(2S,3S)-3-(tert-Butyl-dimethyl-silanyloxy)-2-{(4R,5R)-5-[(R)-2-(tert-butyl-dimethyl-silanyloxy)-1-hydroxy-ethyl]-2,2-dimethyl-[1,3]dioxolan-4-yl}-pyrrolidine-1-carboxylic acid benzyl ester