Process for making montelukast and intermediates therefor

Abstract

A process for making montelukast, a pharmaceutically useful compound of the following formula and salts thereof: using a compound of formula (11) is provided.

1 . A process for the purification of montelukast acid, which comprises filtering a toluene solution of montelukast acid through a polar sorbent. 
   
   
       2 . The process according to  claim 1 , wherein said polar sorbent is silica gel. 
   
   
       3 . The process according to  claim 1 , which further comprises precipitating the montelukast acid from said toluene solution after said filtering step. 
   
   
       4 . The process according to  claim 3 , which further comprises, crystallizing said montelukast acid precipitate from a protic solvent in the absence of light. 
   
   
       5 . The process according to  claim 4 , wherein said protic solvent is an alcoholic solvent. 
   
   
       6 . The process according to  claim 5 , wherein said alcoholic solvent is ethanol. 
   
   
       7 . The process according to  claim 4 , wherein said filtering is performed at least twice before said crystallizing step. 
   
   
       8 . The process according to  claim 4 , wherein said crystallized montelukast acid has a purity of greater than 99%. 
   
   
       9 . The process according to  claim 8 , wherein said crystallized montelukast acid has a purity of greater than 99.5%. 
   
   
       10 . A process for the purification of montelukast acid, which comprises crystallizing montelukast acid from a protic solvent in the absence of light. 
   
   
       11 . The process according to  claim 10 , wherein said protic solvent is an alcoholic solvent. 
   
   
       12 . The process according to  claim 11 , wherein said alcoholic solvent is ethanol. 
   
   
       13 . The process according to  claim 10 , wherein said crystallized montelukast acid has a purity of greater than 99%.