) BACKGROUND OF THE INVENTION It is well-known that the non-ionized form of a drug molecule is absorbed more efficiently than its ionized form. Non-steroidal anti-inflammatory carboxylic acids are significantly ionized and thus hydrophilic in their chemical character at physiological pH. In case of a charged drug molecule, the positively charged drug molecule is more permeable across the negatively charged skin-membrane than the negatively charged drug molecule. Thus the non-steroidal anti-inflammatory carboxylic acids have poor permeation across biological lipid-water membranes, especially across the skin. This limits their pharmaceutical use, especially their topical administration.

Acidic NSAIDs are irritating to the mucous membrane of the gastro-intestinal (GI) tract Topical (i. e. dermal) application of NSAIDs would eliminate the irritation to the GI tract and harmful systemic side-effects due to high systemic drug concentrations after orai administration. In addition, topical application would be more suitable for treatment of local inflammatory and pain conditions due to higher local drug concentration.

Unfortunately, the non-steroidal anti-inflammatory carboxylic acids do not readily pass through skin due to the reasons mentioned above.

A promising approach to eliminate the drawbacks due to the carboxylic acid group of the drug molecule is to prepare ester-prodrugs. Prodrugs are pharmacologically inactive derivatives of drug molecules that require a chemical or favorably enzymatic transformation in order to release the active drug within the body. Thus, the object of the present invention is to design and prepare novel bioreversible prodrugs of NSAIDs containing at least one carboxylic acid group, which are chemically stable in a non- enzyme medium, have suitable aqueous and lipid solubility (able to permeate through the biological membranes, especially through the skin), are not significantly ionized or are positively charged at physiological pH and readily hydrolyze to the parent drug after or during skin permeation in vivo. The present novel aminoacyloxyalkyl double-esters of NSAIDs fulfill the above-mentioned desirable attributes.

Numerous derivatives of non-steroidal anti-inflammatory carboxylic acids have been reported but only a limited number of the reported derivatives are bioreversible prodrugs of NSAIDs. Sloan (US 4,206,220) disclosed various amide-prodrugs of NSAIDs, Ladkani et al. (EP 0 112 130 Bl) disclosed ethoxycarbonyloxy ethyl ester prodrugs of NSAIDs, Bundgaard (EP 0 278 977 Bl) disclosed NSAIDs esters of various hydroxy- amides and Sloan and Roy (EP 0 039 051 A2) disclosed Mannich-base hydroxamic acid prodrugs of NSAIDs. In addition, various prodrugs of NSAIDs, but not aminoacyloxyalkyl double-esters, are described in the following publications : Pharm Res 6: 867-873,1989; Pharm Res 10: 1191-1199,1993; J Pharm Sci 81: 149-154,1992; Biopharm Drug Disposit 16: 201-210,1995; Pharmazie 51: 30-33,1996; In t J Pharm 124: 45-51,1995; Int J Pharm 77 : 21-29,1991; J Control Rel 34: 223-232,1995; J Pharm Sci 83: 1578-1581,1994; Pharm Res 9: 492-496,1992; Pharmazie 49: 422-424, 1994.

DETAILED DESCRIPTION OF THE INVENTION The present invention concerns novel bioreversible aminoacyloxyalkyl prodrugs of non- steroidal anti-inflammatory carboxylic acids of the formula R-COO-R,-O-R2 (I)

wherein: R-COO-represents the acyloxy residue of a carboxylic acid group containing non- steroidal anti-inflammatory agent, i. e. of a non-steroidal anti-inflammatory carboxylic acid R-COOH, Rl represents a saturated or unsaturated, straight-chain, branched or cyclic alkylene or alkylidene group of 1 to 8 carbon atoms, which can optionally be substituted with 1 to 3 groups selected from halogen, hydroxyl, thiol, amino, mono-or dialkylamino, acylamino, carboxyl, alkylcarboxyl, acyl, aryl, aroyl, aralkyl, cyano, nitro, alkoxy, alkenyloxy, alkylcarbonyloxy and arylcarbonyloxy, R2 is an aminoacyl residue of a synthetic or natural amino acid of the formula wherein R3 represents a saturated or unsaturated, straight-chain or branched alkylene or alkylidene group of 1 to 8 carbon atoms, which may be substituted with 1 to 3 groups selected from amino, mono-or dialkylamino, acylamino, hydroxyl, thiol, methylthiol, carboxyl, and phenyl, or R2 is a secondary or tertiary aminoacyl group of the formula wherein R3 is as hereinabove defined; R4 and R5 are the same or different and are selected from hydrogen, a straight-chain or branched C,-C6-alkyl group, which is optionally substituted with 1 to 3 groups selected from halogen, hydroxyl, thiol, amino, mono-or dialkyamino, acylamino, carboxyl, alkylcarboxyl, acyl, aryl, aroyl, aralkyl, cyano, nitro, alkoxy, alkenyloxy, alkylcarbonyloxy and arylcarbonyloxy, or R4 and RsX together with the nitrogen, form a cyclic heteroalkyl radical or a heteroaryl radical, or R2 is a quaternary aminoacyl group of the formula

wherein R3 is as hereinabove defined and R7, Rs and Rg are the same or different and are selected from hydrogen, a straight-chain or branched Cl-C6-alkyl group, which optionally is substituted with 1 to 3 groups selected from halogen, hydroxyl, thiol, amino, mono-or dialkyamino, acylamino, carboxyl, alkylcarboxyl, acyl, aryl, aroyl, aralkyl, cyan, nitro, alkoxy, alkenyloxy, alkylcarbonyloxy and arylcarbonyloxy, as well as the nontoxic pharmaceutically acceptable acid addition salts thereof.

According to the invention, the non-steroidal anti-inflammatory agent comprising at least one carboxylic acid group is preferably selected from the group consisting of : naproxen; ketoprofen; ibuprofen; fenoprofen; flurbiprofen; oxaprofen; diclofenac; tolmetin; tolfenamic acid; mefenamic acid; sulindac; indomethacin; salicylic acid; acetylsalicylic acid; diflunisal; loxoprofen; indoprofen; pirprofen; clidanac; fenclorac; meclofenamate; benoxaprofen; carprofen; isofezolac; aceclofenac; fenbufen; etodolic acid; fleclozic acid; amfenac; efenamic acid; bromfenac; fenclofenac; alcofenac; orpanoxin; zomopirac; flufenamic acid; niflumic acid; pranoprofen; zaltoprofen; suprofen; and ketorolac.

Specific examples of R, as a lower alkylene group include methylene, ethylene, trimethylene, tetramethylene, R2 is advantageously the aminoacyl residue of alanine, glycine, glycylglycine, arginine, cysteine, isoleucine, leucine, lysine, methionine, phenylalanine, proline, hydroxyproline, serine, valine, tryptophan, tyrosine, threonine, ornithine, a-aminobutyric acid, norvaline, or norleucine.

Unless otherwise specified, the various groups and radicals mentioned above and below

have the following meaning.

Alkyl or alkenyl as such or as part of another goup, such as in mono-and dialkylamino, alkylcarbonyl, aralkyl, acyl, alkoxy, alkenyloxy, and alkylcarbonyloxy, means a group containing 1-6 carbon atoms, preferably 1-4 carbon atoms.

Halogen means iodine, fluorine, bromine or chlorine.

Aryl as such or in aroyl and aralkyl means an aromatic group containing up to 10 carbon atoms, and is preferably phenyl or naphtyl, which can be substituted with 1 to 3 substituents selected from lower alkyl with 1 to 4 carbon atoms, hydroxy, halogen, nitro or amino.

Acyl as such or in acylamino is an aliphatic acyl group containing an alkyl or alkenyl group as defined.

The cycloheteroalkyl radical formed from R4 and Rs is preferably morpholinyl, thiomorpholinyl, 1-pyrrolidinyl, piperidinyl, piperazinyl or 4-alkyl-1-piperazinyl, such as 4-lower alkyl-1-piperazinyl, e. g. 4-methyl-1-piperazinyl. A heteroaryl radical is preferably imidazolyl, indoxyl, indolizinyl, oxazolyl, thiazolyl or 1-pyrazolyl.

The novel compounds of the invention can be prepared in the following manner. In a first step, the carboxyl function of a non-steroidal anti-inflammatory agent R-COOH or its acid salt R-COO-M'is esterified, under SN2 conditions, with a compound X-RI-OH to yield the intermediate II, e. g. according to the following reaction scheme: R-COO-M'+ X-R,-OH-----> R-COO-R,-OH + X-M+ II wherein X is a suitable leaving group, e. g., chlorine, tosylate, iodine etc., preferably bromine and Ri is as above defined. Suitable acid salts are the alkaline metal and amine salts, for example, lithium, sodium, potassium, tetrabutylammonium and triethylammonium salts. In the present invention the sodium salt is preferred. The

reaction is ordinarily carried out in a dipolar aprotic solvent which does not take part in the reaction, preferably in dimethylformamide or hexamethylphosphoric triamide.

A second method for preparing the intermediate II comprises reacting an acid R-COOH or a reactive derivative of the acid, such as a halide, an anhydride or a mixed anhydride of the formula R-COZ, wherein Z means the activating group, such as a halide or anhydride residue, with a compound HO-RI-OH, wherein Rl is as above defined, according to the following reaction scheme: R-COZ + HO-R,-OH----> R-COO-R,-OH + HZ II The most useful reactive derivative is the acid chloride (Z=C1), which can be prepared from the corresponding acid by reaction with thionyl chloride or oxalyl chloride. The reaction is ordinarily carried out in the presence of an acid eliminator, such as a tertiary amine, for example pyridine, trimethylamine, triethylamine etc, an alkali carbonate, an alkali hydroxide, a metal hydride or the like, usually in a suitable solvent which does not take part in the reaction and which includes, for example, ether, tetrahydrofuran, benzene, toluene, chloroform, dichloromethane and the like.

When using a free acid as the starting material the reaction must be carried out in the presence of a condensing agent, such as a carbodiimide, e. g. N, N- dicyclohexylcarbodiimide. The reaction utilizing an acid starting material is conveniently carried out in an inert solvent, such as dichloromethane, ethyl acetate, tetrahydrofuran or the like. A catalyst, such as p-toluenesulphonic acid or 4- (N, N- dimethylamino) pyridine, may be added. Alternatively, the condensing agent can be a 2- halo-1-alkylpyridinium salt, or a combination of diethylazodicarboxylate and triphenylphosphine.

In a second step the intermediate II is reacted in the presence of condensing agent with a protected primary or secondary amino acid of the formula

wherein R3 and R4 are as hereinabove defined and P is a protecting group, for example t-butyloxycarbonyl (Boc), or with a tertiary amino acid of the formula, wherein R3, R4 and R5 are as hereinabove defined, or with a quaternary amino acid of the formula: wherein R3, R7, Rs and Rg are as hereinabove defined.

The primary and secondary amine functions of the amino acids must be protected e. g. with a t-butyloxycarbonyl (Boc) protective group. The Boc-protective group is removed by protonation with an anhydrous acid, HY, such as p-toluenesulphonic acid, HCI, or trifluoroacetic acid in ethyl acetate, in dichloromethane, tetrahydrofuran or any other common reagent for removing the Boc-protective group in amino acid chemistry, to give the salt III of the compound according to the following scheme: In case R, is a substituted or unsubstituted methylene group (-CHR'-or-CH2-), these compounds can be prepared by condensing an acid salt of a Boc-protected amino acid V with a halide ester VI of a non-steroidal anti-inflammatory agent and removing the Boc-protective group by protonation with an anhydrous acid, HY, according to

following scheme: In the above formulae, R'has the meaning of hydrogen, a straight or branched alkyl group, preferably an optionally substituted lower alkyl group with 1-6 C-atoms as defined for R4 and R5, or an optionally substituted aryl or aralkyl group, as defined above, and Z the meaning of a halide, preferably the chloride, but can also be the bromide or iodide. Suitable acid salts (compound V) are the alkaline metal and amine salts, for example, lithium, sodium, potassium, tetrabutylammonium and triethylammonium salts.

The halide ester VI can be prepared by the reaction of an acid halide R-COZ where Z is preferably the chloride, but can also be the bromide or iodide, with an aliphatic aldehyde VII by heating the reagents together in the presence of anhydrous zinc chloride according to the following scheme: The novel prodrugs according to the invention may be used to treat any condition for which the parent carboxy containing NSAID is useful. The prodrug according to the invention can be administered for example orally, parenterally, topically or rectally by means of any pharmaceutical formulation useful for said administration, and containing the said prodrug in pharmaceutically acceptable amounts together with pharmaceutically acceptable carriers, adjuvants or vehicles known in the art. The manufacture of such pharmaceutical formulations is well known in the art.

Thus the pharmaceutical composition may be in a dosage form suitable for oral use, such as tablets, capsules, liquid dosage forms, such as suspensions, emulsions, syrups etc. All such formulations are made using per se known formulation techniques and carriers, adjuvants and additives. The prodrugs according to the invention may also be administered parenterally, for example using aqueous or oily suspensions, emulsions, or dispersions containing the active agent in combination with conventional pharmaceutically acceptable excipients. Formulations for rectal use are e. g. suppositories containing the active prodrug in combination with carrier subtstances suitable for rectal use.

Especially contemplated within the invention is the topical administration of the prodrug, for which administration form creams, ointments, jellies, solutions, suspensions or the like are useful which contain a pharmacologically active amount of the said prodrug together with a per se known pharmaceutically acceptable carrier or vehicle.

The therapeutic dose to be given to a patient in need of treatment will vary depending i. a. on the body weight and age of the patient, the particular condition being treated. as well as the manner of administration and are easily determined by a person skilled in the art. Typically a dosage or concentration similar to or less than that of the parent drug would be acceptable. Generally a concentration of 0.01% to 5% of active agent in a suitable carrier would be sufficient for topical use, whereas a dosage form for oral use of 0.1 mg to 5 g, typically 0.1 mg to 500 mg would be suitable for most purposes.

The following examples illustrate the invention without limiting the same in any way.

Example 1 2-(glycyloxy) ethyl 2-(6-methoxy-2-naphthyl)(glycyloxy) ethyl 2-(6-methoxy-2-naphthyl) propanoate (Ri =-CH2CH2- ; R2 =-COCH2-NH2) a) 2-hydroxyethyl 2- (6-methoxy-2-naphthyl) propanoate A mixture of 2- (6-methoxy-2-naphthyl) propanoate sodium salt (900 mg, 3.6 mmol) and 2-bromoethanol (445 mg, 3.6 mmol) in dry N, N-dimethylformamide (20 mL) was stirred at 60 °C for 24 h. Water (50 mL) was added to the reaction mixture and the mixture was extracted with ethyl acetate (2 x 50 mL). The combined extracts were washed with a 5% aqueous solution of NaHC03 (2 x 25 mL) and water (2 x 25 mL), dried over anhydrous CaS04, filtered and evaporated in vacuo to give the desired compound (0.8 g, 82%). b) 2-(glycyloxy) ethyl 2-(6-methoxy-2-naphthyl) propanoate A mixture of 2-hydroxyethyl 2- (6-methoxy-2-naphthyl) propanoate, (1.1 g, 4.2 mmol), Boc-glycine (730 mg, 4.2 mmol), 4- (N, N-dimethylamino) pyridine (25 mg, 0.2 mmol) and N, N'-dicyclohexylcarbodiimide (1.13 g, 5.5 mmol) in dry dichloromethane (60 mL) was stirred at 60 °C for 24 h. The precipitated dicyclohexylurea was filtered off and the filter cake was washed with dichloromethane. The filtrate was evaporated, and the residue was treated with trifluoroacetic acid: dichloromethane (1: 1,14 mL) at 25 °C for 3 h followed by concentration under vacuum. The free base was generated by dissolving the residue in a 5% aqueous solution of NaHCO3 (2 x 25 mL) and extracting the free amine using ethyl acetate (2 x 50 mL). The organic layer was dried over anhydrous CaS04, filtered and evaporated in vacuo. The residue obtained was dissolved in diethyl ether and treated with saturated diethyl ether-HCI to give 2-(glycyloxy) ethyl 2-(6- methoxy-2-naphthyl) propanoate hydrochloride salt (1.20 g, 78 %): mp 113-4 °C ; 1H NMR (CDC13/CD30D 8: 2,400 MHz): 8 7.65,7.37,7.71,7.12,7.13,7.69,3.90,3.87, 1.57,4.30,3.66.

Example 2 2- (L-leucyloxy) ethyl 2- (6-methoxy-2-naphthyl) propanoate (R1-CH2CH2- R2=-COCH CH2CH (CH3) 2-NH2) The compound was prepared as described in the example 1 from 2-hydroxyethyl 2- (6- methoxy-2-naphthyl) propanoate (1. 1 g, 4.2 mmol) and Boc-L-leucine (0.9 g, 4.2 mmol).

Obtained as HCI salt (0.99 g, 56%); mp. 96-7 °C. tH NMR (CDCI3/CD30D 8: 2,400 MHz): 8 7.64,7.38,7.72,7.16,7.12,7.69,3.88,3.90,1.57,4.39/4.33*, 4.41,3.88,1.65, 1.71,0.89,0.88 (*due to the chiral center, the CH2 protons are not equivalent); HR-MS: Calculated mass for C22H29NO5: 387.205. Measured mass: 387.207.

Example 3 2- (Irisoleucyloxy) ethyl 2- (6-methoxy-2-naphthyl) propanoate (RI =-CH2CH2- R2 =-COCHlCH (CH3) CH2CH3-NH2) The compound was prepared as described in the example 1 from 2-hydroxyethyl 2- (6- methoxy-2-naphthyl) propanoate (0.7 g, 2.5 mmol) and Boc-L-isoleucine (0.6 g, 2.5 mmol). Obtained as HCl salt (0.95 g, 90%); mp 99-100 °C.'H NMR (CDC13,400 MHz): 8 7.65,7.38,7.72,7.14,7.15,7.70,3.91,3.88,1.58,4.49/4.30*, 4.33,3.84,1.90, 37/1.20*, 0.84,8.52 (*due the to chiral center, the CH2 protons are not equivalent); HR-MS: Calculated mass for C22H29NO5: 387.205. Measured mass: 387.201.

Example 4 2- (L-phenylalanyloxy) ethyl 2- (6-methoxy-2-naphthyl) propanoate (Ri =-CH2CH2-; =-COCH CH2C6H5J-NH2) The compound was prepared as described in the example 1 from 2-hydroxyethyl 2- (6- methoxy-2-naphthyl) propanoate (0.8 g, 2.9 mmol) and Boc-L-phenylalanine (0.8 g, 2.9 mmol). Obtained as HCl salt (370 mg, 28%); mp. 187-8 °C.'H NMR (CDCI3/CD30D 8: 2,400 MHz): 8 7.63,7.37,7.67,7.05,7.10,7.64,3.88,3.88,1.58,4.39/4.29*, 4.26, 4.09,3.03,7.11,7.28 (*due to the chiral center, the CH2 protons are not equivalent); HR-MS: Calculated mass for C25H27NO5: 421.189. Measured mass: 421.200.

Example 5 3- (glycyloxy) propyl 2- (6-methoxy-2-naphthyl) propanoate (Rl =-CH2CH2CH2- ; R2 =-COCH2-NH2) a) 3-hydroxypropyl 2- (6-methoxy-2-naphthyl) propanoate The compound was prepared as described in the example 1 from the sodium salt of 2- (6- methoxy-2-naphthyl) propanoate (900 mg, 3.6 mmol) and 3-bromo-1-propanol (500 mg, 3.6 mmol) to give the desired compound (0.50 g, 48%).

b) 3- (glycyloxy) propyl 2- (6-methoxy-2-naphthyl) propanoate Obtained as free amine (0.60 g, 72 %) from 3-hydroxypropyl 2- (6-methoxy-2-naphthyl) propanoate (0.70 g, 2.4 mmol) and Boc-glycine (0.40 g, 2.4 mmol).'H NMR (CDCl3, 400 MHz): 5 7.60,7.32,7.65,7.07,7.10,7.65,3.85,3.81,1.52,4.07,1.86,4.11, 3.73, 8.15. HR-MS: Calculated mass for C19H23NO5 345.158. Measured mass: 345.165.

Example 6 4- (L-isoleucyloxy) butyl 2- (6-methoxy-2-naphthyl) propanoate (Rl =-CH2CH2CH2CH2- R2=-COCHlCH (CH3) CH2CH3-NH2) a) 4-hydroxybutyl 2- (6-methoxy-2-naphthyl) propanoate The compound was prepared as described in the example 1 from the sodium salt of 2- (6- methoxy-2-naphthyl) propanoate (900 mg, 3.6 mmol) and 4-bromo-1-butanol (500 mg, 3.6 mmol) to give the desired compound (0.12 g, 22%). b) 4- (L-isoleucyloxy) butyl 2- (6-methoxy-2-naphthyl) propanoate 4-hydroxybutyl 2- (6-methoxy-2-naphthyl) propanoate (0.83 g, 2.7 mmol) and Boc-L- isoleucine (0.63 g, 2.7 mmol) 4- (N, N-dimethylamino) pyridine (0.49 mg, 4.0 mmol) and N, N'-dicyclohexylcarbodiimide (0.83 g, 4.0 mmol) in dry dichloromethane (60 mL) was stirred at room temperature for 36 h. The precipitated dicyclohexylurea was filtered off and the filter cake was washed with dichloromethane. The filtrate was evaporated and the residue was purified by flash silica gel column chromatography eluting with 20% ethyl acetate in petroleum ether to give Boc-protected 4- (L-isoleucyloxy) butyl ester of naproxen (0.96 g, 69 %) as an oil. The Boc-protected ester (420 mg, 0.81 mmol) was treated with 2 N HCI/ethyl acetate (8 mL) and stirred at room temperature for 3h followed by concentration under vacuum. The residue was recrystallized from ethyl acetate to give 4-(L-isoleucyloxy) butyl 2-(6-methoxy-2-naphthyl) propanoate hydrochloride salt (340 mg, 92 %): mp 72-3 °C.'H NMR (CDC13,400 MHz): 5 7.64, 7.38,7.69,7.10,7.13,7.69,3.84,3.90,1.56,4.07,1.62,4.12,3.96, 2.15,1.06, 1.41/1.46*, 0,91,8.82 (*due to the chiral center, the CH2 protons are not equivalent); HR-MS: Calculated mass for C24H33NO5: 415.236. Measured mass: 415.222.

Example 7 4- (L-phenylalanyloxy) butyl 2- (6-methoxy-2-naphthyl) propanoate (Rl-CH2CH2CH2CH2- R2 =-COCH CH2C. H. 1-NH2 Obtained as the free amine from 4-hydroxybutyl 2-(6-methoxy-2-naphthyl) propanoate (0.5 g, 1.7 mmol) and Boc-L-phenylalanine (0.45 g, 1.7 mmol) according to the method described in the example 1. The free amine was purified by flash silica gel column chromatography (30 mL/20 mm column) eluting with 20 % methanol in ethyl acetate to afford 4- (L-phenylalanyloxy) butyl 2- (6-methoxy-2-naphthyl) propanoate (220 mg, 41%).'H NMR (CDCI3,400 MHz): b 7.66,7.40,7.70,7.10,7.13,7.70,3.90,3.84, 1.58,4.01,1.54,4.06,3.68,3.01/2.83*, 7.16,7.27,7.22; (*due to the chiral center, the CH2 protons are not equivalent); HR-MS: Calculated mass for C27H31NO5: 449.220.

Measured mass: 449.225.

Example 8 1-(glycyloxy) ethyl 2-(6-methoxy-2-naphthyl)(glycyloxy) ethyl 2-(6-methoxy-2-naphthyl) propanoate (Rl =-CH (CH3)- ; R2 =-COCH2-NH2) a) 1-chloroethyl 2- (6-methoxy-2-naphthyl) propanoate To a cooled (0-5 °C) mixture of acetaldehyde (3 mL), anhydrous ZnC12 (200 mg) in dry dioxane (10 mL) naproxen acid chloride (2.56 g, 10.3 mmol) was added dropwise over period of lh. After complete addition, the bath was removed, the contents was allowed to warm to room temperature and the reaction mixture was stirred for 16 hours. The mixture was extracted with diethyl ether and washed with a 5% NaHC03-solution and water. Purification with flash silica gel column eluting with 20% ethyl acetate in petroleum ether afforded 1-chloroethyl 2- (6-methoxy-2-naphthyl) propanoate as a yellow oil (1.49 g, 51%).'H NMR (CDCl3): 8 7.8-7.1,6.5,3.9,3.9,1.7,1.6. b) 1- (glycyloxy) ethyl 2- (6-methoxy-2-naphthyl) propanoate Boc-glycine (0.79 g, 4.5 mmol) was dissolved in a NaOH solution (190 mg, 4.5 mmol) and evaporated and dried in vacuo to afford the sodium salt of Boc-glycine. The sodium salt was dissolved in 10 mL of N, N-dimethylformamide and allowed to react with 1- chloroethyl 2- (6-methoxy-2-naphthyl) propanoate (1.31 g, 4.5 mmol) and potassium iodide (0.80 g, 5.3 mmol). The mixture was stirred at room temperature for 24 h and

the N, N-dimethylformamide was removed in vacuo. The residue was taken up in chloroform and washed with a 5% NaHCO3-solution and then twice with saturated aqueous NaCI-solution, dried over MgSO4 and evaporated. The residue was chromatographed (flash silica gel, 1: 2 ethyl acetate: petroleum ether) to give the Boc- protected 1- (glycyloxy) ethyl ester of naproxen (410 mg, 0.93 mmol, 21%) as a viscous oil. The Boc-protected ester (400 mg) was dissolved in dioxane (5 mL) and 4 N HCl/dioxane (4 mL) was added and solution was stirred at room temperature for 4 hours followed by concentration under vacuum. The residue was recrystallized from dioxane to give the 1- (glycyloxy) ethyl 2- (6-methoxy-2-naphthyl) propanoate hydrochloride salt (220 mg, 64 %): mp 149-50 °C. IH NMR (CD30D, 400 MHz): 5 7.71,7.36,7.74,7.20, 7.13,7.74,3.90,3.91,1.55,6.95/6.98*, 1.51/1.42,3.74/3.67; (*two diastereomers, ratio 1: 1); HR-MS: Calculated mass for CIsH21NO5: 331.142. Measured mass: 331.135.

Example 9 1- (L-phenylalanyloxy) ethyl 2- (6-methoxy-2-naphthyl) pro pan oate (Rl =-CH (CH3)- R2 =-COCHtCH2C6Hsl-NH2) Synthesized analogously to the example 8 from naproxen acid chloride (5.1 mmol) and acetaldehyde to yield 1-chloroethyl 2- (6-methoxy-2-naphthyl) propanoate, which was reacted with the sodium salt of Boc-L-phenylalanine (prepared analogously from Boc-L- phenylalanine as described) to afford the Boc-protected 1-(L-phenylalanyloxy) ethyl ester of naproxen as oil (740 mg, 27%). The Boc-protected ester (600 mg) was dissolved in dioxane (5 mL) and 4 N HCI/dioxane (4 mL) was added and solution was stirred at room temperature for 4 hours followed by concentration under vacuum. The residue was recrystallized from tetrahydrofuran to give the hydrochloride salt of 1- (L- phenylalanyloxy) ethyl 2- (6-methoxy-2-naphthyl) propanoate (120 mg, 24%) mp 176°C.

'H NMR (CD30D, 400 MHz): 8 7.69/7.74,7.14/7.13,7.09/7.08, 3.90/3.89,1.57/1.54,6.95/6.91,1.43/1.40,4.22/4.15,3.06/2.86, 7.20-7.14,7.32-7.28,7.28-7.24 (*two diastereomers ratio 7 : 3); HR-MS : Calculated mass for C25H27NO5: 421.189. Measured mass: 421.181.

Example 10 2- 2- (1-morpholinyl) acetyloxy ethyl 2- (6-methoxy-2-naphthyl) propanoate (R, =-CH2CH2- R3 =-CH2-; R4-Rs =-CH2CH20CH2CH2- 2-hydroxyethyl 2- (6-methoxy-2-naphthyl) propanoate (0.32 g, 1.2 mmol) and 2- (1- morpholinyl) acetic acid (0.17 g, 1.2 mmol), 4- (N, N-dimethylamino) pyridine (0.15 mg, 1.2 mmol) and N, N'-dicyclohexylcarbodiimide (0.41 g, 2.0 mmol) in dry dichloromethane (30 mL) was stirred at room temperature for 36 h. The precipitated dicyclohexylurea was filtered off and the filter cake was washed with dichloromethane.

The filtrate was evaporated and the residue was purified by flash silica gel column chromatography eluting with 3% methanol in dichloromethane to give the desired compound (0.20 g, 40%) as a solid: mp 78 °C.'H NMR (CDCl3,400 MHz): 8 7.68, 7.39,7.13,4.27,3.91,3.87,3.69,3.00,2.43,1.58. HRMS: m/z 401.1918, calcd for C22H27NO6 401.1838.

Example 11 4- 2- (1-morpholinyl) acetyloxy butyl 2- (6-methoxy-2-naphthyl) propanoate (R, =-CH2CH2CH2CH2- R3 =-CH2-; R4-Rs =-CH2CH20CH2CH2- The compound was prepared as described in the example 10 from 4-hydroxybutyl 2- (6- methoxy-2-naphthyl) propanoate (0.96 g, 3.2 mmol) and 2- (1-morpholinyl) acetic acid (0.46 g, 3.2 mmol) to give the desired compound (0.28 g, 20%).'H NMR (CDCl3,400 MHz): 8 7.68,7.39,7.13,4.07,3.92,3.84,3.74,3.14,2.55,1.62,1.58. HRMS: m/z 429.2281, calcd for C24H3lNO6 429.2151.

Example 12 2- 2- (4-methyl-1-piperazinyl) acetyloxy ethyl2- (6-methoxy-2-naphthyl) propanoate (RI =-CH2CH2- R3 =-CH2-; R4-Rs =-CH2CH2N (CH3) CH2CH2- 2-hydroxyethyl 2- (6-methoxy-2-naphthyl) propanoate (0.39 g, 1.4 mmol) and 2- (4-methyl- 1-piperazinyl) acetic acid (0.22 g, 1.4 mmol), 4- (N, N-dimethylamino) pyridine (0.15 mg, 1.2 mmol) and N, N'-dicyclohexylcarbodiimide (0.44 g, 2. 1 mmol) in dry dichloromethane (30 mL) was stirred at room temperature for 36 h. The precipitated dicyclohexylurea was filtered off and the filter cake was washed with dichloromethane.

The filtrate was evaporated and the residue was purified by flash silica gel column chromatography eluting with 20% methanol in dichloromethane to give the desired compound (0.41 g, 71%).'H NMR (CDCl3,400 MHz): 8 7.67,7.38,7.13,4.23,3.91,

3.86,3.08,2.54,2.33,1.57. HRMS: m/z 414.2208, calcd for q4H31NO6 414.2155.

Example 13 4- 2- (4-methyl-l-piperazinyl) acetyloxy butyl 2- (6-methoxy-2- naphthyl) propanoate (Rl =-CH2CH2CH2CH2-; R3 =-CH2-; R4-Rs =-CH2CH2N (CH3) CH2CH2- The compound was prepared as described in the example 12 from 4-hydroxybutyl 2- (6- methoxy-2-naphthyl) propanoate (0.17 g, 0.6 mmol) and 2- (4-methyl-l- piperazinyl) acetic acid (0.10 g, 0.6 mmol) to give the desired compound (0.09 g, 35%).

'H NMR (CDCl3,400 MHz): 8 3.16,2.62,2.56, 2.33,1.62,1.57. HRMS: m/z 442.2569, calcd for C25H34N205 442.2468.

Example 14 4- 3- (4-methyl-l-piperazinyl) propionyloxy butyl-2- (6-methoxy-2- naphthyl) propanoate (R, =-CH2CH2CH2CH2- R3 =-CH2CH2-; R4-Rs =- CH2CH2N (CH3) CH2CH2-) The compound was prepared as described in the example 12 from 4-hydroxybutyl 2- (6- methoxy-2-naphthyl) propanoate (2.0 g, 6.6 mmol) and 3- (4-methyl-l- piperazinyl) propionic acid (1.2 g, 6.9 mmol) to give the desired compound (2.45 g, 54%).'H NMR (CDCl3,400 MHz): 8 7.72-7.11 (6H, aromatic), 4.10,4.02,3.91,3.85, 2.66,2.45,2.6-2.3 (8H, N (CH2CH2) 2N), 2.27,1.7-1.5 (4H, CCH., CH2C), 1.57, HRMS: m/z 456.2728, calcd for C, 6H'6N, 05 456.2624.

Example 15 4- 4- (4-methyl-1-piperazinyl) butyryloxy butyl 2- (6-methoxy-2- naphthyl) propanoate (R,-CH2CH2CH2CH2- ; R3 =-CH2CH2CH2- ; R4-Rs=- CH2CH2N (CH3) CH2CH2-) The compound was prepared as described in the example 12 from 4-hydroxybutyl 2- (6- methoxy-2-naphthyl) propanoate (1.0 g, 3.3 mmol) and 4- (4-methyl-l- piperazinyl) butyric acid (0.61 g, 3.3 mmol) to give the desired compound (1.17 g, 75%).

'H NMR (CDCl3,400 MHz): # 7.72-7.11 (6H, aromatic), 4.10,4.00,3.91,3.85,2.6-2.3 (8H, (4H, CCHCH2C), 1.57, HRMS: m/z 470.2593, calcd for C27H38N205 470.2781.

TEST METHODS The compounds of the present invention have been tested in the following tests. A prodrug with good permeation across biological membranes (especially across the skin) should exhibit optimum lipophilicity (partition coefficient) in combination with adequate aqueous solubility. The skin consists of multilamellar bilayers and thus the prodrug must have adequate water-solubility to be able to cross the lipid-aqueous interfaces. In addition to optimum lipophilicity and aqueous solubility, the prodrugs should be stable enough against chemical degradation and release enzymatically the active parent drug during or after absorption/penetration.

1) Aqueous solubility Method The aqueous solubilities of the present compounds were determined in phosphate buffer (0.16 M) at pH 5.0 and 7.4 at room temperature. Excess amounts of each compound were added to 1-4 ml of solvents. The mixtures of phosphate buffers were vortexed either for 60 min (pH 5.0) or for 20-30 min (pH 7.4), filtered (Millipore 0.45 um) and diluted with an appropriate amount of phosphate buffer before HPLC analysis. The pH of the mixtures was checked in the middle of the vortexing and adjusted, if necessary.

Results Aqueous solubilities of the present compounds are shown in Table 1. Due to the acid character of naproxen (pKa 4.15), it is more water soluble at pH 7.4 than at pH 5.0. In contrast to naproxen, the prodrugs are more soluble in acidic than in neutral aqueous solutions due to the ionizable basic group in the promoiety. Therefore, the present prodrugs possess adequate aqueous solubilities compared to naproxen at pH 7.4. At pH 5.0, most prodrugs showed an increase in aqueous solubility compared to naproxen.

2) Lipophilicity Method The lipophilicities of the present compounds were evaluated by apparent partition coefficients (log Papp), and were determined at room temperature in a 1-octanol- phosphate buffer system at pH 5.0 and 7.4. The phosphate buffer and 1-octanol phases were saturated before use by stirring vigorously for 24 h at room temperature. A known concentration of prodrug in phosphate buffer (0.16 M) was shaken with a suitable volume of 1-octanol to achieve equilibrium. After shaking (0.5-1 hours), the phases were separated by centrifugation at 14000 rpm for 5 min before HPLC analysis.

Results The log Papp-values of the present compounds are shown in Table 1. All the prodrugs are clearly more lipophilic than naproxen at pH 7.4. In addition, the prodrugs maintained lipophilicities comparable to that of naproxen at pH 5.0. Table 1. Aqueous solubilities (mean SD; n = 2-4) and apparent partition coefficients (log Papp mean SD; n = 2-3) of naproxen and its various prodrugs. Compound Aqueous Aqueous log Pp at log Pp at Solubility at Solubility at pH 7.4 pH 5.0 pH 7.4 (mM) pH 5.0 (mM) Naproxen 101.9 # 1.3 0.40 # 0.04 0.30 # 0.03 .38 # 0.02 example 1 4.73 # 1.06 10.38 # 0.75 2.80 # 0.01 example 2 0.15 # 0.01 0.31 # 0.04 3.30 # 0.07 2.16 # 0.02 example 3 0.15 0. 011.69 0.32 3.37 0.01 2.13 0.02 example 4 0.03 # 0.00 0.18 # 0.01 2.30 0.00 example 5 3.24 # 0.05 5.87 # 1.04 2.25 # 0.05 0.99 0.04 example 6 0.03 # 0.00 1.07 0.02 2.56 0.07 2.72 0.04 example 7 0.004 # 0.001 0.10 # 0.04 2.90 # 0.10 2.91 # 0.06 example 8 nd 3.66 # 0.01 nd 1.37 0.00 example 9 nd 0.32 # 0.02 nd 3.04 0.00 example 10 0.07 0.002 0.05 0.00 2.14 # 0.08 2.62 # 0.00 example 12 4.11 # 0.37 5.33 # 0.90 1.30 0.25 0.43 0.05 example 13 8.79 # 0.90 16.20 # 1.22 1.30 0.05 0.94 # 0.05 example 14 432.4 # 27.5 141.6 # 0.07 1.20 0.06 example 15 50.0 # 1.9 61.0 # 8.8 2.69 # 0.06 1.41 0.02 nd = values were not determined due to poor aqueous stability of prodrugs

3) Chemical stability Method The chemical stability studies were performed in an aqueous phosphate buffer solution of pH 7.4 and pH 5.0 (0.16M, ionic strength 0.5) at 37 °C. The solutions of prodrugs were prepared by adding an appropriate amount of the compound to the preheated buffer. After vortexing, the solutions were maintained at a constant temperature of 37 °C. At appropriate intervals, samples were taken and analyzed for remaining prodrug by HPLC.

Results Half-lives (tel, for the degradation of prodrugs in aqueous solutions are shown in Table 2. The degradation of all prodrugs followed pseudo-first-order kinetics at pH 5.0 and 7.4. The chemical stability of the prodrugs was substantially greater at pH 5.0 than at 7.4. Besides, the addition of ethanol increased the chemical stability of the prodrugs (data not shown).

4) Enzymatic hydrolysis Method The susceptibility of prodrugs to undergo enzymatic hydrolysis was studied in human serum by diluting to 80% with 0.16 M phosphate buffer of pH 7.4 at 37 °C. The reactions were initiated by adding the prodrug to phosphate buffer and then preheated serum was added. The solutions were kept at a constant temperature of 37 °C and at appropriate intervals, 0.5 ml samples of serum/buffer mixture were withdrawn and added to 1.0 ml of ethanol in order to precipitate protein from the serum homogenate. After immediate mixing and centrifugation, the resulting clear supernatant was analyzed with HPLC for remaining prodrug and formed parent compound.

Results Half-lives (tl, for the degradation of prodrugs in 80% human serum are shown in Table 2. The hydrolysis of all prodrugs followed pseudo-first-order kinetics at pH 7.4.

The prodrugs were highly susceptible to serum catalyzed hydrolysis and they rapidly released parent active compound. The hydrolysis of the acyloxyalkyl esters takes place enzymatically by attack on the carbonyl of the parent drug and on the carbonyl of the promoiety. The bioconversion of the prodrugs is schematically presented below. Drug-COOH + HO (CH2) OH n = 2-4 Enzymatic Enzymatic hydrolysis hydrolysais Drug-COO- (CH2) n-OCOR n Drug-COO- (CH2) nOH + HOCOR hydrolysis Spontaneous I hydrolysis Drug-COOH + HO (CH2) nOCOR Drug-COOH + HCHO Table 2. Rate of hydrolysis of prodrugs in buffer solutions (pH 7.4 and 5.0) and in 80% human serum (pH 7.4) at 37 °C. Compound t½ (h) t½(h) t½ (min) phosphate buffer phosphate buffer 80 % human pH 7.4 pH 5.0 serum example1 2. 6 233 19 example2 3. 2 84 10 example3 13 648 8 example4 3. 7 53 9 example5 4. 2 115 13 example6 81 3552 5 example7 23 72 13 example8 0. 5 5 4 example9 0. 9 7 example10 34 161 20 example11--12 example12 58 1596 25 example13 182 1870 3 example14 17 432 3 example15 48 893 1

5) In vitro skin penetration Method The in vitro drug permeation studies were performed in Franz-type vertical diffusion cells (Amie systems., USA) with an effective diffusional area of 0.71 cm2. The thawed and rehydrated skin specimens were mounted between chambers with the stratum corneum facing the donor chamber. The receptor chamber was filled with isotonic phosphate buffer (0.05 M, pH 7.4) containing 0.02% sodium azide as a preservative.

Samples of naproxen and its prodrugs were applied as suspensions or solutions in this buffer solution or in isotonic phosphate buffer of pH 5.0 (0.05 M). The receptor phase was stirred magnetically and kept at a constant temperature of 37 °C throughout the study. The receptor compartment was sampled at appropriate time intervals with replacement with fresh buffer solution. The samples were assayed for drug concentrations by HPLC and corrected for dilution attributable to the sampling procedure. The skin flux-values (Jss) for rate of delivery of naproxen and its prodrugs were determined by plotting the cumulative amounts (in nmol) of the parent drug, intermediates and intact prodrugs measured in the receptor phase against the time and dividing the slopes of the steady-state position by the surface area of the diffusion cell.

Results The steady-state fluxes (Jss) for prodrugs are shown in Table 3. The diffusion experiments showed that skin permeation of naproxen can be improved by prodrugs. Prodrugs improved skin permeation of naproxen with a maximum enhancement of 4- fold at pH 7.4 and 3-fold at pH 5.0. Table 3. The steady-state fluxes (mean SE, n=3-10) for delivery of total naproxen species through excised human skin in vitro from isotonic phosphate buffer (0.05 M, pH 5.0 or pH 7.4) at 37 °C. Compound Flux (nmol/cm2/h) Flux (nmol/cm2/h) pH 7.4 pH 5.0 Naproxen 6.5 0.6 1.6 0.2 example 1 4.0 0.4 l example 2 1.6 # 0.0 example 3 5.1 0.4 example 51. 5 0.1 example 6 1.8 0.3 example 10 0.67 0.02 0.63 0.04 example 12 24.6 1.0 2.2 0.1 example 13 7. 2 0.1 0.2 0.0 example 14 7.7 1.3 0.60.6 0.0 example 1513. 2 1. 6 1.2 0.2

6) Conclusions The results show that the novel compounds of the present invention 1) are lipophilic at pH 5 and 7. In case of dermal application, the adequate lipophilicity of the prodrug at the pH range 5-7 is necessary due to the structure of the skin; the pH of outer surface of skin is about 5 but will increase up to 7 in its inner parts.

2) have adequate aqueous solubility.

3) are adequately stable against chemical hydrolysis in aqueous solutions and thus they

enable the preparation of water-based formulations.

4) are hydrolyzed enzymatically to the parent active drug, the NSAIDs.

5) improve significantly the permeation of parent drug across the skin. The improved skin penetration is due to the lipophilic character of the prodrugs at pH 5-7 in combination with adequate aqueous solubility. A lipohilic prodrug with poor aqueous solubility is not able to cross the lipid-aqueous phase interfaces of multilamellar bilayers.

The results also show that aqueous solubility, lipophilicity, enzymatic hydrolysis (and thus the formation of the parent drug) and membrane penetration of the present compounds can be easily regulated by changing the chemical group attached to the parent drug.

The improved skin permeation allows for improved topical administration of NSAIDs. Topical administration is desirable because the prodrug will release the parent active drug at the site of inflammation and high systemic drug concentration can be avoided.