| abstract |
A process for the direct crystallization of a compound of the formula I:or a pharmaceutically acceptable salt thereof, is disclosed, wherein R1 and R2 represent H, C1-10 alkyl, aryl or heteroaryl, or substituted C1-10 alkyl, aryl or heteroaryl and X+ represents a charge balancing group, comprising extracting a solution containing a crude compound of formula I or Ia:or a pharmaceutically acceptable salt thereof, wherein each X+ is a charge balancing group, and R1 and R2 are as described above with a C4-10 alcohol, collecting and crystallizing the resulting aqueous phase to produce a crystalline compound of formula I. |