Patent ID: 8318936

Claim:
Process for the preparation of N-methylnaltrexone bromide, wherein a compound of the general formula (I): wherein X − represents an anion selected from HSO 4 − ; SO 4 2− ; [—O—S(O) 2 —O—(C 1-4 )alkyl]; [—O—S(O) 2 —(C 1-4 ) alkyl]; [—O—S(O) 2 —CF 3 ]; or [—O—S(O) 2 -phenyl], wherein the phenyl ring is optionally substituted; R represents hydrogen or a leaving group, (i) is dissolved or dispersed in a suitable polar solvent, said solvent being selected from the group consisting of water, polar organic solvents, aprotic dipolar solvents, and alcohols or a mixture thereof; (ii) the solution or dispersion is mixed with a compound containing bromide anions, and the resulting reaction mixture is stirred until N-methylnaltrexone bromide has formed and crystallised, wherein, in the case where R represents a leaving group, that group is removed during or after the reaction.