TRIAZOLOPYRIDAZINES PROCESS AND INTERMEDIATES FOR THEIR PREPARATION AND THEIR USE AS MEDICAMENTS

Abstract: Triazolopyridazine compound of formula (I), wherein R<1> is hydrogen, halogen or alkyl; R<2> is polycarbon alkyl or cycloalkyl; X is oxygen or S(O)p, wherein p is 0 to 2; Y is (i) a group of formula (a) wherein R<3> and R<4> are hydrogen or alkyl, or (ii) cycloalkylene or cycloalkylidene; R<5> and R<6> are H, alkyl, cycloalkyl, or may bind together for form a nitrogen-containing heterocyclic group; m and n are 0 to 4, or a salt thereof, possessing excellent anti-asthmatic, anti-allergic, anti-PAF, eosinophil chemotaxis inhibiting activities.

Description: DESCRIPTION TRIAZOLOPYRIDAZINES PROCESS AND INTERMEDIATES FOR THEIR PREPARATION AND THEIR USE AS MEDICAMENTS Technical Field The present invention relates to a novel triazolopyridazine derivative exhibiting excellent anti¬ allergic, anti-inflammatory, anti-PAF (platelet activating factor ) , eosinophil chemotaxis inhibiting and other actions, its production and use. Background Art Many compounds having a triazolopyridazine skeleton are currently synthesized as drugs for a variety of diseases . For example, USP3 ,915 ,968 discloses a compound of the formula: wherein R and R 3 are independently a hydrogen atom or a lower alkyl, at least one of R and R 3 is a lower alkyl; R 1 and R 2 form a nitrogen-containing heterocyclic group together with the adjacent nitrogen atom, for example, pyrrolidine, piperidine, piperazine, and morpholine, or a salt thereof. USP4,136,182 discloses a compound of the formula: wherein R is a hydrogen atom, a phenyl or a lower alkylcarbonylamino; R 1 is morpholino or piperidino; R 2 is a hydrogen atom or a lower alkyl, at least one of R and R 2 is a group excluding a hydrogen atom; when R is a phenyl, R 1 is morpholino and R 2 is a lower alkyl, or a salt thereof. EP248413 discloses a compound of the formula: or a salt thereof, as useful as bronchodilators for mitigating bronchial spasms. Also, EP562439 discloses a compound of the formula: wherein R 1 is a hydrogen atom, an optionally substituted lower alkyl group or a halogen atom; R 2 and R 3 are independently a hydrogen atom or an optionally substituted lower alkyl group, or may form a 5- to 7-membered ring together with the adjacent -C=C-; X is an oxygen atom or S(0) Pf wherein p is an integer of 0 to 2; Y is a group of the formula: R 4 R 5 wherein R 4 and R 5 are independently a hydrogen atom or an optionally substituted lower alkyl group or a divalent group derived from a 3- to 7-membered homocycle or heterocycle which is optionally substituted; R 6 and R 7 are independently a hydrogen atom, an optionally substituted lower alkyl group, an optionally substituted cycloalkyl group, or an optionally substituted aryl group, or may form a nitrogen-containing heterocyclic group which is optionally substituted, together with the adjacent nitrogen atom; m is an integer of 0 to 4, and n is an integer of 0 to 4, or a salt thereof; and, as an example of synthetic product, a compound of the formula: which are described as exhibiting anti-asthmatic, anti-PAF, anti-inflammatory and anti-allergic actions. Disclosure of Invention There is demand for the development of a novel compound more satisfactory than conventional anti- asthmatics, anti-allergic agents etc., in terms of action efficacy, sustained action, safety etc. Through various extensive studies, the present inventors produced for the first time a novel [1,2,4]triazolo[l,5-b]pyridazine compound of the formula: wherein R 1 is a hydrogen atom, a halogen atom or an optionally substituted lower alkyl group; R 2 is an optionally substituted polycarbon alkyl group or an optionally substituted cycloalkyl group; X is an oxygen atom or S(0) Pf wherein p is an integer of 0 to 2; Y is (i) a group of the formula: R 3 R 4 wherein R 3 and R 4 are independently a hydrogen atom or an optionally substituted lower alkyl group, or (ii) an optionally substituted cycloalkylene group or an optionally substituted cycloalkylidene group; R 5 and R 6 are independently a hydrogen atom, an optionally substituted lower alkyl group, or an optionally substituted cycloalkyl group, or together with the adjacent nitrogen atom may form a nitrogen-containing heterocyclic group; m and n are independently an integer of 0 to 4, or a salt thereof, whose characteristic feature of the chemical structure lies in the [1,2,4]triazolo[l,5-b]pyridazine having non-substituent at 8 position and a polycarbon alkyl group at 7 position, and found that this compound, owing to its unique chemical structure, exhibits unexpectedly excellent anti-allergic, anti-inflammatory, anti-PAF and eosinophil chemotaxis inhibiting actions, with excellent sustained action and safety, that it serves well as an anti-asthmatic because it suppresses bronchial spasms and dilation, and that it also serves as a prophylactic/therapeutic agent for allergic rhinitis and atopic dermatitis, on the basis of its eosinophil chemotaxis inhibiting action. The inventors conducted further studies based on these findings, and developed the present invention. Accordingly, the present invention relates to: (1) a compound [I] or a salt thereof, (2) a compound as described in (1) above, wherein R 1 is a hydrogen atom or a Cχ- 6 alkyl group, (3) a rsompound as described in (1) above, wherein the polycarbon alkyl group is a lower alkyl group having 2 or more carbon atoms, (4) a compound as described in (3) above, wherein the lower alkyl group having 2 or more carbon atoms is a branched C 3 _ β alkyl group, (5) a compound as described in (1) above, wherein Y is a group of the formula: wherein R 3a and R 4a are independently a hydrogen atom or a Cι_ 6 alkyl group, (6) a compound as described in (1) above, wherein R 5 and R 6 are independently a hydrogen atom or a Cj 6 alkyl group, (7) a compound as described in (1) above, wherein R 1 is a hydrogen atom; R 2 is a C 2 - 6 alkyl group; X is an oxygen atom; Y is a group of the formula: R 3b —C— I R 4b wherein R 3b and R 4 are independently a C 1 - 4 alkyl group; R 5 and R 6 are independently a hydrogen atom or a C 1 - 6 alkyl group; m and n are independently 1 or 2, (8) a compound as described in (7) above, wherein R 2 is a branched C 3 -. 6 alkyl group, (9) a compound as described in (8) above, wherein R 5 and R 6 are a hydrogen atom; m and n are 1, (10) a compound as described in (8) above, wherein the C 3 - 6 alkyl group is an isopropyl group, (11) a compound as described in (8) above, wherein the C 3 - 6 alkyl group is a tert-butyl group, (12) a compound as described in (1) above, which is 6-(2,2- dimethyl-3-sulfamoyl-1-propoxy)-7-ethyl[1,2,4]triazolo[1,5- b]pyridazine or a salt thereof, (13) a compound as described in (1) above, which is 6-(2,2- dimethyl-3-sulfamoyl-1-propoxy)-7-n-propyl[1,2,4]tri- azolo[l,5-b]pyridazine or a salt thereof, (14) a compound as described in (1) above, which is 6-(2,2- dimethyl-3-sulfamoyl-1-propoxy)-7-isopropyl[1,2,4jtri- azolo[l,5-b]pyridazine or a salt thereof, (15) a compound as described in (1) above, which is 6-(2,2- diethyl-3-sulfamoyl-1-propoxy)-7-isopropyl[1,2,4]tri- azolo[l,5-b]pyridazine or a salt thereof, (16) a compound as described in (1) above, which is 6-(2,2- dimethyl-3-sulfamoyl-1-propoxy)-7-isobutyl[1,2,4]tri- azolo[l,5-b]pyridazine or a salt thereof, (17) a compound as described in (1) above, which is 6-(2,2- diraethyl-3-sulfamoyl-1-propoxy)-7-tert-butyl[1,2,4]tri- azolo[l,5-b]pyridazine or a salt thereof, (18) a compound as described in (1) above, which is 6-(2,2- diethyl-3-sulfamoyl-l-propoxy)-7-tert- butyl[l,2,4]triazolo[l,5-b]pyridazine or a salt thereof, (19) a process of producing a compound as described in (1) above which comprises reacting a compound of the formula: or a salt thereof, with a compound of the formula: or a salt thereof, in which Z 1 and Z 2 are a leaving group upon mutual reaction; the other symbols are as described in (1) above, (20) a compound of the formula: wherein W is a leaving group; the other symbols are described in (1) above, or a salt thereof, (21) a composition which comprises a compound as described in (1) above, (22) a pharmaceutical composition which comprises a compound as described in (1) above, (23) an anti-PAF composition, which comprises a compound as described in (1) above, (24) a composition for inhibiting an eosinophil chemotaxis which comprises a compound as described in (1) above, (25) an anti-asthmatic composition, which comprises a compound as described in (1) above, (26) an anti-allergic composition, which comprises a compound as described in (1) above, (27) a composition for preventing or treating allergic rhinitis, which comprises a compound as described in (1) above, and (28) a composition for preventing or treating atopic dermatitis, which comprises a compound as described in (1) above. Provided that compound [I] or a salt thereof contains an asymmetric carbon atom in its molecular structure, optical isomers and racemic mixtures are included in the scope of the present invention. The term "lower alkyl" used in the present specification means, for example, a linear or branched Cι- 6 alkyl grjoup. Examples of the said "Cι_ 6 alkyl group" include methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl, pentyl and hexyl. The term "cycloalkyl group" used in the present specification means, for example, a C 3 - 6 cycloalkyl group. Examples of the said "C 3 -6 cycloalkyl group" include cyclopropyl, cyclobutyl, cyclopentyl and cyclohexyl. The term "polycarbon alkyl group" used in the present specification means, for example, an alkyl group having 2 or more carbon atoms. Preferable examples of polycarbon alkyl group include linear or branched C 2 - 6 alkyl groups (e.g., ethyl, propyl, isopropyl, butyl, isobutyl, tert- butyl, pentyl, hexyl), preferably a branched alkyl group (e.g., isopropyl, isobutyl, tert-butyl). Example of the substituents which the said "lower alkyl," "cycloalkyl group" and "polycarbon alkyl group" optionally have, include hydroxyl groups, amino groups, carboxyl groups, nitro groups, mono- or di-lower alkylamino groups (e.g., mono- or di-Cι_6 alkylamino groups such as methylamino, ethylamino, propylamino, dimethylamino and diethylamino) , lower alkoxy groups (e.g., C 1 - 6 alkoxy groups such as methoxy, ethoxy, propoxy and hexyloxy), lower alkylcarbonyloxy groups (e.g., C 1 - 6 alkylcarbonyloxy groups such as acetoxy and ethylcarbonyloxy) and halogen atoms (e.g., fluorine, chlorine, bromine, iodine), the number of substituents being 1 to 4. The term "halogen atom" used in the present specification means, for example, fluorine, chlorine, bromine, iodine. The term "cycloalkylene group" used in the present specification means, for example, a divalent group obtained by removing the two hydrogen atoms bound to two different carbon atoms of a 3- to 7-membered cycloalkane. The term "cycloalkylidene group" used in the present specification means, for example, a divalent group obtained by removing the two hydrogen atoms bound to one carbon atom of a 3- to 7-membered cycloalkane. Specifically, examples of the cycloalkylidene groups include the following: , preferably, the following: The term "nitrogen-containing heterocyclic group" used in the present specification means, for example, a group obtained by removing the hydrogen atom bound to the nitrogen atom of a 3- to 13-membered nitrogen-containing heterocyclic group that contains one nitrogen atom, in addition to carbon atoms, and that may contain 1 to 3 hetero atoms selected from the atoms comprising nitrogen atoms, oxygen atoms and sulfur atoms. Specifically, examples of the nitrogen-containing heterocyclic groups include 3- to 9-membered nitrogen-containing heterocyclic groups such as the following: - * The substituent which the said "cycloalkylene group", "cycloalkylidene group" and "nitrogen-containing heterocyclic group" optionally have is exemplified by lower alkyl groups (e.g., Ci-β alkyl groups such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl, pentyl, hexyl), amino groups, mono- or di-lower alkylamino groups (e.g., mono- or di-Ci-β alkylamino groups such as methylamino, ethylamino, dimethylamino and diethylamino) , hydroxyl groups, carboxyl groups, nitro groups, lower alkoxy groups (e.g., Ci-β alkoxy groups such as methoxy, ethoxy and propoxy) and halogen atoms (e.g., fluorine, chlorine, bromine, iodine), the number of substituents being 1 to 3. In the above-mentioned formulae, R 1 represents a hydrogen atom, a halogen atom or an optionally substituted lower alkyl group. As the said "halogen atom", "optionally substituted lower alkyl.group" of R 1 , use is made of the same ones as the above-mentioned "halogen atom", "optionally substituted lower alkyl group". Preferable examples of R 1 include a hydrogen atom, a Cι- 6 alkyl (e.g., methyl, ethyl, propyl, isopropyl), especially a hydrogen atom is commonly used. In the above-mentioned formulae, R 2 represents an optionally substituted polycarbon alkyl group or an optionally substituted cycloalkyl group. As the said "optionally substituted polycarbon alkyl group", "optionally substituted cycloalkyl group" of R 2 , use is made of the same ones as the above-mentioned "optionally substituted polycarbon alkyl group", "optionally substituted cycloalkyl group". Preferable examples of R 2 include branched C 3 -6 alkyl groups (e.g., isopropyl, isobutyl, tert-butyl), especially an isopropyl group, a tert-butyl group are commonly used, most preferably an isopropyl group. In the above-mentioned formulae, X represents an oxygen atom or S(0) p , wherein p represents an integer of 0 to 2. Preferable examples of X include an oxygen atom, S, especially an oxygen atom is commonly used. In the above-mentioned formulae, Y represents (i) a group of the formula: wherein R 3 and R 4 independently represent a hydrogen atom or an optionally substituted lower alkyl group, or (ii) an optionally substituted cycloalkylene group or an optionally substituted cycloalkylidene group. As the said "optionally substituted lower alkyl" of R 3 and R 4 , "optionally substituted cycloalkylene group" or "optionally substituted cycloalkylidene group" of Y, use is made of the same ones as the above-mentioned "optionally substituted lower alkyl", "optionally substituted cycloalkylene group" or "optionally substituted cycloalkylidene group". Preferable examples of Y include a group of the formula: R 3a —C— > 4a wherein R 3a and R 4a independently represent a hydrogen atom or a C 1 - 6 alkyl group such as methyl, ethyl, propyl or isopropyl. More preferablly, the following: ,3b ,4b wherein R 3b and R b independently represent a C 1 - 4 alkyl group such as methyl or ethyl is commonly used. Preference is also given to cycloalkylene groups or cycloalkylidene groups for Y; more preferable examples of cycloalkylidene groups include the following: most preferable examples of cycloalkylidene groups include the following: In the above-mentioned formulae, R 5 and R 6 independently represent a hydrogen atom, an optionally substituted lower alkyl group, or an optionally substituted cycloalkyl group, or together with the adjacent nitrogen atom may form a nitrogen-containing heterocyclic ring which is optionally substituted. As the said "optionally substituted lower alkyl group", "optionally substituted cycloalkyl group" of R 5 and R 6 , "nitrogen-containing heterocyclic ring which is optionally substituted" that R 5 and R 6 may form together with the adjacent nitrogen atom, use is made of the same ones as the above-mentioned "optionally substituted lower alkyl group", "optionally substituted cycloalkyl group", "nitrogen-containing heterocyclic ring which is optionally substituted". Preferable examples of R 5 and R 6 include hydrogen atoms and C 1 - 6 alkyl groups (e.g., methyl, ethyl, propyl, isopropyl), especially hydrogen atoms are commonly used. In the above-mentioned formulae, m represents an integer of 0 to 4. Preferably, m is an integer of 1 to 4, especially 1 or 2 is commonly used. In the above-mentioned formulae, n represents an integer of 0 to 4. Preferably, n is an integer of 1 to 4, especially 1 or 2 is commonly used. It is most preferable that m and n are both 1. Preferable examples of the compound [I] or a salt thereof are as follows: a compound, wherein R 1 is a hydrogen atom; R 2 is a C 2 -6 alkyl group; X is an oxygen atom; Y is a group of the formula: wherein R 3b and R b are independently a C 1 - 4 alkyl group; R 5 and R 6 are a hydrogen atom or a C 1 - 6 alkyl group; m and n are independently 1 or 2, or a salt thereof. Preferable practical examples of the compound [I] or a salt thereof are as follows: 6-(2,2-dimethyl-3-sulfamoyl-l-propoxy)-7- ethyl[l,2,4jtriazolo[l,5-b]pyridazine or a salt thereof, 6-(2,2-dimethyl-3-sulfamoyl-1-propoxy)-7-n- propyl[l,2,4]triazolo[l,5-b]pyridazine or a salt thereof, 6-(2,2-dimethyl-3-sulfamoyl-1-propoxy)-7- isopropyl[l,2,4]triazolo[l,5-b]pyridazine or a salt thereof, 6-(2,2-diethyl-3-sulfamoyl-1-propoxy)-7- isopropyl[l,2,4]triazolo[l,5-b]pyridazine or a salt thereof, 6-(2,2-dimethyl-3-sulfamoyl-1-propoxy)-7- isobutyl[l,2,4]triazolo[l,5-b]pyridazine or a salt thereof. 6-(2,2-dimethyl-3-sulfamoyl-1-propoxy)-7-tert- butyl[l,2,4]triazolo[l,5-b]pyridazine or a salt thereof, 6-(2,2-diethyl-3-sulfamoyl-l-propoxy)-7-tert- butyl[l,2,4]triazolo[l,5-b]pyridazine or a salt thereof. The salt of compound [I] of the present invention is exemplified by salts with inorganic acids (e.g., hydrochloric acid, phosphoric acid, hydrobromic acid, sulfuric acid) and salts with organic acids (e.g., acetic acid, formic acid, propionic acid, fumaric acid, maleic acid, succinic acid, tartaric acid, citric acid, malic acid, oxalic acid, benzoic acid, methanesulfonic acid, benzenesulfonic acid), preferably physiologically acceptable acid-adduct salts. Provided that compound [I] of the present invention has an acidic group, such as - COOH, in a substituent thereof, it may form a salt with an inorganic base (e.g., an alkali metal or alkaline earth metal such as sodium, potassium, calcium or magnesium, or ammonia) or an organic base (e.g., a tri-Cι- 3 alkylamine such as triethylamine) . Methods of producing the compound [I] of the present invention or salts thereof are described below. The compound (I) of the present invention or a salt thereof can be synthesized by method (A), in which a compound of the formula: or a salt thereof, react with a compound of the formula: wherein the symbols are of the same meaning as defined above, or a salt thereof. Examples of the leaving groups of Z 1 include halogen atoms (e.g., chlorine, bromine, iodine), Cβ-io arylsulfonyloxy groups (e.g., benzenesulfonyloxy, p- tolylsulfonyloxy) and C 1 - 4 alkylsulfonyloxy groups (e.g., methanesulfonyloxy) . The group of Z 2 which leaves the molecule upon reaction with Z 1 is exemplified by a hydrogen atom or an alkali metal such as sodium or potassium when X is an oxygen atom or a sulfur atom, or by an alkali metal such as sodium or potassium when X is -SO- or -SO 2 -. In this reaction, the compound [III] or a salt thereof is normally used at 1 to 5 mol, preferably 1 to 2 mol, per mol of the compound [II] or a salt thereof. This condensation reaction is preferably carried out in the presence of a base. The base is exemplified by alkali metal hydrides such as sodium hydride and potassium hydride; alkali metal alkoxides such as sodium methoxide and sodium ethoxide; alkali metal hydroxides such as sodium hydroxide and potassium hydroxide; and carbonates such as sodium carbonate and potassium carbonate. Also, this reaction can be carried out in an inert solvent, exemplified by alcohols such as methanol and ethanol; ethers such as dioxane and tetrahydrofuran; aromatic hydrocarbons such as benzene, toluene and xylene; nitriles such as acetonitrile; amides such as dimethylformamide and dimethylacetamide; and sulfoxides such as dimethyl sulfoxide. Reaction temperature ranges usually from 10 to 200 β C, preferably from 50 to 100°C. Reaction time ranges usually from 30 minutes to 24 hours, preferably from 1 to 6 hours. The compound [I] of the present invention or a salt thereof can also be synthesized by method (B) , in which a compound of the formula: wherein the symbols are of the same meaning as defined above, or a salt thereof, react with a compound of the formula: Z 1 -(CH 2 ) m -Y- [ ] wherein the symbols are of the same meaning as defined above, or a salt thereof. In this reaction, the compound [V] or a salt thereof is normally used at 1 to 5 mol, preferably 1 to 2 mol, per mol of the compound [IV] or a salt thereof. This condensation reaction is preferably carried out in the presence of a base. The base is exemplified by alkali metal hydrides such as sodium hydride and potassium hydride; alkali metal alkoxides such as sodium methoxide and sodium ethoxide; alkali metal hydroxides such as sodium hydroxide and potassium hydroxide; and carbonates such as sodium carbonate and potassium carbonate. Also, this reaction can be carried out in an inert solvent, exemplified by alcohols such as methanol and ethanol; ethers such as dioxane and tetrahydrofuran; aromatic hydrocarbons such as benzene, toluene and xylene; nitriles such as acetonitrile; amides such as dimethylformamide and dimethylacetamide; and sulfoxides such as dimethyl sulfoxide. Reaction temperature ranges usually from 10 to 200°C, preferably from 50 to 150°C. Reaction time ranges usually from 30 minutes to 24 hours, preferably from 1 to 10 hours. The compound [I] of the present invention or a salt thereof can still also be synthesized by method (C), in which a compound of the formula: wherein W represents a leaving group; the other symbols are of the same meaning as defined above, or a salt thereof, react with a compound of the formula: wherein the symbols are of the same meaning as those given above, or a salt thereof. Examples of the leaving groups of W include halogen atoms (e.g., chlorine, bromine, iodine), Cβ-io arylsulfonyloxy groups (e.g., benzenesulfonyloxy, p- tolylsulfonyloxy) and C 1 - 4 alkylsulfonyloxy groups (e.g., methanesulfonyloxy) , preferably halogen atoms (e.g., chlorine, bromine, iodine). In this reaction, the compound [VII] or a salt thereof is normally used at 1 to 5 mol, preferably 1 to 2 mol, per mol of the compound [VI] or a salt thereof. This reaction can be carried out in an inert solvent exemplified by alcohols such as methanol and ethanol; ethers such as dioxane and tetrahydrofuran; aromatic hydrocarbons such as benzene, toluene and xylene; nitriles such as acetonitrile; amides such as dimethylformamide and dimethylacetamide; and sulfoxides such as dimethyl sulfoxide. Reaction temperature ranges usually from -20 to 100°C, preferably from -10 to 50°C. Reaction time ranges usually from 30 minutes to 5 hours, preferably from 1 to 3 hours. When the compound [I] is obtained in free form, it can be converted into a salt by a known method. When the compound [I] is obtained as a salt, it can be converted into a free form or another salt. The compound [I] or a salt thereof thus obtained can be isolated and purified by known means such as solvent extraction, pH adjustment, redistribution, salting out, crystallization, recrystallization and chromatography. When compound [I] or a salt thereof is obtained in the obtained in the mixture of optical isomers, it can be separated into the d- and 1- configurations by an ordinary means of optical resolution. Hereinafter described are methods of producing starting compounds [II], [III], [IV], [V], [VI] and [VII] or salts thereof that are used to produce compound [I] or a salt thereof. Salts of these compounds include salts with inorganic acids (e.g., hydrochloric acid, phosphoric acid, hydrobromic acid, sulfuric acid) and salts with organic acids (e.g., acetic acid, formic acid, propionic acid, fumaric acid, maleic acid, succinic acid, tartaric acid, citric acid, malic acid, oxalic acid, benzoic acid, methanesulfonic acid, benzenesulfonic acid) . Provided that these compounds have an acidic group, such as -COOH, in a substituent thereof, it may form a salt with an inorganic base (e.g., an alkali metal or alkaline earth metal such as sodium, potassium, calcium or magnesium, or ammonia) or an organic base (e.g., a tri-Cι- 3 alkylamine such as triethylamine) . The starting compound [II] or a salt thereof can, for example, be synthesized by the method described in the Journal of Organic Chemistry, Vol. 39, p. 2143 (1974) or a modification thereof. The starting compound [III] or a salt thereof and the compound [V] or a salt thereof can, for example, be synthesized by the methods described in Chemische Berichte, Vol. 91, p. 2130 (1958), the Journal of Organic Chemistry, Vol. S , p. 2162 (1987), and EP 381132/1990, or modifications thereof. The starting compound [IV] or a salt thereof can, for example, be synthesized by the method described in EP 381132/1990 or a modification thereof. The starting compound [VI] or a salt thereof can, for example, be synthesized by (1) reacting a compound [II] or a salt thereof with a compound of the formula: Z 2 X—(CH 2 ) m -Y-(CH 2 ) n —S0 2 W [VIII] wherein the symbols are of the same meaning as defined above, or (2) reacting a compound [IV] or a salt thereof with a compound of the formula: Z 1 -(CH 2 ) m -Y-(CH 2 ) n _S0 2 W [ιχ] wherein the symbols are of the same meaning as defined above. In the reaction (1) above, the compound [VIII] is usually used in a ratio of 1 to 5 mol, preferably 1 to 2 mol, per mol of the compound [II] or a salt thereof. This reaction can be carried out in the same manner as the above-described reaction of the compound [II] or a salt thereof and the compound [III] or a salt thereof. In the reaction (2) above, compound [IX] is normally used in a ratio of 1 to 5 mol, preferably 1 to 2 mol, per mol of compound [IV] or a salt thereof. This reaction can be carried out in the same manner as the above-described reaction of the compound [IV] or a salt thereof and the compound [V] or a salt thereof. The starting compound [VII] or a salt thereof and starting compounds [VIII] and [IX] can be synthesized by commonly known methods or modifications thereof. Although the salts that may be formed by the above- described starting compounds are not subject to limitation, as long as the object of the present invention is accomplished, examples of salts include the same salts as the above-described salts that may be formed by compound [I]. Although these starting compounds or salts thereof thus obtained can be isolated and purified by known means such as solvent extraction, pH adjustment, redistribution, salting out, crystallization, recrystallization and chromatography, they may be used as starting materials for the next process, in the form of reaction mixture without purification. When the starting compound used in each of the reactions for synthesizing the above-described desired compounds, the starting compound has an amino group, carboxyl group or hydroxyl group as a substituent, these substituents may have a protective group in common use in peptide chemistry etc.; the desired compound can be obtained by removing, as appropriate, the protective group after completion of the reaction. Amino-protecting groups include, for example, formyl, Cι- 6 alkylcarbonyl groups (e.g., acetyl, ethylcarbonyl) , phenylcarbonyl group, Cι_6 alkyl-oxycarbonyl groups (e.g., methoxycarbonyl, ethoxycarbonyl) , phenyloxycarbonyl group, C 7 - 10 aralkyl-carbonyl group (e.g., benzylcarbonyl) , trityl group, phthaloyl group and N,N-dimethylaminomethylene group, which are optionally substituted. Examples of the substituents which these groups optionally have, include halogen atoms (e.g., fluorine, chlorine, bromine, iodine), C 1 - 6 alkyl-carbonyl groups (e.g., methylcarbonyl, ethylcarbonyl, butylcarbonyl) and nitro groups, the number of substituents being 1 to 3. Examples of the carboxyl-protecting groups include Ci- 6 alkyl groups (e.g., methyl, ethyl, n-propyl, isopropyl, n-butyl, tert-butyl), phenyl, trityl and silyl, which are optionally substituted. Examples of the substituents which these groups optionally have, include halogen atoms (e.g., fluorine, chlorine, bromine, iodine), formyl, Cι_ 6 alkyl- carbonyl groups (e.g., acetyl, ethylcarbonyl, butylcarbonyl) and nitro groups, the number of substituents being 1 to 3. Examples of the hydroxyl-protecting groups include Cχ_ 6 alkyl groups (e.g., methyl, ethyl, n-propyl, isopropyl, n-butyl, tert-butyl), phenyl, C7- 10 aralkyl groups (e.g., benzyl), formyl, C 1 -6 alkyl-carbonyl groups (e.g., acetyl, ethylcarbonyl), phenyloxycarbonyl, benzoyl, C 7 - 10 aralkyl- carbonyl groups (e.g., benzylcarbonyl) , pyranyl, furanyl and silyl, which are optionally substituted. Examples of substituents which these groups optionally have, include halogen atoms (e.g., fluorine, chlorine, bromine, iodine), Cι_ 6 alkyl groups (e.g., methyl, ethyl, n-propyl), phenyl, C 7 -. 10 aralkyl groups (e.g., benzyl) and nitro groups, the number of substituents being 1 to 4. Protecting groups can be removed by commonly known methods or modifications thereof, including treatments with acids, bases, reducing agents, ultraviolet rays, hydrazine, phenylhydrazine, sodium N-methyldithiocarbamate, tetrabutylammonium fluoride, palladium acetate etc. The compound [I] or a salt thereof of this present invention can be safely used as an anti-asthmatic in mammals (e.g., humans, mice, dogs, rats, bovines), because it exhibits excellent anti-allergic, anti-inflammatory, anti-PAF (platelet activating factor) and eosinophil chemotaxis inhibiting actions, with low toxicity (acute toxicity: D 50 > g/kg). The compound [I] or a salt thereof inhibit eosinophil chemotaxis and local eosinophil infiltration in allergic and inflammatory reactions. It is therefore useful as a therapeutic agent for diseases associated with eosinophil infiltration. Specifically, it can be used to treat or prevent eosinophilic diseases in the above-mentioned mammals, including allergic diseases such as urticaria, atopic dermatitis, allergic rhinitis and hypersensitive pneumonitis; dermal diseases such as eczema, herpetic dermatitis and psoriasis; and respiratory diseases such as eosinophilic pneumonia (PIE syndrome). Route of administration may be oral or non-oral. The preparation for the present invention may contain as active ingredients pharmaceutical components other than the compound [I] or a salt thereof (e.g., anti-asthmatics, anti-allergic agents, anti-inflammatory agents, anti¬ bacterial agents, anti-fungal agents). Examples of these pharmaceutical components include anti-asthmatics (e.g., theophylline, procaterol, ketotifen, terfenadine, azelastine, seratrodast) , anti-allergic agents (e.g., ketotifen, terfenadine, azelatine, epinastine), anti- inflammatory agents (e.g., dichlofenac sodium, ibprofen, indometacin) , anti-bacterial agents (e.g., cefixime, cefdinir, ofloxacin, tosufloxacin) , anti-fungal agents (e.g., fluconazole, itraconazole) . These components are not subject to limitation, as long as the object of the present invention is accomplished, and may be used in appropriate mixing ratios. Useful dosage forms include tablets (including sugar-coated tablets and film-coated tablets), pills, capsules (including microcapsules) , granules, fine subtilaes, powders, syrups, emulsions, suspensions, injectable preparations, inhalants and ointments. These preparations are prepared by conventional methods (e.g., methods described in the Pharmacopoeia of Japan). The content of the compound [I] or a salt thereof in the pharmaceutical preparation of the present invention varies with forms of the preparation, and it is usually 0.01 to 100 weight %, preferably 0.1 to 50 weight %, more preferably 0.5 to 20 weight %, relative to the whole weight of the pharmaceutical preparation. Specifically, tablets can be produced by granulating a pharmaceutical as it is, or in a uniform mixture with excipients, binders, disintegrating agents and other appropriate additives, by an appropriate method, then adding lubricants etc., and subjecting the mixture to compressive shaping, or by subjecting to direct compressive shaping a pharmaceutical as it is, or in a uniform mixture with excipients, binders, disintegrating agents and other appropriate additives, or subjecting to compressive shaping previously prepared granules as it is, or in a uniform mixture with appropriate additives. These tablets may incorporate coloring agents, correctives etc. as necessary, and may be coated with appropriate coating agents. Injectable preparations can be produced by dissolving, suspending or emulsifying a given amount of a pharmaceutical in an aqueous solvent such as water for injection, physiological saline or Ringer's solution, or a non-aqueous solvent such as a vegetable oil, and diluting to a given amount, or transferring a given amount of a pharmaceutical into an ampule for injection and sealing the ampule. Useful carriers for oral preparations include substances in common use in pharmaceutical production, such as starch, mannitol, crystalline cellulose and carboxymethyl cellulose sodium. Useful carriers for injectable preparations include distilled water, physiological saline, glucose solutions and transfusions. Other additives in common use for pharmaceutical production can also be added, as appropriate. Depending on patient age, body weight, symptoms, route and frequency of administration and other factors, the daily dose of these preparations is usually 0.1 to 100 mg/kg, preferably 1 to 50 mg/kg, and more preferably 1 to 10 mg/kg, based on daily dose of active ingredient (the compound [I] or a salt thereof), once or in two portions daily for each asthmatic adult. Best Mode for Carrying out the Invention The present invention is hereinafter described in more detail by means of the following working examples, reference examples, preparation examples and experimental examples, which are not to be construed as limitative. In the working examples below, the fraction containing the desired product was detected by observation via TLC (thin-layer chromatography). TLC was conducted on a TLC plate of Merck 6OF 254 , using a UV detector. Reference Example 1 Production of 3,6-dichloro-4-ethylpyridazine To a suspension of 22.5 g of 3,6-dichloropyridazine, 12.7 g of silver nitrate, and 16.3 g of propionic acid in 250 ml of water was added a solution of 49.3 g of sulfuric acid in 250 ml of water at 50°C, followed by addition of 93 g of ammonium peroxodisulfate in 200 ml of water at 60°C for 20 minutes. The reaction mixture was heated at 70 to 75°C for 30 minutes. After cooling, the reaction mixture was adjusted to pH 7 with 25% ammonium hydroxide solution, and extracted with ethyl ether. The extract was washed with water and dried (MgS0 4 ) and the solvent was distilled off under reduced pressure. The residue was purified by silica gel column chromatography to provide 13.5 g of the title compound. NMR (CDC1 3 ) Si 1.32 (3H,t,J=7Hz) , 2.78(2H,q,J=7Hz) , 7.39(lH,s). Reference Example 2 Production of 3,6-dichloro-4-n-propylpyridazine Using 16.6 g of 3,6-dichloropyridazine and 14.4 g of n-butric acid, the same reaction was conducted as in reference example 1 to produce 12.7 g of the title compound. NMR (CDCI 3 ) δ : 1.10(3H,t,J=7Hz), 1.5-1.9(2H,m) , 2.72(2H,t,J=7Hz), 7.37(1H,S) Reference Example 3 Production of 3,6-dichloro-4-isobutylpyridazine Using 22.3 g of 3,6-dichloropyridazine and 19.9 g of isovaleric acid, the same reaction was conducted as in reference example 1 to produce 15.0 g of the title compoun . NMR (CDC1 3 ) δ'. 1.06(6H,d,J=7Hz), 1.8-2.2(lH,m) , 2.60(2H,d,J=7Hz), 7.38(lH,s). Reference Example 4 Production of 3,6-dichloro-4-n-hexylpyridazine Using 11.7 g of 3,6-dichloropyridazine and 23 g of n- heptanoic acid, the same reaction was conducted as in reference example 1 to produce 14.4 g of the title compound. NMR (CDCI 3 ) δ : 0.84-0.97(3H,m), 1.22-1.48(8H,m) , 1.57- 1.76(2H,m), 7.37(lH,s). Reference Example 5 Production of 4-cyclopentyl-3,6-dichloropyridazine Using 22.4 g of 3,6-dichloropyridazine and 25.1 g of cyclopentanecarboxylic acid, the same reaction was conducted as in reference example 1 to produce 28.7 g of the title compound. NMR (CDCI 3 ) δ: 1.4-2.3(8H,m), 3.30(lH,m), 7.38(1H,S) Reference Example 6 Production of 3-amino-6-chloro-5-ethylpyridazine A mixture of 13.5 g of 3,6-dichloro-4-ethyl pyridazine in 150 ml of 25% ammonium hydroxide solution and 10 ml of ethanol was heated at 130 to 140 β C in sealed tube for 22 hours. After cooling, the solvent was distilled off. Water was added to the residue and resulting crystals were collected by filtration and washed with water and ethyl ether to provide 6.96 g of the title compound. NMR (dβ-DMSO) δ: 1.16(3H,t,J=7Hz) , 2.54(2H,q,J=7Hz) , 6.48(2H,s), 6.73(1H,S) Reference Example 7 Production of 3-amino-6-chloro-5-n-propylpyridazine Using 12.7 g of 3,6-dichloro-5-n-propylpyridazine, 150 ml of 25% ammonium hydroxide solution, and 5 ml of ethanol, the same reaction was conducted as in reference example 6 to produce 6.8 g of the title compound. NMR (CDC1 3 ) δ : 1.00(3H,t,J=7Hz) , 1.57-1.76(2H,m) , 2.59(2H,t,J=7Hz), 4.80(2H,br.s) , 6.60(lH,s). Reference Example 8 Production of 3-amino-6-chloro-5-isopropylpyridazine Using 21.7 g of 3,6-dichloro-4-isopropylpyridazine, 170 ml of 25% ammonium hydroxide solution, and 10 ml of ethanol, the same reaction was conducted as in reference example 6 to produce 11.1 g of the title compound. m.p. 164-165 β C NMR (CDCI 3 ) δ: 1.26(6H,d,J=7Hz), 3.16(lH,m), 4.89(2H,br.s) , 6.65(lH,s). Reference Example 9 Production of 3-amino-6-chloro-5-isobutylpyridazine Using 15.0 g of 3,6-dichloro-4-isobutylpyridazine, 180 ml of 25% ammonium hydroxide solution, and 5 ml of ethanol, the same reaction was conducted as in reference example 6 to produce 7.3 g of the title compound. m.p. 122-123°C NMR (CDCI 3 ) δ: 0.96(6H,d,J=7Hz), 1.8-2.2(lH,m) , 2.48(2H,d,J=7Hz), 4.88(2H,br.s) , 6.38(lH,s). Reference Example 10 Production of 3-amino-5-t-butyl-6-chloropyridazine Using 31.1 g of 4-t-butyl-3,6-dichloropyridazine, 150 ml of 25% ammonium hydroxide solution, and 15 ml of ethanol, the same reaction was conducted as in reference example 6 to produce 20.8 g of the title compound. m.p. 185-188°C NMR (CDCI 3 ) δ: 1.44(9H,s), 4.88(2H,br.s) , 6.74(lH,s). Reference Example 11 Production of 3-amino-6-chloro-5-n-hexylpyridazine Using 14.4 g of 3,6-dichloro-4-n-hexylpyridazine, 150 ml of 25% ammonium hydroxide solution, and 150 ml of ethanol, the same reaction was conducted as in reference example 6 to produce 6.2 g of the title compound. m.p. 97-98 β C NMR (CDC1 3 ) δi 0.84-1.02(3H,m) , 1.20-1.48(8H,m) , 1.54- 1.7l(2H,m), 4.97(2H,br.s), 6.62(lH,s). Reference Example 12 Production of 3-amino-6-chloro-5-cyclopentylpyridazine Using 28.7 g of 4-cyclopentyl-3,6-dichloropyridazine, 210 ml of 25% ammonium hydroxide solution, and 70 ml of ethanol, the same reaction was conducted as in reference example 6 to produce 15.5 g of the title compound. NMR (CDCI 3 ) δi 1.4-2.3(8H,m), 3.20(lH,m), 4.84(2H,br.s) , 6.65(lH,s) Reference Example 13 Production of N-(6-chloro-5-ethylpyridazine-3-yl)formamide oxime To a suspension of 4.6 g of 3-amino-6-chloro-5- ethylpyridazine in 58 ml of toluene was added 6.2 ml of dimethylformamide dimethyl acetal and the reaction mixture was refluxed for 2 hours. The solvent was distilled off under reduced pressure. The residue was purified by silica gel column chromatography and elution was carried out with ethyl acetate- ethanol (10:1). The fractions containing the objective compound were pooled and concentrated. The residue was dissolved in methanol (40 ml) and 1.8 g of hydroxylamine hydrochloride was added to the solution and stirred at room temperature for 2 hours. The resulting crystals were collected by filteration and washed with a small amount of methanol to provide 4.40 g of the title compound. m.p. 175-178 β C Elemental analysis for C 7 H9N 4 OCI Calcd.{%): C, 41.91; H, 4.52; N, 27.93 Found (%): C, 41.73; H, 4.65; N, 27.69 Reference Example 14 Production of N-(6-chloro-5-n-propylpyridazine-3-yl) formamide oxime Using 6.8 g of 3-amino-6-chloro-5-n-propylpyridazine, the same reaction was conducted as in reference example 13 to produce 4.7 g of the title compound. NMR (d 6 -DMS0) δi 0.95(3H,t,J=7Hz), 1.5-1.8(2H,m) , 2.57(2H,t,J=7Hz), 7.36(lH,s) 7.91(lH,d,J=10Hz) , 9.65(lH,d,J=10Hz), 10.40(1H,S). Reference Example 15 Production of N-(6-chloro-5-isopropylpyridazine-3-yl) formamide oxime Using 8.6 g of 3-amino-6-chloro-5-isopropylpyridazine, the same reaction was conducted as in reference example 13 to produce 10.6 g of the title compound. m.p. 170-171 β C Elemental analysis for C 8 H 11 N OCI Calcd.(%): C, 44.76; H, 5.17; N, 26.10 Found (%): C, 44.62; H, 5.02; N, 26.01 Reference Example 16 Production of N-(6-chloro-5-isobutylpyridazine-3-yl) formamide oxime Using 7.0 g of 3-amino-6-chloro-5-isobutylpyridazine, the same reaction was conducted as in reference example 13 to produce 4.9 g of the title compound. m.p. 155-158°C Elemental analysis for C9H 13 N 4 OCIΗ 2 O Calcd.(%): C, 43.82; H, 6.13; N, 22.71 Found (%): C, 43.23; H, 6.21; N, 23.00 Reference Example 17 Production of N-(5-t-butyl-6-chloropyridazine-3-yl) formamide oxime Using 11.1 g of 3-amino-5-t-butyl-6-chloropyridazine, the same reaction as conducted as in reference example 13 to produce 12.0 g of the title compound m.p. 221-224°C Elemental analysis for C9H 13 N 4 OCI Calcd . ( % ) : C , 47 . 27 ; H, 5 .73 ; N, 24.50 Found (%): C, 47.10; H, 5.48; N, 24.68 Reference Example 18 Production of N-(6-chloro-5-n-hexylpyridazine-3-yl) formamide oxime Using 6.0 g of 3-amino-6-chloro-5-n-hexylpyridazine, the same reaction as conducted as in reference example 13 to produce 5.7 g of the title compound, m.p. 131-133°C Elemental analysis for C 11 H 1 7N 4 OCI Calcd.(%): C, 51.46; H, 6.67; N, 21.82 Found (%): C, 51.15; H, 6.87; N, 21.59 Reference Example 19 Production of N-(6-chloro-5-cyclopentylpyridazine-3-yl) formamide oxime Using 8.9 g of 3-amino-6-chloro-5- cyclopentylpyridazine, the same reaction as conducted as in reference example 13 to produce 8.05 g of the title compound. m.p. 207-208 p C Elemental analysis for C 10 H 13 N 4 OCI Calcd.(%): C, 49.90; H, 5.44; N, 23.28 Found (%): C, 49.85; H, 5.60; N, 23.31 Reference Example 20 Production of 6-chloro-7-ethyl[l,2,4]triazolo[l,5- b]pyridazine A mixture of 4.02 g of N-(6-chloro-5-ethylpyridazine- 3-yl)formamide oxime and 25 g of polypyhosphoric acid was heated at 110 to 115°C for 1 hour in oil bath. After cooling, the reaction mixture was poured into ice water and extracted with dichloromethane. The extract was washed with water and dried (MgS0 4 ) and the solvent was distilled off under reduced pressure. Hexane was added to the residue and the resulting crystals were collected by filtration, to provide 2.33 g of the title compound, m.p. 84-85°C Elemental analysis for C7H7CIN 4 Calcd.(%): C, 46.04; H, 3.86; N, 30.68 Found (%): C 46.00; H, 3.79; N, 30.59 Reference Example 21 Production of 6-chloro-7-n-propyl[1,2,4]triazolo[l,5- b]pyridazine Using 4.7 g of N-(6-chloro-5-n-propylpyridazine-3- yl)formamide oxime and 23 g of polyphosphoric acid, the same reaction was conducted as in reference example 20 to produce 3.1 g of the title compound. m.p. 61-62 β C Elemental analysis for C 8 H 9 CIN Calcd.(%): C, 48.87; H, 4.61; N, 28.49 Found (%): C, 48.87; H, 4.55; N, 28.55 Reference Example 22 Production of 6-chloro-7-isopropyl[1,2,4]triazolo[1,5- b]pyridazine Using 20.04 g of N-(6-chloro-5-isopropylpyridazine-3- yl)formamide oxime and 97 g of polyphosphoric acid, the same reaction was conducted as in reference example 20 to produce 12.7 g of the title compound. m.p. 53-54 β C Elemental analysis for C 8 H 9 CIN 4 Calcd.(%): C, 48.87; H, 4.61; N, 28.49 Found (%): C 48.85; H, 4.55; N, 28.48 Reference Example 23 Production of 6-chloro-7-isobutyl[l,2,4]triazolo[l,5- b]pyridazine Using 4.6 g of N-(6-chloro-5-isobutylpyridazine-3- yl)formamide oxime and 22 g of polyphosphoric acid, the same reaction was conducted as in reference example 20 to produce 2.2 g of the title compound. m.p. 60-62°C Elemental analysis for C9H 11 CIN 4 Calcd.(%): C, 51.31; H, 5.26; N, 26.60 Found (%): C, 51.33; H, 5.05; N, 26.71 Reference Example 24 Production of 7-t-butyl-6-chloro[l,2,4]triazolo[l,5- b]pyridazine Using 8.0 g of N-(5-t-butyl-6-chloropyridazine-3- yl)formamide oxime and 38 g of polyphosphoric acid, the same reaction was conducted as in reference example 20 to produce 5.13 g of the title compound. m.p.H0-112°C Elemental analysis for C 9 H 11 CIN 4 Calcd.(%): C, 51.31; H, 5.26; N, 26.60 Found (%): C, 51.15; H, 5.15; N, ^6.66 Reference Example 25 Production of 6-chloro-7-n-hexyl[1,2,4]triazolo[l,5- b]pyridazine Using 5.5 g of N-(6-chloro-5-n-hexylpyridazine-3- yl)formamide oxime and 22 g of polyphosphoric acid, the same reaction was conducted as in reference example 20 to produce 2.2 g of the title compound, m.p. 52-53°C Elemental analysis for C 11 H 15 CIN 4 Calcd.(%): C, 55.35; H, 6.33; N, 23.47 Found (%): C, 55.25; H, 6.12; N, 23.52 Reference Example 26 Production of 6-chloro-7-cyclopentyl[1,2,4]triazolo[1,5- b]pyridazine Using 7.76 g of N-(6-chloro-5-cyclopentylpyridazine-3- yl)formamide oxime and 40 g of polyphosphoric acid, the same reaction was conducted as in reference example 20 to produce 5.51 g of the title compound. m.p. 57-59 β C Elemental analysis for C 10 H 11 CI 4 Calcd.(%): C, 53.94; H, 4.98; N, 25.16 Found (%): C, 53.88; H, 4.97; N, 25.07 Reference Example 27 Production of N-(6-chloro-5-isopropylpyridazin-3- yl)acetamide oxime 3.44 g of 3-amino-6-chloro-5-isopropylpyridazine was suspended in 40 ml of toluene; 4.44 g of dimethylacetamide dimethylacetal was added, followed by refluxing for 2 hours. After the mixture was concentrated under reduced pressure, the resulting residue was subjected to silica gel column chromatography and eluted with ethyl acetate. The desired fraction was collected and concentrated; the resulting residue was dissolved in 25 ml of methanol; 1.37 g of hydroxylamine hydrochloride was added, followed by stirring at room temperature for 1 hour. The resulting crystal was collected by filtration to yield 3.42 g of the title compound. m.p. 175-178 β C Elemental analysis for C 9 H 13 N 4 OCI: Calcd. (%): C, 47.27; H, 5.73; N, 24.50 Found (%): C 47.21; H, 5.81; N, 24.21 Reference Example 28 Production of 6-chloro-7-isopropyl-2-methyl[l,2,4]tri- azolo[1,5-b]pyridazine 1.7 g of N-(6-chloro-5-isopropylpyridazin-3- yl)acetamide oxime and 10 g of polyphosphoric acid were thoroughly kneaded together at room temperature, followed by reaction in an oil bath at 110 - 115°C for 1 hour. After the reaction mixture was cooled, ice water was added, followed by extraction with dichloromethane. The extract was washed with water and dried over magnesium sulfate. After the extract was concentrated under reduced pressure, hexane was added to the residue; the resulting crystal was collected by filtration to yield 1.06 g of the title compound. m.p. 58-60 β C Elemental analysis for C9H 11 N 4 CI: Calcd. (%): C, 51.31; H, 5.26; N, 26.60 Found (%): C, 51.24; H, 5.11; N, 26.53 Example 1 Production of 6-{2,2-dimethyl-3-sulfamoyl-l-propoxy)-7- ethyl[1,2,4]triazolo[1,5-b]pyridazine To a solution of 0.836 g of 3-hydroxy-2,2- dimethylpropane-1-sulfonamide in 25 ml of tetrahydrofuran was added 0.42 g of 60% sodium hydride in oil and the mixture was refluxed for 40 minutes. After cooling, to the reaction mixture was added 0.913 g of 6-chloro-7- ethyl[l,2,4]triazolo[l,5-b]pyridazine and the mixture was refluxed with stirring for 2 hours. After cooling, the reaction mixture was poured into water, adjusted to pH6 with lN-hydrochloric acid, and extracted with ethyl acetate-tetrahydrofuran (1:1). The extract was washed with saturated aqueous solution of sodium chloride and dried (MgS0 4 ) and the solvent was distilled off under reduced pressure. The residue was purified by silica gel column chromatography and elution was carried out with dichloromethane-ethyl acetate-methanol (10:10:1). The fractions containing the objective compound were pooled and the resulting crystals were recrystallized from acetone- water to provide 0.787 g of the title compound, m.p. 222-224 p C Elemental analysis for C 12 H 19 N 5 O 3 S Calcd. (%): C, 45.99; H, 6.11; N, 22.35 Found (%): C, 45.87; H, 6.14; N, 20.33 Example 2 Production of 6-(2,2-dimethyl-3-sulfamoyl-l-propoxy)-7-n- propyl[1,2,4]triazolo[1,5-b]pyridazine Using 0.90 g of 3-hydroxy-2,2-dimethyl-l- propanesulfonamide and 1.0 g of 6-chloro-7-n- propyl[l,2,4]triazolo[l,5-b]pyridazine, the same reaction was conducted as in example 1 to produce 0.77 g of the title compound, m.p. 196-197°C Elemental analysis for C 13 H 21 N 5 O 3 SΗ 2 O Calcd. (%): C, 45.20; H, 6.70; N, 20.27 Found (%): C, 45.68; H, 6.39; N, 20.55 Example 3 Production of 6-(2,2-dimethyl-3-sulfamoyl-l-propoxy)-7- isopropyl[1,2,4]triazolo[1,5-b]pyridazine To a solution of 0.669 g of 3-hydroxy-2,2-dimethyl-l- propanesulfonamide in 30 ml of tetrahydrofuran was added 0.336 g of 60% sodium hydride in oil and the mixture was refluxed for 1 hour. After cooling, to the reaction mixture was added 0.748 g of 6-chloro-7- isopropyl[l,2,4]triazolo[l,5-b]pyridazine and the mixture was refluxed with stirring for 4 hours. After cooling, the reaction mixture was poured into ice water, adjusted to pH6 with lN-hydrochloric acid, and extracted with ethyl acetate-tetrahydrofuran (1:1). The extract was washed with saturated aqueous solution of sodium chloride and dried (MgSθ 4 ) and the solvent was distilled off under reduced pressure. The residue was purified by silica gel column chromatography and elution was carried out with dichloromethane-ethyl acetate-methanol (10:10:1). The fractions containing the objective compound were pooled and the resulting crystals were recrystallized from acetone- water to provide 1.10 g of the title compound, m.p. 197-198 β C Elemental analysis for C 13 H 21 N 5 O 3 S Calcd.(%): C, 47.69; H, 6.46; N, 21.39 Found (%): C, 47.84; H, 6.60; N, 21.33 Example 4 Production of 6-(2,2-diethyl-3-sulfamoyl-l-propoxy)-7- isopropyl[l,2,4]triazolo[l,5-b]pyridazine Using 0.586 g of 3-hydroxy-2,2-diethylpropane-l- sulfonamide and 0.561 g of 6-chloro-7- isopropyl[l,2,4]triazolo[l,5-b]pyridazine, the same reaction was conducted as in example 1 to produce 0.967 g of the title compound, m.p. 190-192 β C Elemental analysis for C1 5 H 2 2N 5 O3S Calcd . ( % ) : C , 50 . 68 ; H , 7 . 09 ; N , 19 .70 Found (%): C, 50.90; H, 7.30; N, 19.42 Example 5 Production of 6-(2,2-dimethyl-3-sulfamoyl-l-propoxy)-7- isobutyl[l,2,4]triazolo[l,5-b]pyridazine Using 0.84 g of 3-hydroxy-2,2-dimethylpropane-l- sulfonamide and 1.0 g of 6-chloro-7- isobutyl[l,2,4]triazolo[l,5-b]pyridazine, the same reaction was conducted as in example 1 to produce 0.63 g of the title compound, m.p. 132-135°C Elemental analysis for Ci 4 H 23 Nsθ 3 S*H 2 θ Calcd. (%): C, 46.78; H, 6.45; N, 19.98 Found (%): C, 46.91; H, 6.40; N, 19.79 Example 6 Production of 6-{2,2-dimethyl-3-sulfamoyl-l-propoxy)-7-t- butyl[1,2,4]triazolo[1.5-b]pyridazine Using 1.0 g of 3-hydroxy-2,2-dimethylpropane-l- sulfonamide and 1.2 g of 7-t-butyl-6- chloro[l,2,4]triazolo[l,5-b]pyridazine, the same reaction was conducted as in example 1 to produce 1.13 g of the title compound, m.p. 168-170 β C Elemental analysis for C 14 H 23 N 5 O 3 S Calcd. (%): C, 49.25; H, 6.79; N, 20.51 Found (%): C, 49.12; H, 6.69; N, 20.81 Example 7 Production of 6-(2,2-dimethyl-3-sulfamoyl-l-propoxy)-7-n- hexyl[1,2,4]triazolo[1,5-b]pyridazine Using 0.74 g of 3-hydroxy-2,2-dimethylpropane-l- sulfona ide and 1.0 g of 6-chloro-7-n- hexyl[l,2,4]triazolo[l,5-b]pyridazine, the same reaction was conducted as in example 1 to produce 1.5 g of the title compound. m.p. 150-151°C Elemental analysis for C 16 H 2 7N 5 O 3 S Calcd . ( % ) : C , 52 .01 ; H , 7 . 37 ; N, 18. 95 Found (%): C, 52.00; H, 7.32; N, 19.15 Example 8 Production of 6-(2,2-dimethyl-3-sulfamoyl-l-propoxy)-7- cyclopβJityl[1,2,4]triazolo[1,5-b]pyridazine Using 1.01 g of 3-hydroxy-2,2-dimethylpropane-l- sulfonamide and 1.27 g of 6-chloro-7- cyclopentyl[l,2,4]triazolo[l,5-b]pyridazine, the same reaction was conducted as in example 1 to produce 1.56 g of the title compound, m.p. 170-172 β C Elemental analysis for C 15 H 23 N 5 O 3 SO.5H 2 O Calcd. (%): C, 49.71; H, 6.67; N, 19.32 Found (%): C, 49.65; H, 6.69; N, 19.48 Example 9 Production of 7-isopropyl-6-(3-sulfamoyl-l- propoxy) [1,2,4]triazolo[1,5-b]pyridazine 168 mg of 60% oily sodium hydride was suspended in 25 ml of tetrahydrofuran; 279 mg of 3-hydroxypropane-l-sulfon- amide was added, followed by refluxing for 40 minutes. After the mixture was cooled, 394 mg of 6-chloro-7- isopropyl[l,2,4]triazolo[l,5-b]pyridazine was added, followed by stirring at room temperature for 20 hours. After ice water was added, 5 N hydrochloric acid was added to bring the mixture to pH 5. The solution was then saturated with sodium chloride and extracted with tetra¬ hydrofuran; the extract was washed with saturated saline and dried over magnesium sulfate. After the dry product was concentrated under reduced pressure, the resulting crystal was washed with ethyl ether and recrystallized from 95% ethanol to yield 414 mg of the title compound, m.p. 190-191°C Elemental analysis for C 1 1H17N 5 O 3 S: Calcd. (%): C, 44.14; H, 5.72; N, 23.39 Found (%): C, 44.12; H, 5.77; N, 22.92 Example 10 Production of 6-(2,2-dimethyl-3-sulfamoyl-l-propoxy)-7- isopropyl-2-methyl[1,2,4]triazolo[1,5-b]pyridazine 252 mg of 60% oily sodium hydride was suspended in 30 ml of tetrahydrofuran; 527 mg of 3-hydroxy-2,2-dimethyl- propane-1-sulfonamide was added, followed by refluxing for 1 hour. After the mixture was cooled, 632 mg of 6-chloro- 7-isopropyl-2-methyl[1,2,4]triazolo[1,5-b]pyridazine was added, followed by thermal refluxing for 6 hours. After the mixture was cooled, ice water was added; 5 N hydrochloric acid was added to bring the mixture to pH 5. The solution was then saturated with sodium chloride and extracted with ethyl acetate-tetrahydrofuran (2:1); the extract was washed with saturated saline and dried over magnesium sulfate. After the extract was concentrated under reduced pressure, the resulting residue was subjected to silica gel column chromatography and eluted with dichloromethane-ethyl acetate-methanol (10:10:1). The desired fraction was collected; the resulting crystal was recrystallized from 95% ethanol to yield 746 mg of the title compound, m.p. 196-199°C Elemental analysis for C 14 H 23 N 5 O 3 S: Calcd. (%): C, 49.25; H, 6.79; N, 20.51 Found (%): C, 49.18; H, 6.76; N, 20.44 Example 11 Production of 6-(2,2-diethyl-3-sulfamoyl-l-propoxy)-7-t- butyl[1,2,4]triazolo[1,5-b]pyridazine 380 mg of 60% oily sodium hydride was suspended in 30 ml of tetrahydrofuran; 980 mg of 3-hydroxy-2,2-diethyl- propane-1-sulfonamide was added, followed by refluxing for 1 hour. After the mixture was cooled, 1.0 g of 7-t-butyl- 6-chloro[l,2,4]triazolo[l,5-b]pyridazine was added, followed by refluxing for 3 hours. After the mixture was cooled, ice water was added; 5 N hydrochlo-ric acid was added to bring the mixture to pH 4. The solution was then saturated with sodium chloride and extracted with tetrahydrofuran; the extract was washed with saturated saline and dried over magnesium sulfate. After the extract was concentrated under reduced pressure, the resulting residue was purified by silica gel column chromatography and eluted with dichloromethane-methanol (30:1). The desired fraction was collected to yield 720 mg of the title compound. m.p. 172-174°C Elemental analysis for C 1 6H 2 7N5O 3 S: Calcd. (%): C, 52.01; H, 7.37; N, 18.95 Found (%): C, 51.86; H, 7.31; N, 18.90 Experimental Example 1 The results of a pharmacological test of the compound [I] or salt thereof according to the invention are shown below. Effect on platelte activating factor (PAF)-induced bronchoconstriction in guinea pig Male Hartley guinea pigs (body weights about 500 g) were used. Bronchoconstriction induced by PAF (1 μg/kg i.v.) in guinea pigs was measured according to the method of Konzett-Roessler. The guinea pig immobilized in the dorsal position, tracheotomy was anesthetized with urethane (1.5 g/kg i.v.) and the trachea was connected through a cannula to a respirator. The side branch of the tracheal cannula was connected to a broncho transducer (Model 7020, Ugobasile). The volume of overflow air was recorded on a rectigraph (Recte-Hori-8S, San-ei Sokki) through the brancho transducer. After guinea pig was given gallamine (1 mg/kg i.v.), the guinea pig was treated by PAF (1 μg/kg). The drug suspended in a 5% solution of gum arabic was administered orally in a dose of 3 mg/kg or 1 mg/kg one hour before PAF treatment. The results are presented in Table 1. Table 1 Effect on PAF-induced Bronchoconstriction % Inhibition of PAF-induced Example bronchoconstriction Number 1 mg/kg, P.O. 3 mg/kg, P.O. 1 70 2 67 3 72 4 60 6 43 83 Reference 25 compound Reference compound: Compound of Example 3 in EP562439 6-(2,2-dimethyl-3-sulfamoyl-1-propoxy)-7-methyl[1,2,4]tri- azolo[1,5-b]pyridazine From Table 1, it is seen that the desired compound [I] or a salt thereof of the present invention possesses greater inhibitory effect than that of the compound having a methyl group at 7-position of the triazolopyridazine skeleton. Experimental Example 2 1) Preparation of a guinea pig eosinophil suspension Male Hartley guinea pigs (body weights approx. 300 g) were intraperitoneally treated with 2 ml of horse serum (Whittaker Bioproducts) once a week for 8 consecutive weeks. Forty-eight (48) hours after the last treatment, 75 ml of physiological saline was infused into the peritoneal cavity and the lavage was collected and centrifuged at 400 G (1500 rpm) for 5 minutes. The pellet was suspended in 5 ml of Percoll discontinuous density, gradients (specific gravity d=1.07), layered on top of the Percoll suspensions (specific gravity d=l.112:5 ml, d=l.095:10 ml, d=l.090:10 ml, d=l.085:7 ml) and centrifuged (18°C) at 1000 G (2200 rpm) for 30 minutes. The cell layer formed in the boundary zone between the d=1.112 and d=1.095 layers was collected. The collected cell sediment was subjected to hypotonic treatment (suspended in water for 30 seconds) to remove the contaminant erythrocytes. The sediment was washed three times with Hanks solution containing 10 mM Hepes (Dojin Kagaku) (Hanks- Hepes) and suspended in Hanks-Hepes containing 2% (w/v) human serum albumin (Wako Pure Chemical) (Hanks-Hepes-HSA) at a concentration of 5.56 x 10 6 celles/ml. The eosinophil purity was 92-96% and the viability of eosinophils was not less than 98%. 2) Chemotaxis inhibition assay To a 24-well petri dish, which serves as a lower chamber, 600 μl of LTB 4 (final concentration 10 "8 M, Cascade Biochemical Ltd.) in suspension in Hanks-Hepes-HSA solution, was transferred, followed by incubation at 37°C for 30 minutes in carbon dioxide incubator. Separately, 200 μl (5 10 6 cells/ml) of eosinophil suspension, previously incubated at 37°C for 15 minutes in a constant- temperature chamber, was added to Chemotaxicell (polycarbonate membrane, pore size 3 μm, thickness 10 μm) , which serves as an upper chamber, after the upper chamber was attached to the 24-well petri dish. After 2 hours of reaction in the carbon dioxide incubator, the Chemotaxicell was removed; 60 μl of a 2% (w/v) solution of EDTA in physiological saline was added to the liquid in the lower chamber. After the mixture was ice cooled, the cells migrating into the lower chamber liquid were counted using a blood cell counter (Coulter Counter (trade name)). The test drug, dissolved in dimethyl formamide (DMF), was added to both the upper and lower chambers to a final concentration of 10~ 5 M. Equation 1 Chemotaxis inhibition rate = Table 2 Inhibitory Effect on LTB 4 ~induced Chemotactic of Guinea Pig Eosinophils Compound Chemotaxis Inhibition Rate (%) Example 1 35 Example 2 24 Example 4 23 Example 5 27 Example 6 38 Example 7 24 Reference compound 12 Reference compound: Same as used in Experimental Example 1 From Table 2, it is seen that the desired compound [I] of the present invention or a salt thereof has more potent inhibitory activity against eosinophil chemotaxis than that of the compound having a methyl group at the 7-position in the triazolopyridazine skeleton. Preparation Example 1 (1) Compound of Example 3 10.0 mg (2) Lactose 60.0 mg (3) Corn starch 35.0 mg (4) Gelatin 3.0 mg (5) Magnesium stearate 2.0 mg A mixture of 10.0 mg of the compound obtained in Example 3, 60.0 mg of lactose and 35.0 mg of corn starch was granulated through a sieve of 1 mm mesh, using 0.03 ml of a 10% aqueous solution of gelatin (containing 3.0 mg of gelatin), after which it was dried at 40 β C and again sieved. The resulting granules were mixed with 2.0 mg of magnesium stearate, followed by compression. The resulting core tablets were coated with a sugar coat, using an aqueous suspension of sucrose, titanium dioxide, talc and gum arabic. The coated tablets were polished with beeswax to yield finished coated tablets. Preparation Example 2 (1) Compound of Example 3 10.0 mg (2) Lactose 70.0 mg (3) Corn starch 50.0 mg (4) Soluble starch 7.0 mg (5) Magnesium stearate 3.0 mg 10.0 mg of the compound obtained in Example 3 and 3.0 mg of magnesium stearate were mixed and granulated, using 0.07 ml of an aqueous solution of soluble starch (containing 7.0 mg of soluble starch). The resulting granules were dried and mixed with 70.0 mg of lactose and 50.0 mg of corn starch, followed by compression, to yield tablets. Preparation Example 3 (1) Compound of Example 3 5.0 mg (2) Sodium chloride 20.0 mg (3) Distilled water was added to reach a total quantity of 2 ml. 5.0 mg of the compound obtained in Example 3 and 20.0 mg of sodium chloride were dissolved in distilled water, and diluted with water to reach a total quantity of 2.0 ml. The resulting solution was filtered and aseptically packed in a 2 ml ampule, which was sterilized and sealed to yield a solution for injection. Industrial Applicability Possessing excellent anti-PAF and eosinophil chemotaxis inhibiting activities, the compound [I] or salt thereof of the present invention is useful as a prophylactic/therapeutic drug for asthma, allergic rhinitis, atopic dermatitis etc.

Claims: CLAIMS 1. A compound of the formula: R 1 wherein R 1 is a hydrogen atom, a halogen atom or an optionally substituted lower alkyl group; R 2 is an optionally substituted polycarbon alkyl group or an optionally substituted cycloalkyl group; X is an oxygen atom or S(0) P/ wherein p is an integer of 0 to 2; Y is (i) a group of the formula: R 3 —C— in wherein R 3 and R 4 are independently a hydrogen atom or an optionally substituted lower alkyl group, or (ii) an optionally substituted cycloalkylene group or an optionally substituted cycloalkylidene group; R 5 and R 6 are independently a hydrogen atom, an optionally substituted lower alkyl group or an optionally substituted cycloalkyl group, or together with the adjacent nitrogen atom may form a nitrogen-containing heterocyclic ring which is optionally substituted; m and n are independently an integer of 0 to 4, or a salt thereof. 2. A compound of claim 1, wherein R 1 is a hydrogen atom or a Cι- 6 alkyl group. 3. A compound of claim 1, wherein the polycarbon alkyl group is a lower alkyl group having 2 or more carbon atoms. 4. A compound of claim 3, wherein the lower alkyl group having 2 or more carbon atoms is a branched C 3 - 6 alkyl group. 5. A compound of claim 1, wherein Y is a group of the formula: wherein R 3a and R 4a are independently a hydrogen atom or a C 1 - 6 alkyl group. 6. A compound of claim 1, wherein R 5 and R 6 are independently a hydrogen atom or a C 1 - 6 alkyl group. 7. A compound of claim 1, wherein R 1 is a hydrogen atom; R 2 is a C 2 -6 alkyl group; X is an oxygen atom; Y is a group of the formula: R 3b —C— ,4b wherein R 3b and R 4b are independently a C 1 - 4 alkyl group; R 5 and R 6 are independently a hydrogen atom or a Ci-β alkyl group; and m and n are independently 1 or 2. 8. A compound of claim 7, wherein R 2 is a branched C 3 - 6 alkyl group. 9. A compound of claim 8, wherein R 5 and R 6 are a hydrogen atom; and m and n are 1. 10. A compound of claim 8, wherein the C 3 - 6 alkyl group is an isopropyl group. 11. A compound of claim 8, wherein the C 3 - 6 alkyl group is a tert-butyl group. 12. A compound of claim 1, which is 6-(2,2-dimethyl-3- sulfamoyl-1-propoxy)-7-ethyl[1,2,4]triazolo[1,5- b]pyridazine or a salt thereof. 13. A compound of claim 1, which is 6-(2,2-dimethyl-3- sulfamoy1-1-propoxy)-7-n-propyl[1,2,4]triazolo[1,5- b]pyridazine or a salt thereof. 14. A compound of claim 1, which is 6-(2,2-dimethyl-3- sulfamoyl-1-propoxy)-7-isopropyl[1,2,4]triazolo[1,5- b]pyridazine or a salt thereof. 15. A compound of claim 1, which is 6-(2,2-diethyl-3- sulfamoyl-1-propoxy)-7-isopropyl[1,2,4]triazolo[1,5- b]pyridazine or a salt thereof. 16. A compound of claim 1, which is 6-(2,2-dimethyl-3- sulfamoyl-1-propoxy)-7-isobutyl[1,2,4]triazolo[1,5- b]pyridazine or a salt thereof. 17. A compound of claim 1, which is 6-(2,2-dimethyl-3- sulfamoyl-1-propoxy)-7-tert-butyl[1,2,4]triazolo[1,5- b]pyridazine or a salt thereof. 18. A compound of claim 1, which is 6-(2,2-diethyl-3- sulfamoyl-1-propoxy)-7-tert-butyl[1,2,4]triazolo[1,5- b]pyridazine or a salt thereof. 19. A process of producing a compound of claim 1, which comprises reacting a compound of the formula: or a salt thereof, with a compound of the formula: or a salt thereof, in which Z 1 and Z 2 are a leaving group upon mutual reaction, the other symbols are as defined in claim 1. 20. A compound of the formula: wherein W is a leaving group, the other symbols are as defined in claim 1, or a salt thereof. 21. A composition which comprises a compound of claim 1. 22. A pharmaceutical composition which comprises a compound of claim 1. 23. An anti-PAF composition, which comprises a compound of claim 1. 24. A pharmaceutical composition for inhibiting an eosinophil chemotaxis, which comprises a compound of claim 1. 25. An anti-asthmatic composition, which comprises a compound of claim 1. 26. An anti-allergic composition, which comprises a compound of claim 1. 27. A composition for preventing or treating allergic rhinitis, which comprises a compound of claim 1. 28. A composition for preventing or treating atopic dermatitis, which comprises a compound of claim 1. 29. Use of a compound of claim 1 for manufacturing an anti-PAF composition. 30. Use of a compound of claim 1 for manufacturing a pharmaceutical composition for inhibiting an eosinophil chemotaxis. 31. Use of a compound of claim 1 for manufacturing an anti-asthmatic composition. 32. Use of a compound of claim 1 for manufacturing an anti-allergic composition. 33. Use of a compound of claim 1 for manufacturing a composition for preventing or treating allergic rhinitis. 34. Use of a compound of claim 1 for manufacturing a composition for preventing or treating atopic dermatitis. 35. A method for treating asthma, allergy, allergic rhinitis or atopic dermatitis in a mammal which comprises administering an effective amount of a compound of claim 1 together with a pharmaceutically acceptable carrier or diluent to the mammal in deed.

Inventors: ASHIDA YASUKO, KAWANO YASUHIKO, MIYAKE AKIO, ASHIDA, YASUKO, KAWANO, YASUHIKO, MIYAKE, AKIO
Applicants: TAKEDA CHEMICAL INDUSTRIES LTD, TAKEDA CHEMICAL INDUSTRIES, LTD.
Application year: 1995
Main classification: C07D487
IPC codes: A61K31, C07D403, C07D487