2-oxo-2-phenylethyl (3R,4S)-3-azido-1-[N-(tert-butoxycarbonyl)-4-(trifluoromethyl)phenylalanyl]-4-[3-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)propyl]pyrrolidine-3-carboxylate