Prodrugs of naproxen and diclofenac

Abstract

The present invention relates to a compound of formula (I): wherein R.sub.1 is R.sub.3-IPU and R.sub.2 is the acyloxy residue of diclofenac or naproxen, and specified by the following structures (A) wherein OHR.sub.3-IPU is selected from (B) and R.sub.4 and R.sub.5 may be the same or different selected from (C) and salts, solvates and hydrates thereof. ##STR00001## ##STR00002## ##STR00003##

Claims

1. A prodrug of diclofenac or naproxen of formula: ##STR00017## or salts, solvates or hydrates thereof; wherein: IPU is an Immobility-Promoting Unit comprising a substituted or unsubstituted imidazolyl group, and the IPU has a pKa between 4 and 8.4 at 37 C. in phosphate buffered saline; R.sub.2 is an acyloxy residue of diclofenac or naproxen; R.sub.3 is selected from the following structures for HO-R.sub.3-IPU: ##STR00018## ##STR00019## wherein R.sub.6 is H or CH.sub.3; and R.sub.4 and R.sub.5 are independently selected from the group consisting of: ##STR00020## wherein the prodrug of diclofenac or naproxen according to the formula is selected from the following structures: ##STR00021## ##STR00022## or salts, solvates or hydrates thereof.

2. The prodrug, according to claim 1, selected from the following structures: ##STR00023## or salts, solvates or hydrates thereof.

3. The prodrug according to claim 1, selected from the following structures: ##STR00024## ##STR00025## or salts, solvates or hydrates thereof.

4. A pharmaceutical composition, comprising a therapeutically effective amount of the prodrug according to claim 1, and at least one pharmaceutically acceptable carrier, vehicle or adjuvant.

5. A pharmaceutical composition according to claim 4, wherein the composition is suitable for intra-articular injection.

6. A pharmaceutical composition, comprising a therapeutically effective amount of the prodrug according to claim 3, and at least one pharmaceutically acceptable carrier, vehicle or adjuvant.

7. The pharmaceutical composition according to claim 6, wherein the composition is suitable for intra-articular injection.

8. A method of treating postoperative pain, comprising administering the prodrug according to claim 1 to a subject in need thereof.

9. The method according to claim 8, wherein the postoperative pain is postoperative pain following arthroscopic surgery.

10. The method according to claim 9, further comprising administering one or more local anaesthetic agents selected from the group consisting of amethocine, chlorprocaine, etidocaine, lidocaine, bupivacaine, mepivacaine, prilocaine, ropivacaine, and procaine.

11. The method according to claim 9, further comprising administering one or more opioid or strong analgesics selected from the group consisting of alfentanil, alphaprodine, anilerdine, buprenorphine, buturphenol, codeine, dextromoramide, dextroproproxyphene, dihydrocodeine, fentanyl, dydrocodone, hydromorphone, ketobemidone, meptazinol, methadone, morphine, oxycodone, oxymorphone, pentazocine, pethidine, phenazocine, phenoperidine, and sulfentanil.

12. A method of treating inflammation, comprising administering the prodrug according to claim 1 to a subject in need thereof.

13. A method of treating postoperative pain, comprising administering the prodrug according to claim 3 to a subject in need thereof.

14. The method according to claim 13, wherein the postoperative pain is postoperative pain following arthroscopic surgery.

15. A method of treating inflammation, comprising administering the prodrug according to claim 3 to a subject in need thereof.

16. An intra-articular injection comprising a prodrug according to claim 1, wherein the composition is in the form of an aqueous solution having a pH of from 1.5 to 5, from which the compound of formula I precipitates in the joint, at least partly, after administration.

17. The intra-articular injection according to claim 16, wherein the prodrug is according to claim 3 selected from the following structures: ##STR00026## ##STR00027## or salts, solvates or hydrates thereof.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) FIG. 1 shows factors influencing the pharmacokinetic fate of the prodrug/drug after administration of the prodrug into the joint. The prodrug dissolved is converted into the active drug by enzymatic cleavage of the prodrug bond.

(2) The invention is illustrated in, but not limited to, the following examples

EXAMPLES

(3) The inventors have tested a number of compounds/prodrugs. The prodrugs were tested according to the method for testing solubility below. As expected, all prodrugs exhibited a low although variable solubility at pH 7.4 (due to the very low solubility of the neutral form of the prodrugs).

(4) Standard procedures were used to synthesize the ester derivatives as apparent from the more detailed description of the synthesis of the NSAID ester prodrugs presented below. Purity of the synthesized derivatives exceeded 95% as assessed by .sup.1H-NMR and HPLC.

(5) Method for Testing Solubility

(6) The determination of the solubility of a prodrug at different pH values of interest according to the present invention is carried by adding excess solid prodrug to a container containing a buffer solution with well-defined pH. The mixture is rotated at constant temperature until an equilibrium between solid prodrug and prodrug in solution has established (that is until the prodrug concentration in the supernatant remains constant). At each measurement the pH of the supernatant is controlled and eventually adjusted to the desired pH. In a similar manner the solubility of a prodrug in a tissue fluid including the synovial fluid can be determined.

(7) The following examples illustrate general methods for the preparation of prodrugs and the compounds according to the present invention can be prepared in analogous matter using the desired OHR.sub.3 and IPU moieties.

(8) The following compounds are illustrated:

(9) Examples of prodrugs of the invention, where the NSAID is diclofenac:

(10) ##STR00012## ##STR00013## ##STR00014##

(11) Examples of prodrugs of the invention where the NSAID is naproxen:

(12) ##STR00015## ##STR00016##

(13) These compounds are as far as they are covered by a co-pending, unpublished PCT application not part of the present application.

Example 1: DPX-1-0001 (ALE463)

4-(dimethylamino)phenethyl 2-(2-(2,6-dichlorophenylamino)phenyl)acetate

(14) 2-(4-(dimethylamino)phenyl)ethanol (3.3 mmol, 0.55 g), and Dichlofenac (3.3 mmol, 0.99 g) was suspended in dichloromethane (30 mL) under N.sub.2 and Dicyclohexylcarbodiimid (6.6 mmol, 1.36 g), 4-Dimethylaminopyridine (0.33 mmol, 36 mg) was added. The mixture was stirred overnight before being poured into sat. NH.sub.4Cl (100 mL) and extracted with dichloromethane (450 mL). Drying, filtration and evaporation gave 2.4 g crude material which was purified by Flash Chromatography using EtOAc and Heptanes as eluent giving 0.65 g (43%) of the desired compound. 1H NMR (400 MHz, DMSO-d6) 7.52 (d, J=8.03 Hz, 4H), 7.13-7.24 (m, 4H), 7.04-7.10 (m, 2H), 6.93-7.02 (m, 5H), 6.85 (dt, J=1.25, 7.40 Hz, 2H), 6.58-6.63 (m, 4H), 6.26 (d, J=7.53 Hz, 1H), 4.21 (t, J=7.03 Hz, 4H), 3.78 (s, 2H), 2.82 (s, 11H), 2.77 (t, J=7.03 Hz, 4H) 13C NMR (400 MHz, DMSO-d6) 171.40, 137.07, 130.90, 129.28, 125.86, 123.20, 112.53, 65.51, 37.11, 33.40.

Example 2: DPX-1-0002 (ALE 482)

2-(methyl(phenyl)amino)ethyl 2-(2-(2,6-dichlorophenylamino)phenyl)acetate

(15) Using an Identical Procedure as Described for DPX-1-0001:

(16) 2-(methyl(phenyl)amino)ethanol (3.3 mmol, 0.50 g), Dichlofenac (3.3 mmol, 0.99 g), Dichclohexylcarbodiimid (6.6 mmol, 1.36 g), 4-Dimethylaminopyridine (0.3 mmol, 36 mg) and dichloromethane (30 mL). Crude yield: 1.4 g; yield after Flash Chromatography using ethyl acetate and heptanes as eluent: 0.83 g (59%). .sup.1H NMR (400 MHz, DMSO-d6) 7.52 (d, J=8.28 Hz, 3H), 7.20 (t, J=8.16 Hz, 2H), 7.10-7.15 (m, 4H), 7.05 (dt, J=1.51, 7.78 Hz, 2H), 6.97 (s, 1H), 6.83 (dt, J=1.25, 7.40 Hz, 2H), 6.66-6.72 (m, 3H), 6.56-6.63 (m, 2H), 6.25 (d, J=8.03 Hz, 1H), 4.24 (t, J=5.77 Hz, 3H), 3.74 (s, 3H), 3.58 (t, J=5.77 Hz, 3H), 2.83 (s, 5H). .sup.13C NMR (400 MHz, DMSO-d6) 171.43, 148.71, 142.81, 137.06, 129.13, 128.94, 127.71, 123.02, 115.89, 111.98, 61.90, 50.24, 38.15, 37.02, 31.23, 28.34, 22.07,

(17) Methanesulfonate Salt of DPX-1-0002.

(18) Methanesulfonic acid (113 l, 167 mg, mmol) in dry diethyl ether (10 mL) was added by syringe to a magnetically stirred solution of 2-(methyl(phenyl)amino)ethyl 2-(2-(2,6-dichlorophenylamino)phenyl)acetate (746 mg, 1.74 mmol) in dry diethyl ether (20 mL) under nitrogen cooled in an ice bath. The resulting precipitate in the form of a sticky gum was isolated by decanting off the solvent and washing the gum with dry ether (10 mL). The gum was dried under high vacuum and crystallized from ethanol to afford the title compound as a colourless solid (653 mg). Mp. 143.6-144.6 C. (dec.) (ethanol). .sup.1H NMR (400 MHz, DMSO) 7.53 (d, J=8 Hz, 2H), 7.27-6.78 (m, 11H), 6.26 (dd, J=8.0, 1 Hz, 1H), 4.23 (t, J=5.5 Hz, 2H), 3.75 (s, 2H), 3.68 (t, J=5.5 Hz, 2H), 2.95 (s, 3H), 2.45 (s, 3H). .sup.13C NMR (101 MHz, DMSO) 171.31, 142.83, 137.04, 131.01, 130.73, 129.26, 129.15, 127.76, 125.95, 122.93, 120.59, 115.83, 114.22, 61.21, 51.76, 39.70 (CH3), 36.94. DEPT .sup.13C NMR (101 MHz, DMSO) 131.01, 129.27, 129.16, 127.77, 125.96, 120.60, 115.84, 61.22, 39.70, 36.94.

Example 3: DPX-1-0004 (sdnX-20)

2-(pyridin-2-yl)ethyl 2-(2-((2,6-dichlorophenyl)amino)phenyl)acetate

(19) Using an Identical Procedure as Described for DPX-1-0001:

(20) 2-(pyridin-2-yl)ethanol (37.7 mmol, 4.65 g), Dichlofenac (9.43 mmol, 3.0 g), 4-Dimethylaminopyridin (0.3 mmol, 35 mg), 1-Ethyl-3-(3-dimethylaminopropyl) carbodiimide-HCl (11.32 mmol, 2.17 g), Dichloromethane (15 mL) and Dimethylformamide (10 mL). Yield after Flash Chromatography using ethyl acetate and heptanes as eluent: 1.67 g. The solid HCl-salt was prepared by passing a stream of HCl through an ethereal solution of the product. .sup.1H NMR (CDCl.sub.3) 3.3-3.7 (m, 4H), 4.58 (br s, 2H), 6.24-7.30 (m, 8H), 7.60 (br s, 1H), 7.97 (br s, 1H), 8.57 (br s, 1H). .sup.13C (CDCl.sub.3): 13.76, 22.29, 25.24, 28.61, 30.62, 31.47, 32.39, 38.03, 62.30, 67.58, 111.37, 121.53, 123.17, 124.30, 124.77, 127.39, 127.81, 128.51, 128.59, 129.42, 130.78, 136.85, 140.77, 142.26, 145.15, 153.05.

Example 4: DPX-1-0005 (ALE460-2)

2-(1H-imidazol-1-yl)ethyl 2-(2-(2,6-dichlorophenylamino)phenyl)acetate

(21) Using an Identical Procedure as Described for DPX-1-0001:

(22) 2-(1H-imidazol-1-yl)ethanol (12 mmol, 1.3 g), Dichlofenac (6 mmol, 1.77 g), Dimethylaminopyridin (0.3 mmol, 22 mg), Dicyclohexylcarbodiimid (7.2 mmol, 1.5 g) and Dichloromethane (50 mL). Crude yield: 2.13 g; yield after Flash Chromatography using ethyl acetate and heptanes as eluent: 0.80 g (34%). .sup.1H NMR (400 MHz, DMSO-d6) 7.58 (t, J=1.00 Hz, 3H), 7.50-7.55 (m, 6H), 7.13-7.27 (m, 7H), 7.09 (t, J=1.25 Hz, 3H), 7.06 (dt, J=1.51, 7.65 Hz, 3H), 7.02 (s, 3H), 6.81-6.87 (m, 6H), 6.24 (d, J=7.53 Hz, 1H), 4.30-4.35 (m, 6H), 4.21-4.26 (m, 6H), 3.82 (s, 2H).sup.13C NMR (400 MHz, DMSO-d6) 171.14, 142.85, 137.46, 130.92, 129.13, 127.75, 122.80, 120.50, 119.58, 115.70, 63.98, 45.02, 36.74, 33.33.

Example 5: DPX-1-0006 (JBX022)

2-(1H-benzo[d]imidazol-1-yl)ethyl 2-(2-((2,6-dichlorophenyl)amino)phenyl)acetate

(23) 1-Ethyl-3-(3-dimethylaminopropyl)carbodiimide-HCl (1.10 g, 5.74 mmol) was added solid all at once to a magnetically stirred solution of diclofenac (1.48 g, 5.00 mmol), 2-(1H-benzo[d]imidazol-1-yl)ethanol (0.810 g, 10.0 mmol) and 4-Dimethylaminopyridine (31 mg, 0.25 mmol) in dry Tetrahydrofuran (30 mL) cooled in an ice bath and kept under nitrogen. The reaction mixture was stirred in an ice bath for 1 hour and then at ambient temperature. After stirring for 24 hours at room temperature the mixture was concentrated and the residue partitioned between water (25 mL), saturated NH.sub.4Cl (25 mL) and EtOAc (100 mL). The organic layer was washed with 50% saturated NH.sub.4Cl (240 mL), 50% saturated NaHCO.sub.3 (40 mL) and brine (50 mL). The organic layer was dried and concentrated. Flash Chromatography using ethyl acetate and heptanes as eluent afforded a colourless oil that crystallised from ether (1.53 g) and was recrystallised to afford the title compound as a colourless solid (1.25 g, 57%). Mp. 128.8-129.3 C. (EtOAc-heptane). .sup.1H NMR (400 MHz, DMSO) 8.15 (s, 1H), 7.65-7.60 (m, 2H), 7.51 (d, J=8.0 Hz, 2H), 7.29-7.15 (m, 3H), 7.09-7.01 (m, 2H), 6.94 (s, 1H), 6.80 (td, J=7.5, 1.0 Hz, 1H), 6.23 (d, J=8.0 Hz, 1H), 4.54 (t, J=5.0 Hz, 2H), 4.44 (t, J=5.0 Hz, 2H), 3.75 (s, 2H). .sup.13C NMR (101 MHz, DMSO) 171.13, 144.16, 143.31, 142.82, 137.02, 133.85, 130.90, 130.86, 129.08, 127.74, 125.95, 122.74, 122.31, 121.46, 120.50, 119.38, 115.74, 110.31, 63.21, 43.20, 36.75. .sup.13C-DEPT NMR (101 MHz, DMSO) 144.17, 130.90, 129.09, 127.74, 125.96, 122.32, 121.46, 120.50, 119.38, 115.74, 110.31, 63.21, 43.20, 36.75.

Example 6: DPX-1-0007 (sdnX-18)

2-(2-phenyl-1H-imidazol-1-yl)ethyl 2-(2-((2,6-dichlorophenyl)amino)phenyl)acetate

(24) The required IPU: 2-(2-phenyl-1H-imidazol-1-yl)ethanol was prepared in the following way: A magnetically stirred solid mixture 2-phenylimidazole (37.7 g, 0.261 mol) and ethylene carbonate (28.8 g, 0.327 mol) in a 250 mL three necked flask round bottomed flask equipped with a bubble tube and an internal thermometer was heated in a oil bath to 130-140 C. were evolution of CO.sub.2 started. The mixture was kept at this temperature until evolution of CO.sub.2 ceased. More ethylenecarbonate in portions of 2-3 g was added and the mixture reheated until evolution of CO.sub.2 ceased or full conversion of 2-phenylimidazole as indicated by TLC was achieved. The dark brown mixture was cooled to room temperature and dissolved in water (100 mL) and extracted with ethyl acetate (3-4100 mL). The combined organic layers were washed with brine (100 mL) and dried over Na.sub.2SO.sub.4. Concentration gave a dark brown oily residue (37.7 g) which was crystallised from EtOAc-heptane to give 21.5 g of a brown solid. This material was recrystallised from EtOAc-EtOH to afford the title compound as a pale brown solid in sufficient purity to be used in subsequent steps without further purification (18.7 g, 38%).

(25) DPX-1-0007 was subsequently prepared using an identical procedure as described for DPX-1-0001: 2-(2-phenyl-1H-imidazol-1-yl)ethanol (12 mmol, 2.26 g), Dichlofenac (6 mmol, 1.77 g), 4-Dimethylaminopyridin (0.3 mmol, 22 mg), Dicyclohexylcarbodiimid (7.2 mmol, 1.5 g) and dichloromethane (50 mL). .sup.1H NMR (400 MHz, DMSO) 7.61-7.56 (m, 2H), 7.52 (d, J=8.1 Hz, 2H), 7.48-7.36 (m, 3H), 7.29 (d, J=1.2 Hz, 1H), 7.23-7.17 (m, 1H), 7.10-7.02 (m, 2H), 6.96 (d, J=1.2 Hz, 1H), 6.91 (s, 1H), 6.83 (td, J=7.4, 1.1 Hz, 1H), 6.23 (d, J=7.8 Hz, 1H), 4.38-4.27 (m, 4H), 3.69 (s, 2H).

Example 7: DPX-1-0008 (ALE459-3)

2-(2-propyl-1H-imidazol-1-yl)ethyl 2-(2-(2,6-dichlorophenylamino)phenyl)acetate

(26) Using an Identical Procedure as Described for DPX-1-0001:

(27) Dichlorfenac (6 mmol, 1.7 g), 6-(1H-imidazol-1-yl)ethan-1-ol (12 mmol, 1.8 g), Dicyclohexylcarbidiimide (7.2 mmol, 1.4 g), 4-Dimethylaminopyridine (0.6 mmol, 72 mg) and dichloromethane (50 mL) Crude yield: 3.6 g; yield after Flash Chromatography using ethyl acetate and heptanes as eluent: 1.2 g (46%). .sup.1H NMR (400 MHz, DMSO-d6) 7.52 (d, J=8.03 Hz, 5H), 7.20 (t, J=8.03 Hz, 2H), 7.14 (dd, J=1.51, 7.53 Hz, 2H), 7.06 (dt, J=1.51, 7.78 Hz, 2H), 6.95-7.01 (m, 4H), 6.84 (dt, J=1.13, 7.47 Hz, 2H), 6.70 (d, J=1.25 Hz, 2H), 6.25 (d, J=7.78 Hz, 1H), 4.26-4.35 (m, 2H), 4.10-4.17 (m, 2H), 3.80 (s, 2H), 1.63 (dquin, J=7.28, 7.47 Hz, 2H), 0.90 (t, J=7.40 Hz, 3H). .sup.13C NMR (400 MHz, DMSO-d6) 171.15, 147.40, 142.85, 130.92, 130.82, 129.13, 127.77, 126.48, 125.98, 122.82, 119.44, 115.81, 63.95, 43.69, 27.65, 20.85, 13.75

Example 8: DPX-1-0009 (ALE480-1)

6-(1H-imidazol-1-yl)hexyl 2-(2-(2,6-dichlorophenylamino)phenyl)acetate

(28) Using an Identical Procedure as Described for DPX-1-0001:

(29) Dichlorfenac (6 mmol, 1.7 g), 6-(1H-imidazol-1-yl)hexan-1-ol (6 mmol, 1.0 g) Dicyclohexylcarbidiimide (12 mmol), 4-Dimethylaminopyridine (0.6 mmol, 72 mg) dichloromethane (50 mL). Crude yield: 2.1 g; yield after Flash Chromatography using ethyl acetate and heptanes as eluent: 0.5 g (20%). .sup.1H NMR (400 MHz, DMSO-d6) 7.46-7.66 (m, 5H), 7.16-7.25 (m, 3H), 7.12 (s, 2H), 7.02-7.08 (m, 3H), 6.81-6.88 (m, 3H), 6.26 (d, J=7.78 Hz, 1H), 4.03-4.08 (m, 4H), 3.89 (t, J=7.03 Hz, 3H), 3.79 (s, 2H), 1.64 (quin, J=7.28 Hz, 3H), 1.56 (ddt, J=6.78, 7.03, 7.15 Hz, 3H), 1.22-1.33 (m, 4H), 1.14-1.22 (m, 4H). .sup.13C NMR (400 MHz, DMSO-d6) 171.53, 142.73, 137.06, 129.15, 128.28, 127.67, 125.85, 123.30, 119.15, 115.89, 64.38, 45.75, 37.10, 30.40, 27.92, 25.49, 24.74.

Example 9: DPX-1-0010 (ALE481-2)

6-(2-propyl-1H-imidazol-1-yl)hexyl 2-(2-(2,6-dichlorophenylamino)phenyl)acetate

(30) Using an Identical Procedure as Described for DPX-1-0001:

(31) Dichlorfenac (6 mmol, 1.4 g), 6-(2-propyl-1H-imidazol-1-yl)hexan-1-ol (6 mmol, 1.25 g), Dicyclohexylcarbidiimide (12 mmol, 2.4 g), 4-Dimethylaminopyridin (0.6 mmol, 72 mg) and dichloromethane (60 mL). Crude yield: 1.9 g; yield after Flash Chromatography using ethyl acetate and heptanes as eluent: 0.21 g (10%). .sup.1H NMR (400 MHz, DMSO-d6) 7.52 (d, J=8.03 Hz, 1H), 7.13-7.27 (m, 1H), 6.94-7.09 (m, 2H), 6.81-6.88 (m, 1H), 6.72 (d, J=1.00 Hz, 1H), 6.27 (s, 1H), 4.06 (t, J=6.53 Hz, 2H), 3.72-3.83 (m, 3H), 1.50-1.73 (m, 4H), 1.15-1.36 (m, 3H), 0.91 (t, J=7.40 Hz, 2H). .sup.13C NMR (400 MHz, DMSO-d6) 171.52, 146.91, 142.2, 137.06, 130.84, 130.52, 129.15, 127.66, 123.31, 119.10, 115.89, 64.38, 44.64, 30.35, 27.94, 27.79, 20.92, 13.75

Example 10: DPX-1-0011

2-(1-methyl-1H-imidazol-2-yl)ethyl 2-(2-((2,6-dichlorophenyl)amino)phenyl)acetate

(32) 1-Ethyl-3-(3-dimethylaminopropyl)carbodiimide-HCl (EDC-HCl) (0.661 g, 3.45 mmol) was added solid all at once to a magnetically stirred solution of diclofenac (0.888 g, 3.00 mmol), 2-(1-methyl-1H-imidazol-2-yl)ethanol (0.379 g, 3.00 mmol) and 4-Dimethylaminopyridine (19 mg, 0.15 mmol) in dry tetrahydrofuran (20 mL) cooled in an ice bath and kept under nitrogen. The reaction mixture was stirred in an ice-bath for 30 min and then at ambient. After stirring for 12 hrs at room temperature more EDC-HCl (115 mg, 0.6 mmol) was added and stirring was continued at room temperature for 72 hrs. The mixture was concentrated and the residue partitioned between 50% saturated NH.sub.4Cl (25 mL) and EtOAc (60 mL). The organic layer was washed with 50% saturated NH.sub.4Cl (225 mL), 50% saturated NaHCO.sub.3 (25 mL) and brine (30 mL). The organic layer was dried over Na.sub.2SO.sub.4 and concentrated. Flash Chromatography using ethyl acetate and heptanes as eluent provided the title compound which crystallised from heptane as a colorless solid (196 mg). Mp. 114.5-115.2 C. (EtOAc-Heptane). .sup.1H NMR (400 MHz, DMSO) 7.53 (d, J=8.1 Hz, 2H), 7.24-7.18 (m, 1H), 7.17 (dd, J=7.5, 1.4 Hz, 1H), 7.10 (s, 1H), 7.06 (td, J=7.8, 1.5 Hz, 1H), 6.99 (d, J=1.2 Hz, 1H), 6.83 (td, J=7.4, 1.1 Hz, 1H), 6.71 (d, J=1.2 Hz, 1H), 6.24 (d, J=7.4 Hz, 1H), 4.39 (t, J=7.0 Hz, 2H), 3.79 (s, 2H), 3.52 (s, 3H), 2.98 (t, J=7.0 Hz, 2H). .sup.13C NMR (101 MHz, DMSO) 171.37, 144.11, 142.93, 137.08, 130.98, 130.94, 129.12, 127.72, 126.27, 126.03, 122.91, 121.13, 120.45, 115.63, 62.61 (CH2), 37.08 (CH2), 32.07, 25.48 (CH2). DEPT.sup.13C NMR (101 MHz, DMSO) 130.95, 129.12, 127.73, 126.27, 126.03, 121.13, 120.44, 115.62, 62.61, 37.07, 32.07, 25.48.

Example 11: DPX-1-0012

2-(2-(2-phenyl-1H-imidazol-1-yl)ethoxy)ethyl 2-(2-((2,6-dichlorophenyl)-amino)phenyl)acetate

(33) The required IPU: 2-(2-(2-phenyl-1H-imidazol-1-yl)ethoxy)ethanol was obtained as a byproduct in the synthesis of another IPU: 2-(2-phenyl-1H-imidazol-1-yl)ethanol (see under DPX-1-0007) in the following way: The filtrate from the initial crystallisation was purified by Flash Chromatography using EtOAc:heptane.fwdarw.EtOAc:MeOH as eluent and fractions containing the title compound was combined (7 g) and recrystallised from EtOAc:heptane to give 4.56 g of pale yellow solid. This material was purified again by Flash Chromatography using EtOAc.fwdarw.EtOAc:MeOH (90:10) as eluent. Relevant fractions were combined and recrystallised from toluene to afford the title compound as a colourless solid (1.39 g, 2.3%). Mp. 94.4-95.1 C. (toluene). .sup.1H NMR (400 MHz, DMSO) 7.66-7.62 (m, 2H), 7.51-7.41 (m, 3H), 7.38 (d, J=1.0 Hz, 1H), 7.00 (d, J=1.0 Hz, 1H), 4.59 (t, J=5.5 Hz, 1H), 4.17 (t, J=5.5 Hz, 2H), 3.72 (t, J=5.5 Hz, 2H), 3.49-3.42 (m, 2H), 3.40-3.35 (m, 2H). .sup.13C NMR (101 MHz, CDCl.sub.3) 148.19, 130.91, 129.23, 128.91, 128.72, 128.70, 121.06, 72.68, 70.58, 61.71, 46.73.

(34) Subsequently, DPX-1-0012 was prepared in the following way: 1-Ethyl-3-(3-dimethylaminopropyl)carbodiimide-HCl (EDC-HCl) (551 mg, 2.87 mmol) was added solid all at once to a magnetically stirred solution of Diclofenac (741 mg, 2.50 mmol), 2-(2-(2-phenyl-1H-imidazol-1-yl)ethoxy)ethanol (581 mg, 2.50 mmol) and 4-Dimethylaminopyridine (16 mg, 0.13 mmol) in dry tetrahydrofuran (15 mL) cooled in an ice bath and kept under nitrogen. The reaction mixture was stirred in an ice bath for 30 min and then at ambient temperature. After stirring for 12 hours more EDC-HCl (96 mg, 0.5 mmol) was added and stirring was continued at room temperature for 72 hours. The mixture was concentrated and the residue partitioned between 50% saturated NH.sub.4Cl (25 mL) and EtOAc (50 mL). The organic layer was washed with 50% saturated NH.sub.4Cl (225 mL), 50% saturated NaHCO.sub.3 (25 mL) and brine (30 mL). The organic layer was dried over Na.sub.2SO.sub.4 and concentrated. The residue was purified by Flash Chromatography using ethyl acetate and heptanes as eluent to afford the title compound (274 mg) as thick pale yellow oil. .sup.1H NMR (400 MHz, DMSO) 7.64-7.59 (m, 2H), 7.52 (d, J=8.1 Hz, 2H), 7.48-7.37 (m, 3H), 7.30 (d, J=1.2 Hz, 1H), 7.23-7.18 (m, 1H), 7.16 (dd, J=7.6, 1.4 Hz, 1H), 7.07-7.01 (m, 2H), 6.98 (d, J=1.2 Hz, 1H), 6.82 (td, J=7.4, 1.1 Hz, 1H), 6.25 (d, J=7.8 Hz, 1H), 4.17-4.09 (m, 4H), 3.78 (s, 2H), 3.69 (t, J=5.3 Hz, 2H), 3.59-3.54 (m, 2H). .sup.13C NMR (101 MHz, DMSO) 171.45, 146.93, 142.81, 137.08, 130.92, 130.85, 130.63, 129.14, 128.78, 128.38, 128.30, 127.86, 127.71, 125.88, 123.12, 121.44, 120.62, 115.89, 69.61, 68.18, 63.75, 46.00, 36.94. DEPT .sup.13C NMR (101 MHz, DMSO) 130.85, 129.13, 128.78, 128.38, 128.30, 127.86, 127.71, 125.88, 121.44, 120.62, 115.89, 69.60 (CH2), 68.18 (CH2), 63.75 (CH2), 46.00 (CH2), 36.94 (CH2).

Example 12: DPX-2-0001 (ALE 406)

4-(dimethylamino)phenethyl 2-(6-methoxynaphthalen-2-yl)propanoate

(35) 2-(6-methoxynaphthalen-2-yl)propanoyl chloride (acid chloride of Naproxen) (1 g, 4 mmol) was dissolved in dichloromethane (20 mL) and pyridine (30 mL) was added, and finally a solution of the 2-(4-(dimethylamino)phenyl) ethanol (0.64 g, 4 mmol) in dichloromethane (10 mL) was added. The mixture was left over night under stirring at room temperature. After addition of dichloromethane the reaction mixture was washed with first a saturated bicarbonate solution (100 mL) and second water (100 mL). The organic phase was dried and concentrated to yield an oily residue. The crude product was purified by vacuum liquid chromatography on silica (20-45 m) using heptane (60 mL) followed by heptane-ethyl acetate (4:1 v/v) as eluent. Yield 0.52 g (35%). .sup.1H NMR (300 MHz, CDCl.sub.3): 7.70-7.64 (3H, m); 7.37 (1H, dd, J=6.60; 1.5 Hz); 7.15-7.11 (2H, m); 6.9 (2H, d, J=8.8 Hz); 6.52 (2H, d, J=8.56); 4.27 (2H, t, J=6.88 Hz); 3.92 (3H,$); 3.84 (1H, q, J=7.15 Hz); 2.88 (6H, s); 2.76 (2H, t, J=7.15 Hz); 1.57 (3H, d, J=7.15 Hz). 13C NMR (400 MHz, DMSO-d6) 173.76, 157.18, 135.60, 135.60, 129.24, 126.96, 126.23, 125.73, 118.66, 105.69, 65.29, 55.15, 44.51, 33.30, 18.17.

Example 13: DPX-2-0002 (ALE 412)

2-(methyl(phenyl)amino)ethyl 2-(6-methoxynaphthalen-2-yl)propanoate

(36) Using an identical procedure as described for DPX-2-0001 using 2-(6-methoxynaphthalen-2-yl)propanoyl chloride (1.7 g, 7.2 mmol) and 2-(methyl(phenyl)amino)ethanol (1.10 g, 7.2 mmol). Yield 0.9 g (36%). .sup.1H NMR (300 MHz, CDCl.sub.3): 7.7 (3H, d, J=8.53 Hz); 7.62 (1H, d, J=1.38 Hz); 7.35 (1H, dd, J=8; 1.65 Hz); 7.22-7.10 (2H, m), 6.69 (3H, m); 4.23 (2H, t, J=5.78); 3.92 (3H, s); 3.80 (1H, q, J=7.15 Hz); 3.53 (2H, t, J=5.78 Hz); 2.83 (3H, s); 1.54 (3H, d, J=6.88 Hz). .sup.13C NMR (400 MHz, DMSO-d6) 173.87, 157.17, 135.53, 133.31, 128.92, 126.94, 126.64, 118.71, 115.88, 111.91, 105.70, 61.80, 55.14, 50.18, 44.50, 38.06, 18.22.

Example 14: DPX-2-0003 (ALE 416)

3-(methyl(phenyl)amino)propyl 2-(6-methoxynaphthalen-2-yl)propanoate

(37) Using an identical procedure as described for DPX-2-0001 using 2-(6-methoxynaphthalen-2-yl)propanoyl chloride (1.7 g, 7.14 mmol) and 3-(methyl(phenyl)amino)propan-1-ol (1.19 g; 7.14 mmol). Yield 1.75 g (64%). .sup.1H NMR (300 MHz, CDCl.sub.3): 7.72-7.68 (3H, m); 7.41 (1H, dd, J=6.60 Hz; 1.93 Hz); 7.17-7.10 (3H, m); 7.71-7.53 (2H, m); 4.14 (2H, t, J=6.60 Hz); 3.92 (3H, s); 3.86 (2H, t, J=7.15 Hz); 3.28-3.19 (2H, m); 3.75 (3H, s); 1.84-1.78 (2H, m) 1.605 (3H, d, J=7.15 Hz). .sup.13C NMR (400 MHz, DMSO-d6) 173.84, 157.19, 148.73, 135.71, 133.34, 128.88, 126.99, 125.64, 118.75, 115.56, 111.79, 105.75, 62.10, 55.15, 48.14, 44.48, 37.55, 25.17, 18.13.

Example 15: DPX-2-0004 (sdnX9)

2-(pyridin-2-yl)ethyl 2-(6-methoxynaphthalen-2-yl)propanoate

(38) Using an Identical Procedure as Described for DPX-1-0001:

(39) 2-(pyridin-2-yl)ethanol (8.12 mmol, 1.00 g), Naproxen (8.93 mmol, 2.06 g), Dimethylaminopyridin (0.4 mmol, 50 mg), 1-Ethyl-3-(3-dimethylaminopropyl) carbodiimide-HCl (EDC-HCl) (12.18 mmol, 2.33 g), Acetonitrile (5 mL) and Dimethylformamide (3 mL). Crude yield: 4.3 g. The oil was purified by flash chromatography using ethyl acetate and heptanes as eluent to give a colorless oil. The pure oil was dissolved in diethyl ether (50 mL) and 2M HCl in diethyl ether (500 uL) was added. After drying under oil pump vacuum, white crystals precipitated. .sup.1H (CDCl.sub.3) 1.52 (d, 2H), 3.02 (t, 2H), 3.91-3.95 (m, 1H), 3.98 (s, 3H), 4.36-4.41 (m, 2H), 6.60 (d, 1H), 7.00-7.04 (m, 1H), 7.12-7.19 (m, 2H), 7.24-7.29 (m, 1H), 7.45 (dd, 1H), 7.60 (s, 1H), 7.16-7.20 (m, 2H), 8.46-8.49 (m, 1H). .sup.13C (CDCl.sub.3) 105.53, 118.86, 121.35, 123.32, 125.95, 126.19, 127.02, 128.88, 129.25, 133.63, 135.62, 136.03, 149.26, 157.60, 157.84, 174.39.

Example 16: DPX-2-0005 (JBX019)

2-(1H-benzo[d]imidazol-1-yl)ethyl 2-(6-methoxynaphthalen-2-yl)propanoate

(40) 1-Ethyl-3-(3-dimethylaminopropyl)carbodiimide-HCl (EDC-HCl) (2.20 g, 11.5 mmol) was added solid all at once to a magnetically stirred solution of naproxen (2.30 g, 10.0 mmol), 1-(2-hydroxyethyl)imidazole (1.12 g, 10.0 mmol) and 4-Dimethylaminopyridine (61 mg, 0.5 mmol) in dry tetrahydrofuran (50 mL) cooled in an ice bath and kept under nitrogen. The reaction mixture was stirred in an ice bath for 30 min and at ambient temperature. More EDC-HCl (400 mg, 2 mmol) was added after 13 hrs, 17 hrs. After stirring for 22 hrs at room temperature the mixture was concentrated and the residue partitioned between water (50 mL), saturated NH.sub.4Cl (20 mL) and EtOAc (120 mL). The organic layer was washed with 50% saturated NH.sub.4Cl (250 mL), 50% saturated NaHCO.sub.3 (50 mL) and brine (50 mL). The organic layer was dried and concentrated. The oily residue was purified by Flash Chromatography using ethyl acetate and heptanes as eluent afforded a colourless oil (2.74 g, 84%) after drying in high vacuum. The oil was crystallised from ether and recrystallised from Tert-butylmethylether (20 mL, seeded) to afford the title compound as a colourless solid (2.21 g, 68.3%). Mp. 60.6-61.3 C. .sup.1H NMR (400 MHz, DMSO) 7.80 (d, J=9.0 Hz, 1H), 7.77 (d, J=8.5 Hz, 1H), 7.68 (d, J=1 Hz, 1H), 7.51 (s, 1H), 7.33 (dt, J=5.5, 3 Hz, 1H), 7.30 (d, J=2.5 Hz, 1H), 7.17 (dd, J=9, 2.5 Hz, 1H), 6.98 (t, J=1 Hz, 1H), 6.78 (t, J=1 Hz, 1H), 4.34-4.12 (m, 4H), 3.92 (q, J=7 Hz, 1H), 3.88 (s, 3H), 1.45 (d, J=7 Hz, 3H). .sup.13C NMR (101 MHz, DMSO) 173.52, 157.19, 137.40, 135.30, 133.33, 129.15, 128.37, 128.25, 126.99, 126.20, 125.63, 119.46, 118.73, 105.69, 63.74, 55.15, 44.94, 44.35, 18.19.

Example 17: DPX-2-0006 (JBX017)

2-(1H-benzo[d]imidazol-1-yl)ethyl 2-(6-methoxynaphthalen-2-yl)propanoate

(41) 1-Ethyl-3-(3-dimethylaminopropyl)carbodiimide-HCl (EDC-HCl) (2.20 g, 11.5 mmol) was added solid all at once to a magnetically stirred solution of naproxen (2.30 g, 10.0 mmol), 2-(1H-benzo[d]imidazol-1-yl)ethanol (1.62 g, 10.0 mmol) and 4-Dimethylaminopyridine (68 mg, 0.5 mmol) in dry tetrahydronfuran (50 mL) cooled in an ice bath and kept under nitrogen. The reaction mixture (slurryEDC-HCl failed to dissolve) was stirred in an ice bath for 30 min and at ambient temperature. More EDC-HCl (400 mg, 2 mmol) was added after 3, 5 and 6 hours. After stirring for 48 hours the mixture was concentrated and the residue partitioned between water (50 mL), saturated NH.sub.4Cl (20 mL) and EtOAc (120 mL). The organic layer was washed with 50% saturated NH.sub.4Cl (250 mL), 50% saturated NaHCO.sub.3 (50 mL) and brine (50 mL). The organic layer was dried and concentrated. Flash Chromatography using ethyl acetate and heptanes as eluent afforded the title compound as a colourless solid (3.33 g, 88.8% yield). Mp. 125.0-125.7 C. .sup.1H NMR (400 MHz, DMSO) 8.09 (s, 1H), 7.75 (d, J=9.0 Hz, 1H), 7.71 (d, J=8.5 Hz, 1H), 7.69-7.63 (m, 1H), 7.61-7.54 (m, 2H), 7.28 (d, J=2.5 Hz, 1H), 7.26-7.18 (m, 3H), 7.16 (dd, J=9, 2.5 Hz, 1H), 4.58-4.32 (m, 4H), 3.87 (s, 3H), 3.83 (q, J=7 Hz, 1H), 1.37 (d, J=7 Hz, 3H). .sup.13C NMR (101 MHz, DMSO) 173.52, 157.18, 144.13, 143.29, 135.19, 133.83, 133.29, 129.13, 128.32, 126.93, 126.09, 125.58, 122.25, 121.46, 119.38, 118.69, 110.37, 105.67, 63.03, 55.15, 44.36, 43.10, 18.12. DEPT .sup.13C NMR (101 MHz, DMSO) 144.12, 129.13, 126.93, 126.09, 125.58, 122.25, 121.45, 119.37, 118.69, 110.36, 105.67, 63.03 (CH2), 55.14, 44.36, 43.10 (CH2), 18.12.

Example 18: DPX-2-0007 (JBX018)

2-(2-phenyl-1H-imidazol-1-yl)ethyl 2-(6-methoxynaphthalen-2-yl)propanoate

(42) 1-Ethyl-3-(3-dimethylaminopropyl)carbodiimide-HCl (EDC-HCl) (2.20 g, 11.5 mmol) was added solid all at once to a magnetically stirred solution of naproxen (2.30 g, 10.0 mmol), (1.88 g, 10.0 mmol) and 4-Dimethylaminopyridine (61 mg, 0.5 mmol) in dry tetrahydrofuran (50 mL) cooled in an ice bath and kept under nitrogen. The reaction mixture (slurryEDC-HCl failed to dissolve) was stirred in an ice bath for 30 min and at ambient temperature. More EDC-HCl (400 mg, 2 mmol) was added after 13 hrs and 17 hrs. After stirring for 22 hours at room temperature full conversion of naproxen was obtained. The mixture was concentrated and the residue partitioned between water (50 mL), saturated NH.sub.4Cl (20 mL) and EtOAc (120 mL). The organic layer was washed with 50% saturated NH.sub.4Cl (250 mL), 50% saturated NaHCO.sub.3 (50 mL) and brine (50 mL). The organic layer was dried and concentrated. Flash Chromatography using ethyl acetate and heptanes as eluent afforded the title compound as a pale yellow oil. .sup.1H NMR (400 MHz, DMSO) 7.77 (d, J=9.0 Hz, 1H), 7.74 (d, J=8.6 Hz, 1H), 7.61 (d, J=1.4 Hz, 1H), 7.58-7.51 (m, 2H), 7.45-7.38 (m, 3H), 7.29 (d, J=2.5 Hz, 1H), 7.24 (dd, J=8.5, 1.8 Hz, 1H), 7.19-7.13 (m, 2H), 6.90 (d, J=1.2 Hz, 1H), 4.37-4.20 (m, 4H), 3.86 (s, 3H), 3.77 (q, J=7.1 Hz, 1H), 1.36 (d, J=7.1 Hz, 3H).

(43) HCl-salt of DPX-2-0007: 571 mg of this oil was dissolved in a mixture of dry ether (20 mL) and dry tetrahydrofuran (10 mL) under nitrogen at 0 C. 2M HCl in ether (4 mL, 8 mmol) was added drop wise by syringe resulting in the formation a sticky gum. The solvent was decanted off and the gum was washed with dry ether (20 mL). The gum was dried in high vacuum and then crystallised by dissolving it in ethanol (2 mL) and slowly adding dry diethyl ether until no more solid formed. The free flowing solid was dried in vacuum to afford the title compound (452 mg) as an off white solid. Mp. 188.5-189.6 C. (ethanol/ether). .sup.1H NMR (400 MHz, DMSO) 15.29 (br s, 1H), 7.85 (d, J=2.0 Hz, 1H), 7.80-7.71 (m, 3H), 7.69-7.64 (m, 1H), 7.63-7.53 (m, 5H), 7.30 (d, J=2.5 Hz, 1H), 7.21-7.15 (m, 2H), 4.46-4.35 (m, 4H), 3.88 (s, 3H), 3.81 (q, J=7.0 Hz, 1H), 1.37 (d, J=7.0 Hz, 3H). .sup.13C NMR (101 MHz, DMSO) 173.46, 157.20, 144.42, 135.15, 133.30, 131.88, 129.71, 129.15, 129.06, 128.32, 127.06, 125.81, 125.55, 122.90, 122.34, 119.58, 118.82, 105.77, 62.28, 55.18, 46.50, 44.11, 18.15. DEPT .sup.13C NMR (101 MHz, DMSO) 131.88, 129.71, 129.15, 129.06, 127.06, 125.82, 125.56, 122.90, 119.59, 118.82, 105.77, 62.28 (CH2), 55.18, 46.50 (CH2), 44.11, 18.15.

Example 19Dissolution of Prodrug in Synovial Fluid Followed by Formation of the Active Agent

(44) The stability of a suspension of a prodrug according to the invention in 80% human synovial fluid pH 7.4 (SF) from arthritis patients can be investigated at 37 C. The reaction is initiated by adding 5 ml preheated SF to 2 mg prodrug. At appropriate time intervals, 400 l samples are taken and centrifuged for 5 min at 13.000 rpm and 200 l of the supernatant is deproteinised with 400 l acetonitrile. After centrifugation for 4 min at 13000 rpm, the supernatant is analysed by HPLC for prodrug as well as formed drug.

Example 20Preliminary Precipitation Experiment, No Esterases Present

(45) A concentrated solution of a prodrug according to the invention in 0.01 M HCl is prepared by adding 0.2 ml of 110.sup.5M methanol solution of DPX-4-0001 to 1.0 ml 0.01 M HCl resulting in a final concentration of 1.710.sup.4M. After addition of 300 l of this solution (0.02 mg) to 5 ml 67 mM phosphate buffer pH 7.4, a precipitation process is expected. At appropriate time intervals, samples are withdrawn and centrifuged for 5 min at 13.000 rpm and the supernatant is analysed by HPLC for prodrug and formed drug.

Example 21Solubility of DPX-2-0007 (JBX018) at pH 3.4 and Precipitation in Buffer pH 7.4

(46) A suspension of DPX-2-0007 (as hydrochloride salt) was formed by adding 30 mg to 4 mL demineralized water. After rotation of the suspension at 37 C. for 3 days, 1.0 mL sample was taken and after filtration (disposable syringe filters), the solution was diluted in methanol:water 1:1 and analyzed immediately by HPLC for prodrug. Quantitation of DPX-2-0007 was done from peak area measurements in relations to those of standards analysed by HPLC at the same conditions. The pH in the solution was measured to 3.40. The following HPLC method was used: Merck Hitachi L 6200 pump connected to Merck Hitachi 4250 UV detector. Reversed phase chromatography was performed using a RP 18 Symmetry Shields column (1504.6 mm, 5 m particles) equipped with a SecurityGuard precolumn (Phenomenex, Torrance, Calif., USA). The flow rate was set at 1 mL/min and the column effluent was monitored at 230 nm. The mobile phase consisted of 35% (v/v) acetonitrile and 65% (v/v) of 0.1% (v/v) phosphoric acid pH 3.2. The retention time of naproxen and DPX-2-0007 were 19 and 5.8 min, respectively.

(47) The solubility of DPX-2-0007 at pH 3.4 was determined to 6.80.6 mg/mL. Thus, a 1000-fold increase in the solubility compared to the solubility of DPX-2-0007 in buffer pH 7.4 (PBSsee Table 1).

(48) TABLE-US-00001 TABLE 1 Solubilities of the prodrugs (S.sub.prodrug) in PBS (67 mM phosphate buffer pH 7.4), the apparent pseudo-zero-order rate constant (k.sub.0) and the estimated pseudo first-order rate constant (k.sub.hyd) for cleavage of the prodrugs in PBS and half-lives (t.sub.1/2) for hydrolysis of the prodrugs in 80% human plasma at 37 C. S.sub.prodrug SD k.sub.0 k.sub.hyd t.sub.1/2 in PBS t.sub.1/2 in plasma Prodrug g/mL mM M/day day.sup.1 day min DPX-1-0001 0.01 2 10.sup.5 DPX-1-0002 <0.1 <0.0002 DPX-1-0004 3 1 0.007 0.001 1.1 10.sup.6 1.5 10.sup.1 5 25 DPX-1-0005 1 0.003 DPX-1-0006 7 2 0.015 0.004 2.4 10.sup.6 1.7 10.sup.1 4 3 DPX-1-0007 43 2 0.086 0.003 2.5 10.sup.7 2.9 10.sup.3 242 49 DPX-1-0008 0.3 0.0007 DPX-1-0009 <0.3 <0.0007 DPX-1-0010 <0.4 <0.0008 DPX-1-0011 0.1 0.0002 DPX-1-0012 <0.3 <0.0006 DPX-2-0001 <0.3 <0.0008 DPX-2-0002 <0.2 <0.0006 DPX-2-0003 <1 <0.003 DPX-2-0004 19 1 0.052 0.002 1.7 10.sup.6 3.3 10.sup.2 21 287 DPX-2-0005 146 5 0.45 0.02 64 DPX-2-0006 5 1 0.015 0.002 1.0 10.sup.6 6.6 10.sup.2 11 511 DPX-2-0007 7 1 0.016 0.001 1.0 10.sup.6 6.5 10.sup.2 11 62

(49) Upon addition of 1.0 mL of the concentrated aqueous solution of DPX-2-0007 at pH 3.4 to 1.0 mL 67 mM phosphate buffer pH 7.4, a precipitation was immediately observed. The pH in the suspension was measured to 7.0.

Example 22Solubility of DPX-2-0006 at pH 3 in the Presence of N,N-dimethyl acetamide (DMA)

(50) A suspension of DPX-2-0006 was formed by adding 10 mg to 3 mL demineralized water, 0.05 mL 0.100 M HCl was added to obtain a pH of 3. After rotation of the suspension at 37 C. for 1 days, 0.5 mL sample was taken and after filtration (disposable syringe filters), the solution was diluted in methanol:water 1:1 and analyzed immediately by HPLC for prodrug. Quantitation of DPX-2-0006 was done from peak area measurements in relations to those of standards analysed by HPLC at the same conditions. The HPLC method described in Example 29 was applied and the retention time of DPX-2-0006 was 14 min, respectively. N,N-dimethylacetamide (DMA) was added stepwise to the acidic suspension of DPX-2-0006 and the amount of DPX-2-0006 dissolved in the presence of various volumes of DMA was determined after 1-3 days rotation at 37 C. as described above.

(51) The solubility of DPX-2-0006 at pH 2.9 was 0.18 mg/ml. In the presence of 5%, 15%, 30% and 50% (v/v) DMA, the solubility was increased to 0.25, 0.35, 0.57 and 2.25 mg/ml, respectively.

Example 23Determination of Solubilities and Stabilities of the Prodrugs in Buffer pH 7.4

(52) Suspensions of the prodrugs in 67 mM phosphate buffer pH 7.4 (PBS) were prepared by adding 10 mL PBS to approximately 5 mg prodrug. The suspensions were kept unstirred at 37 C. in an incubator hood. At appropriate time intervals over 23 days, about 500 L samples were taken and after filtration (disposable syringe filters), the solutions were analyzed immediately by HPLC for parent drug and remaining prodrug. Quantitation of parent drug and prodrug was done from peak area measurements in relations to those of standards analysed by HPLC at the same conditions. For the naproxen prodrug, the HPLC method described in example 29 were applied. For the diclofenac and ibuprofen prodrugs, the following method was used: Merck Hitachi L 6000 pump connected to Merck Hitachi 4250 UV detector. Reversed phase chromatography was performed using a C18 Gemini RP column (1504.6 mm, 5 m particles) (Phenomenex, Torrance, Calif., USA) equipped with a SecurityGuard precolumn (Phenomenex, Torrance, Calif., USA). The flow rate was set at 1 mL/min and the column effluent was monitored at 230 nm. The mobile phase consisted of 35% (v/v) acetonitrile and 65% (v/v) of 0.1% (v/v) phosphoric acid pH 3.2. The retention times varied in the range of 3 to 30 min.

(53) From the observed relatively stable concentration of dissolved prodrugs measured in the suspensions after 8-9 day up to 23 days, the solubilities of the prodrugs (S.sub.prodrug) were determined. In this time interval, the rate of appearance of parent drug was determined and an apparent pseudo-zero-order rate constant (k.sub.0) was obtained. By assuming that the dissolution rates were much faster than the conversion of the prodrugs to the parent drug, pseudo first-order rate constants (k.sub.hyd) for cleavage of the prodrugs were calculated according to:

(54) $-\frac{d\left[\mathrm{Prodrug}\right]}{dt}=\frac{d\left[\mathrm{Drug}\right]}{dt}=k_{\mathrm{hyd}}{S}_{\mathrm{prodrug}}=k_0$

(55) All data are summarized in Table 1.

Example 24Hydrolysis of the Prodrugs in 80% Human Plasma

(56) At 370.5 C., the hydrolysis rate of the prodrugs was measured in 80% human plasma. An appropriate aliquot (20-100 L) of 1 mg/ml prodrug solution in methanol was transferred to 5.0 ml of preheated plasma. At appropriate time intervals, 300 l sample aliquots were withdrawn and transferred to 600 l acetonitrile and mixed thoroughly. After centrifugation at 13500 rpm for 5 min, the supernatant was analyzed by HPLC for parent drug and remaining prodrug. The HPLC methods described in Example 29 and 31 were applied.

(57) The half-lives for cleavage of the prodrugs in 80% human plasma were in the range 3-755 min (DPX-3-0006 remained intact after incubation in plasma for 10 h).

REFERENCES

(58) Ref. 1: Reuben et al. Reuben S. S., Connelly N. R. (1995) Postoperative analgesia for outpatient arthroscopic knee surgery with intraarticular bupivacaine and ketorolac. Anesth Analg 80: 1154-1157 Ref. 2: Rasmussen et al. Rasmussen S., Larsen A. S., Thomsen S. T., Kehlet H. (1998) Intra-articular glucocorticoid, bupivacaine and morphine reduces pain, inflammatory response and convalescence after arthroscopic meniscectomy. Pain 78: 131-134 Ref. 3: R. Williams pKa Data Compiled by R. Williams (downloadable from http://research.chem.psu.edu/brpgroup/pKa_compilation.pdf) Ref. 4: Caballero et al. Caballero et al. (2006) Theoretical prediction of relative and absolute pKa values of aminopyridines, Biophysical Chemistry 124(2), p 155-160 (Ref. 3). Ref. 5: Drustrup et al. Drustrup et al. (1991) Utilization of prodrugs to enhance the transdermal absorption of morphine, International Journal of Pharmaceutics 71, 105-116