Pharmaceutically acceptable inorganic and organic salts of 5-methylpyrazine-2-carboxylic acid-4-oxide

1. A method for the preparation of 5-methylpyrazinecarboxylic acid-4-oxide esters comprising:

reacting 5-methylpyrazinecarboxylic acid with a C 1-4 alcohol in the presence of an acidic cation exchange resin, and

oxidizing the so-obtained ester in a homogeneous system consisting of a tungstate or molybdate catalyst and 35% w/w hydrogen peroxide at a pH range of 2.5 to 7.

2. A method for the preparation of the pharmaceutically acceptable organic and inorganic salts of 5-methylpyrazinecarboxylic-4-oxide comprising:

oxidizing an ester of 5-methylpyrazinecarboxylic acid in a homogeneous system consisting of either a tungstate or molybdate catalyst and about 35% w/w hydrogen peroxide at a pH of from about 2.5 to about 7; and

saponifying said oxidized ester with an aqueous alkali or alkaline earth hydroxide to obtain the salt of 5-methylpyrazinecarboxylic-4-oxide.

3. A method for the preparation of a pharmaceutically acceptable inorganic or organic salt of a 5-methylpyrazinecarboxylic acid-4-oxide having the formula I

wherein

M is selected from the group of alkali metal and alkaline earth metal cations consisting of Na, K, Mg, Ca, and the conjugate acid of amine bases selected from the group consisting of tris(hydroxymethyl)aminomethanol, N,N-dimethylanolamine, N-methyl-D-glucamine, L-lysine and L-arginine, comprising the steps of:

reacting 5-methylpyrazinecarboxylic acid-4-oxide having the formula II

wherein

R is H with a C 1-4 alcohol in the presence of 20–40% w/w acidic cation exchange resin to obtain an ester of the formula III

wherein

R is C 1-4 alkyl;

oxidizing the ester of formula III in a homogeneous system consisting of either a tungstate or molybdate catalyst and about 35% hydrogen peroxide at a pH of from about 2.5 to about 7; and

saponifying the oxidation product with an aqueous alkali or alkaline earth hydroxide or with an organic salt forming agent to obtain the salt of formula I.

4. A method for the preparation of a pharmaceutically acceptable organic or inorganic salt of 5-methylpyrazinecarboxylic acid-4-oxide having the formula I

wherein

M is selected from the group consisting of alkali metal and alkaline earth metal cations consisting of Na, K, Mg, Ca and the conjugate acid of the amine bases selected from the group consisting of tris(hydroxymethyl)/aminomethanol, N, N-dimethylethanolamine, N-methyl-D-glucamine, L-lysine, and L-arginine, comprising the steps of:

preparing a homogeneous system consisting of about 35% w/w/hydrogen peroxide and a 2.5 to 9 mole % of a catalyst selected from the group consisting of sodium tungstate, tungstic acid and acidified ammonium heptamolybdate;

dissolving said catalyst in water,

adding 50% w/w sulfuric acid until reaching a pH of 3 to 4 to obtain a solution;

adding about 1.3 to 2.5 equivalents of 35% w/w of aqueous hydrogen peroxide to allow said catalyst to completely react with said aqueous hydrogen peroxide;

adding one molar equivalent of 5-methylpyrazinecarboxylic acid ester and stirring the system at 65° C. to 75° C. for 6 to 28 hrs to obtain a reaction mixture;

cooling the reaction mixture;

collecting the solid product by filtration;

washing the collected product with ice-cold water;

drying the washed isolated ester oxide under vacuum at about 60° C.;

saponifying the ester oxide with an aqueous alkali hydroxide or with an organic salt forming agent at about 50° C. and a pH range of 8 to 15; and

precipitating the salt of 5-methylpyrazinecarboxylic acid oxide by a pharmaceutically acceptable alcohol selected from the group consisting of ethanol, isopropanol and specially denatured alcohol to obtain the product of formula I.

5. The method of claim 4 wherein said tungstic acid is prepared in situ from sodium tungstate and sulfuric acid.

6. The method of claim 4 wherein said saponifying is with sodium, potassium, calcium or magnesium hydroxide.

7. A method for the preparation of a pharmaceutically acceptable inorganic salt of 5-methylpyrazinecarboxylic acid-4-oxide having the formula I

wherein

M is selected from the group consisting of alkali metal and alkaline earth metal cations consisting of Na, K, Mg, and Ca, comprising the steps of:

preparing a homogeneous system consisting of about 35% w/w/hydrogen peroxide and a 2.5 to 9 mole % of a catalyst selected from the group consisting of sodium tungstate, tungstic acid and acidified ammonium heptamolybdate;

dissolving said catalyst in water;

adding 50% w/w sulfuric acid until reaching a pH of 3 to 4 to obtain a solution;

adding about 1.3 to 2.5 equivalents of 35% w/w of aqueous hydrogen peroxide to allow said catalyst to completely react with said aqueous hydrogen peroxide;

adding one molar equivalent of 5-methylpyrazinecarboxylic acid and stirring the system at 65° C. to 75° C. for 6 to 28 hrs to obtain a reaction mixture;

cooling the reaction mixture;

collecting the solid product by filtration;

washing the collected product with ice-cold water;

drying the washed isolated ester oxide under vacuum at about 60° C.;

saponifying the ester oxide in diethyl ether, 2,3,4,5-tetrahydrofuran or toluene to obtain a solution;

collecting the resulting inorganic salt by filtration; and

drying the salt at 50° C. to 65° C. under vacuum.

8. The method of claim 7 wherein said catalyst is present in amounts of 2.5 to 3 mol %.

9. The method of claim 7 wherein said 35% hydrogen peroxide is present in about 1.3 to 1.45 equivalents.

10. The method of claim 7 wherein said saponification is at a pH of about 9 to 9.5.