(1R, 1′R)-atracurium salts separation process
View Patent ↗The present invention provides an improved method of chromatographically separating the isomers of (1R,rR)-atracurium salts by high-performance liquid chromatography (HPLC), in the absence of a strong acid. The separation is preferably performed on a silica gel HPLC column using an eluent containing an organic solvent, a polar aprotic co-solvent and a weak organic acid.
1. A method of obtaining the 1R-cis,1′R-cis isomer from a (1R,1′R)-atracurium isomer mixture, the method comprising separating the mixture by normal phase, preparative HPLC using a non-aqueous eluent comprising an organic solvent, a polar aprotic co-solvent and a weak acid having a pKa value of 2.5 or higher.
2. The method of claim 1 , comprising:
(a) dissolving the (1R,1′R)-atracurium salt isomer mixture in at least one organic solvent;
(b) applying the isomer mixture solution to a preparative HPLC column containing a normal stationary phase;
(c) eluting the column with the eluent;
(d) collecting one or more fractions containing the 1R-cis,1′R-cis isomer;
(e) optionally performing an ion exchange step; and
(f) isolating the 1R-cis,1′R-cis isomer.
3. The method of claim 2 , wherein the organic solvent of step (a) comprises dichloromethane, chloroform, 1,4-dioxane or a mixture thereof.
4. The method of claim 3 , wherein the organic solvent of step (a) comprises dichloromethane.
5. The method of claim 2 , wherein the concentration of the (1R,1′R)-atracurium salt isomer mixture in the organic solvent in step (a) is from 0.1 M to 0.5 M.
6. The method of claim 2 , wherein the organic solvent of the mobile phase of step (c) comprises dichloromethane, chloroform, 1,4-dioxane, or a mixture thereof.
7. The method of claim 6 , wherein the organic solvent of the mobile phase of step (c) comprises dichloromethane.
8. The method of claim 2 , wherein the polar aprotic co-solvent of the mobile phase of step (c) comprises dimethyl sulfoxide (DMSO), N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMA), N-methyl-2-pyrrolidone (NMP) or a mixture thereof.
9. The method of claim 8 , wherein the polar aprotic co-solvent of the mobile phase of step (c) comprises DMSO.
10. The method of claim 2 , wherein the weak acid of step (c) comprises formic acid, acetic acid, propionic acid or a mixture thereof.
11. The method of claim 10 , wherein the weak acid comprises formic acid.
12. The method of claim 2 , wherein the solvent mixture for eluting the column in step (c) comprises dichloromethane, DMSO and formic acid in a ratio ranging from 70-85% vol. (dichloromethane):8-20% vol. (DMSO):5-15% vol. (formic acid).
13. The method of claim 2 , wherein the ion exchange of step (e) comprises contacting an eluted material with an ion exchange resin.
14. The method of claim 2 , wherein isolation step (f) comprises the steps of:
(a) combining eluted fractions containing at least 90% of the 1R-cis,1′R-cis isomer;
(b) washing the combined eluted fractions with acidic brine and separating the phases;
(c) drying the organic phase and evaporating the solvent to obtain a residual oil;
(d) dissolving the oil in a solvent; and
(e) isolating the product by lyophilizing the solution or by precipitation.
15. The method of claim 14 , wherein the solution used for washing is a 10% brine solution acidified with benzenesulfonic acid (BSA).
16. The method of claim 14 , wherein the product is precipitated at least once by adding at least one solvent selected from tetrahydrofuran (THF), 2-methyl-tetrahydrofuran (2-Me-THF), diethyl ether, diisopropyl ether, methyl tert-butyl ether (MTBE), acetone, hexane, heptane, cyclohexane, and mixtures thereof.
17. The method of claim 16 , wherein the solvent or solvent mixture contains formic acid or brine acidified with BSA.
18. The method of claim 2 , further comprising subjecting the isolated product to ion exchange via a strong anion exchange column or cartridge (SAX).
19. The method of claim 2 , wherein the eluent system comprises dichloromethane, DMSO and formic acid, and the content of the 1R-cis,1′R-cis isomer in the eluent system remains unchanged after 26 hours at room temperature.
20. The method of claim 2 , wherein the isolated 1R-cis,1′R-cis isomer has an isomeric purity greater than 99.5%.
21. The method of claim 20 , wherein the (1R,1′R)-atracurium salt isomer mixture is a (1R,1′R)-atracurium besylate isomer mixture, and the isolated 1R-cis,1′R-cis isomer is cisatracurium besylate.