To a solution of 9-(2,3,5-tri-O-benzoyl-β-D-ribofuranosyl)-2,6-dichloro-9H-purine (1.5 g, 2.4 mmol) in dry dioxan (50 ml), the above 2-[(R)-2-aminopropyl-1-propylthio]thiazole dihydrochloride (1.5 g, 7.1 mmol) and triethylamine (0.78 g, 7.7 mmol) were introduced at 20° C. After stirring at 50° C. for 40 h the reaction mixture was concentrated to a yellow oil, which was purified by flash chromatography eluting with a mixture of heptane and ethyl acetate (1:1), to afford the title 2',3',5'-tri-O-benzoyl-2-chloro-N-[(R)-1-(2-thiazolyl)thio-2-propyl]adenosine (1.2 g, 63%) as a foam, TLC Rf 0.19 [SiO2 ; heptane/ethyl acetate (1:1)].
