Prodrugs of 3-(3,4-dichlorobenzyloxy)-2-amino-6-fluorobicyclo[3.1.0]hexane-2,6-dicarboxylic acid (MGS0039): a potent and orally active group II mGluR antagonist with antidepressant-like potential

3-(3,4-Dichlorobenzyloxy)-2-amino-6-fluorobicyclo[3.1.0]hexane-2,6-dicarboxylic acid 5 (MGS0039) is a highly selective and potent group II metabotropic glutamate receptor (mGluR) antagonist (antagonist activities for mGluR2; IC50=20.0 nM, mGluR3; IC50=24.0 nM) and is detected in both plasma (492 ng/mL) and brain (13.2 ng/g) at oral administration of 10 ng/mL [J. Med. Chem.2004, 47, 4750], but the oral bioavailability of 5 was 10.9%. In order to improve the oral bioavailability of 5, prodrugs of 5 were discovered by esterification of carboxyl group on C6-position of bicyclo[3.1.0]hexane ring. Among these compounds, 6-alkyl esters exhibited approximately 10-fold higher concentrations of 5 in the plasma and brain of rats after oral administration (e.g., ethyl ester of 5; plasma, Cmax=20.7+/-1.3 microM) compared to oral administration of 5 (plasma, Cmax=2.46+/-0.62 microM). 3-(3,4-Dichlorobenzyloxy)-2-amino-6-fluorobicyclo[3.1.0]hexane-2,6-dicarboxylic acid 6-heptyl ester (7ao), a prodrug of MGS0039, showed antidepressant-like effects in rat forced swimming test and mouse tail suspension test following oral administration. Moreover, following oral administration of 7ao in mice, high concentrations of MGS0039 were detected in both the brain and plasma, while 7ao was barely detected. In this paper, we report the synthesis, in vitro metabolic stabilities, and pharmacokinetic profiles of the prodrugs of 5, and the antidepressant-like effects of 7ao.     

Enzyme-catalyzed prodrug approaches for the histamine H3-receptor agonist (R)-alpha-methylhistamine

Five novel prodrug types of the potent and selective histamine H3-receptor agonist (R)-alpha-methylhistamine (1) were prepared and pharmacologically tested in vitro as well as in vivo. In particular, an amide of fatty acid, mono- and dicarbamates, an (acyloxy)alkylcarbamate, and a diphthalidyl derivative were synthesized, all of which require initial prodrug activation through an enzyme-catalyzed reaction in contrast to formerly developed azomethine prodrugs which are cleaved by chemical hydrolysis only. Further drug liberation may ensue spontaneously in a cascade to give 1. Since they have diverse stabilities the prodrugs were investigated for drug liberation in vitro under neutral, acidic, and basic conditions at different temperatures as well as with liver homogenates. In vivo investigation of prodrugs after oral administration to mice proved that the fatty amide 2, the Nalpha-methylcarbamate 4a, and the Nalpha-(1-(acetyloxy)ethylcarbamate) 5 showed moderate to high plasma levels of 1. Compound 5 displayed even more than 2.5 times the AUC for 1 than that of the reference azomethine prodrug BP2.94 in the periphery and also displayed a detectable drug level in the central nervous system. It was shown that prodrug approaches based on an initial enzyme-catalyzed liberation step are successfully applicable to different pro-moieties for improved bioavailability and prolonged half-live. These approaches may also be used for other aminergic compounds of this class to optimize pharmacokinetic behavior.     

Novel (E)-2-(aryl)-3-(4-methanesulfonylphenyl)acrylic ester prodrugs possessing a diazen-1-ium-1,2-diolate moiety: design, synthesis, cyclooxygenase inhibition, and nitric oxide release studies

A novel group of hybrid nitric oxide-releasing anti-inflammatory drugs (11) possessing a 1-(N,N-diethylamino)diazen-1-ium-1,2-diolate, or 1-(pyrrolidin-1-yl)diazen-1-ium-1,2-diolate, nitric oxide (.NO) donor moiety attached via a one-carbon methylene spacer to the carboxylic acid group of (E)-3-(4-methanesulfonylphenyl)-2-(phenyl)acrylic acids were synthesized. These ester prodrugs (11) all exhibited in vitro inhibitory activity against the cyclooxygenase-2 (COX-2) isozyme (IC(50)=0.94-31.6 microM range). All compounds released .NO upon incubation with phosphate buffer (PBS) at pH 7.4 (3.2-11.3% range). In comparison, the percentage of .NO released was significantly higher (48.6-75.3% range) when these hybrid ester prodrugs were incubated in the presence of rat serum. These incubation studies suggest that both .NO and the parent anti-inflammatory (E)-3-(4-methanesulfonylphenyl)-2-(phenyl)acrylic acid would be released upon in vivo cleavage by non-specific serum esterases. O(2)-[(E)-2-(4-Acetylaminophenyl)-3-(4-methanesulfonylphenyl)acryloyloxymethyl]-1-(pyrrolidin-1-yl)diazen-1-ium-1,2-diolate (11f) is a moderately potent (IC(50)=0.94 microM) and selective (SI>104) COX-2 inhibitor that released 73% of the theoretical maximal release of two molecules of .NO/molecule of the parent hybrid ester prodrug upon incubation with rat serum. Hybrid ester .NO-donor prodrugs offer a potential drug design concept for the development of anti-inflammatory drugs that are devoid of adverse ulcerogenic and/or cardiovascular side effects.     

Diazen-1-ium-1,2-diolated and nitrooxyethyl nitric oxide donor ester prodrugs of anti-inflammatory (E)-2-(aryl)-3-(4-methanesulfonylphenyl)acrylic acids: synthesis, cyclooxygenase inhibition, and nitric oxide release studies

A new group of hybrid nitric oxide-releasing anti-inflammatory drugs wherein an O(2)-acetoxymethyl-1-(N-ethyl-N-methylamino)diazen-1-ium-1,2-diolate (11a-d), or 2-nitrooxyethyl (12a-d), (*)NO-donor moiety is attached directly to the carboxylic acid group of (E)-3-(4-methanesulfonylphenyl)-2-(phenyl)acrylic acids were synthesized. The 2-nitrooxyethyl ester prodrugs (12a-d) all exhibited in vitro inhibitory activity against the cyclooxygenase-2 (COX-2) isozyme (IC(50)=0.07-2.8 microM range). All compounds released a low amount of (*)NO upon incubation with phosphate buffer (PBS) at pH 7.4 (1.0-4.8% range). In comparison, the percentage (*)NO released was significantly higher (76.2-83.0% range) when the diazen-1-ium-1,2-diolate ester prodrugs were incubated in the presence of rat serum, or moderately higher (7.6-10.1% range) when the nitrooxyethyl ester prodrugs were incubated in the presence of L-cysteine. These incubation studies suggest that both (*)NO and the parent anti-inflammatory (E)-3-(4-methanesulfonylphenyl)-2-(phenyl)acrylic acid would be released upon in vivo cleavage by non-specific serum esterases in the case of the diazen-1-ium-1,2-diolate esters (11a-d), or interaction with systemic thiols in the case of the nitrate esters (12a-d). O(2)-Acetoxymethyl-1-(N-ethyl-N-methylamino)diazen-1-ium-1,2-diolate (E)-3-(4-methanesulfonylphenyl)-2-phenylacrylate (11a) released 83% of the theoretical maximal release of 2 molecules of (*)NO/molecule of the parent hybrid ester prodrug upon incubation with rat serum. Hybrid ester anti-inflammatory/(*)NO donor prodrugs offer a potential drug design concept targeted toward the development of anti-inflammatory drugs that are devoid of adverse ulcerogenic and/or cardiovascular effects.     

O2-acetoxymethyl-protected diazeniumdiolate-based NSAIDs (NONO-NSAIDs): synthesis, nitric oxide release, and biological evaluation studies

A novel group of O2-acetoxymethyl-protected diazeniumdiolate-based non-steroidal anti-inflammatory prodrugs (NONO-NSAIDs) were synthesized by esterifying the carboxylate group of aspirin, ibuprofen, or indomethacin with O2-acetoxymethyl 1-[N-(2-hydroxyethyl)-N-methylamino]diazeniumdiolate. The resulting nitric oxide (*NO)-releasing prodrugs (7-9) did not exhibit in vitro cyclooxygenase (COX) inhibitory activity against the COX-1 and COX-2 isozymes (IC50s>100 microM). In contrast, prodrugs 7 and 8 significantly decreased carrageenan-induced rat paw edema showing enhanced in vivo anti-inflammatory activities (ID50's=552 and 174 micromol/kg, respectively) relative to those of the parent NSAIDs aspirin (ID50=714 micromol/kg) and ibuprofen (ID50=326 micromol/kg). The rate of porcine liver esterase-mediated *NO release from prodrugs 7-9 (2 mol of *NO/mol of test compound in 0.6-6.5 min) was substantially higher compared to that observed without enzymatic catalysis (about 1 mol of *NO/mol of test compound in 40-48 h). These incubation studies suggest that both *NO and the parent NSAID would be released upon in vivo activation (hydrolysis) by esterases. Data acquired in an in vivo ulcer index (UI) assay showed that NONO-aspirin (UI=0.8), NONO-indomethacin (UI=1.3), and particularly NONO-ibuprofen (UI=0) were significantly less ulcerogenic compared to the parent drugs aspirin (UI=57), ibuprofen (UI=46) or indomethacin (UI=34) at equimolar doses. The release of aspirin and *NO from the NONO-aspirin (7) prodrug constitutes a potentially beneficial property for the prophylactic prevention of thrombus formation and adverse cardiovascular events such as stroke and myocardial infarction.     

Synthesis and pharmacological evaluation of nucleoside prodrugs designed to target siderophore biosynthesis in Mycobacterium tuberculosis

The nucleoside antibiotic, 5′-O-[N-(salicyl)sulfamoyl]adenosine (1), possesses potent whole-cell activity against Mycobacterium tuberculosis (Mtb), the etiological agent of tuberculosis (TB). This compound is also active in vivo, but suffers from poor drug disposition properties that result in poor bioavailability and rapid clearance. The synthesis and evaluation of a systematic series of lipophilic ester prodrugs containing linear and α-branched alkanoyl groups from two to twelve carbons at the 3′-position of a 2′-fluorinated analog of 1 is reported with the goal to improve oral bioavailability. The prodrugs were stable in simulated gastric fluid (pH 1.2) and under physiological conditions (pH 7.4). The prodrugs were also remarkably stable in mouse, rat, and human serum (relative serum stability: human ∼ rat ≫ mouse) displaying a parabolic trend in the SAR with hydrolysis rates increasing with chain length up to eight carbons (t_1/2 = 1.6 h for octanoyl prodrug 7 in mouse serum) and then decreasing again with higher chain lengths. The permeability of the prodrugs was also assessed in a Caco-2 cell transwell model. All of the prodrugs were found to have reduced permeation in the apical-to-basolateral direction and enhanced permeation in the basolateral-to-apical direction relative to the parent compound 2, resulting in efflux ratios 5–28 times greater than 2. Additionally, Caco-2 cells were found to hydrolyze the prodrugs with SAR mirroring the serum stability results and a preference for hydrolysis on the apical side. Taken together, these results suggest that the described prodrug strategy will lead to lower than expected oral bioavailability of 2 and highlight the contribution of intestinal esterases for prodrug hydrolysis.     

Identification of 2-hydroxymethyl-4-[5-(4-methoxyphenyl)-3-trifluoromethyl-pyrazol-1-yl]-N-propionylbenzenesulfonamide sodium as a potential COX-2 inhibitor for oral and parenteral administration

Synthesis of prodrugs of orally active COX-2 inhibitor 3 involving sulfamoyl (SO₂NH₂) and hydroxymethyl (CH₂OH) groups, and their biological evaluation are described. Of these prodrugs, the N-propionyl sulfonamide sodium 3k was found to be much superior to the parent compound 3 and other marketed COX-2 inhibitors in carrageenan induced rat paw edema model of inflammation due to highly elevated drug levels in systemic circulation. This prodrug has a potential both for oral as well as parenteral administration due to impressive analgesic activity, antipyretic potency, and extraordinary water solubility.     

Simultaneous determination of 3'-azido-2',3'-dideoxyuridine and novel prodrugs in rat plasma by liquid chromatography

3'-Azido-2',3'-dideoxyuridine (AZDU) is a nucleoside analog structurally similar to zidovudine (AZT) with proven activity against human immunodeficiency virus (HIV). The purpose of this study was to develop and validate a high-performance liquid chromatographic (HPLC) method to quantitatively determine AZDU and its novel prodrugs in rat plasma simultaneously. A reversed-phase gradient elution HPLC method was developed to quantitate AZDU and its prodrugs, N3-pivaloyloxymethyl-3'-azido-2',3'-dideoxyuridine (I), 5'-pivaloyloxymethyl-3'-azido-2',3'-dideoxyuridine (II), 5'-O-valinyl-3'-azido-2',3'-dideoxyuridine hydrochloride (III) and 5'-O-phenylalanyl-3'-azido-2',3'-dideoxyuridine hydrochloride (IV), in rat plasma. AZDU and its prodrugs were analyzed using an octadecyl silane column with a mobile phase consisting of 0.04 microM sodium acetate buffer, pH 5.0, and acetonitrile, running in a segmented gradient manner at a flow rate of 2 ml/min. Acetonitrile was increased from 10 to 50% during the first 8 min by 5% per min, followed by 10% per min until it reached 90% acetonitrile. 3'-Azido-2',3'-dideoxy-5-ethyluridine (CS-85) was used as an internal standard (25 microg/ml). Compounds were detected by UV absorption at 261 nm. Extraction recoveries for all compounds were greater than 80%. Retention times of AZDU, CS-85, prodrugs I, II, III and IV were 3.3, 5.2, 9.1, 8.8, 6.3 and 7.3 min, respectively. Calibration plots were linear over the range of 0.25-100 microg/ml for AZDU and prodrugs II, III, and IV and 0.5-100 microg/ml for prodrug I. The limit of quantitation was 0.25 microg/ml for prodrugs II, III and IV and 0.5 microg/ml for prodrug I. The intra- and inter-day variations were less than 10% and accuracies were greater than 90%. This method is rapid, sensitive and reproducible for the determination of AZDU and prodrugs in rat plasma.     

Design, synthesis, and bioavailability evaluation of coumarin-based prodrug of meptazinol

Based on the known coumarin-based prodrug system, a new meptazinol (Z)-3-[2-(propionyloxy) phenyl]-2-propenoic ester (3) was designed and synthesized as prodrug to minimize the first-pass effect of meptazinol (1) and improve the oral bioavailability. The prodrug (3) showed a 4-fold increase in oral bioavailability over the parent drug meptazinol in rats.     

Synthesis,in vitro,and in vivo evaluation of phosphate ester derivatives of combretastatin A-4

Combretastatin A-4 disodiumphosphate (CA4P), a prodrug formulation of the natural product combretastatin A-4 (CA4), is currently in clinical investigation for the treatment of cancer. In vivo, CA4P is rapidly enzymatically converted to CA4, a potent inhibitor of tubulin polymerization (IC(50)=1-2 microM), and rapidly causes bloodflow shutdown in tumor tissues. A variety of alkyl and aryl di- and triesters of CA4P have been synthesized and evaluated as potential CA4 prodrugs and/or stable CA4P analogues.     

Synthesis and relative bioavailability of meptazinol benzoyl esters as prodrugs

Three meptazinol benzoyl esters (1-3) were synthesized as prodrugs to minimize the first-pass effect of meptazinol and improve the bioavailability. Among these three esters, compound 3 showed better bioavailability than the parent meptazinol. Further, the relative regional bioavailability of prodrug 3 was evaluated using in situ closed loop study in rats, which showed that prodrug 3 has higher absorption efficacy in rat intestine. Thusly, prodrug 3 may be worth for further development.     

In vitro inhibition of simvastatin metabolism in rat and human liver by naringenin.

We demonstrated that naringenin (NRG), the aglycon form of naringin present in grapefruit juice inhibits in vitro the metabolism of simvastatin (SV), a HMG-CoA reductase inhibitor. SV undergoes an important first pass metabolism and this is thought to be partly responsible for its low bioavailability after oral administration. SV is a prodrug that requires metabolic activation through hydrolysis by esterases. In addition, SV is a substrate for cytochrome P450 enzymes. NRG, a potent inhibitor of cytochrome P450 enzymes, interferes with the isoenzymes of cytochrome P450 involved in the hepatic metabolism of SV. NRG inhibits the metabolism of SV in rat hepatocytes (the intrinsic clearance of SV decreases from 26.2 microl/min/10(6) cells in absence of NRG to 4.15 microl/min/10(6) cells in presence of 50 microM NRG). This inhibition is more pronounced in hepatocytes (Ki value approximately 5 microM) than in liver microsomes (Ki approximately 23 microM and approximately 30 microM in human and rat liver microsomes respectively). Therefore, the hepatocytes seem to be the best approach for in vitro interaction study between SV and NRG ; and this should be taken into account in the in vitro/in vivo extrapolation. If this interaction were confirmed in man, the doses of SV should be reduced when co-administered with grapefruit juice because of increased bioavailability of SV.     

Synthesis and evaluation of 2-amino-6-fluoro-9-(2-hydroxyethoxymethyl)purine esters as potential prodrugs of acyclovir

2-Amino-6-fluoro-9-(2-hydroxyethoxymethyl)purine (2) and its ester derivatives 4a–d were synthesized as potential prodrugs of acyclovir, and were evaluated for their oral acyclovir bioavailability in rats and in vivo antiviral efficacy in HSV-1-infected mice. Treatment of 2-amino-6-chloro-9-(2-hydroxyethoxymethyl)purine (3) with trimethylamine in THF/DMF (4:1) followed by a reaction of the resulting trimethylammonium chloride salt 5 with KF in DMF gave 2 in 78% yield. Esterification of 2 with an appropriate acid anhydride (Ac₂O, (EtCO)₂O, (n-PrCO)₂O, or (i-PrCO)₂O) in DMF in the presence of a catalytic amount of DMAP at room temperature produced the esters 4a–d in 90–98% yields. Of the prodrugs tested in rats, the isobutyrate 4d achieved the highest mean urinary recovery of acyclovir (51%) that is 5.7-fold higher than that of acyclovir (9%) and comparable to that of valacyclovir (50%). The prodrug 4d protected dose-dependently the mortality of HSV-1-infected mice, and the group treated with 4d at a dose of 400 mg/kg showed the longest mean survival day (14.6 ± 3.1 days) (mean ± S.D.).     

Design and synthesis of factor Xa inhibitors and their prodrugs

In addition to our previously reported fluoro acrylamides Xa inhibitors 2 and 3, a series of potent and novel cyclic diimide amidine compounds has been identified. In efforts to improve their oral bioavailability, replacement of the amidine group with methyl amidrazone gives compounds of moderate potency (14, IC(50)=0.028 microM). In the amidoxime prodrug approach, the amidoxime compounds show good oral bioavailability in rats and dogs. High plasma level of prodrug 26 and significant concentration of active drug 26a were obtained upon oral administration of prodrug 26 in rats.     

Diazen-1-ium-1,2-diolated nitric oxide donor ester prodrugs of 5-(4-hydroxymethylphenyl)-1-(4-aminosulfonylphenyl)-3-trifluoromethyl-1H-pyrazole and its methanesulfonyl analog: synthesis, biological evaluation and nitric oxide release studies

A new class of hybrid nitric oxide-releasing anti-inflammatory (AI) ester prodrugs (NONO-coxibs 12a-b) wherein an O(2)-acetoxymethyl 1-(2-carboxypyrrolidin-1-yl)diazen-1-ium-1,2-diolate (11, O(2)-acetoxymethyl PROLI/NO) NO-donor moiety was covalently coupled to the bromomethyl group of 5-(4-bromomethylphenyl)-1-(4-aminosulfonylphenyl)-3-trifluoromethyl-1H-pyrazole (9a), and its methanesulfonyl analog (9b), were synthesized. The diazen-1-ium-1,2-diolate compounds 12a-b released a low amount of NO upon incubation with phosphate buffer (PBS) at pH 7.4 (6.1-8.2% range). In comparison, the percentage NO released was significantly higher (76-77% of the theoretical maximal release of two molecules of NO/molecule of the parent hybrid ester prodrug) when the diazen-1-ium-1,2-diolate ester prodrugs 12a-b were incubated in the presence of rat serum. These incubation studies suggest that both NO and the anti-inflammatory 5-(4-hydroxymethylphenyl)-1-(4-aminosulfonylphenyl)-3-trifluoromethyl-1H-pyrazole (10a), and its methanesulfonyl analog (10b), would be released from the parent NONO-coxib 12a or 12b upon in vivo cleavage by non-specific serum esterases. The hydroxymethyl compounds 10a-b were weak inhibitors of the cyclooxygenase-1 (COX-1) and COX-2 isozymes (IC(50)=3.7-10.5 microM range). However, the hydroxymethyl compounds 10a-b and the parent NONO-coxibs 12a-b exhibited good AI activities (ED(50)=76.7-111.6 micromol/kg po range) that were greater than that exhibited by the reference drugs aspirin (ED(50)=710 micromol/kg po) and ibuprofen (ED(50)=327 micromol/kg po), but less than that of celecoxib (ED(50)=30.9mumol/kg po). These studies indicate hybrid ester AI/NO-donor prodrugs (NONO-coxibs) constitutes a plausible drug design concept targeted toward the development of selective COX-2 inhibitory AI drugs that are devoid of adverse cardiovascular effects.     

Synthesis and biological evaluation of L-valine-amidoximeesters as double prodrugs of amidines

In general, drugs containing amidines suffer from poor oral bioavailability and are often converted into amidoxime prodrugs to overcome low uptake from the gastrointestinal tract. The esterification of amidoximes with amino acids represents a newly developed double prodrug principle creating derivatives of amidines with both improved oral availability and water solubility. N-valoxybenzamidine (1) is a model compound for this principle, which has been transferred to the antiprotozoic drug pentamidine (8). Prodrug activation depends on esterases and mARC and is thus independent from activation by P450 enzymes. Therefore, drug-drug interactions or side effects will be minimized. The synthesis of these two compounds was established, and their biotransformation was studied in vitro and in vivo. Bioactivation of N-valoxybenzamidine (1) and N,N'-bis(valoxy)pentamidine (7) via hydrolysis and reduction has been demonstrated in vitro with porcine and human subcellular enzyme preparations and the mitochondrial Amidoxime Reducing Component (mARC). Moreover, activation of N-valoxybenzamidine (1) by porcine hepatocytes was studied. In vivo, the bioavailability in rats after oral application of N-valoxybenzamidine (1) was about 88%. Similarly, N,N'-bis(valoxy)pentamidine (7) showed oral bioavailability. Analysis of tissue samples revealed high concentrations of pentamidine (8) in liver and kidney.     

N-(2-hydroxypropyl)methacrylamide copolymers of a glutathione (GSH)-activated glyoxalase i inhibitor and DNA alkylating agent: synthesis, reaction kinetics with GSH, and in vitro antitumor activities

The incorporation of anticancer prodrugs into polyacrylamide conjugates has been shown to improve tumor targeting via the so-called "enhanced permeability and retention" effect. This strategy has now been expanded to include two different classes of glutathione (GSH)-activated antitumor agents prepared by radical polymerization of N-(2-hydroxypropyl)methacrylamide (HPMA) with 2-methacryloyloxy-methyl-2-cyclohexenone (7) and/or with S-(N-4-chlorophenyl-N-hydroxycarbamoyl-thioethyl)methacrylamide (8), followed by treatment with 3-chloroperoxybenzoic acid, to give the HPMA copolymers of 7 and the 8-sulfoxide, respectively. In aqueous-buffered solution at pH 6.5, GSH reacts rapidly with poly-HPMA-8-sulfoxide (k approximately 2.3 mM(-1) min(-1)) to give S-(N-4-chlorophenyl-N-hydroxycarbamoyl)glutathione (1), a tight-binding transition state analogue inhibitor of the antitumor target enzyme glyoxalase I (K(i) = 46 nM), or with poly-HPMA-7 (k approximately 0.02 mM(-1) min(-1)) to give the electrophilic antitumor agent 3-glutathio-2-methylenecyclohexenone (4). Indeed, B16 melanotic melanoma in culture is inhibited by poly-HPMA-8-sulfoxide and by poly-HPMA-7 with IC(50) values of 168 +/- 8 and 284 +/- 5 microM, respectively. These values are significantly greater than those of the unpolymerized prodrugs suggesting that the cytotoxicity of the polymer prodrugs might be limited by slow cellular uptake via pinocytosis. This prodrug strategy should be applicable to a range of different GSH-based antitumor agents.     

Design and synthesis of novel DFG-out RAF/vascular endothelial growth factor receptor 2 (VEGFR2) inhibitors: 2. Synthesis and characterization of a novel imide-type prodrug for improving oral absorption

As an alternative to the previously reported solid dispersion formulation for enhancing the oral absorption of thiazolo[5,4-b]pyridine 1, we investigated novel N-acyl imide prodrugs of 1 as RAF/vascular endothelial growth factor receptor 2 (VEGFR2) inhibitors. Introducing N-acyl promoieties at the benzanilide position gave chemically stable imides. N-tert-Butoxycarbonyl (Boc) introduced imide 6 was a promising prodrug, which was converted to the active compound 1 after its oral administration in mice. Cocrystals of 6 with AcOH (6b) possessed good physicochemical properties with moderate thermodynamic solubility (19μg/mL). This crystalline prodrug 6b was rapidly and enzymatically converted into 1 after its oral absorption in mice, rats, dogs, and monkeys. Prodrug 6b showed in vivo antitumor regressive efficacy (T/C=-6.4%) in an A375 melanoma xenograft model in rats. Hence, we selected 6b as a promising candidate and are performing further studies. Herein, we report the design, synthesis, and characterization of novel imide-type prodrugs.     

Abacavir prodrugs: microwave-assisted synthesis and their evaluation of anti-HIV activities

The synthesis of a new series of abacavir prodrugs involving N2-substitution with various substituted benzaldehyde and ketone derivatives is described. The in vitro anti-HIV activities indicated that compound (3-(2-(4-methylaminobenzylideneamino)-6-(cyclopropylamino)-9H-purin-9-yl)cyclopentyl)methanol (3) was found to be most potent compound with EC50 of 0.05 microM and CC50 of >100 microM with selectivity index of >2000. Compound 3 was found to be 32 times more potent than the parent drug (EC50 of 1.6 microM). At pH 7.4, 37 degrees C, the hydrolytic t1/2 ranged between 120 and 240 min.     

Novel hepatotrophic prodrugs of the antiviral nucleoside 9-(2-phosphonylmethoxyethyl)adenine with improved pharmacokinetics and antiviral activity.

The device of new hepatotrophic prodrugs of the antiviral nucleoside 9-(2-phosphonylmethoxyethyl)adenine (PMEA) with specificity for the asialoglycoprotein receptor on parenchymal liver cells is described. PMEA was conjugated to bi- and trivalent cluster glycosides (K(GN)(2) and K(2)(GN)(3), respectively) with nanomolar affinity for the asialoglycoprotein receptor. The liver uptake of the PMEA prodrugs was more than 10-fold higher than that of the parent drug (52+/-6% and 62+/-3% vs. 4.8+/-0.7% of the injected dose for PMEA) and could be attributed for 90% to parenchymal cells. Accumulation of the PMEA prodrugs in extrahepatic tissue (e.g., kidney, skin) was substantially reduced. The ratio of parenchymal liver cell-to-kidney uptake-a measure of the prodrugs therapeutic window-was increased from 0.058 +/- 0.01 for PMEA to 1.86 +/- 0.57 for K(GN)(2)-PMEA and even 2.69 +/- 0.24 for K(2)(GN)(3)-PMEA. Apparently both glycosides have a similar capacity to redirect (antiviral) drugs to the liver. After cellular uptake, both PMEA prodrugs were converted into the parent drug, PMEA, during acidification of the lysosomal milieu (t(1/2) approximately 100 min), and the released PMEA was rapidly translocated into the cytosol. The antiviral activity of the prodrugs in vitro was dramatically enhanced as compared to the parent drug (5- and 52-fold for K(GN)(2)-PMEA and K(2)(GN)(3)-PMEA, respectively). Given the 15-fold enhanced liver uptake of the prodrugs, we anticipate that the potency in vivo will be similarly increased. We conclude that PMEA prodrugs have been developed with greatly improved pharmacokinetics and therapeutic activity against viral infections that implicate the liver parenchyma (e.g., HBV). In addition, the significance of the above prodrug concept also extends to drugs that intervene in other liver disorders such as cholestasis and dyslipidemia.