To a solution of compound 11 or 14 (1.0-1.1 eq.) in anhydrous DMF (3 mL), HATU (2 eq.) and DIPEA (3 eq.) were added. The mixture was stirred at room temperature for 0.5 h. Afterwards, a solution of Bocdeprotected compound 4 or 9 (1 eq) in anhydrous DMF (2 mL) was added and the reaction mixture was then stirred for 17 h at room temperature. The mixture was poured into water (100 mL) and extracted with ethyl acetate (3 x 30 mL). The combined organic layer was then washed with water (3 x 50 mL) and followed by brine (50 mL), dried over anhydrous Na2SO4, filtered, and concentrated in vacuo to yield the crude products, which were subsequently purified by silica column chromatography.