Methods for producing nateglinide B-type crystals

Abstract

A method for producing B-type crystals of nateglinide substantially free of H-type crystals is provided, which comprises drying solvated wet crystals of nateglinide at a low temperature until no solvent remains and making a crystal conversion thereof. According to this method, B-type crystals of nateglinide can be produced at an industrial scale without allowing other forms of the crystalline polymorphism to coexist.

What is claimed is:  
     
         1 . A method for producing B-type crystals of nateglinide substantially free of H-type crystals, which comprises drying solvated wet crystals of nateglinide at a low temperature until no solvent remains and making a crystal conversion thereof.  
     
     
         2 . The method of  claim 1 , wherein the resulting B-type crystals of nateglinide are crystals wherein H-type crystals are not detected with DSC.  
     
     
         3 . The method of  claim 1 , wherein the drying is conducted at a temperature of 50° C. or lower.  
     
     
         4 . The method of  claim 1 , wherein the drying is conducted until substantially no solvent remains any longer.  
     
     
         5 . The method of  claim 1 , wherein the solvated wet crystals are hydrates.  
     
     
         6 . The method of  claim 1 , wherein the crystal conversion is conducted by heating the solvated wet crystals at 60 to 110° C.  
     
     
         7 . The method of  claim 1 , wherein said both steps for drying said solvated wet crystal of nateglinide at a low temperature and for the crystal conversion are conducted at an industrial scale.  
     
     
         8 . A method for producing B-type crystals of nateglinide substantially free of H-type crystals, which comprises drying solvated materials containing nateglinide hydrates obtained by crystallizing out from a nateglinide-containing solution under cooling, at a temperature of 50° C. or lower until no solvent remains, and heating the resultant at a temperature of 60 to 110° C. to convert the crystal form of the resultant into B-type crystal.  
     
     
         9 . The method of  claim 8 , wherein the resulting B-type crystals of nateglinide are crystals wherein H-type crystals are not detected with DSC.