Purine derivatives and pharmaceutically acceptable salts thereof

Abstract: An object of the present invention is to offer novel purine derivatives which exhibit an inhibitory action to nasal mucus secretion and are useful as pharmaceuticals, etc. and pharmaceutically acceptable salts thereof. The purine derivatives of the present invention are novel compounds which are represented by the following general formula (I). [In the formula, R is alkyl or cycloalkyl, or optionally-substituted phenyl or phenylalkyl; R' is hydrogen or -COOX; and X is alkyl, alkenyl, alkoxyalkyl, phenyl or phenylalkyl] The compounds of the present invention are useful as therapeutic and preventive agents to various types of rhinitis accompanied by acceleration of nasal mucus secretion and by sneezing reflex such as allergic rhinitis. Moreover, the compounds of the present invention are able to be administered orally and exhibit low toxicity, little side effect and high safety. Accordingly, a continuous administration for long term is possible and they have a very high utility as the drugs.

Description: The present invention relates to a novel purine derivative and a pharmaceutically acceptable salt thereof having an inhibitory action to nasal mucus secretion and also to a pharmaceutical composition which contains said compound as an effective component. Allergy is a sensitive state of living body owing to an antigen-antibody reaction and is classified into four types - type I to type IV - depending upon its reaction mechanism. Bronchial asthma, allergic rhinitis, urticaria, etc. which are representative allergic diseases from which many people suffer are due to an allergic reaction of type I (an immediate type or an anaphylactic type). In the allergic reaction of type I, a degranulation takes place when antigen is bonded with IgE which is bonded with the cell surface of basophiles and mastocytes whereupon inflammatory mediators such as histamine and leucotriene are released resulting in various allergic symptoms. For example, the allergic rhinitis from which increasing people suffer in recent years is classified into a whole-year allergy in which house dusts are main antigen and a seasonal allergy (pollinosis) mostly caused by pollen of Japanese cedar. The former starts in when one is a baby or a small child and its symptom continues. Accordingly, a continuous therapy is particularly necessary whereby there has been a demand for therapeutic and preventive agents which can be administered for long time and exhibit little side effect. In the case of rhinitis such as allergic rhinitis, it is an important therapy to remove unpleasant feel caused by a promotion of secretion of nasal mucus and, therefore, an excellent agent for inhibiting the secretion of nasal mucus can be used as an effective therapeutic agent for rhinitis. With respect to the pharmacological action of purine derivatives, there is a disclosure in the Examined Japanese Patent Publications 58,726/85 and 26,527/86 that 2,8-dihydroxypurine exhibits analgesic, sedative and antiallergic actions. Unfortunately this compound has a very bad solubility to both aqueous and nonaquoue solvents and is very hardly applicable as the drug for practical use. Chem. Abs., 1960, 54 :5682 discloses the compound 2,8-dihydroxy-9-methylpurine. However, no pharmaceutical or medicinal use of this compound is taught. The present inventors have conducted a study on the therapeutic agent for rhinitis which can be administerd for long time and found that the purine derivatives of the present invention exhibit an excellent action for inhibiting the secretion of nasal mucus whereby the present invention has been achieved. An object of the present invention is to offer novel purine derivatives and pharmaceutically active salts thereof which exhibit an inhibitory action to the secretion of nasal mucus and are useful as drugs, etc. According to a first aspect, the present invention provides a compound of general formula (I') or a pharmaceutically acceptable salt thereof: wherein R is C 1 -C 20 alkyl, C 3 -C 8 cycloalkyl, phenyl optionally substituted by C 1 -C 4 alkyl, C 1 -C 4 alkoxy or halogen, or phenyl-C 1 -C 4 alkyl optionally substituted by C 1 -C 4 alkyl, C 1 -C 4 alkoxy or halogen; R' is hydrogen or -COOX; and X is C 1 -C 20 alkyl, C 2 -C 6 alkenyl, C 1 -C 4 alkoxy C 1 -C 4 alkyl, phenyl or phenyl C 1 -C 4 alkyl; with the proviso that if R' represents a hydrogen atom, then R does not represent a methyl group. According to a second aspect, the present invention provides a pharmaceutical composition comprising a compound of general formula (I) or a pharmaceutically acceptable salt thereof, and a pharmaceutically acceptable carrier: wherein R is C 1 -C 20 alkyl, C 3 -C 8 cycloalkyl, phenyl optionally substituted by C 1 -C 4 alkyl, C 1 -C 4 alkoxy or halogen, or phenyl-C 1 -C 4 alkyl optionally substituted by C 1 -C 4 alkyl, C 1 -C 4 alkoxy or halogen; R' is hydrogen or -COOX; and X is C 1 -C 20 alkyl, C 2 -C 6 alkenyl, C 1 -C 4 alkoxy C 1 -C 4 alkyl, phenyl or phenyl C 1 -C 4 alkyl. According to a third aspect, the present invention provides a compound of general formula (I) or a pharmaceutically acceptable salt thereof for use as a medicament: wherein R is C 1 -C 20 alkyl, C 3 -C 8 cycloalkyl, phenyl optionally substituted by C 1 -C 4 alkyl, C 1 -C 4 alkoxy or halogen, or phenyl-C 1 -C 4 alkyl optionally substituted by C 1 -C 4 alkyl, C 1 -C 4 alkoxy or halogen; R' is hydrogen or -COOX; and X is C 1 -C 20 alkyl, C 2 -C 6 alkenyl, C 1 -C 4 alkoxy C 1 -C 4 alkyl, phenyl or phenyl C 1 -C 4 alkyl. Preferred examples of the C 1-20 alkyl represented by R or X in the above-mentioned general formulae (I) and (I') are linear or branched alkyls such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl, tert-butyl, pentyl, isopentyl, neopentyl, tert-pentyl, hexyl, dimethylbutyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl, octadecyl, nonadecyl or icosyl. Preferred examples of the C 3-8 cycloalkyl represented by R are cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl and cyclooctyl. Preferred examples of the phenyl C 1-4 alkyl represented by R or X are those wherein a phenyl group is bonded with a linear or branched alkyl such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl or tert-butyl. The phenyl or phenyl C 1-4 alkyl represented by R is optionally substituted by C 1-4 alkyl (preferably a linear or branched alkyl such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl or tert-butyl), C 1-4 alkoxy (preferably a linear or branched alkoxy such as methoxy, ethoxy, propoxy, isopropoxy, butoxy, isobutoxy, sec-butoxy or tert-butoxy ) and halogen such as fluorine, chlorine, bromine or iodine. Preferred examples of the C 2-6 alkenyl represented by X are linear or branched alkenyls such as ethenyl, 1-propenyl, 2-propenyl, 1-butenyl, 3-butenyl, sec-butenyl, pentenyl, isopentyl, 2-pentenyl, 3-pentenyl, 4-pentenyl, hexenyl or dimethylbutenyl, while those of the C 1-4 alkoxy C 1-4 alkyl represented by X are linear or branched alkyls such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl or tert-butyl, bonded with a linear or branched alkoxy such as methoxy, ethoxy, propoxy, isopropoxy, butoxy, isobutoxy, sec-butoxy or tert-butoxy. Preferred embodiments of the compounds of the present invention represented by the above-given general formulae (I) and (I') having an action for inhibiting the secretion of nasal mucus are as follows. They are the preferred embodiments of the effective components of the inhibiting agent for nasal mucus as well. (1) Compounds of the present invention in which R' in the general formula (I) is hydrogen; (2) Compounds of the present invention in which R is the alkyl in the compounds given in the above (1); (3) A compound of the present invention in which R is isopropoyl in the compounds given in the above (2); (4) Compounds of the present invention in which R' in the general formula (I) is -COOX; (5) Compounds of the present invention in which R is alkyl in the compounds given in the above (4); (6) A compound of the present invention in which R is ethyl in the compounds given in the above (5); (7) A compound of the present invention in which R is propyl in the compounds given in the above (5); (8) A compound of the present invention in which R is isopropyl in the compounds given in the above (5); (9) Compounds of the present invention in which R is a linear or branched alkyl having four carbon atoms in the compounds given in the above (5); (10) Compounds of the present invention in which X is alkyl in the compounds given in any of the above (4) to (9); (11) Compounds of the present invention in which X is a linear or branched alkyl having 1 to 6 carbon atoms in the compounds given in the above (10); (12) A compound of the present invention in which X is methyl in the compounds given in the above (10); (13) A compound of the present invention in which X is ethyl in the compounds given in the above (10); (14) A compound of the present invention in which X is propyl in the compounds given in the above (10); (15) A compound of the present invention in which X is isopropyl in the compounds given in the above (10); (16) Compounds of the present invention in which X is a linear or branched alkyl having four carbon atoms in the compounds given in the above (10); (17) Compounds of the present invention in which X is a linear or branched alkyl having five carbon atoms in the compounds given in the above (10); and (18) Compounds of the present invention in which X is a linear or branched alkyl having six carbon atoms in the compounds given in the above (10); The purine derivatives of the present invention include the pharmaceutically acceptable salts of the compounds represented by the above-mentioned general formula and they are, for example, salts with an alkali metal such as sodium and potassium, with an alkali earth metal such as calcium and magensium and with a metal such as aluminum. The purine derivatives of the present invention include the metal complex compounds thereof and they are, for example, complex compounds with zinc, nickel, cobalt, copper, iron, etc. Such salts or metal complexes may be manufactured by conventional methods starting from the purine derivatives of the present invention in free state or may be converted each other. When there are stereoisomers such as cis-trans isomers, optical isomers, conformational isomers, etc. in the compound of the present invention or when the compound of the present invention exists in a state of hydrates, the present invention includes all of such stereoisomers and hydrates. The compounds of the present invention represented by the general formula (I) may, for example, be manufactured by the following methods. (a) The compounds of the present invention in which the substituent R' is hydrogen may be manufactured by a catalytic reduction of 5-nitro-4-N-substituted cytosine having a substituent corresponding to the above-mentioned R with palladium-carbon or the like followed by melting the resulting 4,5-diamino compound with urea. Alternatively, they may be manufactured by the reaction of 5-aminio-4-N-substituted cytosine with carbonyl diimidazole; and (b) The compounds of the present invention in which the substituent R' is -COOX may be manufactured by introducing a group -COOX into a 7-position of the compound obtained in the above (a). For example, various esters of chloroformic acid (i.e. esters corresponding to X of the -COOX group) are made to react with the compound of the present invention in which the substituent R' is hydrogen whereupon the compounds of the present invention in which the substituent R' is -COOX may be manufactured. The compounds of the present invention prepared as such are purified by conventional means such as distillation and chromatograpy and are identified by means of melting points, elementary analysis, IR, NMR, UV, mass spectrum, etc. [Examples] Example 1. 4-N-Methyl-5-nitrocytosine (3.5 g) was subjected to a catalytic reduction in the presence of 0.7 g of 10% palladium-carbon in 400 ml of methanol to give a diamino compound. This was heated with 7.4 g of urea at 150°C with stirring and the resulting brown solid was dissolved in a 1N sodium hydroxide solution followed by treating with active carbon. This was neutralized with acetic acid and the crystals separated out therefrom were filtered and washed with water. The same treatment with active carbon was repeated for several times to purify whereupon 1.6 g of 9-methyl-1,2,7,8-tetrahydro-9H-purine-2,8-dione (compound 1) were obtained. Melting point was not lower than 320° C. Elementary analysis calculated for C 6 H 6 N 4 O 2 : Calcd: C = 43.38%, H = 3.64%, N = 33.72% Found: C = 43.23%, H = 3.74%, N = 33.69%. Similarly were prepared the following compounds. 9-Ethyl-1,2,7,8-tetrahydro-9H-purine-2,8-dione (Compound 2). Melting point was not lower than 320° C. MS (m/z): 180 (M + ). Elementary analysis calculated for C 7 H 8 N 4 O 2 : Calcd: C = 46.67%, H = 4.48%, N = 31.10% Found: C = 46.87%, H = 4.65%, N = 31.12%. 9-Isopropyl-1,2,7,8-tetrahydro-9H-purine-2,8-dione (Compound 3). Melting point was not lower than 320° C. MS (m/z): 194 (M + ). Elementary analysis calculated for C 8 H 10 N 4 O 2 : Calcd: C = 49.48%, H = 5.19%, N = 28.58% Found: C = 49.79%, H = 5.36%, N = 29.10%. 9-Butyl-1,2,7,8-tetrahydro-9H-purine-2,8-dione (Compound 4). Melting point was not lower than 320° C. MS (m/z): 208 (M + ). Elementary analysis calculated for C 9 H 12 N 4 O 2 : Calcd: C = 51.92%, H = 5.81%, N = 26.91% Found: C = 52.10%, H = 5.87%, N = 26.98%. 9-(1,3-Dimethylbutyl)-1,2,7,8-tetrahydro-9H-purine-2,8-dione (Compound 5). Melting point was not lower than 320°C. MS (m/s): 236 (M + ). Elementary analysis calculated for C 11 H 16 N 4 O 2 .·0.2H 2 O: Calcd: C = 55.09%, H = 6.89%, N = 23.36% Found: C = 55.27%, H = 6.92%, N = 23.07%. 9-Cyclohexyl-1,2,7,8-tetrahydro-9H-purine-2,8-dione (Compound 6). Melting point was not lower than 320°C. MS (m/s): 234 (M + ). Elementary analysis calculated for C 11 H 14 N 4 O 2 : Calcd: C = 56.40%, H = 6.02%, N = 23.92% Found: C = 56.59%, H = 6.05%, N = 24.00%. 9-Phenyl-1,2,7,8-tetrahydro-9H-purine-2,8-dione (Compound 7). Melting point was not lower than 320°C. Elementary analysis calculated for C 11 H 8 N 4 O 2 .0.1AcOH.0.4H 2 O: Calcd: C = 55.72%, H = 3.84%, N = 23.20% Found: C = 55.87%, H = 3.68%, N = 23.14%. 9-Benzyl-1,2,7,8-tetrahydro-9H-purine-2,8-dione (Compound 8). Melting point was not lower than 320°C. Elementary analysis calculated for C 12 H 10 N 4 O 2 : Calcd: C = 59.50%, H = 4.16%, N = 23.13% Found: C = 59.83%, H = 4.10%, N = 23.45%. 9-(2-Phenylethyl)-1,2,7,8-tetrahydro-9H-purine-2,8-dione (Compound 9). Melting point was not lower than 320°C. Elementary analysis calculated for C 13 H 12 N 4 O 2 : Calcd: C = 60.93%, H = 4.72%, N = 21.86% Found: C = 61.07%, H = 4.87%, N = 22.12%. 9-(4-Methoxyphenyl)-1,2,7,8-tetrahydro-9H-purine-2,8-dione (Compound 10). Melting point was not lower than 320° C. Elementary analysis calculated for C 12 H 10 N 4 O 3 .0.1AcOH.0.4H 2 O Calcd: C = 53.98%, H = 4.16%, N = 20.64% Found: C = 53.92%, H = 3.97%, N = 20.77%. 9-(2-Fluorobenzyl)-1,2,7,8-tetrahydro-9H-purine-2,8-dione (Compound 11). Melting point was not lower than 320°C. Elementary analysis calculated for C 12 H 9 FN 4 O 2 : Calcd: C = 55.39%, H = 3.49%, N = 21.53% Found: C = 55.33%, H = 3.36%, N = 21.37%. Example 2. 5-Amino-4-N-isopropylcytosine (21 g) was suspended in 200 ml of dimethylformamide and 22.3 g of carbonyldiimidazole were added thereto at room temperature. After five minutes, the reaction mixture became transparent. This was stirred for 30 minutes and 400 ml of ether were added thereto. The crystals which were separted out therefrom were filtered, washed with ether and dried to give 20.7 g of the compound 3 of the present invention. Example 3. The compound 3 (350 mg) was suspended in a mixed solvent comprising dry dimethylformamide and dry dimethyl sulfoxide and 76 mg of sodium hydride were added thereto at 0° C in an atomosphere of argon. The mixture was stirred for 10 minutes, 0.15 ml of methyl chloroformate was dropped thereinto at 0°C and the mixture was stirred at room temperature for 30 minutes. A saturated aqueous solution of ammonium chloride was added, the mixture was diluted with water and extracted with chloroform three times. The extracted chloroform layer was washed with water and a saturated sodium chloride solution, dried over sodium sulfate and the solvent was evaporated therefrom in vacuo. The resulting crude crystals were recrystallized from ether-chloroform to give 141 mg of 9-isopropyl-7-methoxycarbonyl-1,2,7,8-tetrahydro-9H-purine-2,8-dione (Compound 12) as white crystals. Melting point: 303-306° C. MS (m/z): 252 (M + ). Elementary analysis calculated for C 10 H 12 N 4 O 4 : Calcd: C = 47.62%, H = 4.80%, N = 22.21% Found: C = 47.65%, H = 4.83%, N = 22.18%. Similarly were prepared the following compounds: 7-Ethoxycarbonyl-9-isopropyl-1,2,7,8-tetrahydro-9H-purine-2,8-dione (Compound 13). Melting point: 200-202° C. MS (m/z): 266 (M + ). Elementary analysis calculated for C 11 H 14 N 4 O 4 : Calcd: C = 49.63%, H = 5.30%, N = 21.04% Found: C = 49.57%, H = 5.31%, N = 20.95%. 9-Isopropyl-7-propoxycarbonyl-1,2,7,8-tetrahydro-9H-purine-2,8-dione (Compound 14). Melting point: 206-208° C. MS (m/z): 280 (M + ). Elementary analysis calculated for C 12 H 16 N 4 O 4 : Calcd: C = 51.42%, H = 5.75%, N = 19.99% Found: C = 51.12%, H = 5.72%, N = 19.94%. 9-Isopropyl-7-isopropoxycarbonyl-1,2,7,8-tetrahydro-9H-purine-2,8-dione (Compound 15). Melting point: 216-218° C. MS (m/z): 280 (M + ). Elementary analysis calculated for C 12 H 16 N 4 O 4 .0.4H 2 O: Calcd: C = 50.13%, H = 5.89%, N = 19.49% Found: C = 50.29%, H = 5.61%, N = 19.47%. 7-Allylcarbonyl-9-isopropyl-1,2,7,8-tetrahydro-9H-purine-2,8-dione (Compound 16). Melting point: 201-203° C. MS (m/z): 278 (M + ). Elementary analysis calculated for C 12 H 14 N 4 O 4 : Calcd: C = 51.80%, H = 5.07%, N = 20.14% Found: C = 51.46%, H = 5.10%, N = 19.84%. 7-Butoxycarbonyl-9-isopropyl-1,2,7,8-tetrahydro-9H-purine-2,8-dione (Compound 17). Melting point: 217-219° C. MS (m/z): 294 (M + ). Elementary analysis calculated for C 13 H 18 N 4 O 4 : Calcd: C = 53.05%, H = 6.16%, N = 19.04% Found: C = 53.00%, H = 6.14%, N = 19.00%. 7-Isobutoxycarbonyl-9-isopropyl-1,2,7,8-tetrahydro-9H-purine-2,8-dione (Compound 18). Melting point: 217-219° C. MS (m/z): 294 (M + ). Elementary analysis calculated for C 13 H 18 N 4 O 4 : Calcd: C = 53.05%, H = 6.16%, N = 19.04% Found: C = 53.06%, H = 6.14%, N = 18.96%. 7-Hexyloxycarbonyl-9-isopropyl-1,2,7,8-tetrahydro-9H-purine-2,8-dione (Compound 19). Melting point: 189-191° C. MS (m/z): 322 (M + ). Elementary analysis calculated for C 15 H 22 N 4 O 4 : Calcd: C = 55.89%, H = 6.88%, N = 17.38% Found: C = 55.94%, H = 6.84%, N = 17.41%. 9-Isopropyl-7-octyloxycarbonyl-1,2,7,8-tetrahydro-9H-purine-2,8-dione (Compound 20). Melting point: 185-187° C. MS (m/z): 350 (M + ). Elementary analysis calculated for C 17 H 26 N 4 O 4 : Calcd: C = 58.27%, H = 7.48%, N = 15.99% Found: C = 58.19%, H = 7.40%, N = 16.02%. 7-(2-Ethylhexyloxycarbonyl)-9-isopropyl-1,2,7,8-tetrahydro-9H-purine-2,8-dione (Compound 21). Melting point: (oily substance). MS (m/z): 350 (M + ). Elementary analysis calculated for C 17 H 26 N 4 O 4 : Calcd: C = 58.27%, H = 7.48%, N = 15.99% Found: C = 58.20%, H = 7.54%, N = 16.02%. 7-Hexadecyloxycarbonyl-9-isopropyl-1,2,7,8-tetrahydro-9H-purine-2,8-dione (Compound 22). Melting point: 141-143° C. MS (m/z): 462 (M + ). Elementary analysis calculated for C 25 H 42 N 4 O 4 : Calcd: C = 64.90%, H = 9.15%, N = 12.11% Found: C = 64.78%, H = 9.18%, N = 12.01%. 9-Isopropyl-7-(2-methoxyethoxycarbonyl)-1,2,7,8-tetrahydro-9H-purine-2,8-dione (Compound 23). Melting point: 218-220° C. MS (m/z): 296 (M + ). Elementary analysis calculated for C 12 H 16 N 4 O 5 : Calcd: C = 48.64%, H = 5.44%, N = 18.91% Found: C = 48.64%, H = 5.47%, N = 18.90%. 9-Isopropyl-7-phenoxycarbonyl-1,2,7,8-tetrahydro-9H-purine-2,8-dione (Compound 24). Melting point: 255-257° C. MS (m/z): 314 (M + ). Elementary analysis calculated for C 15 H 14 N 4 O 4 .0.5H 2 O: Calcd: C = 55.73%, H = 4.68%, N = 17.33% Found: C = 55.32%, H = 4.55%, N = 17.21%. 7-Benzyloxycarbonyl-9-isopropyl-1,2,7,8-tetrahydro-9H-purine-2,8-dione (Compound 25). Melting point: 210-212° C. Elementary analysis calculated for C 16 H 16 N 4 O 4 : Calcd: C = 58.53%, H = 4.91%, N = 17.06% Found: C = 58.21%, H = 4.96%, N = 16.86%. Example 4. The compound 2, 4 or 9 was used as a starting material and treated with ethyl chloroformate by the same manner as in Example 3 to give the following compounds. 7-Ethoxycarbonyl-9-ethyl-1,2,7,8-tetrahydro-9H-purine-2,8-dione (Compound 26). Melting point: 220-223° C. MS (m/z): 252 (M + ). Elementary analysis calculated for C 10 H 12 N 4 O 4 .0.1H 2 O: Calcd: C = 47.28%, H = 4.84%, N = 22.06% Found: C = 47.44%, H = 4.73%, N = 21.86%. 9-Butyl-7-ethoxycarbonyl-1,2,7,8-tetrahydro-9H-purine-2,8-dione (Compound 27). Melting point: 209-211° C. MS (m/z): 280 (M + ). Elementary analysis calculated for C 12 H 16 N 4 O 4 : Calcd: C = 51.42%, H = 5.75%, N = 19.99% Found: C = 51.33%, H = 5.75%, N = 19.88%. 7-Ethoxycarbonyl-9-(2-phenylethyl)-1,2,7,8-tetrahydro-9H-purine-2,8-dione (Compound 28). Melting point: 235-237° C. MS (m/z): 328 (M + ). Elementary analysis calculated for C 16 H 16 N 4 O 4 .0.2H 2 O: Calcd: C = 57.90%, H = 4.98%, N = 16.88% Found: C = 58.01%, H = 4.96%, N = 16.89%. 1. Inhibitory action to nasal mucus secretion. 1) Preparation of guinea pigs sensitive to nasal mucous membrane by an active sensitization with egg ovalbumin. Ovalbumin (1 microgram; dissolved in 1 ml of a physiological saline solution) was intraperitoneally administered for 6 to 7 times on a biweekly basis to guinea pigs using 5 mg of aluminum hydride gel as an adjuvant. After two weeks from the final sensitization, 50 microlitre of a 1% ovalbumin solution were nasally administered into both nostrils for not less than 5 times every 3 to 7 days to prepare guinea pigs which were sensitive to nasal mucous membrane. 2) Inhibitory action to the secretion of nasal mucus induced by antigen. Ovalbumin (0.25 mg) was dropped into one of the nostrils to induce a nasal allergic disease and an evaluation of the pharmaceutical effect was carried out using the amount of nasal mucus secretion which was induced in another nostril as an index. The compound to be tested was orally administered (1 mg/kg) at 60 minutes before the nasal disease was induced and the secreted amount of the nasal mucus was measured according to a method by Namimatsu, et al [Int. Arch. Allergy Immunol., vol. 95, pages 29-34 (1991)] using a dyed nasal mucus string whereupon the inhibitory action of the test compound to the secretion of nasal mucus was determined. An example of the results on the inhibitory action to the nasal mucus secretion by the compounds of the present invention is given in Table 1. Compound Tested Inhibiting Rate to Nasal Mucus Secretion Compound 2 14.2% Compound 3 39.6% Compound 4 15.6% Compound 6 13.3% Compound 8 15.4% Compound 11 13.2% 3) Improvement in absorption into blood. It is apparent from the test result given in the above Table 1 that the compounds of the present invention of the general formula (I) in which the substituent R' is hydrogen exhibit an inhibitory action to the secretion of nasal mucus by oral administration. Although those compounds have an improved solubility to various kinds of solvents as compared with 2,8-dihydroxypurine, they are still unable to be easily dissolved in aqueous solvents whereby their absorption into blood is insufficient. In view of the above, an improvement was carried out by introducing a -COOX group into the 7-position of those compounds for increasing their solubility in aqueous solvents such as water and for elevating their absorption into blood. As a result, it has been found that, after being absorbed into blood, the -COOX group introduced into the 7-position was detached and decomposed as a result of hydrolysis, etc. by an esterase existing in the blood whereupon the administered compound was converted to a pharmaceutically effective compound in which the substituent R' was hydrogen. Thus, introduction of the substituent -COOX into the 7-position made it possible to improve the easy solubilization and the absorption into blood of the compounds of the present invention. As shown hereinafter, the compounds of the present invention in which R' is -COOX exhibit a significantly improved absorption of the effective component into blood by oral administration whereupon the above-mentioned nasal mucus inhibitory action is achieved in lower concentrations than in the case of the compounds where R' is hydrogen. An example of the result on the investigation of absorption of the compounds of the present invention having a substituent -COOX at the position 7 into blood by oral administration is given as follows. Thus, 51.5 micromoles/kg of the compound of the present invention were orally administered to a guinea pig and the absorption rate of the compound into blood was given using the blood level of the compound where the substituent at the 7-position was detached (identical with the compound 3) as an index. Compound Blood Level of the Compound 3 (microgram/ml) after 15 min 30 min 1 hr 2 hr 3 (Control) 0.02 0.03 0.14 0.27 12 0.91 1.08 0.79 0.35 13 3.59 2.27 1.17 0.28 14 2.42 2.57 1.57 0.51 15 6.43 5.52 2.85 0.59 16 0.57 0.71 1.30 0.39 17 4.31 3.54 1.79 0.50 18 4.71 3.55 1.47 0.62 19 1.05 1.25 0.71 0.38 21 1.12 0.94 0.80 0.51 24 0.59 0.72 1.01 0.31 25 0.60 0.85 0.90 0.32 As shown in Table 1, the compounds of the present invention exhibit a significant inhibitory action to the nasal mucus secretion induced by antigen in the guinea pig sensitive to nasal mucous membrane by an active sensitization with ovalbumin. It is also apparent from the result of Table 2 that, in the case of the compounds of the present invention where the substituent at the 7-position is -COOX, absorption of the effective component into blood by oral administration was significantly improved and, in addition, an improvement was noted with respect to the dose for achieving the action of nasal mucus secretion. Further, the compounds of the present invention showed an excellent inhibitory action to a sneezing reflex when the guinea pig sensitive to nasal mucous membrane was subjected to an antigenic stimulation. Consequently, the compounds of the present invention are effective as therapeutic and preventive agents to various types of rhinitis accompanied by acceleration of nasal mucus secretion and by sneezing reflex such as allergic rhinitis. Moreover, the compounds of the present invention are able to be administered orally and exhibit low toxicity, little side effect and high safety. Accordingly, a continuous administration for long term is possible and they have a very high utility as the drugs for various rhinitis such as allergic rhinitis which need a therapy for long time. The compounds of the present invention can be made into pharmaceutical preparations by a due combination with a suitable pharmaceutical carriers or diluents. Any of the known methods is capable of giving the preparations such as those for oral administrations (e.g. tablets, capsules, powders, liquids, etc.) and for parentheral ones (e.g. for subcutaneous, intravenous, intramuscular, intrarectal and intranasal administrations). Alternatively, fine particles of the compound of the present invention may be administered to mucous membranes such as nose, throat and trachea in a form of a liquid for spraying, a dry powder or a liquid aerosol. In the prescription, the compounds of the present invention may be used as pharmaceutically acceptable salts thereof. The compounds of the present invention may be used either solely or jointly by a suitable combination or they may be used as a compounded preparation together with other pharmaceutically active components. In the case of the preparation for oral administration, the compounds of the present invention may be made into tablets, diluted powders, granules or capsules either as they are or together with suitable additives such as conventional fillers (e.g. lactose, sugar, glucose, mannitol, corn starch, potato starch, etc.) as well as binders (e.g. crystalline cellulose, cellulose derivatives, gum arabicum, tragacanth solution, sodium alginate solution, gelatin, etc.), disintegrating agents (e.g. corn starch, potato starch, carboxymethyl cellulose, etc.), lubricants (e.g. talc, magnesium stearate, etc.), bulking agents, moisturizing agents, buffers, preservatives, perfumes, and the like. It is also possible to prepare pharmaceutical preparations other than the above-mentioned ones such as suppositories, cataplasms, ointments, etc. which are most suitable for therapy depending upon the state of the patient and the type of the diseases. The preferred dosage of the compound of the present invention varies depending upon the object to be administered (age, body weight, symptom, etc. of the patient), dosage form, route of administration, term for administration, etc. and, in order to achieve the expected result, the compound may be usually administered by oral route with a daily dose of 0.02-200 mg, preferably 0.1-100 mg, to common adults either once daily or several times a day. In the case of parentheral administration using injections for example, the preferred dosage will be from one-third to one-tenth of the above-mentioned dosage by oral route because of the affection by absorption, etc. In the case of local administration such as by an intranasal route, the amount of 0.01-50 mg of the effective component is locally given into nostrils several times a day whereby an expected effect can be achieved. An example of the pharmaceutical preparations using the compound of the present invention as an effective component is given as hereunder though the present invention is not limited thereto. Formulation Example 1 (Tablets) Components Amount per Tablet Compound of the Present Invention 1 mg Lactose 150 mg Corn starch 40 mg Magnesium stearate 10 mg Total 201 mg

Claims: A compound of general formula (I') or a pharmaceutically acceptable salt thereof: wherein R is C 1 -C 20 alkyl, C 3 -C 8 cycloalkyl, phenyl optionally substituted by C 1 -C 4 alkyl, C 1 -C 4 alkoxy or halogen, or phenyl-C 1 -C 4 alkyl optionally substituted by C 1 -C 4 alkyl, C 1 -C 4 alkoxy or halogen; R' is hydrogen or -COOX; and X is C 1 -C 20 alkyl, C 2 -C 6 alkenyl, C 1 -C 4 alkoxy C 1 -C 4 alkyl, phenyl or phenyl C 1 -C 4 alkyl; with the proviso that if R' represents a hydrogen atom, then R does not represent a methyl group. A compound according to Claim 1, wherein R' is -COOX. A compound according to Claim 2, wherein X is a C 1 -C 20 alkyl group. A compound according to Claim 3, wherein X is a linear or branched alkyl group having 1 to 6 carbon atoms. A compound according to Claim 1, wherein R' is a hydrogen atom. A compound according to any preceding Claim, wherein R is a C 1 -C 20 alkyl group. A compound according to Claim 6, wherein R is isopropyl. A pharmaceutical composition comprising a compound of general formula (I) or a pharmaceutically acceptable salt thereof, and a pharmaceutically acceptable carrier: wherein R is C 1 -C 20 alkyl, C 3 -C 8 cycloalkyl, phenyl optionally substituted by C 1 -C 4 alkyl, C 1 -C 4 alkoxy or halogen, or phenyl-C 1 -C 4 alkyl optionally substituted by C 1 -C 4 alkyl, C 1 -C 4 alkoxy or halogen; R' is hydrogen or -COOX; and X is C 1 -C 20 alkyl, C 2 -C 6 alkenyl, C 1 -C 4 alkoxy C 1 -C 4 alkyl, phenyl or phenyl C 1 -C 4 alkyl. The use of a compound according to any of Claims 1 to 7, or a composition according to Claim 8 for the manufacture of a medicament for inhibiting nasal mucous secretion. A compound of general formula (I) or a pharmaceutically acceptable salt thereof for use as a medicament: wherein R is C 1 -C 20 alkyl, C 3 -C 8 cycloalkyl, phenyl optionally substituted by C 1 -C 4 alkyl, C 1 -C 4 alkoxy or halogen, or phenyl-C 1 -C 4 alkyl optionally substituted by C 1 -C 4 alkyl, C 1 -C 4 alkoxy or halogen; R' is hydrogen or -COOX; and X is C 1 -C 20 alkyl, C 2 -C 6 alkenyl, C 1 -C 4 alkoxy C 1 -C 4 alkyl, phenyl or phenyl C 1 -C 4 alkyl.

Inventors: HASEGAWA TAISUKE, NAMIMATSU AKIO, OKAMOTO KAORU, HASEGAWA, TAISUKE, NAMIMATSU, AKIO, OKAMOTO, KAORU, HASEGAWA, TAISUKE, C/O INST. OF BIO-ACTIVE SCIENCE, NAMIMATSU, AKIO, C/O INST. OF BIO-ACTIVE SCIENCE, OKAMOTO, KAORU, C/O INST. OF BIO-ACTIVE SCIENCE
Applicants: NIPPON ZOKI PHARMACEUTICAL CO, NIPPON ZOKI PHARMACEUTICAL CO., LTD.
Application year: 1995
Main classification: C07D473
IPC codes: A61P11, A61K31, A61P27, C07D473