Process for the preparation of cis-2-methylspiro (1,3-oxathiolane 5-3′) quinuclidine
Methods are provided for making pharmaceutical-grade cis-2-methylspiro(1,3-oxathiolane-5,3′)quinuclidine and pharmaceutically acceptable salts thereof by isomerizing racemic 2-methylspiro(1,3-oxathiolane-5,3′)quinuclidine to cis-2-methylspiro(1,3-oxathiolane-5,3′)quinuclidine and subsequent purification of the C-MSOQ by salt formation with inexpensive and commercially available material such as sulfuric acid. Purification methods are disclosed which employ an organic solvent/water system and recrystallization with an organic solvent such as acetone.
1. A process for the preparation of pharmaceutical grade cis-2-methylspiro(1,3-oxathiolane-5,3′)quinuclidine hydrochloride having a purity >99.5% comprising:
a) treating an epoxide of 3-methylenequinuclidine with hydrogen sulfide gas in a solvent selected from the group consisting of methanol, isopropanol, butanol, and mixtures thereof to obtain 3-hydroxy-3-mercaptomethyl quinuclidine;
b) treating 3-hydroxy-3-mercaptomethyl quinuclidine with acetaldehyde in the presence of a boron trifluoride etherate to generate 2-methylspiro(1,3-oxathiolane-5,3′)quinuclidine base;
c) treating the 2-methylspiro(1,3-oxathiolane-5,3′)quinuclidine base with hydrochloric acid to form a racemic hydrochloride salt;
d) isomerizing the racemic hydrochloride salt with a Lewis acid and an organic solvent to obtain the isomer cis-2-methylspiro(1,3-oxathiolane-5,3′)quinuclidine having a purity of >90%;
e) Purifying the cis isomer having >90% purity by treatment with an inorganic acid and an organic solvent to obtain the cis isomer having a purity of >99.5%.
2. The process according to claim 1 wherein the quantity of hydrogen sulfide gas employed is from 1 to 5 moles.
3. The process according to claim 1 wherein the step of treating an epoxide of 3-methylenequinuclidine, the solvent is methanol.
4. The process according to claim 1 wherein excess hydrogen sulfide is removed by passing nitrogen gas through the reaction mixture.
5. The process according to claim 1 wherein the preparation of 3-hydroxy-3-mercaptomethyl quinuclidine is carried out at a temperature range of −10 to 5° C.
6. The process according to claim 1 wherein the prepared 3-hydroxy 3-mercaptomethyl quinuclidine is not isolated and carried in situ to next step.
7. The process according to claim 1 wherein the formation of 2-methylspiro(1,3-oxathiolane5,3′) quinuclidine base from 3-hydroxy-3-mercaptomethyl quinuclidine is carried out at 0 to 30° C. in the presence of 1 to 5 mole of a catalyst per mole of 3-hydroxy-3-mercaptomethyl quinuclidine.
8. The process according to claim 1 wherein the Lewis acid in the isomerizing step is titanium tetrachloride.
9. The process according to claim 8 wherein the quantity of titanium tetrachloride employed is from 1 to 10 moles.
10. The process according to claim 1 wherein the solvent used for the isomerizing step is selected from the group consisting of dichloromethane, methanol, dimethyl sulfoxide, toluene and mixtures thereof.
11. The process according to claim 1 wherein the isomerizing step is carried out at a temperature of −10 to 50° C.
12. The process according to claim 1 wherein the inorganic acid used in the purifying step is concentrated sulfuric acid.
13. The process according to claim 1 wherein the solvent used in the purifying step is selected from the group consisting of acetone, methyl ethyl ketone, methyl isobutyl ketone, toluene and mixtures thereof.
14. The process according to claim 1 wherein the purifying step further comprises treatment with an organic solvent and water mixture.
15. The process according to claim 14 wherein the organic solvent mixed with water is acetone.