(R)-5-((S)-3-Benzenesulfonyl-6-{(6S,7R)-7-[2-(tert-butyl-dimethyl-silanyloxy)-ethyl]-6,7-dimethyl-1,4-dioxa-spiro[4.5]dec-6-yl}-2-methyl-4-oxo-hexyl)-2,2-dimethyl-oxazolidine-3-carboxylic acid benzyl ester