Pyrazine-2-carboxamide derivatives useful in treating allergic disease

The present invention relates to novel derivatives of yyrazine and pharmaceutically-acceptable salts thereof which exhibit an effective anti-allergic activity and can be used for treatment of allergic disease, to a process for the preparation thereof, pharmaceutical compositions of thereof, and a method of treating therewith.
It is already known that disodium cromoglycate(generic name, The Merck Index, 10th Edition, 2580) represented by formula (II) ##STR3## and tranilast(generic name, The Merck Index, 10th Edition, 9392) represented by formula (III) ##STR4## have effective anti-allergic activity and are useful as agents for bronchial asthma and have already have been marketed widely for clinical use.
Furthermore, it is also known that 6-methyl-N-(1H-5-tetrazolyl) pyridine-2-carboxamide (TA-5707F, Jpn, Kokai Tokyyo Koho 82-95984), represented by formula(IV): PG,3 ##STR5## is in some stage of development as an anti-allergic agent.
It has been gradually revealed after the progress of extensive studies in the allergological field that allergic bronchial asthma appears as a result of an antigen-induced allergic reaction of type I upon the entrance of an allergen into the human body, whereupon chemical mediators are released from mast cells. For treating such allergic diseases, an agent which can prevent the release of chemical mediators has been used.
Disodium cromoglycate represented by formula (II) is an agent which has been used for the first time in clinical praxis.
However, it must be administered as only by inhalation in the form of powder or solution, because it can not be used in oral administration, which is disadvantageous because of the use of a special apparatus is required for aspiration and because of a feeling of physical discomfort in the throat.
The second commercial product, tranilast represented by formula (III) is known as an orally active anti-allergic agent for inhibiting the release of chemical mediators.
However the effect of this drug is not adequate. The daily dosage for effective treatment is about 300 mg and this is accompained by side effects in the digestive system, such as nausea, abdominal pain, and gastric discomfort.
As explained above the effect of the known drugs of this field was not yet sufficient, so that it was necessary to find and develop another drug for this purpose.
As a result of extensive investigation on new drugs, which can inhibit the release of chemical mediators, it has been found that, after study of the compounds having a tetrazole group in the structure, the pyrazine derivatives of this application possess an effective antiallergic activity and thus the present invention has been accomplished.
The invention of this application relates to derivatives of pyrazine represented by the general formula ##STR6## wherein R represents hydrogen atom or ##STR7## wherein R.sub.1 and R.sub.2, which may be the same or different, represent hydrogen atom, straight or branched-chain lower alkyl group or cycloalkyl group having 3 to 6 carbon atoms, phenyl group, which may be substituted with halogen, lower alkyl group or lower alkoxyl group, or 5 to 7 membered-ring together with the neighborous nitrogen atom, which may have oxygen atom nitrogen atom or sulfur atom as ring-member and may be substituted with substituent, and pharamaceutically-acceptable salts thereof.
As examples of straight or branched-chain lower alkyl groups, R.sub.1 and R.sub.2 of the general formula (I) are methyl-, ethyl-, propyl-, isopropyl-, butyl-, isobutyl-, sec-butyl-, tert-butyl-, hexyl-, and dodecyl-group.
Examples of cycloalkyl group having 3 to 6 carbon atoms ar cyclopropyl-, cyclobutyl-, cyclopentyl-, and cyclohexy-group.
The examples of substituent of the phenyl group are halogen such as fluorine, chlorine, bromine, iodine atom, lower alkyl group such as methyl-, ethyl-, propyl-, isopropyl-, butyl-, isobutyl-group etc. and lower alkoxyl group such as methoxy-, ethoxy-, propoxy-group etc. Examples of 5 to 7membered-ring, which together with the neighborous nitrogen atom, are pyrrolidinyl-, piperidinyl-, methylpiperidinyl-, hydroxypiperidinyl-, hexahydroazepinyl-, piperazinyl-, 4-methylpiperazinyl-, 4-ethylpiperazinyl-, 4-acetylpiperazinyl-, 4-phenylpiperazinyl-, morpholinyl-, thiomorpholinyl-, homopiperazinyl-, 4-methylhomopiperazinylgroup etc.
Pharmacologically-acceptable salts of the compound having the said general formula (I) are acid additional salt or alkali additional salts. The former includes mineral acid salts such as hydrochloride, sulfate, nitrate, hydrobromide, hydroiodide, phosphate, etc.; or organic acid salts such as acetate, maleate, fumarate, citrate, or tartarate, etc. The latter includes inorganic alkali salts such as sodium, potassium, calcium or ammonium salt, etc.; or organic base salts such as ethanol amine salt, N,N-dialkyl ethanol amine salt, and tris (hydroxymethyl) aminomethane etc.; or basic amino acid salts such as lysine, arginine, and histidine salt etc.
In the first method, the compound having the said formula (I) is obtained by reacting a 6-halogenopyrazine derivative having the following general formula(V), ##STR8## wherein X is a halogen atom, with an amine derivative represented by the following general formula (VI), ##STR9## wherein R.sub.1 and R.sub.2 each has the same meaning as that described above, in the presence or absence of a solvent.
The solvent used in this reaction can be any kind so far as it does not inhibit the reaction. The example of solvent is water, alcohols such as methanol, ethanol, propanol, buaanol; ethers such as ethyleneglycol dimethyl ether (monoglyme), diethyleneglycol dimethyl ether (diglyme), triethyleneglycol dimethyl ether (triglyme); aprotic polar solvents such as dimethylformamide, dimethylsulfoxide or hexamethylphosphoric triamide; aromatic hydrocarbons such as benzene or toluene; or organic bases such as pyridine, picoline, lutidine, collidine or trietylamine. Preferably can be used ethanol, benzene, dimethysufoxide.
The reaction can be carried out under normal or elevated pressure and at a temperature from room temperature to 200.degree. C., prefeable from 80.degree. C. to 110.degree. C.
The starting material of this method, represented by the general formula (V) can be prepared by following method.
The compound having the said formula (V) is obtained by reacting pyrazine carboxylic acid derivatives of the following general formula (VII), ##STR10## wherein X has the same meaning as that described above, with 5-amino-1H-tetrazole represented by the following formula (VIII). ##STR11##
According to the second method, the inventive compound represented by the general formula (I) is prepared from derivatives of pyrazine-2-carboxylic acid represented by the following general formula (IX), ##STR12## wherein R has the same meaning as that described above, after conversion of the carboxyl group to a functional group, for example acid chloride, acid anhyrride, mixed acid anhydride, with a 5-amino-1H-tetrazole(VIII) in the presence or absence of a solvent.
The base used in the process of this invention is, for example, pyridine, picoline, lutidine, collidine, N-methylpiperidine, N-methylpyrrolidine, N-methylmorpholine, triethylamine, potassium carbonate, sodium carbonate etc. Preferably can be used the triethylamine.
The inert organic solvent used in this reaction can be any kind so far as it does not inhibit the reaction. The examples are ether, benzene, tetrahydrofuran, dioxane, chloroform, methylene chloride, dimethylsulfoxide, N, N-dimethylformamide etc., preferably can be used tetrahydrofuran.
The reaction can be carried out at a temperature from -10.degree. C. to boiling point, preferably at a temperature from room temperature to the boiling point of the solvent used.
The derivatives of pyrazine-2-carboxylic acid represented by formula (IX), which can be used as a starting material for the process of this invention are known, in literatures, Dissertationes pharmaeutiae pharmacologicae, 24, p.577, (1972).
The thus prepared derivatives of pyrazine represented by formula (I) and pharmaceutically-acceptable salts thereof exhibit an effective anti-allergic activity, expectorant activity, and can be used extremely favourably as medicine for treating of bronchial asthma, food allergy, hay fever, alergic urticaria, allergic rhinitis, allergic conjunctivitis and can be used topically or by oral administration.
As an example to show the excellent effect of the present compounds, its inhibitory effect of histamine release is shown below in Table 1 an the acute toxicity values in Table 2.
1. Inhibitory effect of histamine release
The inhibitory effect of histamine release was examined with the under method, while using disodium cromoglycate(II), tranilast (III), and TA-5707F(IV)as reference drugs.
Mixed peritoneal cells obtained from male Wistar rats weighing 350-400 g were sensitized by incubating for 2 hr at 37.degree. C. with anti-DNP-As rat serum (produced according to the method of Tada and Okumura [Tada, T. and Okmura, K.: J. Immunology, 106,1002 (1971)]. The cell suspension containing about 1.times.10.sup.5 mast cells/ml was prepared in Hepes Tyrode buffer containing heparin (10 unit/ml ) and BSA (0.3%). This suspension was divided into 0.8 ml aliquots in separate polyethylene tubes. Aliquots of the cell suspension were preincubated at 37.degree. C. for 10 min, and then 0.1 ml of the test compounds were added in various concentrations. After incubation at 37.degree. C. for 1 min, 0.1 ml of DNP-As solution (50.mu.g/ml) were added, followed by incubation at 37.degree. C. for 2 min. The reactio was terminated by adding 2 ml of the cold buffer. The supernatants were separated by centrifugation, the cell pellets were resuspended in 3 ml buffer and placed for 3 min in the heating block (100.degree. C.) to release the residual histamine into cells. The histamine was quantitated using the spedrofluorometric technique of modified Shore's method. The IC .sub.50 was obtained from the dose-response curve.
Results are shown in Table 1.
TABLE 1______________________________________Inhibitory effect on histamine releaseTest compound IC.sub.50 (M) value______________________________________Example 2 2.5 .times. 10.sup.-9Example 3 2.0 .times. 10.sup.-9Example 4 1.7 .times. 10.sup.-8Example 5 5.0 .times. 10.sup.-9Example 6 .sup. 4.7 .times. 10.sup.-10Example 7 1.5 .times. 10.sup.-8Example 8 (free) 1.2 .times. 10.sup.-9Example 9 5.6 .times. 10.sup.-9Example 14 3.6 .times. 10.sup.-8Example 15 3.6 .times. 10.sup.-8Example 16 .sup. 6.2 .times. 10.sup.-11disodium cromoglycate (II) 1.9 .times. 10.sup.-7tranilast (III) 2.4 .times. 10.sup.-5TA-5707F (IV) 4.6 .times. 10.sup.-8______________________________________
2. Acute toxicity test
Male ICR mice 5 weeks old were used as 5 animals at a group. The compounds were administered orally at each dosage.
Results are shown in Table 2.
TABLE 2______________________________________Acute Toxicity LD.sub.50test compound (mg/kg)______________________________________Example 8 >2000(free)Example 8 >2000(sodium salt)______________________________________
A compound of the present invention represented by general formula (I) can be administrated per os, e.g., in the form of pills or tablets, in which it may be present together with any of the usual pharmaceutical carriers, conventionally by compounding a compound of this invention together with a customary carrier or adjuvant, such as talc, magnesium stearate, starch, lactose, gelatin, any of numerous gums, and the like. Thus, in their most advantageous form, the compositions of this invention will contain a non-toxic pharmaceutical carrier in addition to the active ingredient of the present invention. Exemplary solid carriers are lactose, magnesium stearate, calcium stearate, starch, terra alba, dicalcium acacia, or the like. Representative liquid carriers are peanut oil, sesame oil, olive oil, water, or the like. The active agents of this invention can be conveniently administered in such compositions containing active ingredient so as to eventually be within the dosage range illustrated hereafter. Thus, a wide variety of pharmaceutical forms suitable for many modes of administration and dosages may be employed. For oral administration, the active ingredient and pharmaceutical carrier may, for example, take the form of a granule, pill, tablet, lozenge, elixir, syrup, or other liquid suspension or emulsion, whereas, for parenteral administration, the composition may be in the form of a sterile solution.
The method of using the compounds of this invention comprises internally or externally administering a compound of this invention, preferably orally or parenterally and preferably admixed with the pharmaceutical carrier, for example, in the form of any of the above compositions, or filled into a capsule, to aleviate conditions to be treated and symptoms thereof in a living animal body. Illustratively, it may be used in an amount of about 1 to about 1000 mg per day (divided into three parts), preferably in amount of 1 to 100 mg per day (divided into three parts) for an oral dose, while parenteral dosages are usually less and ordinarily about one-half of the oral dose. The unit dose is preferably given a suitable number of times daily, typically three times. For dropping lotion in the dyes and nose it may be used in an amount of about 0.1 to 100 mg preferably 1 to 50 mg at a time.
The unit dose may vary depending upon the number of times given. Naturally, a suitable clinical dose must be adjusted in accordance with the condition, age, and weight of the patient, and it goes without saying that the enhanced activities of the compounds of the invention, together with their reduced side effects, also make them suitable for wide variations, and this invention therefore should not be limited by the exact ranges stated. The exact dosage, both unit dosage and daily dosage, will of course have to be determined according to established medical principles.

The following examples are given by way illustration only and are not to be construed as limitations of this invention, many variations of which are possible without departing from the scope and spirit thereof.
Reference: 6-Chloro-N-(1H-5-tetrazolyl)pyrazine-2-carboxamide
To a suspension of 1.59 g of 6-chloropyrazine-2-carboxylic acid in 30 ml of tetrahydrofuran, 1.54 ml of triethylamine and 1.36 ml of pivaloyl chloride were added dropwise successively at 0.degree. C. under stirring. After stirring for 1 hour at 0.degree. C., 0.94 g of 5-amino-1H-tetrazol was added to the mixture, and the reaction mixture was refluxed for 18 hours. After cooling, 50 ml of water was added to the reaction mixture. The precipitate was collected by filtration, and recrystalized from a mixture of dimethylsulfoxide and methanol affording 0.78 g of the desired compound as pale red crystals, m.p. 261.degree.-26.degree. C. (decomp.).
Analysis: C.sub.6 H.sub.4 ClN.sub.7 O: Calcd. %: C, 31.94; H, 1.79; N, 43.46. Found %: C, 32.03; H, 1.70; N, 43.68.
EXAMPLE 1
N-(1H-5-Tetrazolyl)pyrazine-2-carboxamide
To a suspension of 1.50 g of pyrazine-2-carboxylic acid in 50 ml of tetrahydrofuran, 1.85 ml of triethylamine and 1.27 ml of ethyl chlorocarbonate were added dropwise successively at 0.degree. C. under stirring. After stirring for 30 minutes at 0.degree. C., 1.35 g of 5-amino-1H-tetrazole was added to the mixture, and the reaction mixture was stirred for 28.5 hours at room temperature. The precipitate was collected by filtration, and washed with dilute hydrochloric acid affording 2.05 g as colorless crystals, which was recrystalized from dimethylsulfoxide giving colorless crystals, m.p. 291.degree.-296 .degree. C. (decomp.).
Analysis:C.sub.6 H.sub.5 N.sub.7 O: Calcd. %: C, 37.70; H, 2.64; N, 51.29. Found %: C, 37.43; H, 2.97; N, 51.74.
EXAMPLE 2
6-(Methylamino)-N-(1H-5-tetrazolyl)pyrazine-2-carboxamide
To a suspension of 2.26 g of 6-chloro-N-(1H-5-tetrazolyl)pyrazine-2-carboxamide in 30 ml of ethanol, 6.50 ml of 30%-methylamine ethanol solution was added, and the mixture was heated for 24 hours at 80.degree.-90 .degree. C. in a sealed tube. The reaction mixture was adjusted with ethanolic hydrogen chloride to pH 3. The precipitate was collected by filtration, and recrystalized from a mixture of dimethylsulfoxide and methanol affording 1.57 g of the desired compound as pale yellow needles, m.p. 260.degree. C. (decomp.).
Analysis:C.sub.7 H.sub.8 N.sub.8 O: Calcd. %: C, 38.18; H, 3.66; N, 50.89.
Found %: C, 38.16; H, 3.85; N, 51.14.
EXAMPLE 3
6-(Ethylamino)-N-(1H-5-tetrazolyl)pyrazine-2-carboxamide
To a suspension of 2.26 g of 6-chloro-N-(1H-5-tetrazolyl)pyrazine-2-carboxamide in 30 ml of ethanol, 4.05 ml of 70%-ethylamine aqueous solution was added, and the mixture was heated for 24 hours at 80.degree.-90 .degree. C. in a sealed tube. The reaction mixture was adjusted with ethanolic hydrogen chloride to pH 3. The precipitate was collected by filtration, and recrystalized from a mixture of dimethylsulfoxide and methanol affording 1.66 g of the desired compound as pale yellow needles, m.p. 272.degree.-273.5 .degree. C. (decomp.).
Analysis:C.sub.8 H.sub.10 N.sub.8 O: Calcd. %: C,41.02; H,4.30; N,47.84. Found %: C,40.95; H,4.45; N,47.99.
EXAMPLE 4
6-(n-Propylamino)-N-(1H-5-tetrazolyl)pyrazine-2-carboxamide
To a suspension of 1.13 g of 6-choloro-N-(1H-5-tetrazolyl)pyrazine-2-carboxamide in 20 ml of ethanol, 2.06 ml of n-propylamine was added, and the mixture was heated for 24 hours at 80.degree.-90 .degree. C. in a sealed tube. The reaction mixture was adjusted with ethanolic hydrogen chloride to pH 3. The precipitate was collected by filtration, and recrystalized from a mixture of dimethylsulfoxide and methanol affording 0.91 g of the desired compound as pale yellow needles, m.p. 278.degree.-279.5 .degree. C. (decomp.).
Analysis:C.sub.9 H.sub.12 N.sub.8 O: Calcd. %: C,43.54; H,4.87; N,45.14. Found %: C,43.42; H,5.23; N,44.91.
EXAMPLE 5
6-(Isopropylamino)-N-(1H-5-tetrazolyl)pyrazine-2-carboxamide
To a suspension of 2.26 g of 6-chloro-N-(1H-5-tetrazolyl)pyrazine-2-carboxamide in 30 ml of ethanol, 4.26 ml of isopropylamine was added, and the mixture was heated for 44 hours at 80.degree.-90 .degree. C. in a sealed tube. The reaction mixture was adjusted with ethanolic hydrogen chloride to pH 3. The precipitate was collected by filtration, and recrystalized from a mixture of dimethylsulfoxide and methanol affording 1.36 g of the desired compound as pale yellow needles, m.p. 272.degree.-274 .degree. C. (decomp.).
Analysis:C.sub.9 H.sub.12 N.sub.8 O: Calcd. %: C,43.54; H,4.87; N,45.14. Found %: C,43.51; H,5.00; N,45.49.
EXAMPLE 6
6-(Dimethylamino)-N-(1H-5-tetrazolyl)pyrazine-2-carboxamide
(a) To a suspension of 30 g of 6-chloro-N-(1H-5-tetrazolyl)pyrazine-2-carboxamide in 260 ml of ethanol, 60 ml of 50%-dimethylamine aqueous solution was added, and the mixture was heated for 9 hours at 80.degree.-90 .degree. C. in an autoclave. The reaction mixture was adjusted with concentrated hydrochloric acid to pH 2. The precipitate was collceted by filtration, and recrystalized from a mixture of dimethylsulfoxide and methanol affording 23.1 g of the desired compound as yellow needles, m.p. 267.degree.-269.degree. C. (decomp.).
Analysis:C.sub.8 H.sub.10 N.sub.8 O: Calcd. %: C,41.02; H,4.30; N,47.84. Found %: C,40.95; H,4.63; N,47.83.
(b) To a suspension of 0.58 g of 6-(dimethylamino)pyrazine-2-carboxylic acid in 10 ml of tetrahydrofuran, 0.53 ml of triethylamine and 0.47 ml of pivaloyl chloride were added dropwise successively at 0 .degree. C. under stirring. After stirring for 1 hour at 0 .degree. C., 0.33 g of 5-amino-1H-tetrazole was added to the mixture, and the reaction mixture was stirred for 1 hour at room temperature, and then refluxed for 6 hours. After cooling, 70 ml of water was added to the reaction mixture. The precipitate was collected by filtration, and recrystalized from a mixture of dimethylsulfoxide and methanol affording 0.36 g of the desired compound as yellow needles. The obtained crystal was consistent with that of (a).
EXAMPLE 7
6-(Diethylamino)-N-(1H-5-tetrazolyl)pyrazine-2-carboxamide
To a suspension of 1.13 g of 6-chloro-N-(1H-5-tetrazolyl)pyrazine-2-carboxamide in 20 ml of benzene, 20 ml of diethylamine was added, and the mixture was heated for 24 hours at 80.degree.-90 .degree. C. in a sealed tube. The reaction mixture was evaporated. Water was added to the residue, and then the aqueous solutron was adjusted with dilute hydrochloric acid to pH 3. The precipitate was collected by filtration, and recrystalized from a mixture of dimethylsulfoxide and methanol affording 0.75 g of the desired compound as yellow plates, m.p. 217.degree.-218 .degree. C.
Analysis:C.sub.10 H.sub.14 N.sub.8 O: Calcd. %: C,45.80; H,5.38; N,42.72. Found %: C,45.57; H,5.67; N,42.84.
EXAMPLE 8
6-(1-Pyrrolidinyl)-N-(1H-5-tetrazolyl)pyrazine-2-carboxamide
(a) To a suspension of 200 g of 6-chloro-N-(1H-5-tetrazolyl)pyrazine-2-carboxamide in 1800 ml of ethanol, 220 ml of pyrrolidine was added, and the mixture was refluxed for 22 hours. The reaction mixture was adjusted with concentrated hydrochloric acid to pH 3. The precipitate was collected by filtration, and recrystalized from a mixture of dimethylsulfoxide and methanol affording 193 g of the desired compound as yellow needles, m.p. 273.degree.-275 .degree. C. (decomp.).
Analysis:C.sub.10 H.sub.12 N.sub.8 O: Calcd. %: C,46.15; H,4.65; N,43.05. Found %: C,46.14; H,4.91; N,43.43.
(b) To a suspension of 2.90 g of 6-(1-pyrrolidinyl) pyrazine-2-carboxylic acid in 45 ml of tetrahydrofuran, 2.30 ml of triethylamine and 2.00 ml of pivaloyl chloride were added dropwise successively at 0 .degree. C. under stirring. After stirring for 1 hour at 0 .degree. C., 1.40 g of 5-amino-1H-tetrazole was added to the mixture, and the reaction mixture was stirred for 1 hour at room temperature, and then refluxed for 12 hours, The reaction mixture was evaporated, and water was added to the residue. The precipitate was collected by filtration, and recrystalized from dimethylsulfoxide affording 1.63 g of the desired compound as yellow needles. The obtained crystal was consistent with that of (a)
6-(1-Pyrrolidinyl)-N-(1H-5-tetrazolyl)pyrazine-2-carboxam ide sodium salt.
21.6 g of 6-(1-pyrrolidinyl)-N-(1H-5-tetrazolyl) pyrazine-2-carboxamide was dissolved in 110 ml of water and 29.8 ml of 10%-sodium hydroxide aqueous solution. 465 Ml of ethanol was added to the aqueous solution, and the mixture was cooled for 1 hour at 0 .degree. C. The precipitate was collected by filtration, and recrystalized from aqueous ethanol affording 17.6 g of the sodium salt as yellow columns, m.p. 300>.degree. C.
Analysis:C.sub.10 H.sub.11 N.sub.8 O Na: Calcd. %: C,42.56; H,3.93; N,39.70. Found %: C,42.44; H,4.16; N,39.89.
EXAMPLE 9
6-(1-Piperidinyl)-N-(1H-5-tetrazolyl)pyrazine-2-carboxamide
(a) To a suspension of 30 g of 6-chloro-N-(1H-5-tetrazolyl)pyrazine-2-carboxamide in 270 ml of ethanol, 39.4 ml of piperidine was added, and the mixture was refluxed for 15 hours. The reaction mixture was adjusted with ethanolic hydrogen chloride to pH 3. The precipitate was collected by filtration, and recrystalized from a mixture of dimethylsulfoxide and methanol affording 26.4 g of the desired compound as yellow columns, m.p. 247.degree.-250 .degree. C. (decomp.).
Analysis: C.sub.11 H.sub.14 N.sub.8 O: Calcd. %: C,48.17; H,5.14; N,40.85. Found %: C,48.12; H,5.38; N,40.93.
(b) To a suspension fo 1.28 g of 6-(1-piperidinyl) pyrazine-2-carboxylic acid in 18 ml of tetrahydrofuran, 0.95 ml of triethylamine and 0.84 ml of pivaloyl chloride were added dropwise successively at 0 .degree. C. under stirring. After stirring for 1 hour at 0 .degree. C., 0.58 g of 5-amino-1H-tetrazole was added to the mixture, and the reaction mixture was stirred for 30 minutes at room temperature, and then refluxed for 12 hours. The reaction mixture was evaporated, and water was added to the residue. The precipitate was collected by filtration, and recrystalized from a mixture of dimethylsulfoxide and methanol affording 0.55 g of the desired compound as yellow columns. The obtained crystal was consistent with that of (a).
EXAMPLE 10
6-(3-Methyl-1-piperidinyl)-N-(1H-5-tetrazoly1)pyrazine-2-carboxamide
To a suspension of 1.13 g of 6-chloro-N-(1H-5-tetrazolyl)pyrazine-2-carboxamide in 20 ml of benzene, 2.94 ml of 3-methylpiperidine was added, and the mixture was refluxed for 6 hours. The reation mixture was evaporated, ethanol was added to the residue, and then the ethanol solution was adjusted with ethanolic hydrogen chloride to pH 3. The precipitate was collected by filtration, and recrystalized from a mixture of dimethylsulfoxide and methanol affording 0.81 g of the desired compound as pale yellow columns, m.p. 236.5.degree.-238.5 .degree. C.
Analysis: C.sub.12 H.sub.16 N.sub.8 O: Calcd. %; C,49.99; H,5.59; N,38.87. Found %; C,49.77; H,5.77; N,38.79.
EXAMPLE 11
6-(4-Methyl-1-piperidinyl)-N-(1H-5-tetrazolyl)pyrazine-2-carboxamide
To a suspension of 1.13 g of 6-chloro-N-(1H-5-tetrazolyl)pyrazine-2-carboxamide in 20 ml of benzene, 2.96 ml of 4-methylpiperidine was added, and the mixture was refluxed for 5 hours. The reaction mixture was evaporated, ethanol was added to the residue, and then the ethanol solution was adjusted with ethanolic hydrogen chloride to pH 3. The precipitate was collected by filtration, and recrystalized from a mixture of dimethylsulfoxide and methanol affording 1.02 g of the desired compound as yellow columns, m.p. 246.5.degree.-248.5.degree. C. (decomp.).
Analysis: C.sub.12 H.sub.16 N.sub.8 O: Calcd. %; C,49.99; H,5.59; N,38.87. Found %; C,49.72; H,5.94; N,38.91.
EXAMPLE 12
6-(3-Hydroxy-1-piperidinyl)-N-(1H-5-tetrazolyl)pyrazine-2-carboxamide
To a suspension of 1.13 g of 6-chloro-N-(1H-5-tetrazolyl)pyrazine-2-carboxamide in 20 ml of ethanol, 1.52 g of 3-hydroxypiperidine was added, and the mixture was refluxed for 6 hours. The reaction mixture was adjusted with ethanolic hydrogen chloride to pH 3. The precipitate was collected by filtration, and recrystalized from a mixture of dimethylsulfoxide and methanol affording 0.93 g of the desired compound as yellow crystals, m.p. 257.degree.-259.degree. C. (decomp.).
Analysis: C.sub.11 H.sub.14 N.sub.8 O.sub.2 : Calcd. %: C,45.51; H,4.86; N,38.60. Found %: C,45.41; H,5.16; N,38.42.
EXAMPLE 13
6-(4-Hydroxy-1-piperidinyl)-N-(1H-5-tetrazolyl-)pyrazine-2-carboxamide
To a suspension of 1.13 g of 6-chloro-N-(1H-5-tetrazolyl)pyrazine-2-carboxamide in 20 ml of ethanol, 1.52 g of 4-hydroxypiperidine was added, and the mixture was refluxed for 6 hours. The reaction mixture was adjusted with ethanolic hydrogen chloride to pH 3. The precipitate was collected by filtration, and recrystalized from a mixture of dimethylsulfoxide and methanol affording 1.00 g of the desired compound as pale yellow crystals, m.p. 259.5.degree.-261.degree. C. (decomp.).
Analysis: C.sub.11 H.sub.14 N.sub.8 O.sub.2 : Calcd. %: C,45.51; H,4.86; N,38.60. Found %: C,45.35; H,5.15; N,38.57.
EXAMPLE 14
6-(4-Morpholinyl)-N-(1H-5-tetrazolyl)pyrazine-2-carboxamide
(a) To a suspension of 2.26 g of 6-chloro-N-(1H-5-tetrazolyl)pyrazine-2-carboxamide in 30 ml of ethanol, 4.36 ml of morpholine was added, and the mixture was refluxed for 18 hours. The reaction mixture was adjusted with concentrated hydrochloric acid to pH 2. The precipitate was collected by filtration, and recrystalized from a mixture of dimethylsulfoxide and methanol affording 2.06 g of the desired compound as yellow needles, m.p. 276.degree.-278.degree. C. (decomp.).
Analysis: C.sub.10 H.sub.12 N.sub.8 O.sub.2 : Calcd. %: C,43.48; H,4.38; N,40.56. Found %: C,43.47; H,4.56; N,40.70.
(b) To a suspension of 2.50 g of 6-(4-morpholinyl) pyrazine-2-carboxylic acid in 50 ml of tetrahydrofuran, 3.60 ml of triethylamine and 1.60 ml of pivaloyl chloride were added dropwise successively at 0.degree. C. under stirring. After stirring for 1 hour at 0.degree. C., 1.12 g of 5-amino-1H-tetrazole was added to the mixture, and the reaction mixture was stirred for 1 hour at room temperature, and then refluxed for 12 hours. The reaction mixture was evaporated, and water was added to the residue. The precipitate was collected by filtration, and recrystalized from a mixture of dimethylsulfoxide and methanol affording 1.74 g of the desired compound as yellow needles. The obtained crystal was consistent with that of (a).
EXAMPLE 15
6-(4-Methyl-1-piperazinyl)-N-(1H-5-tetrazolyl)pyrazine-2-carboxamide hydrochloride hydrate
To a suspension of 2.26 of 6-chloro-N-(1H-5-tetrazolyl) pyrazine-2-carboxamide in 30 ml of ethanol, 5.55 ml of N-methylpiperazine was added, and the mixture was refluxed for 6 hours. The reaction mixture was adjusted with ethanolic hydrogen chloride to pH 1. The precipitate was collected by filtration, and recrystalized from a mixture of dimethylsulfoxide and methanol affording 2.27 g of the desired compound as pale yellow crystals, m.p. 246.degree.-250 .degree. C. (decomp.).
Analysis: C.sub.11 H.sub.15 N.sub.9 O.HCl.H.sub.2 O: Calcd. %: C,38.43; H,5.28; N,36.67. Found %: C,38.22; H,5.15; N,36.71.
EXAMPLE 16
6-(Phenylamino)-N-(1H-5-tetrazolyl)pyrazine-2-carboxamide
To a suspension of 1.13 g of 6-chloro-N-(1H-5-tetrazolyl)pyrazine-2-carboxamide in 5 ml of dimethylsulfoxide, 4.55 ml of aniline was added, and the mixture was heated for 17 hours at 80.degree.-90 .degree. C. Water and 10%-sodium hydroxide aqueous solution were added to the reaction mixture, and the aqueous alkaline solution was washed with chloroform. The aqueous layer was filtered, and the filtrate was adjusted with 10%-hydrochloric acid to pH 3. The precipitate was collected by filtration, and recrystalized from a mixture of dimethylsulfoxide and ethanol affording 0.80 g of the desired compound as yellow needles, m.p. 290.degree.-293.5.degree. C. (decomp.).
Analysis: C.sub.12 H.sub.10 N.sub.8 O: Calcd. %: C,51.06; H,3.57; N,39.70. Found %: C,51.16; H,3.86; N,39.68.
EXAMPLE 17
6-[(3-Cholorophenyl)amino]-N-(1H-5-tetrazolyl)pyrazine-2-carboxamide
To a suspension of 1.13 g of 6-chloro-N-(1H-5-tetrazolyl)pyrazine-2-carboxamide in 10 ml of dimethylsulfoxide, 5.39 ml of m-chloroaniline was added, and the mixture was heated for 76 hours at 80.degree.-90 .degree. C. Water and 10%-sodium hydroxide aqueous solution were added to the reaction mixture, and the aqueous alkaline solution was washed with chloroform. Aqueous layer was filtered, and the filtrate was adjusted with 10%-hydrochloric acid to pH 3. The precipitate was collected by filtration, and recrystalized from a mixture of dimethylformamide and ethanol affording 0.34 g of the desired compound as yellow crystals m.p. 281.degree.-289 .degree. C. (decomp.).
Analysis: C.sub.12 H.sub.9 ClN.sub.8 O: Calc..%: C,45.51; H,2.86; N,35.38. Found %: C,45.26; H,3.10; N,35.03.
EXAMPLE 18
6-[(2-Methylphenyl)amino]-N-(1H-5-tetrazolyl)-pyrazine-2-carboxamide
To a suspension of 1.13 g of 6-chloro-N-(1H-5-tetrazolyl)pyrazine-2-carboxamide in 5 ml of dimethylsulfoxide, 5.35 ml of o-toluidine was added, and the mixture was heated for 24 hours at 100.degree.-110 .degree. C. Water and 10%-sodium hydroxide aqueous solution were added to the reaction mixture, and the aqueous alkaline solution was washed with chloroform. Aqueous layer was filtered and the filtrate was adjusted with 10%-hydrochloric acid to pH 3. The precipitate was collected by filtration, and recrystalized from a mixture of dimethylformamide and ethanol affording 0.19 g of the desired compound as dark yellow crystals, m.p. 277.degree.-282.degree. C. (decomp.).
Analysis: C.sub.13 H.sub.12 N.sub.8 O: Calcd. %: C,52.70; H,4.08; N,37.82. Found %: C,52.85; H,4.28; N,38.18.
EXAMPLE 19
6-[(3-Methylphenyl)amino]-N-(1H-5-tetrazolyl)-pyrazine-2-carboxamide
To a suspension of 1.13 g of 6-chloro-N-(1H-5-tetrzolyl) pyrazine-2-carboxamide in 10 ml of dimethylsulfoxide, 5.40 ml of m-toluidine was added, and the mixture was heated for 22 hours at 100.degree.-110.degree. C. Water and 10 %-sodium hydroxide aqueous solution was added to the reaction mixture, and the aqueous alkaline solution was washed with chloroform. Aqueous layer was filtered, and the filtrate was adjusted with 10%-hydrochloric acid to pH 3. The precipitate was collected by filtration, and recrystalized from a mixture of dimethylsulfoxide and methanol affording 0.68 g of the desired compound as yellow needles, m.p. 278.5.degree.-284 .degree. C. (decomp.).
Analysis: C.sub.13 H.sub.12 N.sub.8 O: Calcd.%: C, 52.70; H,43.08; N,37.82. Found %: C,52.56; H,4.17; N,38.18.
EXAMPLE 20
6-[(4-Methylphenyl)amino]-N-(1H-5-tetrazolyl)-pyrazine-2-carboxamide
To a suspension of 1.13 g of 6-chloro-N-(1H-5-tetrazolyl)pyrazine-2-carboxamide in 15 ml of dimethylsulfoxide, 5.36 g of p-toluidine was added, and the mixture was heated for 18 hours at 80.degree.-90 .degree. C., and heated for 6 hours at 100.degree.-110 .degree. C. Water and 10%-sodium hydroxide aqueous solution was added to the reaction mixture, and the aqueous alkaline solution was washed with chloroform. Aqueous layer was filtered, and the filtrate was adjusted with 10%-hydrochloric acid to pH 3. The precipitate was collected by filtration, and recrystalized from a mixture of dimethylsulfoxide and methanol affording 0.93 g of the desired compound as yellow needles, m.p. 289.5.degree.-294 .degree. C. (decomp.).
Analysis: C.sub.13 H.sub.12 N.sub.8 O: Calc. %: C,52.70; H,4.08; N,37.82. Found %: C,52.83; H,4.29; N,38.08.
EXAMPLE 21
6-[(4-Methoxyphenyl)amino]-N-(1H-5-tetrazoly)pyrazine-2-carboxamide
To a suspension of 1.13 g of 6-chloro-(1H-5-tetrazolyl)pyrazine-2-carboxamide in 15 ml of dimethylsulfoxide, 6.16 g of p-anisidine was added, and the mixture was heated for 18 hours 80.degree.-90 .degree. C. Water and 10%-sodium hydroxide aqueous solution was added to the reaction mixture, and the aqueous alkaline solution was washed with chloroform. Aqueous layer was filtered, and the filtrate was adjusted with 10%-hydrochloric acid to pH 3. The precipitate was collected by filtration, and recrystalized from a mixture of dimethylsulfoxide and methanol affording 1.02 g of the desired compound as reddish yellow crystals, m.p. 291.degree.-294 .degree. C. (decomp.).
Analysis:C.sub.13 H.sub.12 N.sub.8 O.sub.2 : Calcd. %: C,50.00; H,3.87; N,35.88. Found %: C,50.08; H,4.05; N,36.05.
The compounds described in Example 22-34 were prepared in the same manner as that described in Example 1-21. The physical properties of the compounds described in Examples 22-34 were shown in Tables 3-4.
TABLE 3__________________________________________________________________________ ##STR13## No.pleam-Ex- R.sub.1 R.sub.2 free baseSalt or Crystals Melting point Solvent ##STR14##__________________________________________________________________________22 H n-butyl free base pale yellow needles 269.about.272.degree.(decomp.) DMFEtOH C.sub.10 H.sub.14 N.sub.8 C, 45.80; H, 5.38; N, 42.72 C, 45.65; H, 5.53; N, 42.8323 H isobutyl free base pale yellow prisms 265.about.275.degree.(decomp.) DMSOEtOH C.sub.10 H.sub.14 N.sub.8 C, 45.80; H, 5.38; N, 42.72 C, 45.77; H, 5.38; N, 42.8224 H sec-butyl free base pale yellow needles 265.about.269.degree.(decomp.) DMFEtOH C.sub.10 H.sub.14 N.sub.8 C, 45.80; H, 5.38; N, 42.72 C, 45.54; H, 5.36; N, 42.4925 H tert-butyl free base yellow crystals 266.about.270.degree.(decomp.) DMFEtOH26 H n-hexyl free base colorless needles 263.about.267.degree.(decomp.) DMFEtOH C.sub.12 H.sub.18 N.sub.8 C, 49.64; H, 6.25; N, 38.60 C, 49.54; H, 6.26; N, 38.4827 H n-do- free base colorless needles 250.about.259.degree.(decomp.) DMSOEtOH C.sub.18 H.sub.30 N.sub.8 C, 57.73; H, 8.07; N, 29.92 decyl C, 57.85; H, 8.09; N, 29.9228 H cyclo- free base pale yellow crystals 272.about.280.degree.(decomp.) DMSOEtOH C.sub.9 H.sub.10 N.sub.8 C, 43.90; H, 4.09; N, 45.51 propyl C, 44.01; H, 4.20; N, 45.7029 H cyclo- free base pale yellow needles 287.about.291.degree.(decomp.) DMSOEtOH C.sub.12 H.sub.16 N.sub.8 C, 49.99; H, 5.59; N, 38.87 hexyl C, 49.99; H, 5.76; N, 38.88__________________________________________________________________________
TABLE 4__________________________________________________________________________ ##STR15## No.pleam-Ex- ##STR16## basefreeSalt or Crystals pointMelting Solvent ##STR17##__________________________________________________________________________30 ##STR18## free base pale yellow crystals >300.degree. H.sub.2 O C.sub.10 H.sub.13 N.sub.9 O.1/2H.sub.2 O C, 42.25; H, 4.96; N, 44.34 C, 41.90; H, 4.89; N, 44.2331 ##STR19## HCl salt yellow crystals 230.about.243.degree. (decomp.) DMSOMeOH C.sub.12 H.sub.17 N.sub.9 C, 42.42; H, 5.34; N, 37.10 C, 42.59; H, 5.55; N, 36.8332 ##STR20## free base yellow needles 250.about.262.degree. (decomp.) DMFEtOH C.sub.16 H.sub.17 N.sub.9 C, 54.69; H, 4.84; N, 35.88 C, 54.66; H, 4.92; N, 36.0233 ##STR21## free base pale yellow crystals 295.about.300.degree. (decomp.) H.sub.2 O C.sub.11 H.sub.15 N.sub.9 C, 45.67; H, 5.23; N, 43.57 C, 45.37; H, 5.42; N, 43.4234 ##STR22## free base pale >300.degree.tals H.sub.2 O C.sub.12 H.sub.17 N.sub.9 C, 47.52; H, 5.65; N, 41.50 C, 47.71; H, 5.66; N,__________________________________________________________________________ 41.32

Number	Date	Country	Kind
60-291916	Dec 1985	JPX
61-256875	Oct 1986	JPX

Number	Name	Date
3966965	Sellstedt et al.	Jun 1976
4044144	Sellstedt et al.	Aug 1977
4112094	Sellstedt et al.	Sep 1978
4404214	Takeda et al.	Sep 1983

Pyrazine-2-carboxamide derivatives useful in treating allergic disease

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Honma et al., J. Med. Chem. 1984, vol. 27, No. 2, pp. 125-128.
Ford et al., J. Med. Chem. 1986, vol. 29, No. 4, pp. 538-549.