In a reaction flask, sirolimus (10 g, 10.9 mmol), ethyl di-isopropyl amine (78 g, 603.5 mmol), methylene chloride (35 ml) and 2-ethoxyethyl triflate (20 g, 88 mmol), each having a quantity about 10 times of that used in Example 3B, were added into the flask, which is filled with nitrogen gas. The reaction mixture is heated to 60° C. and is agitated for one hour and twenty minutes. Then, it is cooled, added with ethyl acetate (500 ml) and aqueous solution of hydrochloric acid (1N, 500 ml) and is further agitated. After agitation, it is settled for separating the layers. The organic layer is collected and respectively washed with pure water (500 ml), saturated saline (400 ml). The washed organic layer is dried and concentrated. The residue is then separated and purified by silica gel column chromatography to obtain white product of Biolimus A9 (2.9 g, 2.9 mmol), having a yield of 26.8% only.
