METHODS FOR PREPARING OLTIPRAZ
The invention provides improved methods of synthesizing oltipraz, which result in higher overall yield and better purity of the desired product.
1 - 20 . (canceled)
21 . A method of making a purified oltipraz composition, comprising the steps of:
(i) reacting a quantity of pyrazine-2-carboxylic acid methyl ester with methyl propionate to form methyl 2-methyl-3-oxo-3-(pyrazin-2-yl)propanoate, wherein the reaction is carried out in the presence of a base and a solvent comprising 1,4-dioxane in tetrahydrofuran (THF), wherein the ratio of 1,4-dioxane in the THF is at least about 1:5;
(ii) adding at least one aqueous liquid to quench the reaction in Step (i);
(iii) adding a nonpolar organic solvent and an ionic salt, thereby forming a composition comprising an aqueous component and an organic component, wherein the organic component comprises the nonpolar solvent and methyl 2-methyl-3-oxo-3-(pyrazin-2-yl) propanoate;
(iv) separating the organic component from the aqueous component;
(v) reacting the methyl 2-methyl-3-oxo-3-(pyrazin-2-yl)propanoate ester in the organic component with P 2 S 5 in the presence of a nonpolar organic solvent to form 4-methyl-5-(pyrazin-2-yl)-3H-1,2-dithiole-3-thione (oltipraz);
(vi) quenching the reaction with an aqueous composition to yield a composition comprising (i) an aqueous component and (ii) an organic component that comprises oltipraz;
(vii) separating the organic component comprising oltipraz to yield an organic composition comprising oltipraz in the nonpolar organic solvent;
(viii) reducing the amount of solvent in the organic composition;
(ix) precipitating the oltipraz in the organic composition to yield a composition comprising oltipraz;
(x) separating the precipitated oltipraz; and
(xi) purifying the separated oltipraz precipitate.
22 . The method according to claim 21 , wherein the step of purifying comprises recrystallization.
23 . The method according to claim 21 , wherein the step of purifying does not comprise chromatographic separation.
24 . The method according to claim 22 , wherein the step of purifying comprises recrystallization and does not comprise chromatographic separation.
25 . The method according to claim 21 , wherein step (viii) comprises evaporating at least a portion of the solvent in the organic composition, step (ix) comprises adding to the organic composition a solvent that causes the oltipraz to precipitate, and step (x) comprises separating the oltipraz by filtering.
26 . The method according to claim 21 , wherein the reaction of step (i) is carried out in the presence of a base comprising potassium t-butoxide or sodium pentanoate.
27 . The method according to claim 26 , wherein the base comprises potassium t-butoxide.
28 . The method according to claim 26 , wherein the mole ratio of the base to methyl propionate is from about 3:1 to about 1:1.
29 . The method according to claim 21 , wherein the ratio of 1,4-dioxane to THF in Step (i) is from about 1:5 to about 1:3.
30 . The method according to claim 29 , wherein the ratio of 1,4-dioxane to THF in Step (i) is from about 1:4.
31 . The method according to claim 21 , wherein the nonpolar solvent in Step (iii) is the same nonpolar solvent used in Step (v).
32 . The method according to claim 31 , wherein the nonpolar organic solvent used in Step (iii) comprises an aromatic solvent.
33 . The method according to claim 32 , wherein the nonpolar organic solvent in Step (v) comprises toluene or xylene.
34 . The method according to claim 33 , wherein the nonpolar solvent in Step (iii) and Step (v) is toluene.
35 . The method according to claim 21 , wherein the reaction of step (i) is carried out in the presence of a base comprising potassium t-butoxide or sodium pentanoate, and the ratio of 1,4-dioxane to THF in Step (i) is from about 1:5 to about 1:3.
36 . The method according to claim 35 , wherein the mole ratio of the base to methyl propionate in step (i) is from about 3:1 to about 1:1, and the ratio of 1,4-dioxane to THF in Step (i) is about 1:4.
37 . The method according to claim 22 , wherein the reaction of step (i) is carried out in the presence of a base comprising potassium t-butoxide or sodium pentanoate, and the ratio of 1,4-dioxane to THF in Step (i) is from about 1:5 to about 1:3.
38 . The method according to claim 37 , wherein the mole ratio of the base to methyl propionate in step (i) is from about 3:1 to about 1:1, and the ratio of 1,4-dioxane to THF in Step (i) is about 1:4.
39 . The method according to claim 23 , wherein the reaction of step (i) is carried out in the presence of a base comprising potassium t-butoxide or sodium pentanoate, and the ratio of 1,4-dioxane to THF in Step (i) is from about 1:5 to about 1:3.
40 . The method according to claim 39 , wherein the mole ratio of the base to methyl propionate in step (i) is from about 3:1 to about 1:1, and the ratio of 1,4-dioxane to THF in Step (i) is about 1:4.