Conventionally, the following methods have been known as methods producing an (R)-3-[4-(trifluoromethyl)phenylamino]-pentanoic acid amide derivative.
That is, an amino group of (R)-2-amino-1-butanol is protected by a tert-butoxycarbonyl group, and then mesylation and/or cyanation of a hydroxyl group and protection release of an amino protecting group are successively carried out to produce (R)-3-aminopentanenitrile. Thereafter, the product is coupled with 4-(trifluoromethyl)chlorobenzene using a catalyst produced from palladium acetate and 2-dicyclohexylphosphino-2′-(N,N-dimethylamino)-1,1′-biphenyl to produce (R)-3-[4-(trifluoromethyl)phenylamino]-pentanenitrile. Then, this product is hydrated with concentrated sulfuric acid to produce (R)-3-[4-(trifluoromethyl)phenylamino]-pentanoic acid amide. Furthermore, the (R)-3-[4-(trifluoromethyl)phenylamino]-pentanoic acid amide is reacted with a chlorocarbonic acid ester in the presence of a base to be converted into an (R)-3-[4-(trifluoromethyl)phenylamino]-pentanoic acid amide derivative (WO 02/088069, WO 02/088085).
However, the method comprises a large number of steps, using a highly toxic sodium prussiate and even using very expensive palladium catalyst and phosphine ligand, and therefore, the method cannot necessarily be said to be industrially advantageous.