[(2R,4S,6S,8S,10S)-4-(tert-Butyl-dimethyl-silanyloxy)-8-((2S,3S)-2,4-dihydroxy-3-methyl-butyl)-10-hydroxy-10-methyl-1,7-dioxa-spiro[5.5]undec-2-yl]-acetic acid tert-butyl ester