Abstract: This invention relates to 4-(4-fluorobenzylamino)-1-methylpiperidine trihydrate and a process for the preparation of 4-(4-fluorobenzylamino)-1-methylpiperidine trihydrate comprising treating 4-(4-fluorobenzylamino)-1-methylpiperidine with water. The invention also relates to a process for the preparation of pimavanserin comprising reacting 4-(4-fluorobenzylamino)-1-methylpiperidine trihydrate with 1-isobutoxy-4-(isocyanatomethyl)benzene; to a process for the preparation of a pimavanserin acid addition salt comprising reacting 4-(4-fluorobenzylamino)-1-methylpiperidine trihydrate with 1-isobutoxy-4-(isocyanatomethyl)benzene and converting pimavanserin into a pimavanserin acid addition salt, pimavanserin and pimavanserin acid addition salts obtainable by the process, and to the use of 4-(4-fluorobenzylamino)-1-methylpiperidine trihydrate for preparing pimavanserin or an acid addition salt thereof.

Abstract: This invention relates to a process for the preparation of pimavanserin comprising: (i) providing an acid addition salt of pimavanserin; (ii) dissolving the acid addition salt of pimavanserin in an aqueous solvent to form an aqueous solution; (iii) washing the aqueous solution obtained in step (ii) with an organic solvent; and (iv) adding a base to the washed aqueous solution to form pimavanserin. The invention also relates to a process for the preparation of an acid addition salt of pimavanserin additionally comprising step (v) of converting pimavanserin into an acid addition salt of pimavanserin. The invention also relates to pimavanserin or an acid addition salt thereof obtainable by the process, and to the use of pimavanserin hydrochloride, pimavanserin hydrogen sulfate or pimavanserin acetate for preparing pimavanserin or an acid addition salt thereof.