of DTPA (C2E4), was only detected in human and rat. The primary metabolite in human and dog hepatic fractions was C2E4, whereas the predominant species identified in rat hepatic fractions was the triethyl ester (C2E3). Hepatic hydrolysis of C2E5 causes the formation of C2E4 in human, dog, and rat and C2E3 in rat only. Minimal C2E5 hydrolysis was observed in human and dog plasma, whereas in rat plasma C2E5 converted to C2E3 rapidly, followed by slower further metabolism. Both recombinant CES1 and CES2 play roles in C2E5 metabolism. Together, these data suggest that dogs may be the most appropriate species for predicting human C2E5 metabolism, whereas rats might be useful for clarifying the potential toxicity of C2E5 metabolites.

Anti-Inflammatory and Gastroprotective Evaluation of Prodrugs of Piroxicam

Therapeutically potential prodrugs of piroxicam were synthesized by effective masking of enolic hydroxyl group through generation of ester congeners. The reaction facilitated using N,N′-dicyclohexylcarbodiimide coupled with acetic acid, benzoic acid, p-toluic acid, m-toluic acid, and cinnamic acid. Synthesized prodrugs were characterized for confirmation of the said structures. The modification of piroxicam showed better anti-inflammatory activity as evoked by all prodrugs. Interestingly, compound 3e, cinnamic acid ester prodrug, depicted 75 percent inhibition of rat paw edema as compared to 56 percent for parent piroxicam at 6 h of study. The present work proves the applicability not only with increased anti-inflammatory activity, but also with marked attenuation in ulcerogenicity. Novel prodrug 3e, cinnamic acid derivative, was found to be the least ulcerogenic having ulcer index of 0.67 as compared to parent drug piroxicam with 2.67.

Biological conversion of aripiprazole lauroxil - An N-acyloxymethyl aripiprazole prodrug

N-acyloxyalkylation of NH-acidic compounds can be a prodrug approach for e.g. tertiary or some N-heterocyclic amines and secondary amides and have the potential to modify the properties of the parent drug for specific uses, for example its physicochemical, pharmacokinetic or biopharmaceutical properties. Aripiprazole lauroxil was prepared as a model compound for such prodrugs and its bioconversion was investigated both in vitro and in vivo. Theoretically, N-acyloxyalkyl derivates of NH-acid compounds undergo a two-step bioconversion into the parent NH-acidic drug through an N-hydroxyalkyl intermediate. However, to our knowledge no published studies have investigated the formation of an intermediate in vivo. In the present study, it was demonstrated that the assumed N-hydroxymethyl intermediate was readily observed both in vitro and in vivo. In vivo, the observed plasma concentration of the intermediate was at the same level as the drug (aripiprazole). When prodrug intermediates are formed, it is important to make a proper pharmacological, pharmacokinetic and toxicological evaluation of the intermediates to ensure patient safety; however, several challenges were identified when testing an N-acyloxyalkyl prodrug. These included the development of a suitable bioanalytical method, the accurate prediction of prodrug bioconversion and thereby the related pharmacokinetics in humans and the toxicological potential of the intermediate.

Nimesulide Based Novel Glycolamide Esters: Their Design, Synthesis, and Pharmacological Evaluation

The nimesulide based novel glycolamide esters were designed and synthesized for the first timeviaa three-step method starting from nimesulide. Structures of the synthesized compounds were confirmed by spectroscopic analysis. All the synthesized compounds were examined for their cytotoxic effectsin vitro,some of which showed significant cytotoxic activities against HCT-15 human colon cancer cell line.

Diglyceride prodrug strategy for enhancing the bioavailability of norfloxacin

Prodrug approach using diglyceride as a promoiety is a promising strategy to improve bioavailability of poorly absorbed drugs and the same was explored in the present work to improve oral bioavailability of norfloxacin; a second generation fluoroquinolone antibacterial. The prodrug was synthesized by standard procedures using dipalmitine as a carrier and the structure was confirmed by spectral analysis. Higher LogP indicated improved lipophilicity. The ester linkage between norfloxacin and dipalmitine would be susceptible to hydrolysis by lipases to release the parent drug and carrier in the body. In vivo kinetic studies in rats indicated 53% release of norfloxacin in plasma at the end of 8h. The prodrug exhibited improved pharmacological profile than the parent compound at equimolar dose that indirectly indicated improved bioavailability.

Design, synthesis, hydrolysis kinetics and phamacodynamic profiles of histidine and alanine conjugates of aceclofenac

The gastrointestinal toxicity associated with aceclofenac can be reduced by condensing its carboxylic acid group with methyl esters of amino acids like histidine and alanine to give amide linkage by the Schotten-Baumann method. Physicochemical characterization of the conjugates was carried out by various analytical and spectral methods. The synthesized conjugates were also subjected to in vitro hydrolysis in simulated gastric fluid (SGF) at pH 1.2, simulated intestinal fluid (SIF) at pH 7.4 and SIF+ 80% human plasma at pH 7.4. The release of free aceclofenac from histidine and alanine conjugated aceclofenac showed negligible hydrolysis in SGF compared to SIF. This indicated that the conjugates do not break in stomach, but release aceclofenac in SIF. Both synthesized conjugates showed excellent pharmacological response and encouraging hydrolysis rate in SIF and SIF + 80% human plasma. Marked reduction of the ulcer index and comparable increase in analgesic and anti-inflammatory activities were obtained in both cases compared to aceclofenac alone. These findings suggest that the conjugates are better in action compared to the parent drug and have fewer gastrointestinal side-effects.

1-[2-(4-Isobutyl-phen-yl)propano-yl]thiosemicarbazide

In the title compound, C₁₄H₂₁N₃OS, inter­molecular N—H⋯O inter­actions generate ten-membered rings with R₂²(10) ring motifs, whereas N—H⋯S inter­actions generate eight, 14- and 16-membered rings with R₂²(8), R₄⁴(14) and R₄⁴(16) ring motifs, respectively. There are weak intra­molecular N—H⋯π inter­actions which might influence the conformation of the mol­ecule. The compound has a stereogenic center but the space group is centrosymmetic so the mol­ecule exists as a racemate.

Bisphosphonated fluoroquinolone esters as osteotropic prodrugs for the prevention of osteomyelitis

Osteomyelitis is a difficult to treat bacterial infection of the bone. Delivering antibacterial agents to the bone may overcome the difficulties in treating this illness by effectively concentrating the antibiotic at the site of infection and by limiting the toxicity that may result from systemic exposure to the large doses conventionally used. Using bisphosphonates as osteophilic functional groups, different forms of fluoroquinolone esters were synthesized and evaluated for their ability to bind bone and to release the parent antibacterial agent. Bisphosphonated glycolamide fluoroquinolone esters were found to present a profile consistent with effective and rapid bone binding and efficient release of the active drug moiety. They were assessed for their ability to prevent bone infection in vivo and were found to be effective when the free fluoroquinolones were not.

Bioreversible derivatives of phenol. 1. The role of human serum albumin as related to the stability and binding properties of carbonate esters with fatty acid-like structures in aqueous solution and biological media

With the overall objective of assessing the potential of utilizing plasma protein binding interactions in combination with the prodrug approach for improving the pharmacokinetics of drug substances, a series of model carbonate ester prodrugs of phenol, encompassing derivatives with fatty acid-like structures, were characterized in vitro. Stability of the derivatives was studied in aqueous solution, human serum albumin solution, human plasma, and rat liver homogenate at 37 degrees C. Stability of the derivatives in aqueous solution varied widely, with half-lives ranging from 31 to 1.7 x 10(4) min at pH 7.4 and 37 degrees C. The carbonate esters were subject to catalysis by plasma esterases except for the t-butyl and acetic acid derivatives, which were stabilized in both human plasma and human serum albumin solutions relative to buffer. In most cases, however, hydrolysis was accelerated in the presence of human serum albumin indicating that the derivatives interacted with the protein, a finding which was confirmed using the p-nitrophenyl acetate kinetic assay. Different human serum albumin binding properties of the phenol model prodrugs with fatty acid-like structure and neutral carbonate esters were observed. In the context of utilizing plasma protein binding in combination with the prodrug approach for optimizing drug pharmacokinetics, the esterase-like properties of human serum albumin towards the carbonate esters potentially allowing the protein to act as a catalyst of parent compound regenerations is interesting.

Evaluation of nitrate-substituted pseudocholine esters of aspirin as potential nitro-aspirins

Herein we explore some designs for nitro-aspirins, compounds potentially capable of releasing both aspirin and nitric oxide in vivo. A series of nitrate-bearing alkyl esters of aspirin were prepared based on the choline ester template preferred by human plasma butyrylcholinesterase. The degradation kinetics of the compounds were followed in human plasma solution. All compounds underwent hydrolysis rapidly (t(1/2) approximately 1min) but generating exclusively the corresponding nitro-salicylate. The one exception, an N-propyl, N-nitroxyethyl aminoethanol ester produced 9.2% aspirin in molar terms indicating that the nitro-aspirin objective is probably achievable if due cognisance can be paid to the demands of the activating enzyme. Even at this low level of aspirin release, this compound is the most successful nitro-aspirin reported to date in the key human plasma model.

Study of Ibuprofen Glucopyranoside Derivative Synthesis byCandida antarcticaLipase in Organic Solvent

The direct esterification of ibuprofen and methyl alpha-D-glucopyranoside in organic solvent by Novozym 435 was investigated in terms of the main variables controlling the process, including initial water activity (a(w), 0.05-0.75), incubation time, (0-168 h) and substrate concentration. The results showed that the lower initial aw values resulted in higher enzymatic activity and bioconversion yield. The most appropriate initial aw and incubation time were 0.06 and 144 h, respectively. The results also showed that the optimal ratio of ibuprofen to methyl alpha-D-glucopyranoside was 2.0. By optimizing these parameters, the yield increased about 50%. In addition, the product was confirmed to be methyl 6-O-(2'-(4'-isobutylphenyl) propionyl) D-alpha-glucopyranoside.

Pharmacological activity and hydrolysis behavior of novel ibuprofen glucopyranoside conjugates

Novel ester prodrugs (II, III and IV) of ibuprofen (I) were synthesized using alpha-methyl, ethyl and propyl glucopyranoside as promoieties and tested for their anti-inflammatory, analgesic and ulcerogenic activities. Study of their chemical hydrolysis in aqueous buffer (pH 3.0-10.0) showed that these compounds acted as true prodrugs of ibuprofen, giving the ibuprofen and alkyl glucopyranoside. Additionally, all the derivatives studied did cleave rapidly inside the biological system and on oral administration did elicit a pharmacological profile quite similar to that of ibuprofen, but, unlike this drug, they displayed reduced gastric ulceration. In conclusion, these alkyl glucopyranoside esters have promising properties as prodrugs for oral delivery of ibuprofen.

A QSAR Approach for the Prediction of Stability of Benzoglycolamide Ester Prodrugs

A method consisting of quantitative structure-activity relationship (QSAR) (MLR) was developed to predict the hydrolytic rate constant of 37 benzoglycolamide ester prodrugs. The regression method was used as a calibration model for calculating the hydrolytic rate constant and investigating their linear characteristics. The QSAR study indicated the importance of the descriptors charge on amide nitrogen (AN), lipophilic parameter (log P) and nucleophilic frontal density (NUFD) in contribution to the ester hydrolysis with the correlation coefficient value of 0.908 for the developed MLR model. The models were validated by leave one out (LOO) technique as well as by the calculation of statistical parameters for the developed MLR models.

Synthesis and anti-inflammatory activity of a series of N-substituted naproxen glycolamides: nitric oxide-donor naproxen prodrugs

A series of glycolamide naproxen prodrugs containing a nitrate group as a nitric oxide (NO) donor moiety has been synthesized. These compounds were evaluated for their anti-inflammatory activity, naproxen release, and gastric tolerance. Compounds 4a, 4b, 5a, 5b, 7b, and 7c exhibited anti-inflammatory activity equivalent to that of the parent NSAID, naproxen-Na, in the rat carrageenan paw edema model. At equimolar doses relative to naproxen-Na, the NO-donor glycolamide derivatives 4a, 4b, 5a, 5b, 7b, and 7c were gastro-sparing in the rat. Naproxen formation from these NO-donor glycolamides varied among the structures examined, with the N-substituent on the amide group having a particular influence, and demonstrated their prodrug nature. Compound 7b was selected for exemplary demonstration that the glycolamide nitrates can be bioactivated to release NO. These data open the possibility that naproxen glycolamide nitrates may represent a safer alternative to naproxen as anti-inflammatory medicines.

Quantitative determination of CGS 26214, a cholesterol lowering agent, in human plasma using negative electrospray ionization liquid chromatography-tandem mass spectrometry

CGS 26214 is a synthetic cholesterol-lowering agent shown to be active in the rat, dog and monkey. The present work was conducted to develop a sensitive liquid chromatography-tandem mass spectrometry (LC-MS-MS) method for quantitative determination of the compound in human plasma following clinical doses of 10-100 microg per day. A number of analytical challenges were encountered during the development of the assay. The compound was an ester and susceptible to hydrolysis under experimental conditions. A lower limit of quantitation of 50 pg/ml was needed due to the low clinical doses. Positive electrospray ionization of CGS 26214 yielded insufficient sensitivity needed for the studies. Consequently, LC-MS-MS conditions were optimized for the negative ion mode of detection. The sample preparation steps proved to be critical in order to reduce the possibility of microbore column (50 mm x 1.0 mm I.D.) obstruction, chromatographic deterioration, and matrix mediated electrospray ion suppression. The present method addressed the above issues. The method was accurate and reproducible and was successfully applied to generate plasma concentration-time profiles for human subjects after low oral doses of the compound.

Activity profile of glycolamide ester prodrugs of ibuprofen

Glycolamide esters of ibuprofen (I), namely, unsubstituted (II), N,N dimethyl (III), and N,N diethyl (IV), were synthesized and studied for different physicochemical, pharmacological, and toxicological properties. They were comparable with I in respect of anti-inflammatory and analgesic activity but did not exhibit reduction in the ulcerogenicity on oral administration. However, all three exhibited significantly better topical activity in carrageenan-induced rat paw edema assay. In the same assay, they provided significant protection against inflammation when applied at a site remote to the inflammation site.

Species-dependent and site-specific intestinal metabolism of ester prodrugs

In order to select a species for drug absorption studies of ester prodrugs and to identify a possible absorption window with low esterase activity and hence increased absorption of the ester prodrug, the esterase activity was investigated in homogenates from various intestinal segments of different species. p-Nitrophenyl acetate and tenofovir disoproxil [bis(POC)-PMPA] were used as substrates for esterases. p-Nitrophenyl acetate is a model substrate for esterase activity, while tenofovir disoproxil (fumarate salt) is an ester prodrug of the potent antiviral nucleoside phosphonate analogue tenofovir. As esterase-mediated degradation during transepithelial transport may be a limiting factor for its oral absorption, targeting the prodrug to a region of the intestine with lower esterase activity may lead to an increase in oral absorption of the prodrug. The results obtained with p-nitrophenyl acetate and tenofovir disoproxil showed both a site-specific (duodenum > or = jejunum > ileum > or = colon) and species-dependent (rat > man > pig) degradation in intestinal homogenates. Degradation of tenofovir disoproxil in homogenates from Caco-2 monolayers (0.016+/-0.003 nmol. s(-1). mg protein(-1)) was low compared to its degradation in homogenates from human ileum (0.177+/-0.052 nmol. s(-1). mg protein(-1)). Rat ileum appears to be a suitable model to evaluate the influence of esterase activity on the oral absorption of the ester prodrug, as the degradation rate for tenofovir disoproxil (0.245+/-0.054 nmol. s(-1). mg protein(-1)) in rat ileum was similar to degradation in human ileum. The results also suggest that colon targeting may be a useful strategy to reduce the esterase-mediated degradation of ester prodrugs, hence resulting in a possible increase in their oral absorption.

Acyloxymethyl as a drug protecting group. Part 6: N-acyloxymethyl- and N-[(aminocarbonyloxy)methyl]sulfonamides as prodrugs of agents containing a secondary sulfonamide group

Tertiary N-acyloxymethyl- and N-[(aminocarbonyloxy)methyl]sulfonamides were synthesised and evaluated as novel classes of potential prodrugs of agents containing a secondary sulfonamide group. The chemical and plasma hydrolyses of the title compounds were studied by HPLC. Tertiary N-acyloxymethylsulfonamides are slowly and quantitatively hydrolysed to the parent sulfonamide in pH 7.4 phosphate buffer, with half-lives ranging from 20 h, for 7d, to 30 days, for 7g. Quantitative formation of the parent sulfonamide also occurs in human plasma, the half-lives being within 0.2-2.0 min for some substrates. The rapid rate of hydrolysis can be ascribed to plasma cholinesterase, as indicated by the complete inhibition observed at [eserine] = 0.10 mM. These results suggest that tertiary N-acyloxymethylsulfonamides are potentially useful prodrugs for agents containing a secondary sulfonamide group, especially with pKa < 8, combining a high stability in aqueous media with a high rate of plasma activation. In contrast, N-[(aminocarbonyloxy)methyl]sulfonamides 7h-j do not liberate the parent sulfonamide either in aqueous buffers or in human plasma and thus appear to be unsuitable for development as sulfonamide prodrugs.

Surfactant effect on enhancing (S)-naproxen prodrug production from racemic naproxen by lipase

In the enantioselective esterification of racemic naproxen with 4-(2-hydroxyethyl) morpholine by Lipase MY in organic solvents, a productivity improvement of the desired (S)-naproxen ester from 0.42 to 0.72 mM at the reaction time of 130 h was observed, when the surfactant bis (2-ethylhexyl) sodium sulfosuccinate (AOT) was added in the reaction mixture. The presence of a small amount of exogenously added water dramatically activated the enzyme in AOT/cyclohexane-reversed micelles. Desorption of the surfactant molecule from the enzyme mass and solubilization of the enzyme into reversed micelles were used to elucidate an existing maximum of the initial rate of (S)-naproxen synthesis with the water content. Moreover, the effects of alcohol and surfactant concentration on the enzyme activity are reported.

Acyloxymethyl as a drug protecting group: Part 4. The hydrolysis of tertiary amidomethyl ester prodrugs of carboxylic acid agents

PURPOSE

Novel tertiary amidomethyl esters were synthesized and evaluated as potential prodrugs of carboxylic acid agents.

METHODS

The hydrolyses of the title compounds in buffer solutions and in plasma were studied by UV spectroscopy and HPLC.

RESULTS

Amidomethyl esters were hydrolyzed by acid-catalyzed, base-catalyzed and pH-independent pathways. Both the acid-catalyzed, kH+, and pH-independent processes, ko, were strongly affected by the electronic and steric nature of the N-substituent in the pro-moiety. For both processes, the electronic effect exerted greater influence, and electron-withdrawing substituents retarded reaction. The pH-independent hydrolysis of amidomethyl esters were dependent on the pKa of the carboxylate leaving group, giving a Brönsted beta(1g) value -0.91. The base-catalyzed, kOH-, pathway was mainly affected by the steric bulk of the nitrogen substituents in the amide moiety, the reactivity being reduced with larger N-substituents. Hydrolysis in human plasma appeared to be mediated by enzymic processes and is dependent upon the steric bulk in the carboxylic acid moiety. Plasma hydrolysis rates were inversely dependent on the lipophilicity of the ester.

CONCLUSIONS

Derivatives containing the ethyl hippurate carrier are useful prodrugs for carboxylic acid-containing drugs with pKa > 3.5, such as non-steroidal anti-inflammatory agents and valproic acid.

Pharmacokinetic analysis of the microscopic distribution of enzyme-conjugated antibodies and prodrugs: comparison with experimental data

A mathematical model was developed to improve understanding of the biodistribution and microscopic profiles of drugs and prodrugs in a system using enzyme-conjugated antibodies as part of a two-step method for cancer treatment. The use of monoclonal antibodies alone may lead to heterogeneous uptake within the tumour tissue; the use of a second, low molecular weight agent may provide greater penetration into tumour tissue. This mathematical model was used to describe concentration profiles surrounding individual blood vessels within a tumour. From these profiles the area under the curve and specificity ratios were determined. By integrating these results spatially, average tissue concentrations were determined and compared with experimental results from three different systems in the literature; two using murine antibodies and one using humanised fusion proteins. The maximum enzyme conversion rate (Vmax) and the residual antibody concentration in the plasma and normal tissue were seen to be key determinants of drug concentration and drug-prodrug ratios in the tumour and other organs. Thus, longer time delays between the two injections, clearing the antibody from the blood stream and the use of 'weaker' enzymes (lower Vmax) will be important factors in improving this prodrug approach. Of these, the model found the effective clearance of the antibody outside of the tumour to be the most effective. The use of enzyme-conjugated antibodies may offer the following advantages over the bifunctional antibody-hapten system: (i) more uniform distribution of the active agent; (ii) higher concentrations possible for the active agent; and (iii) greater specificity (therapeutic index).

Synthesis and pharmacological evaluation of oligoethylene ester derivatives as indomethacin oral prodrugs

Five indomethacin oligoethylene ester derivatives (3-7) were synthesized and evaluated for their anti-inflammatory, analgesic, and ulcerogenic activity after oral administration. The molecular weight of the oligoethylene glycols used for synthesizing esters 3-7 ranged from 106 to 282. The chemical and enzymatic stabilities of esters 3-7 were evaluated in pH 7.4 and 2.0 buffers and in human plasma, respectively. All the prodrugs showed a good stability both in pH 7.4 phosphate buffer and in pH 2.0 buffer, and they were readily hydrolyzed by human plasma. Esters 3-7 showed an anti-inflammatory activity, determined as the percent inhibition of carrageenan-induced edema, similar to that of indomethacin, although at higher doses. From writhing test results, we observed that all the prodrugs exhibited better or similar analgesic activity compared to indomethacin. Esters 3-7 were significantly less irritating to the gastric mucosa than indomethacin, after oral administration, and esters 3-5 did not show any ulcerogenic activity, although they were administered at higher doses than indomethacin.

Stereoselective enzymatic hydrolysis of various ester prodrugs of ibuprofen and flurbiprofen in human plasma

The hydrolysis kinetics of various alkyl, glycolamide, aminoethyl, and 2-(1-imidazolyl)ethyl esters of ibuprofen and flurbiprofen in 80% human plasma were investigated using a direct high-performance liquid chromatographic assay for the enantiomers of these acids. In each case, the R-isomer ester was found to undergo faster plasma-catalyzed hydrolysis than the corresponding S-isomer. The difference in the hydrolysis rates between the enantiomeric forms ranged from a factor of 1.4 for the N,N-diethylglycolamide ester of ibuprofen to a factor of 50 and 25 for the 2-(1-imidazolyl)ethyl ester of ibuprofen and flurbiprofen, respectively. Therefore, enantioselective differences in plasma-catalyzed ester prodrug hydrolysis must be taken into account when evaluating prodrugs of racemic mixtures of chiral drugs.