Process for obtaining pure oseltamivir

Abstract

The present invention provides a process for obtaining highly pure crystalline form of oseltamivir free base, thus, for example, suspending or dissolving impure or non-crystalline oseltamivir free base in a hydrocarbon solvent and then isolating crystals to obtain oseltamivir free base in well defined crystalline form. The present invention also provides a process for preparation of oseltamivir phosphate in high purity.

1 . A process for isolation of pure crystalline oseltamivir free base, which comprises suspending or dissolving impure or non-crystalline oseltamivir free base in a hydrocarbon solvent and then isolating crystals to obtain oseltamivir free base in well defined crystalline form. 
   
   
       2 . The process as claimed in  claim 1 , wherein the hydrocarbon solvent is selected from the group consisting of n-hexane, n-heptane, cyclohexane, toluene, xylene and a mixture thereof. 
   
   
       3 . The process as claimed in  claim 2 , wherein the hydrocarbon solvent is n-heptane, toluene or a mixture thereof. 
   
   
       4 . The process as claimed in  claim 1 , wherein the suspension is stirred for at least 30 minutes at below boiling temperature of the solvent used. 
   
   
       5 . The process as claimed in  claim 4 , wherein the suspension is stirred for 1 hour to 4 hours at 15-60° C. 
   
   
       6 . The process as claimed in  claim 5 , wherein the suspension is stirred for 1 hour to 3 hours at 20-40° C. 
   
   
       7 . The process as claimed in  claim 1 , wherein the isolation of the crystalline oseltamivir free base is carried out by filtration or centrifugation. 
   
   
       8 . The process as claimed in  claim 1 , wherein the isolation of the crystalline oseltamivir free base is carried out by cooling, seeding, partial removal of the solvent from the solution or by adding an anti-solvent to the solution; or a combination thereof.