To a suspension of 4-(2-Ethyl-imidazo[4,5-c]quinolin-1-yl)-butylamine obtained in step VI in tetrahydrofuran was added acetic acid (1 eq.) and dihydrothiophen-3-one (1.1 eq.). Resulting reaction mixture was stirred for 10 min. Sodium triacetoxyborohydride (2.2 eq.) was added to reaction mixture over a period of 1 hrs and resulting suspension was then stirred for 4-5 hrs. Reaction was then quenched with methanol and concentrated to dryness. Reaction mixture was basified using aq.sodium hydroxide solution and extracted with chloroform. Organic layer was dried over sodium sulphate and concentrated under reduced pressure to yield sticky solid. Product was then purified by silica gel column chromatography to afford [4-(2-Ethyl-imidazo[4,5-c]quinolin-1-yl)-butyl]-(tetrahydro-thiophen-3-yl)-amine.
