Thionyl chloride (5.2 cc) is added to a suspension, cooled to 5° C., of 10-[(2RS)-1-(1-pyrrolidinyl)-2-propyl]-2-phenothiazinecarboxylic acid hydrochloride (3.9 g) in methylene chloride (120 cc). The suspension is stirred for 3 hours at 25° C. and then concentrated to dryness at 30° C. under reduced pressure (30 mm Hg; 4 kPa) to give a yellow residue which is taken up in methylene chloride (50 cc) at 5° C. Cyclopentylamine (5 cc) is added and the mixture is stirred for 12 hours at 25° C., and saturated sodium bicarbonate solution (150 cc) is then added. The mixture is extracted with ethyl acetate (2×100 cc). The organic phase is washed successively with distilled water (100 cc) and with brine (100 cc), dried over magnesium sulphate, filtered and concentrated to dryness at 40° C. under reduced pressure (30 mm Hg; 4 kPa) to give a yellow oil which is dissolved in boiling acetonitrile (70 cc). Crystallization is primed by scratching. After cooling, the solid is separated by filtration, washed with acetonitrile (2×3 cc) and dried at 40° C. under reduced pressure (1 mm Hg; 0.13 kPa). N-Cyclopentyl-10-[(2RS)-1-(1-pyrrolidinyl)-2-propyl]-2-phenothiazinecarboxamide (2.1 g) is obtained in the form of cream-coloured crystals, m.p. 132° C.
