A mixture of 4.9 g of methyl (3R,4R)-4-[3-oxo-3-(6-methoxyquinolin-4-yl)propyl]piperidine-3-acetate, 2.9 g of 2-chloroethyl cyclopentyl sulfide, 9 g of potassium carbonate, and 2.7 g of potassium iodide in 130 cm3 of acetonitrile was stirred for 17 hours at a temperature in the region of 65° C. After cooling to a temperature in the region of 20° C., the reaction mixture has 150 cm3 of water added and was extracted with 3 times 60 cm3 of ethyl acetate. The organic extracts were combined, washed with 2 times 50 cm3, dried over magnesium sulfate, filtered, and concentrated under reduced pressure (5 kPa) at a temperature in the region of 40° C. An oil was obtained, which product was purified by chromatography at atmospheric pressure on a column of silica gel (particle size 20-45 μm; diameter 4 cm; silica volume 300 cm3), elution was carried out with pure ethyl acetate, and approximately 70-cm3 fractions were collected. The fractions comprising the expected product were combined and then concentrated under the above conditions. 2.6 g of methyl (3R,4R)-4-(3-oxo-3-(6-methoxyquinolin-4-yl)propyl]-1-[2-(cyclopentylthio)ethyl]piperidine-3-acetate were obtained in the form of an oil with a yellow color.
